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While improved crop water‐deficit tolerance is considered of primary importance, many phenotyping efforts focusing on quantifying structural root traits make assumptions about architecture representing root function. Therefore, the aim of this study was to quantify whole plant water‐use traits among disparate peanut (Arachis hypogaea L.) genotypes and determine their impact on water‐deficit tolerance. Mini‐rhizotrons were installed to evaluate genotypic root architecture and developmental changes to two irrigation regimes imposed during early development. Following the early‐season irrigation regimes, above‐ and below‐ground traits were studied across a range of soil water conditions through measures of: (a) leaf‐level gas exchange and (b) soil water depletion quantified using a novel soil water probe inserted into mini‐rhizotrons allowing for matched root architecture and soil water depletion measures. While differential water treatments influenced root system architecture development among the genotypes, soil water depletion locations were primarily determined by water availability in the soil profile, not simply by having greater root length at a given soil location. This contradicts the assumption that greater root presence is a consistent indicator of increased root activity. Phenotypic selection of root traits for improving the efficiency of crop water use should consider both structural and functional traits in relation to the intended production environments slated for future cultivar development. [ABSTRACT FROM AUTHOR]

Climate change is predicted to increase the frequency of drought conditions and alter plant–insect interactions. Despite over 530 studies on the effects of water‐deficit stress on plant–insect interactions, we still cannot accurately predict plant–insect interactions under drought conditions. Most studies have focused on how insect herbivores respond to water‐deficit‐stressed plants, with little attention on how stressed plants and changes in plant physiology may contribute to the variation in herbivore response. Variation in herbivore response to water‐deficit‐stressed plants may be due to stress‐induced changes in plants and how these changes differ with stress severity. In this study, we determined the effects of water‐deficit stress on cotton (Delta Pine 174RF) physiology in an agroecosystem using pulsed moderate and severe stress. Our goal was to determine how moderate and severe water‐deficit stress affect cotton (Gossypium hirsutum L.) physiology differently in terms of photosynthesis, development, water use, and nutrient content. We found that moderate and severely stressed plants had many different physiological responses that may contribute to the variation we see in herbivore response to stressed plants. For instance, moderately stressed plants were more vigorous and more developed than severely stressed plants, whereas severely stressed plants had more amino acids than moderately stressed plants. We predict that insect herbivores feeding on moderately and severely stressed plants would encounter differences in C assimilation, water content (stomatal conductance, transpiration), chlorophyll content, and concentrations of amino acids and digestible carbohydrates. It is clear that field studies should consider how differences in stress severity can affect plant–insect interactions. [ABSTRACT FROM AUTHOR]

Cultivated peanut produces pods of varying maturity throughout most of the plant developmental stages, often leading to a considerable proportion of immature seeds at harvest. Plants originating from immature seeds not only have reduced emergence and physiological performance, but also reduced vigor of both mature and immature seeds produced in subsequent generations. Therefore, seed maturity effects on plant performance could potentially extend from physiology to the initiation and progression of reproduction. This study aimed to elucidate the impacts of seed maturity on plant performance and productivity. In this two-year experiment, season-long physiological and reproductive performance was compared among plants established from mature and immature seed of eight peanut cultivars differing in maturity potential. Our results suggest that plants produced from mature seeds had higher emergence and canopy coverage than plants produced from immature seeds over the season. Further, descendent seed quality was also affected: plants that originated from immature seeds produced mature seeds with average 9.91 % decreased mass, particularly for those formed earliest in plant development, and average 37.18 % less mature pods formed latest in plant development. At harvest, seeds were collected and tested for biochemical characteristics. Seeds that were produced by plants originating from mature seeds generally had higher carbohydrates, protein, oleic acids and lower lipid content than seeds produced by plants originating from immature seeds. Given these results, the use of mature seeds in production appears to be of utmost importance for both the performance of the subsequent plant and the resulting quality of the seed produced by these plants. • This two-year study tested peanut plant performance and the quality of their offspring seeds that formed at different time periods (represented as cohort groups) based on whether the plants and their offspring seeds originated from mature or immature seeds. • Plants produced from mature seeds had enhanced emergence and greater canopy cover than plants produced from immature seeds over the season. • Plants originating from immature vs. mature seeds produced pods/seeds differed in the numbers of mature pods, seed mass and biochemical compounds within each cohort group. • The impact of seed maturity on plant development is highly dependent to environmental influence. [ABSTRACT FROM AUTHOR]

Priming is a strategy that potentiates a plant’s response to stress. Primed acclimation (PA) in crop irrigation scheduling is the use of a temporary period of regulated deficit irrigation (RDI), imposing mild or moderate deficits, to evoke a primed state, after which full evapotranspiration replacement is resumed. Although little has been reported regarding physiological impacts of PA, the technique has been used to maintain or improve yields in agronomic crops in drought-prone regions. The first objective of this study was to test a plant-based approach to determine the appropriate level of soil water potential needed to evoke a primed response in papaya plants. This was done through a substrate (potting medium) dry-down experiment with one group of plants irrigated to field capacity and a second group of plants for which the soil was allowed to dry gradually. Physiological responses were assessed to determine at what point a mild to moderate level of stress was reached. The second objective was to test the effects of a priming stress (the level set in the first objective) on leaf gas exchange (net photosynthesis [ A ], stomatal conductance [ g s ], transpiration [ E ]) and chlorophyll fluorescence in papaya as compared to a control treatment in which soil water content was maintained at field capacity. The most sensitive variable in the dry-down experiment was g s , which was used to select a soil water potential target of −30 kPa for subsequent priming treatments. Priming treatments using this predetermined target resulted in increased A and leaf chlorophyll index (SPAD) during the period when irrigation to field capacity was restored. According to OJIP analysis, primed plants had increased fluorescence performance indices, reduced antennae size per Photosystem II reaction center, and increased fluxes and efficiencies from plastoquinone A through Photosystem I. Thus, increased A as a result of priming had both stomatal and photochemical components. However, increased A due to priming of papaya appeared to be temporary. These results show that papaya has the capacity to reach a primed state and provide the soil water potential levels that could be utilized to achieve the appropriate level of water deficit for priming. This vital information can be used in the development of management techniques to capitalize on papaya’s priming ability under commercial irrigation management schemes. [ABSTRACT FROM AUTHOR]

Proper irrigation scheduling in potato (Solanum tuberosumL.) can lead to higher returns and more sustainable production practices when compared to systems that do not take plant water demand into account. In an attempt to reduce irrigation applications while minimizing yield reduction, we evaluated a novel deficit irrigation treatment utilizing a mild irrigation reduction during tuber bulking by comparing a typical commercial irrigation schedule to a partial irrigation schedule. Physiological, yield, and quality effects were quantified. Reducing the number of irrigation applications by 14 in 2011 and by 9 in 2012 minimally affected most parameters measured. However, a significant yield reduction of 11,713 kg/ha in the partial irrigation treatment occurred in 2011, likely because of the irrigation treatment commencing at the latter portion of tuber initiation. In 2012, the initiation of the partial irrigation was delayed and resulted in no significant difference in yield between the partial and full irrigation treatments. This study shows the potential for a reduced irrigation schedule for use by Florida potato growers as a sustainable option for potato production in this region. [ABSTRACT FROM PUBLISHER]

Highlights: [•] Yield and oil percentage were measured for castor (Ricinus communis L.) in Florida. [•] The castor cultivar Hale out-yielded the cultivar Brigham in Florida. [•] Root architecture was quantified during the season using minirhizotrons. [•] Mepiquat chloride may not be an effective plant growth regulator for castor. [•] Paraquat is a more effective harvest aid than tribufos for termination of the crop. [ABSTRACT FROM AUTHOR]

Highlights: [•] Indian breeding lines in the field exhibited differences in nitrogen accumulation. [•] Commercial lines did not show difference in nitrogen accumulation under field drought. [•] Nitrogen fixation tolerance of commercial cultivars to soil drying was moderate. [•] Field test was reasonable screen to identify genotypes for intensive measurement. [ABSTRACT FROM AUTHOR]

Abstract: Water-deficits and high temperatures are the predominant factors limiting peanut production across the U.S., either because of regional aridity or untimely rainfall events during crucial crop developmental periods. In the southern High Plains of west Texas and eastern New Mexico, low average annual rainfall (450mm) and high evaporative demand necessitates the use of significant irrigation in production systems. In this west Texas study, the primary objective was to develop irrigation schemes that maximized peanut yield and grade while reducing overall water consumption. Therefore, a large-scale field experiment was established in 2005 and 2006 that utilized 15 treatment combinations of differing rates of irrigation (50, 75, and 100% of grower applied irrigation) applied at different periods of peanut development (early, middle, and late season). Precipitation patterns and ambient temperatures showed greater stress levels in 2006 which likely reduced yields across all treatments in comparison to 2005. Yields were reduced 26 (2005) and 10% (2006) in the lowest irrigation treatment (50% full season) compared with full irrigation (100% full season); but early-season water deficit (50 and 75% in the first 45days after planting) followed by 100% irrigation in the mid- and late-seasons were successful at sustaining yield and/or crop value. Root growth was significantly enhanced at 50% irrigation compared with 100% irrigation, through greater root length, diameter, surface area, and depth, suggesting greater access to water during mid- and late-season periods. These results suggest that early to mid-season deficit irrigation has the potential to maintain peanut yield without altering quality, and to substantially reduce water use in this semi-arid environment. [Copyright &y& Elsevier]

