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Concerns over water availability and water quality increasingly require more efficient use of water resources in irrigated agriculture. Center pivot (CP) systems designed with variable rate irrigation (VRI) technology have the potential to improve application and water-use efficiency while reducing environmental impacts from excess runoff and poor water quality. The objective of this study was to develop a computer model (MOPivot) to automate management zone delineation for irrigation scheduling based on the minimum area that can be controlled by the CP system (based on sprinkler spacing and location, and wetted diameter) matched to VRI capabilities and GIS site-specific grid-based field data affecting water storage and runoff. To ensure that the CP was capable of meeting scheduled VRI prescriptions, application uniformity was validated along the lateral length for sprinkler pulse percentages of 20 to 100 percent using catch collectors spaced 3-m apart along thirteen radial lines (82 m long, beginning 68 m from the pivot point and covering 10° of pivot rotation) for both clockwise and counter-clockwise rotation. Results indicated that the system achieved high application uniformity over a range of VRI application depths. The MOPivot management zones were in close agreement with GIS grid-based soil survey geographic database (SSURGO) and soil apparent electrical conductivity (ECa) derived soil texture input data (82.8% and 93.5% overall accuracy, respectively). The model successfully established the minimum azimuthal angle and sector length for VRI zone-control VRI and automatically delineated management zones useful in developing VRI irrigation prescriptions. [ABSTRACT FROM AUTHOR]

As population density (POP) increases in a soybean [G!ycine max (L.) Merr.] crop, maximum light interception (LI) occurs earlier in the season. Earlier canopy closure would be expected to increase the cumulative radiation intercepted. We hypothesized that if radiation use efficiency (RUE) was constant across a range of population densities in a nonstressful environment, then increasing POP would increase biomass at the end of the season. To test this hypothesis, we evaluated the response of total biomass produced during the season to cumulative intercepted photosynthetically active radiation (PAR) in field experiments at Fayetteville, AR, with soybean cultivars selected from Maturity Groups (MGs) 00 to IV. Additionally, from field experiments at Keiser, AR, with MG IV soybean cultivars, we assessed the response of RUE to POP. At both locations with MG IV cultivars, a late sowing date shortened the life cycle of the crop by 13 to 25 d compared with an early sowing date, resulting in less PAR accumulated. Similarly, early maturing cultivars had less time for PAR and biomass accumulation relative to later maturing cultivars. At Keiser, in three of the four environments, RUE decreased linearly by 26 to 30% as the POP increased from 7 to 135 plants [m.sup.-2]. Final biomass at the end of the season, as a function of PAR accumulated from emergence to the full-seed-size stage of development, responded linearly to intercepted PAR up to ≅ 400 MJ [m.sup.-2]. Above 400 MJ [m.sup.-2], the response was curvilinear with little increases in biomass >700 MJ [m.sup.-2]. Our data clearly indicate that RUE decreased as POP increased and that maximum biomass production in these environments was not limited by intercepted PAR., THE INTERCEPTION OF SOLAR RADIATION by plants and the utilization of radiant energy for plant biomass production represent the fundamental processes governing crop growth and yield. The amount of biomass [...]

ABSTRACT Short-season soybean [Glycine max (L)Merr.] production systems, such as double cropping and late sowing, require high populations to optimize yield, but effects of high populations on seed number and [...]

Soybean [Glycine max (L.) Merr.] production systems that utilize short-season cultivars for double cropping and late sowing often have insufficient time to establish a complete canopy prior to reproductive development. Our objectives were to evaluate plant population as a tool to manage crop growth, maximum biomass (BM), the time required for canopy closure, and yield. Field tests were sown on 8 July 1997 and 26 June 1998 at Keiser, AR (35 ° 67' N, 90 ° 83' W) in 0.19-, 0.57-, and 0.95-m rows with maturity group IV soybean cultivars Asgrow 4922 (A4922) and d. Yield from irrigated and nonirrigated treatments increased as population density increased from 7 to 134 plants [m.sup.-2], except when lodging occurred. Populations recommended for early-season sowing (25-35 plants [m.sup.-2]) resulted in many plots not achieving 90% light interception (LI), especially in 1998 when weather was hotter and drier than in 1997. The time required after emergence to begin linear crop growth ([t.sub.b] was dependent on LI, and as density increased, [t.sub.b] decreased. The values of [t.sub.b] varied from 16 to 27 d in 1997 and 22 to 37 d in 1998, with up to 12 d difference in achieving [is greater than] 90% LI. In this short-season production system, yield, crop growth rate between RI and R5, BM, and [t.sub.b] were dependent upon the early establishment of a high LI. Losses attributable to excessive delays in canopy establishment and slow crop growth could be minimized by using high populations in narrow rows. Our research indicates that higher populations than are traditionally recommended provide a way to optimize grain yields in time-constrained systems., WHEN A SOYBEAN CROP IS TIME LIMITED because of late sowing or double cropping, yields are frequently lower than their longer season counterparts (Kane et al., 1997). Soybean sown after [...]

