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• The nitrification inhibitors DCD and DMPP were effective in mitigating N 2 O emissions from urea applied to potato cultivated on sandy soil. • The biostimulant containing N-fixing microorganisms increased nitrate leaching one growing season and N 2 O emissions over both seasons. • Nitrification inhibitors and biostimulants had modest agronomic benefits due to adequate available N for potato production. • Further studies should assess biostimulants performance and investigate their effects on biological processes in other agro-ecosystems. Urea is the dominant form of nitrogen (N) fertilizer used globally. Various additives have been designed for co-application with urea to improve performance of N-intensive crops including potato (Solanum tuberosum L.). Few if any studies have compared 'inhibitor' additives with 'biostimulants' designed to enhance plant growth or microbial activity. Over two potato growing seasons (2015–2016) in an irrigated loamy sand in Minnesota, we quantified agronomic performance and N losses as both nitrate (NO 3 −) and nitrous oxide (N 2 O) in treatments receiving urea, with and without additives including: nitrification inhibitors dicyandiamide (DCD) or 3,4-dimethylpyrazole phosphate (DMPP), alone or combined with the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), or a biostimulant containing N-fixing microbes (NFM) by itself or combined with an amino acid blend (AAB). The biostimulants produced modest (˜10%) improvements in tuber yield, under limited conditions, compared to urea alone. However, NFM increased N 2 O emissions by 32–56%, in contrast to the inhibitors, which decreased N 2 O emissions by 42–75%. Compared to urea alone, the inhibitors tended to increase soil ammonium and decrease soil NO 3 − concentrations; however, no differences in soil inorganic N in the upper 0.3 m of the profile were observed with the biostimulants. During the growing season with greater rates of soil water flux (2015), none of the inhibitors decreased NO 3 − leaching, while NFM increased NO 3 − leaching by 23%. When AAB was combined with NFM, reactive N losses did not differ from the urea-only treatment. Biostimulants can have unintended impacts on reactive N losses and should be used with caution pending additional study to better understand their effects on biological processes, and to quantify their performance in other agro-ecosystems. [ABSTRACT FROM AUTHOR]

The affirmation of acrylamide as a probable carcinogen by the European Food Safety Authority has reinforced the need to lower acrylamide content in fried potato products. Selected for low reducing sugars and acrylamide-forming potential, recently released cultivars ‘Alpine Russet’, ‘Dakota Trailblazer’, and ‘Ivory Crisp’ were evaluated for their processing quality when grown with varying nitrogen (N) fertilizer regimes. The objective of this study was to determine the effects of N fertilizer rate (34, 135, 202, 269 and 336 kg ha−1) on tuber glucose and acrylamide concentration following processing of new cultivars relative to standard cultivars ‘Russet Burbank’ and ‘Snowden’ at harvest, and after 3, 6 and 9 months of storage at 7.2 °C over 2 years. Glucose and acrylamide responses to N rate were similar for chip cultivars, which linearly decreased in 2011, and quadratically increased then decreased in 2012 with increasing N rate. The N rate effect on French fry glucose concentration varied by cultivar and either decreased or did not respond to elevated N rate. Glucose and acrylamide concentrations of chip cultivars generally increased during storage, with a dramatic increase in ‘Snowden’ resulting from senescence sweetening after 9 months of storage. Environmental conditions significantly affected glucose and acrylamide responses of French fry cultivars to storage time. Glucose and acrylamide concentrations of all French fry cultivars generally increased during storage in 2011. In contrast, glucose concentrations of French fry cultivars were stable or increased, while acrylamide concentrations generally decreased during storage in 2012. The relationship between chip color and glucose concentration was significant, but differed by year. Glucose and acrylamide concentrations of French fry and chip cultivars were significantly correlated (R2 = 0.52 and 0.66, in 2011 and 2012, respectively). Generally, acrylamide in fried potato products can be minimized by using low reducing sugar cultivars supplied with a N fertilizer rate that optimizes yield and quality during growing seasons with minimal environmental stress. [ABSTRACT FROM AUTHOR]