Human activities release tremendous amounts of nitrogenous compounds into the atmosphere. Wet and dry deposition distributes this airborne nitrogen (N) on otherwise pristine ecosystems. This eutrophication process significantly alters the species composition of native grasslands; generally a few nitrophilic plant species become dominant while many other species disappear. The functional equilibrium model predicts that, compared to species that decline in response to N enrichment, nitrophilic grass species should respond to N enrichment with greater biomass allocation aboveground and reduced allocation to roots and mycorrhizas. The mycorrhizal feedback hypothesis states that the composition of mycorrhizal fungal communities may influence the composition of plant communities, and it predicts that N enrichment may generate reciprocal shifts in the species composition of mycorrhizal fungi and plants. We tested these hypotheses with experiments that compared biomass allocation and mycorrhizal function of four grass ecotypes (three species), two that gained and two that lost biomass and cover in response to long-term N enrichment experiments at Cedar Creek and Konza Long-Term Ecological Research grasslands; Local grass ecotypes were grown in soil from their respective sites and inoculated with whole-soil inoculum collected from either fertilized (FERT) or unfertilized (UNFERT) plots. Our results strongly support the functional equilibrium model. In both grassland systems the nitrophilic grass species grew taller, allocated more biomass to shoots than to roots, and formed fewer mycorrhizas compared to the grass species that it replaced. Our results did not fully support the hypothesis that N- induced changes in the mycorrhizal fungal community were drivers of the plant community shifts that accompany N eutrophication. The FERT and UNFERT soil inoculum influenced the growth of the grasses differently, but this varied with site and grass ecotype in both expected and unexpected ways suggesting that ambient soil fertility or other factors may be interacting with mycorrhizal feedbacks. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi are integral components of grasslands because most plants are associated with interconnected networks of AM hyphae. Mycorrhizae generally facilitate plant uptake of nutrients from the soil. However, mycorrhizal associations are known to vary in their mutualistic function, and there is currently no metric that links AM functioning with fungal colonization of roots. Mycorrhizal structures differ in their physiological and ecological functioning, so changes in AM allocation to intraradical (inside roots) and extraradical (in soil) structures may signal shifts in mycorrhizal function. We hypothesize that the functional equilibrium model applies to AM fungi and that fertilization should reduce allocation to arbuscules, coils, and extraradical hyphae, the fungal structures that are directly involved in nutrient acquisition and transfer to plants. This study compared AM responses to experimental N enrichment at five grasslands distributed across North America. Samples were collected from replicated N-enriched (and some P-enriched) and control plots throughout the growing season for three years. Intraradical AM structures were measured in over 1400 root samples, extraradical hyphal density was measured in over 590 soil samples, and spore biovolume was analyzed in over 400 soil samples. There were significant site × N interactions for spore biovolume, extraradical hyphae, intraradical hyphae, and vesicles. Nitrogen enrichment strongly decreased AM structures at Cedar Creek, the site with the lowest soil N:P, and it increased AM structures at Konza Prairie, the site with the highest soil N:P. As predicted by the functional equilibrium model, in soils with sufficient P, relative allocation to arbuscules, coils, and extraradical hyphae was generally reduced by N enrichment. Allocation to spores and hyphae was most sensitive to fertilization. At the mesic sites, this response was associated with a shift in the relative abundance of Gigasporaceae within AM fungal communities. This study demonstrates that N enrichment impacts mycorrhizal allocation across a wide range of grassland ecosystems. Such changes are important because they suggest an alteration in mycorrhizal functioning that, in turn, may impact plant community composition and ecosystem function. [ABSTRACT FROM AUTHOR]

Populus deltoides var. wislizenii (S. Wats.) Eckenwalder (cottonwood) forests along the Rio Grande drainage are predicted to disappear within this century. We evaluated stand health over 3 years by examining the sex ratio, size, and spatial distribution of male, female, and nonreproductive trees in six even-aged stands of P. deltoides spanning 280 km along the Rio Grande drainage. There was no evidence of biased sex ratios or spatial segregation of sexes; however, tree mortality was strongly related to reproductive status. In the most stressed population, over half of the mature trees remained nonreproductive and a substantial number switched from reproductive to nonreproductive status. Logistic regression revealed that over all populations, tree size, reproductive status in previous years, and population were significant factors affecting reproduction. By considering physiological and environmental differences, we determined two groups of nonreproductive individuals: those previously reproductive that became nonreproductive and those that remained nonreproductive over the 3 years. The former group appeared to be under greater physiological and environmental stress. Monitoring the rate at which individuals change reproductive status provides an effective and simple measurement that can predict survival of riparian cottonwood populations.Key Words: Populus deltoides, sex ratio, Rio Grande basin, reproductive status, nonreproductive.On prédit que les forêts de Populus termuloides var. wislizenii (S. Wats.) Eckenwalder, le long du bassin du Rio Grande, disparaîtront au cours du siècle. Les auteurs ont évalué l'état de santé de ces forêts pendant 3 ans, en examinant les ratios sexuels ainsi que la dimension et la distribution spatiale des arbres mâles, femelles et non-reproductifs, dans six peuplements de même âge du P. tremuloides bordant 280 km de rives le long du bassin du Rio Grande. Il n'y a pas de preuve de ratios sexuels biaisés ou de ségrégation spatiale sur la base des sexes; cependant, la mortalité des arbres est fortement reliée au statut reproductif. Chez les populations les plus stressées, plus de la moitié des arbres adultes ne se reproduisent pas, et un nombre substantiel passe de l'état reproductif à non reproductif. La régression logistique révèle que pour l'ensemble des populations, la dimension de l'arbre, le statut reproductif au cours des années précédentes, et la population constituent des facteurs qui affectent significativement la reproduction. En considérant les différences physiologiques et environnementales, les auteurs ont déterminé deux groupes d'individus non-reproducteurs : ceux qui étaient préalablement reproductifs et sont devenus non-reproductifs, et ceux qui sont demeurés non-reproductifs au cours des trois années. Le premier groupe semble subir de plus forts stress physiologiques et environnementaux. Le suivi du taux selon lequel les individus modifient leur statut reproductif fournit un moyen simple et efficace, susceptible de prédire la survie des populations de peupliers deltoïdes.Mots clés : Populus deltoides, ratio sexuel, bassin du Rio Grande, statut reproductif, non-reproductif.[Traduit par la Rédaction] [ABSTRACT FROM AUTHOR]

Reports on a common garden that was established using genotypes of Populus deltoides var. wislizenii (S. Wats.) Eckenwalder from four New Mexico populations (Abiquiu, Corrales, Bernardo, and San Antonio) to examine physiological and morphological differentiation within and among populations. Populations that were located within the same watershed along the Rio Grande and one of its tributaries, the Rio Chama; Measurement of physiological and morphological variation to determine the extent of inter- and intra-population variation in these traits; Determination to see if the same traits varied among male, female, and nonreproductive trees; Differences within and among populations that occurred for photosynthesis, transpiration, and stomatal conductance; Leaf morphological traits that also differed within and among populations, including leaf size, chlorophyll content, and specific leaf mass; Stomatal conductance that differed significantly between female and nonreproductive trees in both years; Study that demonstrated the existence of genetic variation in ecophysiological and morphological traits within and among cottonwood populations and among cottonwoods of differing reproductive status within a single watershed.

• Irrigation decision support systems (DSS) are needed for new crops introduced to regions to ensure efficient use of water resources. • Irrigation DSS may be particularly important for drought tolerant crops to capitalize on inherent crop water deficit resistance. • SesameFARM1 was developed using FAO crop coefficients for sesame to calculate daily plant available water based on weather data, crop evapotranspiration, and maximum rooting depth. • SesameFARM2 was an improvement of the original model made by using annual leaf area index and root architecture measurement over six years of research. • In yearly simulations, SesameFARM2 was a more conservative irrigation DSS than SesameFARM1, reducing water application recommendation and likely improving overall irrigation crop water productivity. Irrigation decision support systems (DSS) are tools that can help achieve higher system level water use efficiency by more accurately targeting water application to crop need. They also have a role to play in preventing over-irrigation of drought tolerant crops that can be sensitive to flooded conditions. However, there are challenges in developing DSS for newly introduced crops in regions where they have not typically been produced. One such crop is sesame, a recently introduced drought tolerant crop in the southeastern United States where up to 50% of the agronomic crop production is irrigated. A first irrigation DSS, called SesameFARM1, was developed in 2013 by estimating a water demand curve using the Food and Agricultural Organization (FAO) crop coefficient (Kc) values, seasonal measures of the leaf area index (LAI) for the crop measured in 2012, and an estimated maximum rooting depth. On a daily time-step, SesameFARM1 estimated crop evapotranspiration using the product of the Kc and the ETo obtained from a local weather station, and an estimation of the maximum plant available water based on the available water capacity for the soil type and the maximum crop rooting depth. To improve SesameFARM1, LAI data from 6 years of field trials along with root data from a previous study were used to develop a breakpoint regression model for LAI and total functional root length. In SesameFARM2, the resulting curve for LAI was used to estimated continuous Kc values; and total measured functional root length replaced the estimation of maximum rooting depth in a new variable called root water access. SesameFARM2 performance was compared to SesameFARM1 using 6 years of weather data from Citra FL. SesameFARM2 consistently recommended less water be applied, and recommendations of water application during the senescence phase of the crop were reduced. Because of sesame's inherent drought tolerance, a more conservative irrigation recommendation is likely more appropriate. Therefore, SesameFARM2 is likely a better model than SesameFARM1 and may help growers unfamiliar with sesame achieve irrigation higher irrigation crop water productivity. [ABSTRACT FROM AUTHOR]

