Development of switchgrass (Panicum virgatum L.) as a dedicated biomass crop for conversion to energy requires substantial increases in biomass yield. Most efforts to breed for increased biomass yield are based on some form of indirect selection. The objective of this paper is to evaluate and compare the expected efficiency of several indirect measures of breeding value for improving sward-plot biomass yield of switchgrass. Sward-plot biomass yield, row-plot biomass, and spaced-plant biomass were measured on 144 half-sib families or their maternal parents from the WS4U-C2 breeding population of upland switchgrass. Heading date was also scored on row plots and anthesis date was scored on spaced plants. Use of any of these indirect selection criteria was expected to be less efficient than direct selection for biomass yield measured on sward plots, when expressed as genetic gain per year. Combining any of these indirect selection criteria with half-sib family selection for biomass yield resulted in increases in efficiency of 14 to 36%, but this could only be achieved at a very large cost of measuring phenotype on literally thousands of plants that would eventually have no chance of being selected because they were derived from inferior families. Genomic prediction methods offered the best solution to increase breeding efficiency by reducing average cycle time, increasing selection intensity, and placing selection pressure on all additive genetic variance within the population. Use of genomic selection methods is expected to double or triple genetic gains over field-based half-sib family selection.

Nitrogen recommendations designed to increase wheat (Triticum aestivum L.) yields may diminish wheat quality. By understanding fertility management impacts on quality, it may be possible to optimize N recommendations to sites and climates. The objective of this study was to quantify the combined and individual impacts of N and water stress on winter wheat grain yield, grain protein, dough quality, and water and N use efficiency. A field experiment using five N rates (ranging from 0 to 1.5 times the current university recommendation) and two water levels (adequate and deficient) was conducted in South Dakota in 2007 and 2008. Dough characteristics were measured using a farinograph. In 2007, soil N mineralization was high (192 kg N ha−1), supplemental water increased grain yield and grain N use efficiency (GNUE) by 25% and reduced yield loss due to N stress from 1141 to 480 kg ha−1, whereas relative to 0 N, the recommended N rate increased water use efficiency by 21% and reduced yield loss due to water stress from 737 to 481 kg ha−1. These benefits were achieved without a loss of dough quality. In 2008, N mineralization was low (99 kg N ha−1), water did not impact GNUE, and the adequate water treatment had lower grain protein (12.5 vs. 13.1 g kg−1) and arrival (3.3 vs. 4.3 min) and peak times (6.1 vs. 7.8 min) than the deficient water treatment. These findings suggest that the implementation of strategically applied N fertilizer may require improved estimates of N mineralization.

Water leaving roadside ditches has the potential to affect the quality of downstream waters.

In‐season N applications to winter wheat (Triticum aestivum L.) may increase profits and improve N fertilizer accuracy. The objectives of this experiment were to determine the impact of N and water stress on crop reflectance and N sufficiency index (SI) values. The experiment contained five N rates, two water treatments, and four blocks. Crop reflectance was measured at the stem extension and flag leaf growth stages, sufficiency index (SI)‐NDVIwf was ratio between the underfertilized normalized difference vegetation index value {NDVI = [near infrared (NIR)‐red]/[NIR+red]} and the NDVI value from well fertilized and well watered treatments, while SI‐NDVImz was ratio between underfertilized NDVI values and NDVI values from well fertilized plots within a water stress treatment. Yield losses due to water and N stress were determined using 13C isotopic discrimination. This research shows that: (i) at the stem extension and flag leaf growth stages, water stress and N stress increased, green, red, and red‐edge reflectance and reduced NDVI values (ii) following the economic optimum nitrogen rate (EONR) produced grain with greater than 120 g kg−1 protein and <10 min stability; (iii) at stem elongation and flag leaf, N fertilizer induced yield gains had a stronger relationship with SI‐NDVImz (stem extension, r = 0.49*; flag leaf, r = 0.51**) than SI‐NDVIwf (stem extension, r = 0.29; flag leaf, r = 0.33); and (iv) SI‐NDVImz had greater fertilizer recommendation accuracy than SI‐NDVIwf. These findings suggest that in wheat production, SI should be referenced to well fertilized areas within a management zone.