• Nitrogen use efficiency [NUE] is best understood in terms of its constituent parts. • Interpreting N utilization efficiency depends on both N nutrition index and biomass. • A critical N utilization efficiency curve can be defined based on previous theory. • Increasing N uptake efficiency [NUpE] will reduce N losses to the environment. • Maximizing NUE does not necessarily improve agronomic or environmental outcomes. Maximizing nitrogen (N) use efficiency [NUE] is commonly identified as a key strategy to improve both agronomic and environmental outcomes; however, interpretation of NUE requires explicit consideration of crop N status. In this study, we derived a set of novel theoretical relationships between the nitrogen nutrition index [NNI] and NUE used to better interpret values for nitrogen uptake efficiency [NUpE] and nitrogen utilization efficiency [NUtE]. A small-plot trial for potato [ Solanum tuberosum (L.) 'Russet Burbank'] was conducted in 2016 and 2017 in Central Minnesota, USA, on a Hubbard loamy sand with six N rate, source, and timing treatments and two irrigation rate treatments. Impacts of treatments on NNI, NUpE, NUtE, NUE, biomass, harvest index, and potential N losses were interpreted within the context of a theoretical quantitative relationship between NUE and NNI. We found that for a constant NNI value, NUtE values increased non-linearly as biomass increased; at an NNI value of 1.0, this relationship defines the critical N utilization efficiency curve. As N rate increased from 40 to 270 kg N ha−1, NUtE significantly decreased from 109.8–69.7 g g−1 N, corresponding with a significant increase in both biomass (from 12.0–17.8 Mg ha−1) and in NNI (from 0.520 to 0.973), respectively. Additionally, we found that potential N losses (e.g., leaching) decreased as NUpE increased, or as total N inputs decreased. Potential N loss was lower in 2016 than 2017 (135 and 187 kg N ha−1, respectively) due to both greater NUpE and lower total N input from all sources in 2016 (0.602 g N g-1 N and 339 kg N ha-1, respectively) than in 2017 (0.526 g N g-1 N and 395 kg N ha-1, respectively). Interpreting NUE to evaluate agronomic and environmental outcomes requires separate consideration of its constituent factors (e.g., NUpE, NUtE, and HI) and explicit consideration of both NNI and biomass. [ABSTRACT FROM AUTHOR]

• We found no sorption of bromide to woodchips in laboratory column experiments. • Actual hydraulic retention time is more accurate using effective porosity. • Field tracer tests showed an average 82.1% bromide recovery from seven beds. • There is a need to ascertain the cause of low bromide recovery in beds. One biotechnology that can reduce nitrate concentration in subsurface drainage water is called a denitrification bed. Bromide tracer testing has been used to determine the hydraulic properties of these systems to be used in design and modeling, but efficacy of bromide tracers has not been investigated. One important hydraulic property of woodchip beds is its in-situ effective porosity. The objectives of this study were to (1) determine if bromide is a suitable tracer for evaluating the hydraulics of woodchip beds based on laboratory sorption experiments and field tracer testing, and (2) to determine the in-situ effective porosity of denitrification beds. To achieve this goal, we conducted bromide sorption experiments in the laboratory, and conducted bromide tracer testing in seven denitrification beds near Willmar, Minnesota, USA. We did not find sorption (neither adsorption nor absorption) of bromide to woodchips in our laboratory sorption experiments. In contrast, bromide tracer tests showed an average bromide recovery of 82%, revealing that bromide was retarded in the woodchip denitrification beds. To the best of our knowledge, our experiment is the first study to estimate the in-situ effective porosity (average of 0.61) of a typical field-scale denitrification bed using a tracer test. A more accurate estimate of the actual hydraulic retention time (HRT) can be obtained by using the in-situ effective porosity rather than total porosity. Our laboratory experiment did not show any sorption of bromide to woodchips, but in contrast and for unclear reasons, our field tracer testing showed bromide retardation. [ABSTRACT FROM AUTHOR]

Sulfur is applied to irrigated corn (Zea mays L.) grown on sandy soils. The objective of this study was to evaluate the sprinkler-irrigated corn response to S. Treatments were a factorial combination of 0, 14, 28, and 42 kg S ha-1 as (NH4)2SO4 applied on the soil surface at four locations at planting and in season (V5). Tissue samples were collected at V8 and R2 and evaluated along with corn grain yield and soil pore water SO4 2--S concentration measured at 60 cm with suction tube lysimeters. Application of S increased V8 plant mass, V8 whole plant S concentration and S uptake, and R2 leaf S concentration but did not increase corn grain yield. Decreased V8 plant mass was a result of S deficiency and was only corrected when some S was applied at planting. A total of 28 kg S ha-1 was sufficient to ensure adequate plant growth and S uptake whether S was applied at planting, in-season, or as a combination of the two timings. Concentrations of S were elevated in soil pore water from at planting and in-season S application indicating a portion of the S applied were still available for most'and at the end of'the growing season. Sulfur fertilizer is crucial early in the growing season for irrigated corn to ensure optimal corn growth. Rate of application is more important than time of S application in irrigated corn production. Incidental applications of S may reduce the need of S fertilizer for irrigated corn.