Maturity is not only critical for vigour and other seed quality characteristics but also impacts the subsequent plant performance. If these impacts on the subsequent plant are long lasting, the potential to produce vigorous, mature seed may also be affected. This scenario lends itself to the concept of seed maturity memory (SMM) – an understanding of how seed maturity may impact subsequent generations of plants and the vigour of the seeds with different maturity they produce. This study aimed to assess the existence and perpetuation of SMM in peanut, with an emphasis on early seedling vigour. Field physiological measurements and bioassay assessments were carried out on the second generation (G2) and third generation (G3) of peanut seeds with distinct parental maturity backgrounds. Our results suggested maintaining mature seed in both prior and offspring generations helped maintain high seed vigour in subsequent generations. The SMM effects varied between cultivars, with TUFRunner™ '727' exhibiting SMM, whereas FloRun™ '107' did not show SMM in the effects from first generation (G1) to G2 maturities. Overall, a seed resulting from parental plants established from immature seed somewhere in their pedigree was less vigorous than that maintained mature seeds in their pedigree. However, patterns of possible SMM were not always consistent, which could be partially attributed to differing environmental conditions each generation of seed experienced during development. These results highlight the importance of maintaining mature seeds in agricultural production and bring up the issue of ensuring seed maturity consistency during stress memory research assessing vigour characteristics. [ABSTRACT FROM AUTHOR]

Many crop species, including cultivated peanut (Arachis hypogaea L.), modify their above‐ and below‐ground growth to cope with water deficit stress. This acclimation to water deficit often triggers a biomass partitioning shift—allocating more biomass to the roots, to increase the accessibility of roots to water resources. However, additional carbon partitioning to roots may not always translate into increased water use and maintenance of aboveground biomass (ABM) and yield. Therefore, selecting an efficient root system architecture (RSA) should aim to sustain a high ABM production under a water deficit scenario. To better understand the associations of above and belowground biomass partitioning under moderate water deficit, this study evaluated the genotypic stability of 40 peanut genotypes in ABM and RSA in greenhouse experiments and further assessed genotypic differences in 4 site‐year field experiments. Our results suggested that higher ABM‐producing genotypes generally had high plasticity when subjected to water deficit whereas the low ABM‐producing genotypes had relatively high stability. Hierarchical clustering analysis further revealed that genotypes with a high root‐to‐shoot ratio potentially had increased genotypic stability in ABM underwater deficit. Interestingly, genotypes that maintained the highest ABM underwater deficit did not have the highest total root biomass and length. Instead, these genotypes had the highest root length in the top layer of soil (0–0.3 m) and relatively fewer roots in the deeper layer of soil (0.3–1 m). Greenhouse‐screened stable genotypes exhibited minimal yield reduction when subjected to mid‐season water deficit in some of the field validation experiments, but it also happened to some plastic genotypes, indicating that further validation of controlled environment screenings for genotypic water‐deficit tolerance in the field is necessary. [ABSTRACT FROM AUTHOR]

• An Unmanned Autonomous Octocopter equipped with a hyperspectral sensor was used to take imagery of peanut plant cover at various stages of maturity. The model was verified using later imagery. • Comparison between the model-predicted and real values showed that the model yields an inaccurate estimate of maturity up to 60 days after planting, but the accuracy improved over time. • Assessment of the model indicates need for calibration for more accurate prediction of maturity. This could be achieved by expanding the maturity versus leaf spectra database by taking data more frequently close to harvest. An Unmanned Autonomous Octocopter equipped with a multispectral camera was used to take imagery of peanut plant cover at different stages of maturity. Vegetation indexes (Normalized Difference Vegetation Index, Transformed Difference Vegetation Index, Modified Soil Adjusted Vegetation Index, Modified Chlorophyll Absorption Ratio Index and the Modified Triangular Vegetation Index) were stacked and used to mask out the peanut canopy cover from background soil, shadows and any other surficial materials. Masked peanut canopy was used to develop a peanut maturity-spectral reflectance prediction model. The model was built using partial least squares. Comparison between the model- predicted and real values showed that the model does not give an accurate estimate of maturity up to 60 days after planting, but the accuracy of the model increases with time. This may since the difference between chlorophyll a and become more significant in mature peanuts more than immature ones. The overall assessment of the model indicates that the model needs to be calibrated for more precise prediction of the peanut maturity. This could be achieved by expanding the peanut maturity, versus peanut leaf spectra, database by taking data more frequently, especially close to harvest. Data collection should be started two months after planting when the ratios between chlorophyll a and b become more detectable in the leaf reflectance spectra. [ABSTRACT FROM AUTHOR]

Sesame (Sesamum indicum L.) is being considered for commercial production in the southeastern USA, but very little is known about its potential and the appropriate management practices required to achieve sustainable yield potential in the area. This study thus aims to determine the optimal planting date and row spacing for several sesame cultivars. Traits examined were yield, plant height, number of nodes on the main stem, number of branches, height to first capsule on the main stem, and number of plants per meter. A first trial investigated three planting dates in Citra, FL (May, June, and July); whereas a second one examined several row spacings at two locations: 19 and 38.1 cm in Citra; and 19, 38.1, and 76.2 cm in Live Oak, FL. The May planting date showed higher yields, number of nodes, and taller plants than the other dates. Accumulated air and soil growing degree days (GDDs), rainfall, and solar radiation values were calculated for each planting date in both years. Soil GDDs provided similar results to air GDDs; thus, either model would seem appropriate for predicting crop development in this region. Plant height, number of nodes with capsules, and number of branches were increased at wider row spacings in the Live Oak trials as compared with narrow rows. These two trials illustrated the potential of sesame for attaining economically sustainable yields in the southeastern USA, but further exploration and modeling of agronomic traits will be needed to reach the crop’s full yield potential in these regions. [ABSTRACT FROM AUTHOR]

Integrating bahiagrass (Paspalum notatum Flueggé) into peanut (Arachis hypogaea L.) production systems can improve soil structure, and increase peanut yield. A study was conducted in 2012 and 2013 in north Florida to evaluate practices for planting peanut into bahiagrass with three tillage methods i.e.; strip till (ST), ST and high residue cultivation (ST/HRC), and conventional (CT) tillage. Tillage times were 30 d before planting (DATE1) and at planting (DATE2). Peanut grown under CT outyielded ST/HRC (6940, 6580, and 6370 kg ha−1 for CT, ST, and ST/HRC, respectively), but there was no difference in economic return across treatments (adjusted revenue avg. = US $2478 ha−1). Tillage DATE2 increased total root length compared with DATE1, particularly for CT and ST. The ST/HRC had increased total root length below 30 cm for DATE1. When peanut was planted into bahiagrass, conservation tillage practices maintained adjusted revenue comparable with CT while providing environmental benefits. [ABSTRACT FROM AUTHOR]

Splitting N fertilizer application is recommended to increase crop N use efficiency by reducing risk of leaching. The objective of this study was to optimize the timing and rate of split N fertilizer applications to maximize tuber yield and quality of chipping potatoes grown using seepage irrigation in Florida. A two-year study was conducted on two commercial farms using cultivars Atlantic and FL1867. A factorial of two N rates applied at pre-plant (N pre-pl ) 0 or 56 kg ha −1 30 days before planting followed by four N rates applied at plant emergence (N emerg ) 0, 56, 112, or 168 kg ha −1 were randomized in a complete block design with four replicates. At tuber initiation, all treatments received an additional 56 kg ha −1 of N. All applications of N were of granular ammonium nitrate banded. Total N applied for the various treatments ranged from 56 to 280 kg ha −1 of N. Soil N was monitored in the 0–20 cm soil depth layer throughout the season. Whole plant biomass peaked at 8.5–8.7 Mg ha −1 with N emerg rates between 112–143 kg ha −1 . Plant N uptake range from 66 to 157 kg ha −1 . N uptake use efficiency decreased with increasing N rates. Potato yield ranged from 25 to 42 Mg ha −1 in both years. In 2013, application of 56 kg ha −1 of N pre-pl produced 2.5–5.1 Mg ha −1 higher yield than treatments receiving 0 N. In 2014, there was an interaction between N pre-pl and N emerg on yield. The higher 56 kg ha −1  N pre-pl resulted in higher yield only when N emerg was at or below 56 kg ha −1 . For cv. Atlantic when no N pre-pl was supplied, yield increased linearly in response to N emerg rates, while with 56 kg ha −1 of N pre-pl , yield responded quadratically to N emerg reaching a maximum at 114 kg ha −1 . For cv. FL1867 yield increased quadratically to N emerg peaking at 138 and 126 kg ha −1 of when 0 or 56 kg ha −1 of N pre-pl was applied, respectively. The study shows that while the risk of N pre-pl loss is high, N pre-pl can result in higher yield, especially when subsequent N rates are low. Application of N pre-pl was particularly effective in a dry year. By contrast, when soil mineral N from N pre-pl was largely lost to leaching in a high rainfall year, yield was increased by the N pre-pl application only when subsequent N emerg rates were less than 112 kg ha −1 . When early-season soil N was low, the N emerg had a larger impact on tuber yield due to minimum loss to leaching, maximizing yield when N emerg was 128–168 kg ha −1 . This indicates that applying N fertilizer prior to emergence is necessary to maximize tuber yield. [ABSTRACT FROM AUTHOR]

