Soybean improvement via plant breeding has been critical for the success of the crop. The objective of this study was to quantify genetic change in yield and other traits that occurred during the past 80 yr of North American soybean breeding in Maturity Groups (MGs) II, III, and IV. Historic sets of 60 MG II, 59 MG III, and 49 MG IV soybean cultivars, released from 1923 to 2008, were evaluated in field trials conducted in 17 U.S. states and one Canadian province during 2010 to 2011. Averaged over 27 MG II and MG IV and 26 MG III site-years of data, the estimated rates of yield improvement during the 80 yr were 23 kg ha -1 yr -1 for MGs II and III, and 20 kg ha -1 yr -1 for MG IV cultivars. However, a two-segment linear regression model provided a better fit to the data and indicated that the average current rate of genetic yield gain across MGs is 29 kg ha -1 yr -1 . Modern cultivars yielded more than old cultivars in all environments, but particularly in high-yielding environments. New cultivars in the historic sets used in this study are shorter in height, mature later, lodge less, and have seeds with less protein and greater oil concentration. Given that on-farm soybean yields in the United States are also increasing at a rate of 29 kg ha -1 yr -1 , it can be inferred that continual release of greater-yielding cultivars has been a substantive driver of the U.S. onfarm realized yield increases.

Wheat straw is a potential cellulosic feedstock for bioethanol. This study was conducted to evaluate straw yield potential and its relationship with grain yield for wheat (Triticum spp.) grown in the United States. The specific objective was to determine if differences in straw yield and harvest index (HI) exist between and within regions and/or wheat classes. Using ongoing variety performance trials in eight states, a total of 255 varietal trial entriess from five classes of wheat were surveyed for above-ground biomass. Averaged over all wheat classes and regions the HI was 0.45. Soft red winter wheat in Kentucky had, on average, the highest HI and lowest straw yield among regions and wheat classes. Soft white winter wheat under irrigation in the Pacific Northwest produced the highest straw yield. Hard red winter wheat in the southern plain states of Texas and Oklahoma had, on average, the lowest HI. Differences in the amount of precipitation and cultivars were the major contributors to the variation detected within wheat classes. The amount of wheat straw available as cellulosic feedstock in a state or wheat class can be estimated using the grain yield estimates provided by the National Agricultural Statistics Service and the class specific HI.

Hail influence on corn (Zea mays L.) yield depends on defoliation timing and severity. Complete defoliation during early vegetative stages can have minimum yield effects if plants’ growing point is not affected but can generate some delays in the planting to flowering period. Low‐severity defoliations after V10 can reduce yield up to 30%. Higher severities gradually increase yield penalties to a peak around flowering and decrease progressively during the grain‐filling period. Charts to estimate the percentage of corn yield loss due to defoliation developed in the late 1960s are still accurate in most situations but fail to describe particular situations. Defoliation around VT commonly affects time to silking, anthesis–silking interval, and plant growth rate, but not time to anthesis, and is commonly explained by lower kernel number (KN). Defoliation at R2 commonly affects kernel weight (KW), without changing KN. However, several studies showed a reduction in both KW and KN with R2 defoliations. Under low plant disease pressure, fungicides applied around VT do not help reduce any yield defoliation impact. Specific genotypes, row spacing, and hybrid maturity can influence crop yield defoliation responses. More studies are warranted to confirm the potential for narrow rows to reduce yield loss after defoliation.

Core Ideas Limited data on the effect of row width on defoliation in modern hybrids.Yield loss in 38 cm was less for all defoliation treatments vs. 76‐cm rows.Different hybrids responded differently to defoliation at different row widths.Defoliations had greater impact on kernel number than kernel weight in both hybrids.Some defoliations during effective grain‐filling period reduced kernel number. Corn (Zea mays L.) defoliation experiments have been conducted for more than 130 yr in the United States. However, there are limited data on the effect of row width on defoliation in modern hybrids. A 2‐yr experiment was conducted in Lexington, KY, with two hybrids (113 relative maturity [RM] and 120 RM), two row widths (38 and 76 cm) and a combination of defoliation timings and severities: 0% defoliation (control), V7 growth stage, and 100% defoliation (V7–100%), V14–50%, V14–100%, R2–50%, and R2–100%. No yield difference among hybrids was observed in 2012. Yields were 26% greater in 38‐cm rows than 76‐cm rows in 2012. For 2013, corn yield for 38 cm was 10% greater, but hybrid, row width, and defoliation interacted. Lowest yields were caused by V14–100% followed by R2–100% defoliations. Defoliations of V14–50% and R2–50% reduced yields in some cases. Complete defoliations at V7 did not reduce yields in most comparisons. Kernel number and kernel weight were most reduced by V14–100% and R2–100% defoliations, respectively. There is a potential for corn in 38‐cm narrow rows to reduce grain yield losses after a defoliation event, when compared with corn in 76‐cm standard rows.