Phosphorus (P) fertilizer recommendations based on the build and maintain (B&M) or the sufficiency philosophies were compared at six sites across Minnesota. Various levels of soil test P (STP) levels were established over four growing seasons. Applied P and P removed in harvested grain were monitored and used to develop a soil net P balance (Net P). Linear regression of net P with changes in STP was highly significant. Initial STP levels could be maintained at four of the six sites with a negative Net P. At those same sites, a zero Net P would tend to slowly increase STP over time. A sequential soil P fractionation analysis was conducted on soils from the six sites at the initiation and at the end of the 4‐year period. Nine total soil P fractions were extracted that represented both inorganic P (Pi) and organic P (Po) in the labile and non or less labile soil P pools. A positive linear relationship between Net P and changes in Pi fractions was significant. As Net P increased, so did the changes in Pi in the Resin, BiCarb, and NaOH fractions. These three fractions accounted for 66% to >100% of the changes in Net P with Resin and NaOH accounting for the majority of Net P. Changes in Net P that were accounted for in the less labile P pools, Sonic and HCl fractions, variable, and difficult to determine. There was little effect of Net P on Po fractions. Core ideas: Soil net P balance was positively correlated with changes in STP over four growing seasons.Medium STP interpretation class was maintained in most of these soils with a slight negative soil net P balance.In those same soils, a zero‐soil net P balance would tend to raise STP over time.Soil net P balance is positively related to changes in soil P, mostly in the labile and moderately labile fractions. [ABSTRACT FROM AUTHOR]

Denitrification beds are being used to reduce the transport of water-soluble nitrate via subsurface drainage systems to surface water. Only recently has the non-linearity of water flow through woodchips been ascertained. To successfully design and model denitrification beds with optimum nitrate removal, a better understanding of flow in denitrification beds is needed. The main objectives of this study were to characterize the hydraulic properties of old degraded woodchips and provide a better understanding of the factors affecting flow. To achieve this goal, we conducted constant-head column experiments using old woodchips that were excavated from a four-year old denitrification bed near Willmar, Minnesota, USA. For Izbash’s equation, the non-Darcy exponent ( n ) ranged from 0.76 to 0.87 that indicates post-linear regime, and the permeability coefficient ( M 10 ) at 10°C ranged from 0.9 to 2.6 cm s −1 . For Forchheimer’s equation, the intrinsic permeability of 5.6 × 10 −5 cm 2 and ω constant of 0.40 (at drainable porosity of 0.41) closely resembled the in-situ properties found in a previous study. Forchheimer’s equation was better than that of Izbash’s for describing water flow through old woodchips, and the coefficients of the former provided stronger correlations with drainable porosity. The strong correlation between intrinsic permeability and drainable porosity showed that woodchip compaction is an important factor affecting water flow through woodchips. Furthermore, we demonstrated the importance of temperature effects on woodchip hydraulics. In conclusion, the hydraulic properties of old woodchips should be characterized using a non-Darcy equation to help design efficient systems with optimum nitrate removal. [ABSTRACT FROM AUTHOR]

To use remotely sensed spectral data for determining rates and timing of variable rate nitrogen (N) applications at a commercial scale, the most reliable indicators of crop N status must be determined. This study evaluated the ability of hyperspectral remote sensing to predict N stress in potatoes ( Solanum tuberosum ) during two growing seasons (2010 and 2011). Spectral data were evaluated using ground based measurements of leaf N concentration. Two canopy-scale hyperspectral images were acquired with an AISA-Eagle hyperspectral camera in both years. The experiment included five N treatments with varying rates and timing of N fertilizer and two potato cultivars, Russet Burbank (RB) and Alpine Russet (AR). Partial Least Squares regression (PLS) models resulted in the best prediction of leaf N concentration ( r 2 = 0.79, Root Mean Square Error of Cross Validation (RMSECV) = 14% across dates for RB; r 2 = 0.77, RMSECV = 13% across dates for AR). Applying the Nitrogen Sufficiency Index (NSI) formula to spectral indices/models made them mostly insensitive to the effects of cultivar. The most promising technique for determining N stress in potato based on spectral indices was found to be the MERIS Terrestrial Chlorophyll Index (MTCI) due to a combination of relatively high r 2 values, lower RMSECVs, and high accuracy assessment. Pairwise comparison tests from the means separation showed that spectral indices/models from the imagery resulted in more statistically significant groupings of crop stress levels for the spectra than leaf N concentration because canopy-scale spectral data are affected by both tissue N concentration and biomass. The results of this study suggest that upon proper sensor calibration, canopy-scale spectral data may be the most sensitive tool available to detect N status of a potato crop. [ABSTRACT FROM AUTHOR]

