Field studies were conducted in 2016 and 2017 under rain-fed conditions in south-central Louisiana, (a) to determine the effects of plant density levels on plant height, ear height, stalk diameter, lodging, corn grain yield, test weight, and photosynthetically active radiation with modern corn hybrids in central Louisiana and (b) to test the hypothesis that the response of grain yield to plant population density would depend on the reproductive plasticity (flex, semiflex, or fixed ear) of the hybrids evaluated. Rainfall was above average while air temperatures were below average during the growing season in both years. Grain yield showed a hybrid response in one of two years (fixed ear greater than semiflex ear) while yields increased as plant populations increased. Test weights were less with the fixed ear hybrid and the effect of plant populations was inconsistent with increased populations resulting in greater test weight in one of two years. Lodging increased as plant populations increased with the fixed ear hybrid resulting in greater lodging in one of two years. There was a hybrid by plant population interaction for ear height and seed weight. The effect of plant populations is an important factor for corn yield; however, yield gains associated with higher plant populations may be dependent on the genetic predisposition of corn hybrids (regardless of the reproductive plasticity) to tolerate various environmental conditions and stresses associated with higher populations.

All herbicides will move off-target to sensitive crops when not applied correctly. Therefore, low-dose applications of flumioxazin and metribuzin were evaluated in soybean at the unifoliate, V2, and V4 growth stages. Rates evaluated were 12.5%, 25%, and 50% of the labeled use rates of 72 and 316 g ai ha−1 of flumioxazin and metribuzin, respectively. Flumioxazin injury was characterized by necrosis and visible height and width reduction. Injury increased with rate 3 d after treatment (DAT), with unifoliate, V2, and V4 soybean injured 15% to 30%, 18% to 27%, and 5% to 8%, respectively. Unifoliate and V4 soybean were injured more than V4 soybean 3 to 14 DAT, but injury decreased to <5% by 42 DAT. Soybean yields in the flumioxazin study were 92% to 96% of the nontreated, resulting in a yield loss of 196 to 393 kg ha−1 and a revenue loss of 71 to 141 US$ ha−1. Metribuzin injury was primarily chlorosis with necrosis and a visible reduction in soybean height and width. Soybean at the V2 growth stage was injured 14% more than V4 soybean 3 DAT, regardless of metribuzin rate. Injury to V2 and V4 soybean was similar 14 DAT, with injury of 21% to 40% across rates. Soybean injury when treated at the V2 and V4 growth stages was 6% to 29% 42 DAT compared to unifoliate soybean at 0 to 17%. Soybean yields in the metribuzin study yields were 96% to 98% of the nontreated. However, a 2% to 4% reduction equates to a loss of 90 to 180 kg ha−1 and a revenue loss of 32 to 65 US$ ha−1. Unifoliate and V2 soybean are more sensitive to a low dose of flumioxazin POST, and V2 and V4 soybean are more sensitive to a low dose of metribuzin POST. Injury and the impact on soybean growth could potentially cause economic loss for a soybean producer.

The effects of postemergence (POST) herbicides off-target movement on cotton has been evaluated, but no data is available evaluating simulated off-target movement of residual herbicides. Therefore, low-dose POST applications of flumioxazin were evaluated in cotton at the cotyledon, two- and four-leaf growth stages. Rates evaluated were 12.5, 25, and 50% of the labeled use rate of 72 g ai ha-1. Necrosis, cotton height and width reduction was observed. Cotyledon cotton was injured 69 to 86%, 80 to 91%, and 84 to 97% following the 12.5, 25, and 50% flumioxazin rates, respectively, 3 through 42 DAT. Injury of two-leaf cotton increased from 3 to 14 DAT for all flumioxazin rates with maximum injury of 40, 47, and 58% following the 12.5, 25, and 50% rates, respectively, 14 DAT, but injury decreased following the 14 DAT evaluation. Injury of four-leaf cotton was 46 to 58% 3 DAT and decreased over time regardless of rate. At 42 DAT, two- and four-leaf cotton was injured 14 to 33% and increased with flumioxazin rate. Cotton height and width averaged 40, 80, 86% of the nontreated following the cotyledon, two-, and four-leaf application timings, respectively, 42 DAT. In addition, height was more influenced by flumioxazin rate than cotton width. Yields were 24, 52, and 62% of the nontreated following the cotyledon, two-, and four-leaf applications timings, respectively. In addition, yields following the 12.5, 25, and 50% rates were 53, 45, and 40% of the nontreated. Low-doses of flumioxazin reduced revenue $1,172 to $2,344 ha-1 for lint and $212 to 423 ha-1 for cotton seed. Low-doses of flumioxazin POST can have negative effects on cotton growth and yield and could cause severe economic loss for a cotton producer.