Papaya ( Carica papaya L.) production in south Florida is limited by trade winds, storm wind damage, and papaya ringspot virus (PRSV) infection. This study was implemented to test a system intercropping sunn hemp ( Crotalaria juncea L.) with papaya during papaya establishment, then mowing the intercrop and using it as a mulch on papaya beds. The study was performed in 2014 and repeated in 2015. Treatments included no sunn hemp (No-SH), sunn hemp mown early (SH-ME) 65 days after transplanting (DAT), and sunn hemp mown late (SH-ML) at 100 DAT. Wind speeds, sunn hemp growth and biomass contribution, papaya above ground growth, yield, flowering date, weeding time, and gas exchange variables, including net CO 2 assimilation ( A ) and stomatal conductance ( g s ) of H 2 O were measured. In 2015, additional measurements included PRSV infection rates and root growth via minirhizotron imaging. Results indicated a positive establishment environment as a result of the sunn hemp intercrop-mulching system. The system reduced weed pressure, reduced wind speed within papaya rows, and increased papaya growth after mowing and mulching. In 2015, standing sunn hemp reduced PRSV infection rates and hastened flowering. Mulching increased root growth in 2015, and A and g s for 2 months after mulching. The SH-ML treatment led to elongation and reduced growth due to excessive shading. With the appropriate timing of mowing, this system promises improved production efficiency and reduced risks for south Florida papaya producers. [ABSTRACT FROM AUTHOR]

Although castor ( Ricinus communis L.) oil has high commercial value for industrial uses as well as a feedstock for biodiesel, the United States has relied on imported castor oil since 1972. In Florida, the crop has been considered as an alternative crop to the more traditional agronomic row crops and would likely be produced under center pivot or other irrigation systems to maximize yield and fit with existing cropping systems. To develop an appropriate K c value for the central Florida region, research was conducted at the University of Florida’s Plant Science Research and Education Unit in Citra, FL. Season-long crop transpiration was measured for the castor cultivar ‘Brigham’ in 2011 and 2012 and soil evaporation rates were quantified in 2012. Crop transpiration was obtained by sap flow analysis when the plots had reached complete canopy cover, were fully irrigated, and when daily solar radiation levels were at or above a historical radiation average to accurately reflect optimum growing conditions. Daily average plant transpiration (57,199 and 56,560 L ha −1 in 2011 and 2012, respectively) were predominantly greater than daily soil evaporation (38 L ha −1 in 2012), and as a result, the season long plant transpiration was the main factor included for the calculation of crop evapotranspiration (ET c ). The ET c was evaluated against the reference evapotranspiration (ET o ) from site specific meteorological data to calculate daily K c values. The 10-day K c averages were compared to published K c values from the Food and Agriculture Organization (FAO) for castor. The crop developmental timeframes in this study were roughly aligned with the FAO timeframes when making these comparisons. The mid-season K c values were similar to the FAO reference (1.19, Florida vs. 1.15 FAO ref.), but the late season K c values for castor in Florida were higher as compared to the FAO reference (1.50 vs. 0.55, respectively). The increase in water use during this late season developmental period could be explained by a lack of physiological decline in this sub-tropical climate and continued irrigation application for this trial during the latter part of the season. These results provide appropriate K c values for central Florida and will aid growers in irrigation decisions when producing castor in this region. [ABSTRACT FROM AUTHOR]

Water-use efficiency is often genetically correlated with specific leaf area (SLA) and leaf C isotopic composition (δ13C) in peanut (Arachis hypogaea L.). The objectives of this study were to examine the effects of environment, genotype, and genotype × environment interaction on SLA, δ13C, harvest index (HI), and yield and to estimate heritability and the genetic relationships. Fifteen genotypes were tested at two locations with different drought intensities for 2 yr. The additive main effects and multiplicative interaction analysis based on yield data divided eight environments (locations × treatments × years) into four clusters, which reflected a gradient in drought stress, indicating yield trait is a good indication of drought stress. The genotype Exp8-12 was identified as a best drought tolerant germplasm across environments. Heritability estimates for HI (0.68 to 0.89) and δ13C (0.75 to 0.89) were higher than those for SLA (0.31 to 0.88) and yield (0.12 to 0.65). A positive but small genetic correlation coefficient (rg) (0.26) was found between HI and yield, and low to moderate rg (0.14 to 0.55) were observed between HI and SLA. A relative high negative genetic correlation rg (-0.81 to -0.57) was found between δ13C and yield. In theory, the high heritability and no G×E interaction for δ13C make it possible a surrogate that can be used to assess drought tolerance in peanut breeding. [ABSTRACT FROM AUTHOR]

Summary • We enumerated arbuscular mycorrhizal (AM) fungal spore communities for 3 yr as part of a long-term CO2 enrichment experiment at Cedar Creek, Minnesota, USA. Complete factorial combinations of two levels of CO2 and N, and 16 perennial plant species grown in monoculture and 16-species polyculture were arranged in a split-plot design. • In 1998–2000, spore communities were quantified under monocultures of eight plant species. In 2000, measurements were expanded to include monocultures and polycultures of all of the plant species. • Under plant monocultures, only Glomus clarum responded significantly to CO2 elevation out of 11 species present. This response was not detectable under plant polycultures. Glomus clarum was also significantly more abundant under plant polycultures. Nitrogen addition had small negative effects on AM fungal spore abundance and species richness in 2000. The interaction of CO2 and N did not affect arbuscular mycorrhizal fungal spore communities. • We show that CO2 enrichment and plant species richness impact arbuscular mycorrhizal fungal community structure. These findings are important because altered symbiotic functioning may result. [ABSTRACT FROM AUTHOR]

Long-term ecological experiments provide unique opportunities to observe the effects of natural selection. The Park Grass Experiment at Rothamsted Experiment Station in Hertfordshire, UK, is the longest running ecological experiment that incorporates fertilization treatments and has been ongoing since 1856. In the 1970s, local adaptation was observed in the grass Anthoxanthum odoratum to the elevated soil aluminium levels of the fertilized plots. Gould et al. () have utilized this system to reevaluate the extent of local adaptation, first documented nearly 45 years ago (Snaydon ), and to use emerging molecular approaches to identify candidate genes for the adaptation. From their work, they identify several plausible candidate loci for aluminium tolerance. This work shows the power of long-term field-based trials in a scientific age concentrated on rapidly emerging molecular techniques often utilized in short, narrowly focused laboratory or controlled environment experiments. The current study clearly illustrates the benefits gained by combining these molecular approaches within long-term monitoring experiments that can be regularly revisited in a changing world and used to address questions on evolutionary scales. [ABSTRACT FROM AUTHOR]

• Most sesame roots were present between 20 to 50 cm deep, and root diameter did not exceed 2 mm. • There was evidence of a lag in senescence between below- and aboveground parts of the plant. • Genotypic differences between non-dehiscent cultivars did not translate into strong rooting architectural differences. This study described sesame's rooting behavior and the relationship between above- and belowground biomass in architecture and senescence dynamics. Six non-dehiscent sesame cultivars, branched and non-branched, were grown for two years in North Central Florida's sandy soils in 2013 and 2014. The root systems were imaged in situ with a minirhizotron camera 5 times in 2013 and 7 times in 2014. Total root length, surface area and diameter were measured for each image, and roots were separated between alive, dying and dead. Leaf area index was recorded 5 times both years. Results showed that averaged maximum root diameter for all cultivars was <2 mm. Most roots were present between 20 to 50 cm deep, and a multivariate approach, namely a canonical discriminant analysis, showed that some cultivars tended to have more roots in the soil mid-depth ranges than others. However, these observations were not stable throughout the season. Leaf area index showed differences between cultivars, but these did not translate into contrasting yields. Results also highlighted a lag between leaf area index and total root length senescence, the former declining about 2 weeks before the latter. This study is among the first to describe sesame rooting characteristics in details. [ABSTRACT FROM AUTHOR]