High tunnels are an important season extension tool for horticultural production in cold climates, however maintaining soil health in these intensively managed spaces is challenging. Cover crops are an attractive management tool to address issues such as decreased organic matter, degraded soil structure, increased salinity, and high nitrogen needs. We explored the effect of winter cover crops on soil nutrients, soil health and bell pepper (Capsicum annuum) crop yield in high tunnels for 2 years in three locations across Minnesota. Cover crop treatments included red clover (Trifolium pratense) monoculture, Austrian winter pea/winter rye biculture (Pisum sativum/Secale cereale), hairy vetch/winter rye/tillage radish (Vicia villosa/ S. cereale/Raphanus sativus) polyculture, and a bare-ground, weeded control. Cover crop treatments were seeded in two planting date treatments: early planted treatments were seeded into a standing bell pepper crop in late Aug/early September and late planted treatments were seeded after bell peppers were removed in mid-September At termination time in early May, all cover crops had successfully overwintered and produced biomass in three Minnesota locations except for Austrian winter pea at the coldest location, zone 3b. Data collected include cover crop and weed biomass, biomass carbon and nitrogen, extractable soil nitrogen, potentially mineralizable nitrogen, microbial biomass carbon, permanganate oxidizable carbon, soil pH, soluble salts (EC), and pepper yield. Despite poor legume performance, increases in extractable soil nitrogen and potentially mineralizable nitrogen in the weeks following cover crop residue incorporation were observed. Biomass nitrogen contributions averaged 100 kg·ha-1 N with an observed high of 365 kg·ha-1 N. Cover crops also reduced extractable soil N in a spring sampling relative to the bare ground control, suggesting provision of nitrogen retention ecosystem services. [ABSTRACT FROM AUTHOR]

Phosphorus (P) is a non-renewable resource that will become an economic limiting factor for food production in the future. Potato (Solanum tuberosum L.) is a relatively shallow rooted crop and often responds positively to P fertilizer even in soils with high soil-test P. Therefore, high-rate P fertilizers are commonly applied to produce high tuber yields in commercial potato fields. The purpose of this study was to evaluate the effects of P rate, cultivar, and soil fumigation on potato yield, quality, P uptake, P use efficiency and economic returns under high soil test P conditions. A field study with a split-plot randomized complete block design was conducted in 2021 and 2022, with fumigation treatments (no fumigant or fall-applied metam sodium) being the main plots and cultivars (Ivory Russet or Russet Burbank) as subplots. Each subplot was further divided into five sub-subplots with different P rates: 0, 37, 73, 147 and 220 kg P ha-1. The results indicated that Russet Burbank produced higher total yield than Ivory Russet. Fumigation significantly increased tuber yield and dry matter percentage. Both cultivars responded to P application and tuber P uptake increased with P rate even under very high soil test P conditions. Both partial factor productivity (PFP) and P recovery efficiency (PRE) were very low and significantly decreased with the P rate. Russet Burbank had higher PFP and PRE than Ivory Russet, and fumigated plots had significantly higher PRE than non-fumigated plots. The tuber yield output and net revenue of Russet Burbank was higher than Ivory Russet, and the highest economic return was obtained in fumigated plots at 147 kg P ha-1. These results suggest that cultivar selection and control of soil-borne diseases should be considered to optimize P input, tuber yield, and to conserve P resources. [Display omitted] • Tuber yield of Russet Burbank was higher than Ivory Russet due to higher tuber set. • Fumigation significantly increased tuber yield and its response to P application. • Potato P use efficiency was very low, especially when high P rates were applied. [ABSTRACT FROM AUTHOR]

Aims: Soil microbiomes and their interactions with crop plants are important drivers of agricultural health and productivity. Our objective was to examine short-term responses of soil microbiota to agricultural management (i.e. cover cropping and nitrogen fertilization). Methods: Following three years of cropping, soil samples were collected from replicated field plots at two southern Minnesota field sites (Lamberton and Waseca). We used amplicon-based gene sequencing (ITS2 and 16S rRNA V4) to investigate short-term soil fungal and bacterial community responses to cover crops and urea-nitrogen (N) fertilization (0, 80, 100, and 120% of recommended rates) in a corn (Zea mays)-soybean (Glycine max) cropping system planted with and without cover crops. Results: We found that rates of N-fertilizer applied, more than cover crops, significantly impacted soil chemical properties at both sites. Different cropping or N fertilization treatments did not lead to strong differences in fungal or bacterial alpha (local) diversity. At both sites, cover crop was a significant predictor of fungal community compositions and specific fungal and bacterial taxa were significantly impacted by cover crops. While, N fertilization was not a strong predictor of community compositions, urea-N additions, at any rate, resulted in changes in the relative abundances of the fungal phyla Glomeromycota in addition to a number of bacterial phyla. Conclusions: Our findings suggest that after three years of cropping, fungal communities respond to cover crops, while bacterial community responses may depend on soil chemical conditions. [ABSTRACT FROM AUTHOR]

In North America, potato early dying is often controlled using soil fumigants. Fumigants confer benefits on plant health but also impact soil microbial activity, including nitrogen (N) cycling. The purpose of this study was to evaluate the effects of two soil fumigants, chloropicrin and metam sodium, on potato crop yield, N uptake, and N use efficiency (NUE), as well as soilborne pathogens, soil microbial respiration rates and soil concentrations of NH4+-N and NO3−-N. We established a field study with a split-plot randomized complete block design in 2016 and 2017, with whole plots divided among three fumigation treatments (no fumigant, chloropicrin, or metam sodium) and split into five subplots, each receiving a different total application rate of N (45, 135, 202, 269, or 336 kg·ha−1 N). Both fumigants suppressed Verticillium dahliae propagule concentrations and foliar symptoms of potato early dying while increasing yield, final tuber set, N uptake, and NUE. Fumigation did not affect the agronomic optimum N rate, nor the response of marketable yield to N rate, but it did increase yield per unit N applied (partial factor productivity) by 16% and 35% over the non-fumigated controls in 2016 and 2017, respectively. Chloropicrin, but not metam sodium, reduced the prevalence of common scab symptoms in tubers. Both fumigants decreased microbial respiration rates before planting and at midseason. Fumigants reduced nitrification rates before planting and at midseason, with chloropicrin having a particularly strong effect before planting. While fumigation conferred benefits to yield and NUE, its effects on microbial community structure and function merit further study. [ABSTRACT FROM AUTHOR]

