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Cotton (Gossypium hirsutum L.) requires potassium (K) in large amounts for crop growth and development and is more sensitive to low K availability in soils than other agronomic crops. Low K concentrations within the plant may decrease the rate of photosynthesis, which will impact plant growth and development. Cotton yield potential has increased due to genetic improvements, which may have increased the quantity and rate at which cotton takes up K. This research aimed to determine the effect of K fertilizer rates within irrigation level on boll distribution and yield contribution from specific node zones. This study was conducted at New Deal, TX in 2016 and 2017. Muriate of potash (KCl) was applied using knife injection at rates of 0, 45, 90, 135, and 180 kg K h−1 with 80% and 30% evapotranspiration (ET) irrigation levels. Differences were not noted for estimated box mapping yield between K rates in 2016 (p = 0.3996). When 180 kg K ha−1 was applied, total bolls and estimated box mapping yield within 30% ET increased in the early and middle node zones and total nodes over all other K application rates in 2017. It was observed with box mapping that the early and middle node zones were able to utilize applied K more effectively due to the increase in bolls and yield compared to the late and vegetative node zones. Our results suggest that K is an important nutrient in cotton production due to the impacts it has on the early and middle node zones. Core Ideas: Potassium impacts cotton boll distribution and yield contribution from specific node zones within irrigation levels.The early and middle node zones for yield were the greatest with the 180 kg K ha−1 rate within 30% evapotranspiration.The early and middle node zones benefited from added potassium through increased boll formation and yield. [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]

Many irrigation scheduling methods utilized in commercial production settings rely on soil water sensors that are normally purchased as off-the-shelf technology or through contracted services that install and monitor readings throughout the season. These systems often assume a direct relationship between the parameters measured by these soil water sensors (voltage, unitless values, or calibrated soil moisture values) and the water use and deficit stress of the crop. Because of this assumed relationship, these sensors are purported to be useful for triggering irrigation applications by monitoring relative changes in sensor values that represent either a 'dry' or 'wet' condition in the field. However, there is often little confirmation that these sensors accurately reflect crop water uptake or what soil depths will best represent that relationship. In an attempt to quantify the association between the use of soil water sensors and crop water use in a commercial potato field, measurements of soil water using capacitance probes and plant water use using sap flow sensors were monitored. Measurements were taken in two water application treatments: a normal (full) and partial irrigation schedule because it was hypothesized that the relative strength of the relationship between sensor reading and crop water use may be highly dependent on field soil water status. Relative soil moisture readings and plant water use data were compiled and both linear and quadratic regressions were performed. The correlation between sap flow and soil sensor readings was significant; but the relationship was relatively weak with the strength dependent on the soil depth that was monitored, indicating that care must be taken when utilizing sensor readings for irrigation scheduling. [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]

To address the effectiveness of predawn leaf water potential in plant-based irrigation scheduling, Gossypium hirsutum L. plants were grown under fully irrigated and dryland conditions and under three predawn water potential (ΨPD) thresholds (-0.5, -0.7, and -0.9 MPa). Measurements included ΨPD, plant height, mainstem node number, lint yield, water productivity, and continuous crop canopy temperature. We found that ΨPD produced similar yields to current practices, while decreasing overall water use from 7 to 31%, depending on rainfall levels and the treatment utilized. When considered across both years of the study (2013 and 2014), using a -0.5-MPa ΨPD irrigation threshold consistently resulted in less irrigation applied than the checkbook method and maximum water productivity and lint yield. Using a well-watered baseline developed in 2013 for canopy temperature versus vapor pressure deficit, we calculated a crop water stress index (CWSI) that exhibited a very strong, nonlinear relationship with season average ΨPD values between approximately -0.4 and -0.7 MPa (r² = 0.81). A strong, nonlinear relationship was also seen between CWSI and lint yield (r² = 0.81). Predawn water potential appears to be an effective means of determining the need for irrigation in cotton, and in the current study, yield and water productivity were maximized at a season-long average ΨPD threshold of -0.5 MPa. Furthermore, when calibrated using ΨPD--based irrigation triggers, canopy-temperature derived CWSI appears to be a promising tool for future automated plant-based irrigation scheduling in the southeastern United States. [ABSTRACT FROM AUTHOR]