The soils of the Everglades Agricultural Area (EAA) are mainly organic soils (Histosols), and their artificial drainage promoted aeration and resulted in soil subsidence. Sugarcane (Saccharum spp.) nitrogen (N) requirement has been fulfilled historically by organic matter mineralization, so very shallow soils could be limiting N availability for the crop. The objectives of this study were to measure sugarcane leaf N concentration and levels of available N across EAA organic soils with variable soil depth and then determine if there are relationships among soil depth, soil N concentration, and sugarcane leaf N concentration in Florida Histosols. A total of 60 plots were established in 30 commercial sugarcane fields in the EAA with soil depth varying from 15 to 145 cm over limestone bedrock. In each location, soil depth, soil, and leaf nutrient concentrations, and leaf chlorophyll measurements were determined during the grand growth period (June 1 – October 15) of the crop. There were no significant correlations between soil depth and either leaf N concentration or leaf chlorophyll measurements. There were positive correlations between soil water and soil NH4+-N concentration and between soil NO3–N concentration and leaf N concentration. Our results determined that mineralization is still providing adequate N supply for sugarcane. [ABSTRACT FROM AUTHOR]

Rhizoma peanut (RP, Arachis glabrata Benth.) is an important perennial forage legume, but its adoption can be limited by relatively slow establishment. Genotype and temperature after planting of rhizomes likely affect partitioning of stored and new photoassimilates, but their impact on establishment rate is not known. To assess these relationships, planting date and RP entry effects were measured on biomass partitioning and growth responses. Treatments were all combinations of two planting dates (spring and summer) and four entries ('Florigraze', 'UF Peace', 'UF Tito', and the germplasm Ecoturf) replicated four times, with new plots planted in each of 2 yr. Spring‐planted Florigraze outperformed UF Peace in shoot count, shoot biomass, and root‐rhizome biomass through much of the year of planting. When planted in summer, UF Tito and UF Peace generally had earlier and greater shoot emergence, lesser root‐rhizome/shoot ratio, taller canopy height, and lesser leaf/stem ratio than Ecoturf or Florigraze. Across years, shoot biomass in the year after planting was greater for UF Peace and UF Tito than for Ecoturf and Florigraze when planted in summer (490, 387, 265, and 157 g m−2, respectively) and greater for UF Peace than Ecoturf or Florigraze planted in spring (349, 243, and 201 g m−2, respectively). UF Tito and UF Peace had greater shoot biomass in the year after planting for summer than for spring plantings, but there was no season effect for Ecoturf and Florigraze. Summer planting favored rapid establishment of upright cultivars UF Tito and UF Peace, but Ecoturf and Florigraze were less affected by season. [ABSTRACT FROM AUTHOR]

Seed maturity in peanut (Arachis hypogaea L.) determines economic return to a producer because of its impact on seed weight (yield), and critically influences seed vigour and other quality characteristics. During seed development, the inner mesocarp layer of the pericarp (hull) transitions in colour from white to black as the seed matures. The maturity assessment process involves the removal of the exocarp of the hull and visually categorizing the mesocarp colours into varying colour classes from immature (white, yellow, orange) to mature (brown, and black). This visual colour classification is time consuming because the exocarp must be manually removed. In addition, the visual classification process involves human assessment of colours, which leads to large variability of colour classification from observer to observer. A more objective, digital imaging approach to peanut maturity is needed, optimally without the requirement of removal of the hull's exocarp. This study examined the use of a hyperspectral imaging (HSI) process to determine pod maturity with intact pericarps. The HSI method leveraged spectral differences between mature and immature pods within a classification algorithm to identify the mature and immature pods. Therefore, there is no need to remove the exocarp nor is there a need for subjective colour assessment in the proposed process. The results showed a consistent high classification accuracy using samples from different years and cultivars. In addition, the proposed method was capable of estimating a continuous-valued, pixel-level maturity value for individual peanut pods, allowing for a valuable tool that can be utilized in seed quality research. This new method solves issues of labour intensity and subjective error that all current methods of peanut maturity determination have. • Peanut maturity estimated without pod blasting or a maturity profile board. • Hyperspectral imagery is used to estimate pixel-level maturity. • Trained classification model is applied to peanuts of different years and cultivars. • Peanut maturity classification on testing data averages of 91.15% overall accuracy. [ABSTRACT FROM AUTHOR]

Harvest index (HI) is conventionally measured using end-of-season biomass, but leaf abscission during crop growth can represent a substantial portion of total crop biomass for several species. A field study was conducted in Florida, USA, to determine the accuracy of conventional and alternative HI methods using sesame (Sesamum indicum L.) as a model species and to assess biomass and nutrient contributions from abscised leaves. Seed and nutrient HI was determined from three cultivars using the following four methods: (1) total biomass method that included both end-of-season and seasonal abscised biomass; (2) conventional method based solely on end-of-season biomass; (3) early-bloom method in which biomass collected during early-bloom stage was used as the nonseed biomass component; (4) mid-bloom method where biomass from mid-bloom stage was used for nonseed biomass. Early- and mid-bloom methods overestimated all HI and underestimated biomass and nutrient return to the soil. Most nutrient HI based on the conventional method was higher than the values based on the total biomass method. Compared to the total biomass method, the conventional method underestimated biomass and nutrient return to soil per ha by 714.8 kg biomass, 28.5 kg nitrogen, 3.6 kg phosphorus, 34.7 potassium, 4.6 magnesium, 25.7 calcium, 3.4 kg sulfur, 26.5 g boron, 361 g zinc, 25.9 g manganese, 527.2 g iron, and 18.7 g copper. Including abscised leaves when determining HI may not be feasible in field experiments due to labor constraints but is an option when measuring HI for species under similar management at regional scales to improve estimates of nutrient cycling. [ABSTRACT FROM AUTHOR]

Abstract: Spotted wilt, caused by tomato spotted wilt virus (TSWV), is a major disease of peanut (Arachis hypogaea) in the south‐eastern United States. Cultivar resistance is the most important factor in disease control. However, spotted wilt resistance in current cultivars still carries risk in the absence of other practices when disease is severe. In contrast, a newly developed cultivar, Florida‐EP™ “113,” has demonstrated excellent resistance even when spotted wilt is severe. Information on heritability of this resistance can help breeders better utilize it in breeding. F2‐derived populations from the cross Florida‐EP™ “113”/Georgia Valencia were developed and tested in field experiments in Florida from 2012 to 2014. Disease symptoms were evaluated visually, and the frequency of TSWV infection was measured by ImmunoStrip®. Heritability estimated from ImmunoStrip® was higher (0.66) compared to visual ratings (0.48). Genetic correlations among evaluation methods (rA = 0.92–0.99) and environments (rB = 0.86–0.99) were high. These results indicate that resistance in Florida‐EP™ “113” is highly heritable and that selection in a high disease risk environment is feasible without significant erosion of genetic gain. [ABSTRACT FROM AUTHOR]

The indeterminate nature and underground fruiting habit of peanut (Arachis hypogaea L.) makes it a challenge to determine the optimal harvest time. The objectives of this study were (1) to gain additional information about how maturity and canopy health influence peg strength, yield, and grade and (2) to address anecdotal claims of differences in peg strength and digging losses among cultivars. Field trials were established in Citra, FL, and Tifton, GA. Two peanut cultivars (“Georgia-06G” and “Tifguard”) were grown under two fungicide programs (full program: every 14-day spraying interval; and reduced program: every 28-day spraying interval), and harvested at three different maturity levels (early, optimum, and late based on an accumulated growing degree day method). The fungicide program had a significant impact on yield only in 2013 at Citra, likely because the canopy structure was decreased because of fungal disease known as leaf spots (causal agents: Cercospora arachidicola and Cercosporidium personatum). The timing of the harvest had a significant impact on yield, grade, peg strength, and digging loss. In addition, yield, grade, peg strength, and digging losses differed between the peanut cultivars. These results show that reduced fungicide program might affect the yield because of the disease severity and that the optimal harvest time should consider the level of the defoliation. Although there was no correlation between peg strength and digging loss, over-maturity can cause more digging losses compared to optimal harvest time. Tifguard had higher digging loss than Georiga-06G. This study provides additional useful information on cultivars to growers. [ABSTRACT FROM AUTHOR]

Fertilization of perennial grass pastures is a major expense in beef cattle operations, and grass pastures may degrade in the absence of N fertilization. Grass--legume mixtures can reduce the demand for N fertilizer use while increasing productivity of the system. Arachis spp. have shown potential for use in association with grasses in the southeastern United States. During 2014, 2015, and 2016, we evaluated one annual peanut species (Arachis hypogaea L. TUFRunner '727') and two perennial peanut species, pintoi peanut (A. pintoi Krap. & W.C. Greg 'Amarillo') and rhizoma peanut (A. glabrata Benth. 'Florigraze' and germplasm Ecoturf), when planted into previously established 'Pensacola' bahiagrass (Paspalum notatum Flügge) sod. Responses measured included herbage accumulation (HA), botanical composition, nutritive value, biological N2 fixation, and belowground root-rhizome responses. TUFRunner 727 showed reseeding ability, illustrating potential for use as a short-term forage, but by 2016, its contribution was negligible. In 2016, Ecoturf--bahiagrass had greater HA than unfertilized bahiagrass (4160 and 2710 kg ha-1, respectively), and the Ecoturf contribution to HA was ~30% in 2016. Average N concentrations for Ecoturf and Florigraze were 25 and 22 g kg-1, respectively, and in vitro digestible organic matter concentration was 700 g kg-1 for both. Pintoi peanut contributed little to mixture HA in the first 2 yr, but it persisted and increased in proportion with time. Over the course of 3 yr, Ecoturf rhizoma peanut performed better than all other entries, exhibiting increasing participation in mixtures each year and the greatest total HA in 2016. [ABSTRACT FROM AUTHOR]