Potato (Solanum tuberosum L.) production on sandy soils requires added N. Only 40–60% of the applied N is acquired by the crop. Increased N use efficiency (NUE) and its components, N utilization efficiency (NUtE) and N uptake efficiency (NUpE), could reduce fertilizer rates and environmental losses. We compared N efficiency in fresh‐market red potato varieties, in terms of yield and quality traits, and examined potential mechanisms for that efficiency including uptake, utilization, and increased root growth. We grew selections from a red potato breeding population and commercial varieties under two N rates: 101 and 202 kg N ha−1. We compared NUE, NUpE, and NUtE in low and high N. We compared root phenotypes at tuber initiation and yield and skin quality metrics at harvest. Values for NUtE correlated with NUE and yield in low N and NUpE correlated with NUE and yield in high N. Low‐N conditions produced smaller tubers, while high N resulted primarily in medium tubers. Nitrogen did not affect skinning and redness but low N did result in slightly lighter skin color. Total root mass 45 d after planting (DAP) correlated with final yield and NUE but did not correlate with measures of N uptake across treatments. Larger roots correlated with NUpE only in the high‐N treatment. Selection under low N may reveal NUE and expose more stable representations of the genetic components of skin quality phenotypes. While skinning and skin color were more variable among varieties in low N, within variety they exhibited year‐to‐year consistency. [ABSTRACT FROM AUTHOR]

Understanding the variables that affect the anaerobic potentially mineralizable N (PMNan) test should lead to a standard procedure of sample collection and incubation length, improving PMNan as a tool in corn (Zea mays L.) N management. We evaluated the effect of soil sample timing (preplant and V5 corn development stage [V5]), N fertilization (0 and 180 kg ha−1) and incubation length (7, 14, and 28 d) on PMNan (0–30 cm) across a range of soil properties and weather conditions. Soil sample timing, N fertilization, and incubation length affected PMNan differently based on soil and weather conditions. Preplant vs. V5 PMNan tended to be greater at sites that received < 183 mm of precipitation or < 359 growing degree-days (GDD) between preplant and V5, or had soil C/N ratios > 9.7:1; otherwise, V5 PMNan tended to be greater than preplant PMNan. The PMNan tended to be greater in unfertilized vs. fertilized soil in sites with clay content > 9.5%, total C < 24.2 g kg−1, soil organic matter (SOM) < 3.9 g kg−1, or C to N ratios < 11.0:1; otherwise, PMNan tended to be greater in fertilized vs. unfertilized soil. Longer incubation lengths increased PMNan at all sites regardless of sampling methods. Since PMNan is sensitive to many factors (sample timing, N fertilization, incubation length, soil properties, and weather conditions), it is important to follow a consistent protocol to compare PMNan among sites and potentially use PMNan to improve corn N management. [ABSTRACT FROM AUTHOR]

Soil microbiota play important and diverse roles in agricultural crop nutrition and productivity. Yet, despite increasing efforts to characterize soil bacterial and fungal assemblages, it is challenging to disentangle the influences of sampling design on assessments of communities. Here, we sought to determine whether composite samples—often analyzed as a low cost and effort alternative to replicated individual samples—provide representative summary estimates of microbial communities. At three Minnesota agricultural research sites planted with an oat cover crop, we conducted amplicon sequencing for soil bacterial and fungal communities (16SV4 and ITS2) of replicated individual or homogenized composite soil samples. We compared soil microbiota from within and among plots and then among agricultural sites using both sampling strategies. Results indicated that single or multiple replicated individual samples, or a composite sample from each plot, were sufficient for distinguishing broad site-level macroecological differences among bacterial and fungal communities. Analysis of a single sample per plot captured only a small fraction of the distinct OTUs, diversity, and compositional variability detected in the analysis of multiple individual samples or a single composite sample. Likewise, composite samples captured only a fraction of the diversity represented by the six individual samples from which they were formed, and, on average, analysis of two or three individual samples offered greater compositional coverage (i.e., greater number of OTUs) than a single composite sample. We conclude that sampling design significantly impacts estimates of bacterial and fungal communities even in homogeneously managed agricultural soils, and our findings indicate that while either strategy may be sufficient for broad macroecological investigations, composites may be a poor substitute for replicated samples at finer spatial scales. [ABSTRACT FROM AUTHOR]