Temperature and drought are major abiotic limitations to crop productivity worldwide. While abiotic stress physiology research has focused primarily on fully expanded leaves, no studies have investigated photosynthetic tolerance to concurrent drought and high temperature during leaf ontogeny. To address this, Gossypium hirsutum plants were exposed to five irrigation treatments, and two different leaf stages were sampled on three dates during an abnormally dry summer. Early in the growing season, ontogenic PSII heat tolerance differences were observed. Photosystem II was more thermotolerant in young leaves than mature leaves. Later in the growing season, no decline in young leaf net photosynthesis (P N ) was observed as leaf temperature increased from 31 to 37 °C, as average midday leaf water potential (Ψ MD ) declined from −1.25 to −2.03 MPa. In contrast, mature leaf P N declined 66% under the same conditions. Stomatal conductance (g s ) accounted for 84–98% of variability in leaf temperature, and g s was strongly associated with Ψ MD in mature leaves but not in young leaves. We conclude that young leaves are more photosynthetically tolerant to heat and drought than mature leaves. Elucidating the mechanisms causing these ontogenic differences will likely help mitigate the negative impacts of abiotic stress in the future. [ABSTRACT FROM AUTHOR]

Respiratory carbon evolution by leaves under abiotic stress is implicated as a major limitation to crop productivity; however, respiration rates of fully expanded leaves are positively associated with plant growth rates. Given the substantial sensitivity of plant growth to drought, it was hypothesized that predawn respiration rates ( R PD ) would be (1) more sensitive to drought than photosynthetic processes and (2) highly predictive of water-induced yield variability in Gossypium hirsutum . Two studies (at Tifton and Camilla Georgia) addressed these hypotheses. At Tifton, drought was imposed beginning at the onset of flowering (first flower) and continuing for three weeks (peak bloom) followed by a recovery period, and predawn water potential ( Ψ PD ), R PD , net photosynthesis ( A N ) and maximum quantum yield of photosystem II ( F v / F m ) were measured throughout the study period. At Camilla, plants were exposed to five different irrigation regimes throughout the growing season, and average Ψ PD and R PD were determined between first flower and peak bloom for all treatments. For both sites, fiber yield was assessed at crop maturity. The relationships between Ψ PD , R PD and yield were assessed via non-linear regression. It was concluded for field-grown G. hirsutum that (1) R PD is exceptionally sensitive to progressive drought (more so than A N or F v / F m ) and (2) average R PD from first flower to peak bloom is highly predictive of water-induced yield variability. [ABSTRACT FROM AUTHOR]

Much effort has been expended to improve irrigation efficiency and drought tolerance of agronomic crops; however, a clear understanding of the physiological mechanisms that interact to decrease source strength and drive yield loss has not been attained. To elucidate the underlying mechanisms contributing to inhibition of net carbon assimilation under drought stress, three cultivars of Gossypium hirsutum were grown in the field under contrasting irrigation regimes during the 2012 and 2013 growing season near Camilla, Georgia, USA. Physiological measurements were conducted on three sample dates during each growing season (providing a broad range of plant water status) and included, predawn and midday leaf water potential ( Ψ PD and Ψ MD ), gross and net photosynthesis, dark respiration, photorespiration, and chlorophyll a fluorescence. End-of-season lint yield was also determined. Ψ PD ranged from −0.31 to −0.95 MPa, and Ψ MD ranged from −1.02 to −2.67 MPa, depending upon irrigation regime and sample date. G. hirsutum responded to water deficit by decreasing stomatal conductance, increasing photorespiration, and increasing the ratio of dark respiration to gross photosynthesis, thereby limiting P N and decreasing lint yield (lint yield declines observed during the 2012 growing season only). Conversely, even extreme water deficit, causing a 54% decline in P N , did not negatively affect actual quantum yield, maximum quantum yield, or photosynthetic electron transport. It is concluded that P N is primarily limited in drought-stressed G. hirsutum by decreased stomatal conductance, along with increases in respiratory and photorespiratory carbon losses, not inhibition or down-regulation of electron transport through photosystem II. It is further concluded that Ψ PD is a reliable indicator of drought stress and the need for irrigation in field-grown cotton. [ABSTRACT FROM AUTHOR]