Elephantgrass (Pennisetum purpureum Schum.) and energycane (Saccharum spp.) are promising perennial bioenergy crops in the southeastern United States. Despite plentiful rainfall in this region, these perennial grasses have a long growing season and are subject to intermittent drying cycles frequently during summer and fall, yet there is little information on their response to intermittent drought stress. The objectives of this study were to investigate water relations of elephantgrass and energycane genotypes under optimal water inputs and in response to progressive soil drying. Three elephantgrass genotypes ('UF-1', 'Merkeron', and 'PI-300086') and three energycane genotypes ('L79-1002', 'US84-1047', and '875-3') were grown in a greenhouse. Under well-watered conditions, elephantgrass and energycane exhibited similar daily and total water use, but energycane possessed greater average daily transpiration per unit leaf area (EAVE,leaf) and lower shoot transpiration efficiency (TEshoot) than elephantgrass. Consistent with EAVE, leaf, energycane demonstrated higher stomatal conductance than elephantgrass, but lower assimilation to transpiration ratio (A/T). Among all genotypes, UF-1 elephantgrass exhibited relatively high A/T, shoot mass production, and TEshoot. In response to progressive soil drying, elephantgrass genotypes closed their stomata at a lower fraction of transpirable soil water and produced higher shoot mass during the drying cycle than energycane genotypes. The different plant water use patterns indicated a species difference in the sensitivity to mild drought stress and could be correlated with their stomatal density and size. The results from this study indicated that elephantgrass is more suited to the frequent mild drought stress between rainfall events common during summer in the southeastern United States. [ABSTRACT FROM AUTHOR]

Land use conversion of row crops to bioenergy cropping systems in the southeastern United States (U.S.) creates concerns associated with water use and NO 3 -N leaching. Production of energy from biomass is associated with large amounts of byproducts generated during biofuel processing. Biochar and vinasse are two nutrient rich byproducts that could be land-applied to bioenergy crops to reduce reliance on synthetic fertilizer. However, effects on water dynamics of applying these byproducts to support biomass production is poorly understood, particularly when bioenergy crops replace traditional row crops. Thus, this study aimed to compare a cotton ( Gossypium hirsutum L.)-peanut ( Arachis hypogaea L.) rotation to sweet sorghum [ Sorghum bicolor (L.) Moench] receiving annual applications of biochar and vinasse, on biomass yield, crop evapotranspiration, water use efficiency (WUE), NO 3 -N leaching, and soil volumetric water content. A field study was conducted from 2013 to 2015 to assess the following treatments: cotton + 150 kg N ha −1 (COT), peanut + 30 kg N ha −1 (PEA), and sweet sorghum receiving one of the following i) 30 kg N ha −1 (S30); ii) 30 kg N ha −1 + biochar (S30B); iii) 30 kg N ha −1 + vinasse (S30V); and iv) 150 kg N ha −1 (S150). Similar aboveground dry matter yields were obtained in 2013 and 2015 for cotton and all sweet sorghum treatments and were on average 19 Mg ha −1 for both years. S30 and S150 achieved similar yields. Sweet sorghum and COT exhibited the highest WUE (∼5 g kg −1 ). S30B increased soil moisture retention at 0–0.2 m depth 36, 29, and 24% in 2013, 2014, and 2015, respectively. Biochar incorporated at 0.15 m soil depth increased soil moisture retention down to 0.4 m. Low N rate application combined with biochar in S30B could represent an alternative management practice to minimize N leaching, recycle nutrients, and increase soil water retention if sweet sorghum were to be widely adopted by farmers in the southeastern U.S. [ABSTRACT FROM AUTHOR]

Changing pasture land to the production of bioenergy crops will affect regional water dynamics. Returning by-products of industrial conversion of bioenergy crops like fermentation residual or biochar back to the field could be used to improve sustainable nutrient management, but could also impact water quantity and quality in ways that are poorly understood. The objective of this study was to assess the effects of land-use conversion from low-input bahiagrass ( Paspalum notatum Flüggé) pastures to elephantgrass [ Pennisetum purpureum (L.) Schum.] for bioenergy production under different nutrient management practices on biomass yield, crop water dynamics and nitrate-nitrogen (NO 3 -N) leaching during growing and dormant seasons. Treatments evaluated were 1) bahiagrass + 50 kg N ha −1 ; 2) elephantgrass + 50 kg N ha −1 ; 3) elephantgrass + 50 kg N ha −1 + fermentation residual; 4) elephantgrass + 50 kg N ha −1 + biochar; and 5) elephantgrass + 250 kg N ha −1 . Data were collected on crop evapotranspiration (ET), water use efficiency, drainage, NO 3 -N leaching, and aboveground dry matter accumulation. Dry matter yield of elephantgrass was 4- to 7-fold greater than bahiagrass after the first growing season, but was similar among elephantgrass treatments. Elephantgrass produced with no residual amendments reduced drainage (approx. 43% across all growing seasons) compared to bahiagrass, and this reduction was exacerbated in the residual treatments. Reduced drainage was associated with increased ET. Elephantgrass, regardless of treatment, reduced the amount of NO 3 -N lost through drainage compared to bahiagrass. Therefore, replacing bahiagrass with elephantgrass will increase cropping system water use and diminish the rate of groundwater replenishment during the growing season, which could have detrimental effects for other ecosystem processes that rely on this water resource. However, elephantgrass increased the efficiency with which water was used to produce biomass and reduced NO 3 -N leaching to groundwater. [ABSTRACT FROM AUTHOR]

Soil physical quality indicator, Least Limiting Water Range (LLWR) is the range of soil water content, where water, oxygen and mechanical resistance are not limiting factors to root growth. The objective of this study was to evaluate LLWR, soil water availability, potato root growth and tuber yield under different water table management levels. Water table level was managed targeting 0.36 and 0.76 m below the soil surface, denoted as high (HI) and low (LO) level, respectively. Undisturbed soil core samples were obtained in the 0–0.15, 0.15–0.30 and 0.30–0.45 m soil layers to assess the LLWR. Root parameters were assessed using mini-rhizotrons installed into the soil along the potato row. Overall, LLWR decreased in depth due to a decrease in soil organic matter and an increase soil bulk density. The LO resulted in a narrower range for LLWR than HI. In the 0–0.15 m soil layer, the soil water content in the HI treatment fell inside the LLWR limits with high frequency during the growing season, but both water table levels resulted in similar root growth. In contrast, in the 0.15–0.30 and 0.30–0.45 m soil layers, soil water content fell inside LLWR more frequently in the LO than HI treatment. The LO management increased potato root length and surface area in the 0.15–0.30 m soil layer compared to HI; while in the 0.30–0.45 m soil layer, roots were not present in the HI likely due to the soil water content that was above LLWR. Optimal potato root growth was observed when the soil water content fell within the LLWR range at the highest frequency during the season. Despite impacts on the root system, similar tuber yields were achieved between LO and HI treatments. Nevertheless, the treatment HI used three times more water to supply the crop water requirement than LO. [ABSTRACT FROM AUTHOR]

Sesame is a new crop for the southeastern USA, most recently being considered for this region because of frequent drought events in the historical farming area of the crop, that is, Texas and Oklahoma, and for overall expansion of its domestic production. Although sesame was introduced in the USA in the 19th century, its commercial cultivation was not possible before the 1990s with the release of non-dehiscent cultivars. The southeastern USA has been considered promising because of its greater annual precipitation as compared with the southwestern USA. In addition, sesame has some highly valuable agronomic characteristics that could make the crop a beneficial addition to crop rotations in the southeast. These crop characteristics include the following: nematode resistance potential, drought tolerance, nitrogen recovery ability, rotational suitability with the predominant agronomic crops in the region, and capacity to attract a wide variety of pollinators. Since very little United States-based literature is available on the crop, the objective of this review is to provide: 1) a sesame history in the USA; 2) a description of the botanical characteristics of the crop that make it suitable for mechanized production in the USA; and 3) an overview of the principal sesame production methods of interest for the southeastern USA. [ABSTRACT FROM PUBLISHER]