Nitrogen provided to crops through mineralization is an important factor in N management guidelines. Understanding of the interactive effects of soil and weather conditions on N mineralization needs to be improved. Relationships between anaerobic potentially mineralizable N (PMNan) and soil and weather conditions were evaluated under the contrasting climates of eight US Midwestern states. Soil was sampled (0.30 cm) for PMNan analysis before pre-plant N application (PP0N) and at the V5 development stage from the pre-plant 0 (V50N) and 180 kg N ha-1 (V5180N) rates and incubated for 7, 14, and 28 d. Even distribution of precipitation and warmer temperatures before soil sampling and greater soil organic matter (SOM) increased PMNan. Soil properties, including total C, SOM, and total N, had the strongest relationships with PMNan (R2 < 0.40), followed by temperature (R2 < 0.20) and precipitation (R2 < 0.18) variables. The strength of the relationships between soil properties and PMNan from PP0N, V50N, and V5180N varied by .10%. Including soil and weather in the model greatly increased PMNan predictability (R2 < 0.69), demonstrating the interactive effect of soil and weather on N mineralization at different times during the growing season regardless of N fertilization. Delayed soil sampling (V50N) and sampling after fertilization (V5180N) reduced PMNan predictability. However, longer PMNan incubations improved PMNan predictability from both V5 soil samplings closer to the PMNan predictability from PP0N, indicating the potential of PMNan from longer incubations to provide improved estimates of N mineralization when N fertilizer is applied.

Cold temperatures limit nitrate-N load reductions of woodchip bioreactors in higher-latitude climates. This two-year, on-farm (Willmar, Minnesota, USA) study was conducted to determine whether field-scale nitrate-N removal of woodchip bioreactors can be improved by the addition of cold-adapted, locally isolated bacterial denitrifying strains (bioaugmentation) or dosing with a carbon (C) source (biostimulation). In Spring 2017, biostimulation removed 66% of the nitrate-N load, compared to 21% and 18% for bioaugmentation and control, respectively. The biostimulation nitrate-N removal rate (NRR) was also significantly greater, 15.0 g N m−3 d−1, versus 5.8 and 4.4 g N m−3 d−1, for bioaugmentation and control, respectively. After five weeks of operation, bioclogging of the biostimulation beds limited dosing for the remainder of the experiment; NRR was greater for biostimulation in Fall 2017, but in Spring 2018 there were no differences among treatments. Carbon dosing did not increase outflow of dissolved organic C concentration. The abundance of one of the inoculated strains, Cellulomonas cellacea strain WB94, increased over time, while another, Microvirgula aerodenitrificans strain BE2.4, increased briefly, returning to background levels after 42 d. Eleven days after inoculation in Spring 2017, outflow nitrate-N concentrations of bioaugmentation were sporadically reduced compared to the control for two weeks, but the effects were insignificant over the study period. The study suggests that biostimulation and bioaugmentation are promising technologies to enhance nitrate removal during cold conditions. A means of controlling bioclogging is needed for biostimulation, and improved means of inoculation and maintaining abundance of introduced strains is needed for bioaugmentation. In conclusion, biostimulation showed greater potential than bioaugmentation for increasing nitrate removal in a woodchip bioreactor, whereas both methods need improvement before implementation at the field scale. [ABSTRACT FROM AUTHOR]

Multiple critical N dilution curves [CNDCs] have been previously developed for potato; however, attempts to directly compare differences in CNDCs across genotype [G], environment [E], and management [M] interactions have been confounded by non-uniform statistical methods, biased experimental data, and lack of proper quantification of uncertainty in the critical N concentration [%N c ]. This study implements a partially-pooled Bayesian hierarchical method to develop CNDCs for previously published and newly reported experimental data, systematically evaluates the difference in %N c [∆%N c ] across G × E × M effects, and directly compare CNDCs from the Bayesian framework to CNDCs from conventional statistical methods. The partially-pooled Bayesian hierarchical method implemented in this study has the advantage of being less susceptible to inferential bias at the level of individual G × E × M interactions compared to alternative statistical methods that result from insufficient quantity and quality of experimental datasets (e.g., unbalanced distribution of N limiting and non-N limiting observations). This method also allows for a direct statistical comparison of differences in %N c across levels of the G × E × M interactions. Where found to be significant, ∆%N c was hypothesized to be related to variation in the timing of tuber initiation (e.g., maturity class) and the relative rate of tuber bulking (e.g., planting density) across G x E × M interactions. In addition to using the median value for %N c (i.e., CNDC), the lower and upper boundary values for the credible region (i.e., CNDC lo and CNDC up) derived using the Bayesian framework should be used in calculation of N nutrition index (and other calculations) to account for uncertainty in %N c. Overall, this study provides additional evidence that%N c is dependent upon G × E × M interactions; therefore, evaluation of crop N status or N use efficiency must account for variation in %N c across G × E × M interactions. • Critical N dilution curves [CNDCs] for potato are subject to G x E x M effects. • Bayesian methods can quantify uncertainty in critical N concentration [%N c ]. • Partial pooling Bayesian method enables direct comparison of G x E x M effects. • Variation in %N c for potato due to tuber initiation timing and tuber bulking rate. • N use efficiency and N nutrition index depend on %N c variability and uncertainty. [ABSTRACT FROM AUTHOR]