Abstract. Although prior research has shown that irrigation can increase cotton fiber yields in coastal plain soils of the Carolinas, only 2.7% of North Carolina’s and 7.8% of South Carolina’s planted hectares are irrigated, compared to 39% nationally. Little research has addressed the impact of compacted subsurface soil layers on the value of irrigation. Economic analysis of irrigation is also difficult due to the lack of long-term irrigation data for the region. The objectives of this study were to adapt the CSM-CROPGRO-Cotton simulation model to production conditions in the coastal plain of the Carolinas and use it to evaluate both the agronomic and economic value of irrigation to upland cotton production. Field data collected near Lewiston-Woodville, North Carolina, in 2015-2016 were used in model calibration and validation. Soil profiles were established using historical weather and cotton yield data for 16 cotton-producing counties in North and South Carolina from 1979 to 2015. Soil profiles were fit both with and without a root-restrictive (compacted) layer for each county. To evaluate the value of irrigation for these counties, simulations were conducted using ten irrigation levels, including non-irrigated, triggered when plant-available water (PAW) reached a maximum allowable depletion of 50%. The economic analysis made use of Cotton Incorporated’s Cotton Irrigation Decision Aid to determine the economic feasibility of irrigation using investment analysis tools such as cash flow, payback period, and net present value (NPV). Predicted agronomic and economic responses to irrigation were strongly dependent on seasonal rainfall. Fiber yield of non-irrigated cotton was reduced by more than 10% of fully irrigated cotton yield in more than 70% of the site-years simulated. This study suggests that irrigation is a feasible investment for cotton producers in North and South Carolina, as positive average cash flows and NPVs were observed over all counties and soils evaluated. Keywords: Cotton, CROPGRO, Crop simulation model, Economic analysis, Irrigation, Water use efficiency, Yield loss.

In 2012, only 2.7% of North Carolina’s cotton (Gossypium hirsutum L.) was irrigated compared to the national average of 39%. The small size and nonuniform shape of most North Carolina fields are not conducive for a center pivot system. However, benefits to yield due to irrigation in North Carolina have been reported, specifically in years receiving below average or sporadic rainfall. The objective of this research was to investigate the impact of subsurface drip irrigation (SDI) on growth and yield of early- and late-maturing cotton cultivars at varying planting dates in eastern North Carolina. In 2014, the site received more than 750 mm of rainfall and no differences were observed for any parameters between irrigated and non-irrigated plots. Total rainfall in 2015 and 2016 was lower with several extended periods without rain events. There was a greater plant height increase and dry weight accumulation throughout the growing season in response to SDI. Cotton yields were increased by SDI in 2015 and 2016. Cultivar only influenced lint yield in 2016 with the earlier-maturing ‘PHY 333 WRF’ having greater lint yield than ‘PHY 499 WRF’. Planting date did not influence yield under irrigated conditions, and the timing of rainfall played a role similar to previous reports in North Carolina. Irrigation applied via SDI will increase cotton plant stature, fruit retention, and yield in response to deficit moisture conditions, independent of planting date or cultivar.