A better understanding of changes in root growth and distribution when soil is treated with biochar is needed. The aim of this study was to assess root distribution responses when biochar is added to the soil. A greenhouse study was conducted to investigate the effects of topdressing or incorporating four biochar rates on soybean [Glycine max (L.) Merr.] root distribution during early vegetative stages grown in lysimeters (depth: 35 cm). On average, topdressing either 10 or 25 Mg biochar ha−1 increased root length density (RLD) 39% and root surface area (RSA) 36% in the 0- to 0.05-m soil layer compared with the control. In the 0.05- to 0.15-m soil layer, incorporation of 10 Mg ha−1 increased RLD 35%. Similarly, incorporation of either 10 or 25 Mg biochar ha−1 increased RSA 38% compared with the control. Incorporation of 25 and 50 Mg biochar ha−1 in the top 0.15 m of soil increased leaf area 29 and 31% compared with topdressing 50 Mg biochar ha−1 and with the control, respectively. Biochar increased soybean RLD, RSA, and leaf area, especially when incorporated into the soil. Overall, our findings indicate that biochar application and placement within the soil affects plant-rooting distribution, which represents an important management practice to increase RLD and RSA. Future research should focus on evaluating biochar rates and application methods under field conditions. [ABSTRACT FROM AUTHOR]

Plant root architecture offers the potential for increasing soil water accessibility, particularly under water-limited conditions. The objectives of this study were to evaluate the root architecture in two genotypes of sorghum (Sorghum bicolor(L.) Moench) differing in root angles and to assess the influence of different deficit irrigation regimes on root architecture. The response of two sorghum genotypes, ‘Early Hegari-Sart’ (EH; steep root angle) and ‘Bk7’ (shallow root angle) to four irrigation treatments was investigated in two replicated outdoor studies using large pots. The results indicated that EH possessed steeper brace and crown root angles, fewer brace roots, greater root biomass, and root length density than Bk7 at deeper soil depths (i.e., 15–30 and 30–45 cm) compared with a shallower depth (i.e., 0–15 cm). Across the soil profile, EH had greater root length density and length of roots of small diameter (<1 mm) than Bk7. Accordingly, EH showed more rapid soil-water capture than Bk7. Different levels of irrigation input greatly affected root architecture. Severe deficit irrigation (25% of full crop transpiration throughout the season) increased the angle and number of crown roots, root biomass, and root length density compared with 75 and 100% of full crop transpiration treatments. Consequently, root system architecture can be effectively manipulated through both genotypic selection and irrigation management to ensure optimal performance under different levels of soil available water. [ABSTRACT FROM AUTHOR]

Second-generation biofuels and bio-based products derived from lignocellulosic biomass are likely to replace current fuels derived from simple sugars and starch because of greater yield potential and less competition with food production. Besides the high aboveground biomass production, these bioenergy grasses also exhibit extensive root systems. The decomposition of root biomass greatly influences nutrient cycling and microbial activity and subsequent accumulation of carbon (C) in the soil. The objective of this research was thus to characterize root morphological and chemical differences in six perennial grass species in order to better understand root decomposition and belowground C cycling of these bioenergy cropping systems. Giant reed ( Arundo donax), elephantgrass ( Pennisetum purpureum), energycane ( Saccharum spp.), sugarcane ( Saccharum spp.), sweetcane ( Saccharum arundinaceum), and giant miscanthus ( Miscanthus × giganteus) were established in Fall 2008 in research plots near Gainesville, Florida. Root decomposition rates were measured in situ from root decomposition bags over 12 months along with initial and final root tissue composition. Root potential decomposition rate constant ( K) was higher in elephantgrass (3.64 g kg−1 day−1) and sweetcane (2.77 g kg−1 day−1) than in sugarcane (1.62 g kg−1 day−1) and energycane (1.48 g kg−1 day−1). Notably, K was positively related to initial root tissue total C (Total C), total fiber glucose ( TFG), total fiber xylose ( TFX), and total fiber carbohydrate ( TFC) concentrations, but negatively related to total fiber arabinose ( TFA) and lignin ( TL) concentrations and specific root volume ( SRV). Among the six species, elephantgrass exhibited root traits most favorable for fast decomposition: high TFG, high TFX, high TFC, high specific root length ( SRL), and a low SRV, whereas giant reed, sugarcane, and energycane exhibited slow decomposition rates and the corresponding root traits. Thus, despite similar aboveground biomass yields in many cases, these species are likely to differentially affect soil C accumulation. [ABSTRACT FROM AUTHOR]

Keeping soil moisture content at field-capacity in the root zone tends to maximize crop yield. However, this is challenging in sandy soils with a shallow water table and low water holding capacity. Seepage irrigation (SEP) relies on capillarity water movement from a water table to irrigate the crop, creating uneven soil moisture distribution across the field, which could be improved with drip irrigation. The objectives of this study were to evaluate irrigation water use efficiency (IWUE) for potatoes and soil moisture distribution uniformity of two drip tape installation depths (surface at 0.05 m, SUR and subsurface at 0.15 m, SUB) as an alternative method to SEP. The design of the experiment was a randomized complete block with irrigation treatments as main plots, and potato varieties (Atlantic, Fabula, and Red LaSoda) as subplots. The volume of water applied, water table level, and soil volumetric water content were continuously measured for two seasons, 2011 and 2012. Drip irrigation significantly increased the moisture distribution uniformity in the potato ridge. The majority of the plant root system was concentrated in the upper soil layer (∼0.3 m), regardless of irrigation treatment. Similar marketable yield between SUR and SEP were achieved for Fabula and Atlantic in the first season, while lower yields were reported for Red LaSoda under drip in both years. The SUB produced lower yield in both years attributed to limited water capillarity. Drip irrigation reduced water use 48% and 88% in 2011 and 2012, respectively. Higher IWUE was obtained with drip compared to SEP for all varieties in 2012. The SEP used more irrigation water to supply the crop than SUR resulting in a difference in IWUE of 5.7 kg m −3 . The SUR was capable of adequately irrigating the potato shallow root producing similar yield to SEP for Atlantic and Fabula varieties. [ABSTRACT FROM AUTHOR]

'Florigraze' rhizoma peanut (RP; Arachis glabrata Benth.) is a persistent forage legume for the US Gulf Coast, but peanut stunt virus (Cucumovirus spp.) reduces herbage accumulation (HA). Less susceptible germplasms and cultivars of RP have been released, but their responses to grazing management are not known. The objective was to quantify aboveground and belowground sward responses to grazing management of RP entries differing in growth habit to explain HA and persistence. Treatments were all combinations of four RP entries (Florigraze, 'UF Peace', 'UF Tito', and germplasm Ecoturf), two grazing intensities (50 and 75% removal of pre-grazing canopy height), and two regrowth intervals (3 or 6 wk). UF Tito swards were the tallest and Ecoturf the shortest, but Ecoturf had greater herbage bulk density than any entry. Pre-grazing leaf percentage was greatest for Ecoturf (61%); there were no differences among the upright entries (56-57%). Ecoturf (0.88) and UF Tito (0.76) had greater post-grazing residual leaf area index than Florigraze (0.61). Ecoturf and UF Tito had greater rhizome-root mass (4450 and 4110 kg ha-1, respectively) than Florigraze and UF Peace (3490 and 3170 kg ha-1, respectively). Pre-grazing light interception was greater for the 6-than 3-wk grazing frequency (85 vs. 70%, respectively), and rhizome-root mass followed a similar pattern (3990 vs. 2730 kg ha-1, respectively). Sward structure, leaf, and rhizome-root data explain lack of differences among entries in HA, excellent persistence of Ecoturf and UF Tito, and generally greater HA and persistence for 6vs. 3-wk regrowth intervals. [ABSTRACT FROM AUTHOR]

Understanding rooting dynamics using the minirhizotron technique is useful for cultivar selection and to quantify nematode damage to roots. A 2-yr microplot study including five bermudagrass ('Tifway', Belonolaimus longicaudatus susceptible; two commercial cultivars [TifSport and Celebration] and two genotypes ['BA132' and 'PI 291590'], which have been reported to be tolerant to B. longicaudatus) and two St. Augustinegrass ('FX 313', susceptible, and 'Floratam' that was reported as tolerant to B. longicaudatus) genotypes in a 5 x 2 and 2 x 2 factorial design with four replications, respectively, was initiated in 2012. Two treatments included were uninoculated and B. longicaudatus inoculated. In situ root images were captured each month using a minirhizotron camera system from April to September of 2013 and 2014. Mixed models analysis and comparison of least squares means indicated significant differences in root parameters studied across the genotypes and soil depths of both grass species. 'Celebration', 'TifSport' and 'PI 291590' bermudagrass, and 'Floratam' St. Augustinegrass had significantly different root parameters compared to the corresponding susceptible genotypes (P ≤ 0.05). Only 'TifSport' had no significant root loss when infested with B. longicaudatus compared to non-infested. 'Celebration' and 'PI 291590' had significant root loss but retained significantly greater root densities than ' Tifway' in B. longicaudatus-infested conditions (P ≤ 0.05). Root lengths were greater at the 0 to 5 cm depth followed by 5 to 10 and 10 to 15 cm of vertical soil depth for both grass species (P≤ 0.05). 'Celebration', 'TifSport', and 'PI 291590' had better root vigor against B. longicaudatus compared to Tifway. [ABSTRACT FROM AUTHOR]