Specific gravity (SpGr) is often used to measure the processing quality of potato (Solanum tuberosum L.) tubers for French fries or potato chips because of its strong correlation with dry matter content and ease of measurement. For French fry processing genotypes, the desirable range for mean SpGr is typically 1.080 to 1.095, and a small variance around the mean is essential for product uniformity. Two multi-year, multi-location trials were conducted to investigate the genetics of SpGr in elite russet germplasm. Consistent with earlier studies, the mean SpGr was measured with high repeatability within each environment: the median plot-basis value was 0.83 for a national trial with six locations and 3 yr. In contrast, the median repeatability of the SD between tubers was only 0.21. Thus, multi-environment trials are needed to identify genotypes with a narrow SpGr distribution. Finlay--Wilkinson stability analysis of the mean SpGr established one genotype as an outlier: when best linear unbiased predictions were regressed on the environment means, this genotype had a regression coefficient of 2.1, compared with 0.4 to 1.4 for the others. The genetic correlation between environments showed a consistent regional pattern in mean SpGr over the years. There was a higher mean correlation between environments within the Pacific Northwest (0.97), Upper Midwest (0.91), and Northeast (0.85) than between environments from the different regions (0.35-0.78). Although breeding for national adaptation is an attractive idea, our results suggest that genetic gain may be easier to achieve at the regional level. [ABSTRACT FROM AUTHOR]

Transport of nitrogen and phosphorus from agricultural and urban landscapes to surface water bodies can cause adverse environmental impacts. The main objective of this long-term study was to quantify and compare contaminant transport in agricultural drainage water and urban stormwater runoff. We measured flow rate and contaminant concentration in stormwater runoff from Willmar, Minnesota, USA, and in drainage water from subsurface-drained fields with surface inlets, namely, Unfertilized and Fertilized Fields. Commercial fertilizer and turkey litter manure were applied to the Fertilized Field based on agronomic requirements. Results showed that the City Stormwater transported significantly higher loads per unit area of ammonium, total suspended solids (TSS), and total phosphorus (TP) than the Fertilized Field, but nitrate load was significantly lower. Nitrate load transport in drainage water from the Unfertilized Field was 58% of that from the Fertilized Field. Linear regression analysis indicated that a 1% increase in flow depth resulted in a 1.05% increase of TSS load from the City Stormwater, a 1.07% increase in nitrate load from the Fertilized Field, and a 1.11% increase in TP load from the Fertilized Field. This indicates an increase in concentration with a rise in flow depth, revealing that concentration variation was a significant factor influencing the dynamics of load transport. Further regression analysis showed the importance of targeting high flows to reduce contaminant transport. In conclusion, for watersheds similar to this one, management practices should be directed to load reduction of ammonium and TSS from urban areas, and nitrate from cropland while TP should be a target for both. [ABSTRACT FROM AUTHOR]

Accurate high-resolution yield maps are essential for identifying spatial yield variability patterns, determining key factors influencing yield variability, and providing site-specific management insights in precision agriculture. Cultivar differences can significantly influence potato (Solanum tuberosum L.) tuber yield prediction using remote sensing technologies. The objective of this study was to improve potato yield prediction using unmanned aerial vehicle (UAV) remote sensing by incorporating cultivar information with machine learning methods. Small plot experiments involving different cultivars and nitrogen (N) rates were conducted in 2018 and 2019. UAV-based multi-spectral images were collected throughout the growing season. Machine learning models, i.e., random forest regression (RFR) and support vector regression (SVR), were used to combine different vegetation indices with cultivar information. It was found that UAV-based spectral data from the early growing season at the tuber initiation stage (late June) were more correlated with potato marketable yield than the spectral data from the later growing season at the tuber maturation stage. However, the best performing vegetation indices and the best timing for potato yield prediction varied with cultivars. The performance of the RFR and SVR models using only remote sensing data was unsatisfactory (R2 = 0.48–0.51 for validation) but was significantly improved when cultivar information was incorporated (R2 = 0.75–0.79 for validation). It is concluded that combining high spatial-resolution UAV images and cultivar information using machine learning algorithms can significantly improve potato yield prediction than methods without using cultivar information. More studies are needed to improve potato yield prediction using more detailed cultivar information, soil and landscape variables, and management information, as well as more advanced machine learning models. [ABSTRACT FROM AUTHOR]