Cotton is one of the major crops in the Mid- South growing region of the U.S. and producers there often farm numerous fields spread across a large area. Although sufficient groundwater is available for surface irrigation in many areas, the supply and cost of labor is always a concern. Producers commonly employ patterns such as every-other-furrow irrigation to allow them to irrigate fields in one set and thereby avoid the time and labor required to change sets. In many years there is sufficient rainfall that no obvious deleterious effect is observed from the non-irrigated furrows, however producers are concerned that yield could be reduced. A study was conducted at the University of Missouri Fisher Delta Research Center near Portageville during the 2014 through 2016 growing seasons to investigate the impact of different furrow irrigation patterns on cotton yield and canopy properties. Although yield loss due to waterlogging is a constant concern in the region, in 2014, with four irrigations followed by = 25 mm of rain within the subsequent three days, all irrigated plots yielded significantly more seed cotton than the rainfed treatment. Canopy temperature, plant height, and normalized difference vegetation index were all effective in differentiating between the rainfed and irrigated treatments including differences among some of the irrigation pattern treatments. [ABSTRACT FROM AUTHOR]

Cotton is a vital component of the economies of Mid-South states. Producers and landowners are looking for ways to reduce the variability of irrigated yields, and soil apparent electrical conductivity (ECa) is a readily obtained parameter that can indicate soil variability. A study was conducted in 2011 and 2012 at the Fisher Delta Research Center in Portageville, MO, with the objective to determine the impact of soil spatial variability on yield and irrigation water use efficiency for cotton. Observed ECa values were low, consistent with average sand contents that ranged from 59 to 82% in the upper 0.76 m of the soil profile. Spatial autocorrelation was present in the data and thus spatial analyses were used. In 2011, yields for two treatments were not significantly different from the mean field effect; however, the ECa effect was significant, indicating that soil variability impacted yield more than irrigation differences for the two treatments. In 2012, yields for four of the six treatments were significantly different from the mean field effect; however, the ECa effect was not significant. A quadratic equation was fit to the combined data from irrigated and rainfed plots in 2012. The resulting equation had a maximum of 3,372 kg ha-1 at 135 mm total irrigation and the median observed ECa value (3.0 mS m-1). Future efforts will include additional fields and environments, which should increase the understanding of the impact of soil variability and allow for improved selection of optimum management zones for site specific application of water and other inputs. [ABSTRACT FROM AUTHOR]

Growing conditions in the U.S. Midsouth allow for large soybean [Glycine max L. (Merr.)] yields under irrigation, but there is limited information on planting dates (PD) and maturity group (MG) choices to aid in cultivar selection. Analysis of variance across eight (2012) and 10 (2013) locations, four PD, and 16 cultivars (MG 3-6), revealed that the genotype by environment (GxE) interaction accounted for 38 to 22% of the total yield variability. Stability-analysis techniques and probability of low yields were used to investigate this interaction. Planting dates were grouped within early- and late-planting systems. Results showed that MG 4 and 5 cultivars in early-planting systems had the largest average yields, whereas for late-planting systems, late MG 3 to late MG 4 cultivars had the largest yields. Least square means by MG within planting systems at each environment showed that MG 4 cultivars had the greatest yields or were not significantly different from the MG with the greatest yields in 100% of the environments for both early- and late-planting systems. Yields of MG 5 cultivars were similar to those of MG 4 in 100% of the environments with an early planting but only in 20% of the environments with a late planting. The MG 3 cultivars were the best second choice for late plantings, with similar yields to MG 4 cultivars in 55 to 75% of the environments. These results have profound implications for MG recommendations in irrigated soybean in the U.S. Midsouth and indicate the need to reconsider common MG recommendations. [ABSTRACT FROM AUTHOR]

The water table of the primary irrigation source for agriculture in the Lower Mississippi River Basin is declining at an alarming rate. Irrigation practices that sustain cotton lint yields and reduce irrigation water use include adoption of termination guidelines based on plant growth stage and weather conditions. Production records from a large northeastern Arkansas cotton farm were examined to gauge how well a plant maturity- based irrigation termination guideline (final irrigation at 350 Growing Degree Days (60°F base) following crop cutout) was followed. Irrigation logs and yield records from the producer plus plant monitoring data from the farm's crop advisor were used to evaluate irrigation practices in 70 field entities over eight production seasons. Results indicate that irrigation termination timing for furrow-irrigated fields generally occurred prior to the termination guideline. Adherence to the termination guideline allowed the producer to reduce late season pumping. These results are encouraging given that yields from the studied fields were above county averages for all years studied, which spanned wet to dry conditions. Nearly twice the amount of water was applied in furrow-irrigated compared to pivot-irrigated fields, yet lower average yields were produced in furrow-irrigated fields in six of the eight years. Furrow-irrigated fields had higher yield variability compared to fields with pivot irrigation. These results suggest that conversion of furrow irrigation to pivot irrigation likely would result in increased productivity and reduced water use, and that use of plant-based irrigation termination guideline could reduce the need for costly, late season pumping without a yield penalty. [ABSTRACT FROM AUTHOR]

The introduction of transgenic cotton (Gossypium hirsutum L.) cultivars with resistance to certain herbicides has increased the interest in ultra-narrow-row production systems. A field study was conducted on Sharkey silty clay soil (very-fine, smectitic, thermic Chromic Epiaquerts) from 1995 through 1997 to evaluate the effects of ultra-narrow-row (UNR) and conventional wide-row (CONV) production systems on plant growth and yield components. Cotton grown in 19-cm rows with 530 000 seed ha-1 and harvested with a stripper was compared with cotton grown in 97-cm rows with 155 000 seed ha-1 and harvested with a spindle picker. Percentage of first position boll retention was higher in CONV than UNR in two of three years and averaged 30% in CONV and 27% in UNR across the three years. An average of 8.5% of the second position bolls were retained with UNR compared with 15% in CONV. The UNR plants were shorter, had fewer nodes, and had fewer total sympodia than the CONV plants. The UNR plants had fewer bolls than CONV plants, with a higher percentage of the total boll number in the first sympodial position and a lower percentage in the second position. Higher seed cotton yield of UNR cotton in 1995 and 1997 appeared to result from the higher plant populations, although the findings indicated that seeding rates lower than the one used in this study could have been used for UNR. Plant populations were also higher for UNR in 1996, but the low rainfall during fruiting appeared to impact the UNR more than CONV, possibly due to the high plant density. [ABSTRACT FROM AUTHOR]