Subirrigation requires precise control of the water table level to provide adequate soil water content (SWC) for promoting plant growth. Optimizing water table level management has been shown to improve soil aeration, reduce N-leaching, and reduce risk of crop losses. The objectives of this study were to: i) assess if water table level and N-fertilizer rate impact potato growth, root development, plant N uptake, or tuber yield; and ii) estimate the optimum water table level threshold that provides sufficient soil upward water flux to meet plant water requirements. The study was conducted in 2013 and 2014 in Hastings, FL, USA. Water table level was automatically controlled in three independent irrigation zones of 1.4 ha at 36, 54, and 71 cm from the top of the hilled row, termed as high (HWT), medium (MWT), and low (LWT) water table treatments, respectively, and SWC measured at 22 cm depth was used as covariate to compare treatments. A randomized complete block with three replications was used to evaluate potato cultivars 'Atlantic' and 'FL1867′ under 0, 112, 224, and 336 kg ha−1 of N-fertilizer within water table treatments. Marketable yield in 2013 was lower than 2014, owing to the high precipitation (421 mm) during tuber bulking that led to high SWC and tuber decay. Total and marketable tuber yields were maximized when N fertilizer rates ranged from 243 to 336 kg ha−1. The highest yield and proportion of large tubers occurred when SWC at 22 cm ranged from 0.13 to 0.16 m3 m−3. The HWT significantly limited root length, diameter, and surface area, compared to the LWT. In 2014, variation of SWC at 22 cm depth had little effect on tuber yield. The HWT was not detrimental to tuber yield, but rather it compounded the negative effect that high precipitation rate had on fluctuating SWC in the root zone, resulting in reduced yield and tuber quality. Optimal SWC in the root zone can be achieved by adjusting the water table level and upward soil water flux throughout the season, according to the crop evapotranspiration for each crop stage, which reduces irrigation water requirements and minimizes the risks of soil water saturation and tuber yield losses. • Water table level can be adjusted according to crop evapotranspirative demand. • Increase in potato root length with lower water table level. • High water table level increases risk of tuber loss due to soil water saturation. [ABSTRACT FROM AUTHOR]

• We compiled two datasets of peanut and switchgrass root imagery for this study. • Well-trained model overcame errors in human-labeled ground truth masks. • With small datasets, transfer learning is effective to improve model performance. • Both pre-trained encoder and decoder help with performance in U-net based model. • The relevance of pre-trained dataset is more important than the size. Minirhizotron technology is widely used to study root growth and development. Yet, standard approaches for tracing roots in minirhiztron imagery is extremely tedious and time consuming. Machine learning approaches can help to automate this task. However, lack of enough annotated training data is a major limitation for the application of machine learning methods. Transfer learning is a useful technique to help with training when available datasets are limited. In this paper, we investigated the effect of pre-trained features from the massive-scale, irrelevant ImageNet dataset and a relatively moderate-scale, but relevant peanut root dataset on switchgrass root imagery segmentation applications. We compiled two minirhizotron image datasets to accomplish this study: one with 17,550 peanut root images and another with 28 switchgrass root images. Both datasets were paired with manually labeled ground truth masks. Deep neural networks based on the U-net architecture were used with different pre-trained features as initialization for automated, precise pixel-wise root segmentation in minirhizotron imagery. We observed that features pre-trained on a closely related but relatively moderate size dataset like our peanut dataset were more effective than features pre-trained on the large but unrelated ImageNet dataset. We achieved high quality segmentation on peanut root dataset with 99.04% accuracy at the pixel-level and overcame errors in human-labeled ground truth masks. By applying transfer learning technique on limited switchgrass dataset with features pre-trained on peanut dataset, we obtained 99% segmentation accuracy in switchgrass imagery using only 21 images for training (fine tuning). Furthermore, the peanut pre-trained features can help the model converge faster and have much more stable performance. We presented a demo of plant root segmentation for all models under https://github.com/GatorSense/PlantRootSeg. [ABSTRACT FROM AUTHOR]

• Peanut is said to provide N credits to future crops in the southeastern USA but evidence is lacking to support this claim. • We evaluated wheat performance following peanut, cotton, and fallow in a conservation tillage cropping system. • Peanut residues contained up to 93 kg N ha-1, but available N at wheat planting was usually not affected by cropping history. • Peanut did not provide detectible N credits to wheat, but there were cases of lower yield after cotton relative to peanut. Agricultural extension services in many peanut (Arachis hypogaea L.)-producing regions recommend that farmers reduce nitrogen (N) fertilization rates, or apply N credits, to crops planted after peanut but do not typically specify how peanut residue management or planting schedules of subsequent crops affect the magnitude of peanut N credits. The objective of this study was to quantify peanut N credits to winter wheat (Triticum aestivum L.) in a conservation tillage cropping system in different subtropical growing environments. A five site-year study was conducted in Florida, USA beginning in 2016. A split-plot experimental design was arranged in which summer crop [peanut, cotton (Gossypium hirsutum L.), and weed-free fallow] was the main plot factor, while N rate (0, 34, 67, and 101 kg N ha−1) to winter wheat was the split plot factor. Peanut and cotton were planted under strip-tillage, while winter wheat was drilled into peanut and cotton residues and weed-free fallow plots without tillage. Although peanut residues accumulated 54–93 kg N ha−1, plant available N at winter wheat planting in the 0–15 cm soil depth range of former peanut plots was only higher than in former cotton or fallow plots for one site-year. A previous peanut crop did not affect winter wheat grain yield, but there were cases of lower grain yield, grain N removal, and agronomic efficiency following cotton relative to peanut depending on site. Nonlinear regression procedures predicted that N rates required to optimize grain yields following peanut would exceed 94 kg N ha−1, further indicating the absence of detectible peanut N credits in this study. These results suggest that assuming peanut provides N credits to subsequent crops in the southeastern USA is not justified and, if assumed, will reduce the productivity of subsequent crops. [ABSTRACT FROM AUTHOR]

• Mexico's wheat production is likely to decline under future climate change. • Expanding wheat area to recently used land for wheat may be the most effective adaptation strategy to combat production loss from future climate change. • Combining new adaptive crop genetic traits with increased N fertilizer will also improve yield for irrigated and rainfed wheat for current and future climate scenarios. Mexico's 3.3 million tons current wheat production is projected to decline due to climate change. To counteract these negative impacts, we explored a range of plausible adaptation measures including change in crop management (early sowing and nitrogen fertilizer applications), crop genetic traits (early vigor, late flowering and heat tolerance) and wheat growing area expansion. Adaptation measures were simulated individually and in various combinations with a multi-crop model and multi-Global Climate Model ensemble across representative wheat growing regions and aggregated to national wheat production. Under both baseline (current) and future climate scenarios, most of the suggested individual and combined genetic traits resulted in a positive impact on irrigated wheat but were less beneficial in rainfed systems, with the largest responses observed with late flowering and increased N fertilizer. Increased N fertilizer applications on its own, but particularly combined with crop genetic traits showed the highest yield increase in the baseline, with further positive impacts in the future scenarios. Yield benefits from new crop genetic traits combined with increased N fertilizer applications could add about 672,000 t year−1 to national wheat production, after losing 200,000 t year−1 due to climate change by 2050s. Most effectively, expanding wheat to include all areas where wheat was previously grown during the last two decades could add 1.5 million t year−1 now and 1.2 million t year−1 in the future. Breeding for new crop genetic traits will reduce some of the negative impacts from future climate change, but improved cultivars need to be implemented with suitable crop management, especially N fertilizer management. [ABSTRACT FROM AUTHOR]

Perennial bioenergy grasses can potentially replace fossil fuels and offset atmospheric CO 2 through soil C sequestration. However, limited information relevant to the impacts of bioenergy cropping on ecosystem services, especially above- and below-ground productivity and soil C sequestration is available for subtropical environments (e.g., southeastern USA). The objective of this study was to evaluate the impacts of perennial bioenergy cropping on C cycling and accumulation in the soil following four years of production in North Florida. Treatments consisted of six perennial grass species: giant reed, elephantgrass, energycane, sugarcane, sweetcane, and giant miscanthus. Elephantgrass, energycane, sweetcane, and sugarcane produced great shoot biomass (31–41 Mg ha−1) when harvested once per year. Giant reed's shoot biomass responded favorably to two harvests per year (27–43 Mg ha−1), whereas giant miscanthus did not perform well in any of the years (9–21 Mg ha−1). Additionally, giant reed, sweetcane, and giant miscanthus produced greater root biomass (9–11 Mg ha−1) compared with the other three species (2.5–3.2 Mg ha−1). Among the six grasses, sweetcane, energycane, and elephantgrass resulted in increases in soil C stocks (~15 Mg ha−1) relative to the initial level. Conversely, giant reed and giant miscanthus had no increase in soil C stock. Results suggested that interspecies differences observed in biomass yield among the six perennial bioenergy grasses could therefore affect soil C accumulation. High biomass yielding species such as sweetcane, energycane, and elephantgrass can effectively increase soil C within a few years following establishment in a subtropical environment. • Giant reed, sweetcane, sugarcane, energycane, and elephantgrass were able to produce high shoot biomass in North Florida. • Giant miscanthus could not produce comparable shoot biomass with other species in the subtropical environment. • Sweetcane, energycane, and elephantgrass exhibited significant increases in soil C stock over four growing seasons. • Sweetcane, energycane, and elephantgrass are able to provide multiple ecosystem services rapidly following establishment. [ABSTRACT FROM AUTHOR]