Potassium (K) is a primary macronutrient for overall plant growth, yield potential, product quality and stress resistance of crops. Potato (Solanum tuberosum L.) crops require a high amount of potassium to achieve the ideal yield and quality. Therefore, the determination of optimum K rate and efficient source for potato is necessary because K affects crop physiological processes, dry matter production, cooking, and processing requirements. Through modeling on the pooled data extracted from 62 studies, the highest tuber yields might be obtained at an exchangeable soil K level of 200 mg kg−1 approximately, dependent on soil pH, texture, and organic matter. Through modeling on the data of 48 studies, it also revealed that application of potassium sulfate (K2SO4) and potassium chloride (KCl) at rates of 200 kg ha−1 and potassium nitrate (KNO3) at a rate of 100 kg ha−1 might achieve the ideal yield, implying the importance of K sources in potato production. However, these values (either soil exchangeable K content, or fertilizer rates) might not be applicable in a specific growing environment for a specific potato variety. It seems that there is no discrimination among split, pre-plant or in-season application of K, although pre-plant fertilization might be a trustworthy strategy for economic tuber yield. Owing to the luxury consumption of K by potato crop, a combination of factors, including soil exchangeable K level, petiole K concentration, crop removal amount, soil conditions, management practices, climatic conditions, and potato variety, should be considered in order to make rational K fertilizer recommendations. [ABSTRACT FROM AUTHOR]

• A comprehensive assessment of the effectiveness of nitrification inhibitor DMPP under varying N rates and application timings on potato yield and NUE under tropical conditions was performed. • Compared to the conventional practice, split applied ammonium sulfate nitrate with DMPP (ASN + DMPP), at either 75% or 100% of recommended N rate (RNR), reduced N surplus in site-years with greater rainfall events and consistently increased potato tuber yield. • At reduced N rate (75% of RNR), single ASN + DMPP application at planting decreased potato yield, but at 100% of RNR potato production was not different from that receiving conventional N fertilization. • The mutual agronomic, economic, and environmental benefits of split-applied ASN + DMPP at 75% of RNR can contribute to the increased sustainability of tropical potato cropping systems. However, further studies are needed to confirm these benefits in other agro-ecosystems. Urea is the dominant nitrogen (N) fertilizer used for potato (Solanum tuberosum L.) cultivation in most parts of the world. Fertilizers containing a nitrification inhibitor (NI) claim to improve performance of crops including potato. No studies to date have conducted comprehensive assessment of N sources and the effectiveness of NI under varying N rates or application timings to enhance potato yield, tuber quality or N-use efficiency (NUE) in tropical regions. Three field experiments were conducted on irrigated sandy soils in southeastern Brazil to determine whether single or split application of ammonium sulfate nitrate (ASN) with the NI 3,4-dimethylpyrazole phosphate (DMPP) at reduced (75%) or recommended N rates (RNR, 100% = 160 kg ha-1) could improve yield, quality and/or NUE of 'Agata' potato over conventional split-applied urea at 100% of RNR. Compared to the conventional practice, split-applied ASN + DMPP, at either 75% or 100% of RNR, increased fresh tuber yield by an average of 15% across all site-years (SYs) and reduced N surplus in SYs with greater rainfall events suggesting that reactive N losses to the environment were also reduced. With split-applied ASN + DMPP at 75% of RNR, fresh tuber yield per unit of applied N increased by 34% compared to split-applied ASN + DMPP at 100% of RNR, and by 50–75% compared to a single application of ASN + DMPP at planting. These results demonstrate a mutually beneficial opportunity, where the rate of split-applied ASN + DMPP can be reduced by 25% while at the same time increasing yields, thus resulting in agronomic, economic, and environmental benefits due to the decreased potential for off-site reactive N losses. [ABSTRACT FROM AUTHOR]

Commercial sweet corn (Zea mays convar. saccharata var. rugosa) production has a proportionally high potential for nutrient loss to waterways, due to its high nitrogen (N) requirements and low N use efficiency. Cover crops planted after sweet corn can help ameliorate N lost from the field, but farmers are reluctant to utilize cover crops due to a lack of economic incentive. Pennycress (Thlaspi arvense L.) is a winter annual that can provide both economic and environmental benefits. Five N-rates (0, 65, 135, 135 split and 200) were applied pre-plant to sweet corn. After the sweet corn harvest, pennycress was planted into the sweet corn residue with two seeding methods and harvested for seed the following spring. Residual inorganic soil N (Nmin), pennycress biomass, biomass N and yield were measured. The nitrogen rate and seeding method had no effect on pennycress yield, biomass, or biomass N content. The nitrogen rate positively affected Nmin at pennycress seeding, wherein 200N plots had 38–80% higher Nmin than 0N plots, but had no effect on Nmin at pennycress harvest. Control treatments without pennycress had an average of 27–42% greater Nmin. In conclusion, pennycress can act as an effective N catch crop, and produce an adequate seed yield after sweet corn without the need for supplemental fertilization. [ABSTRACT FROM AUTHOR]