Producers in the Great Plains are exploring alternative crop rotations with the goal of reducing the use of fallow. In 1990, a study was established with no-till practices to compare eight rotations comprising various combinations of winter wheat (W), spring wheat (SW), corn (C), chickpea (CP), dry pea (Pea), soybean (SB), or fallow (F). After 12 yr, we characterized weed communities by recording seedling emergence in each rotation. Downy brome, cheat, redroot pigweed, and green foxtail were the most common weeds observed. Weed community density was highest for W–CP, being 13-fold greater than with Pea–W–C–SB. Downy brome and cheat were rarely observed in rotations where winter wheat was grown only once every 3 or 4 yr; in contrast, density of the brome species was 75-fold greater in W–CP. Warm-season weeds were also affected by rotation design; density of redroot pigweed and green foxtail was sixfold greater in W–C–CP compared with Pea–W–C–SB or W–F. One rotation design that was especially favorable for low weed density was arranging crops in a cycle of four, with two cool-season crops followed by two warm-season crops.

Corn rootworms (Diabrotica spp.) are the most economically destructive insect pests of corn (Zea mays L.) in the U.S. Midwest. The objective of this 2‐yr field study was to measure plant response and yield under ridge tillage or spring disk tillage in fields artificially infested with western corn rootworm (D. virgifera virgifera LeConte). Corn rootworm infestations were applied at 0, 1650, 3300, or 6600 viable eggs m−1. We measured insect survival to adult, root damage ratings, nodal root volume (Nodes 4 and above) at maximum insect damage, and grain yield. In 1988, which was characterized by above‐normal temperature and below‐normal precipitation, root damage increased (6.7 rating at 1650 eggs m−1 to 7.9 at 6600 eggs m−1) and insect survival to adult decreased (4.9% at 1650 eggs m−1 to 1.2% at 6600 eggs m−1) with increasing infestation level under both tillage systems. During the 1988 season, plants grown under ridge tillage had larger nodal root systems (17.9 mL) than under spring disk tillage (9.9 mL). Ridge‐tilled plants also had greater yield (5.5 vs. 4.1 Mg ha−1 with no rootworm eggs; 4.3 vs. 3.1 with 1650 eggs m−1; and 4.1 vs. 2.2 Mg ha−1 with 3300 eggs m−1). In 1989, which had near normal temperature but below‐normal precipitation during the growing season, root damage increased (from a 1.1 to 5.9 rating as the infestation level increased from 0 to 6600 eggs m−1) and insect survival to adult decreased (from 1.3 to 0.7% as the infestation level increased from 1650 to 6600 eggs m−1) under both tillage systems. Tillage practice had no effect on plant response to rootworm feeding or yield. However, the number of nodal root axes per plant (22.4) and grain yield (8.8 Mg ha−1) were increased significantly under both tillage systems infested with 6600 eggs m−1 of row (29.0 axes per plant and 10.2 Mg ha−1). These results suggest that during a hot, dry growing season, ridge tillage increased yield for uninfested and rootworm‐infested plants when compared with yields produced using spring disk tillage.

Corn (Zea mays L.) plants express unexpected K‐deficiency symptoms when grown under certain conservation tillage production systems on high‐K‐testing soils. This field study was conducted to determine if K fertilizer treatments interact with P and N planting‐time fertilizer placement treatments to affect crop growth, nutrient composition, and yield in an irrigated no‐till corn production system on high‐K‐testing soil. The 3‐yr study was conducted on Lowry silt loam soils (coarse‐silty, mixed, superactive, mesic Typic Haplustolls) near Pierre, SD. Fertilizer placement (main plot) treatments consisted of P and N fertilizers that were applied with the corn planter to (i) the soil surface, (ii) the seed furrow, or (iii) a band 5 cm to the side of the seed furrow and 5 cm deep. Fertilizer products containing K, also applied at planting time, provided a with‐K subplot comparison with subplots that received no added K fertilizer. Corn plants were sampled for root pull resistance, shoot dry weight, and shoot mineral nutrient composition at the tassel stage of development and grain yield. Data combined over the 3 yr of the study revealed that added K fertilizer had no effect on grain yield and did not interact with P and N fertilizer placement treatments to affect grain yield. When P fertilizer was placed with the seed and N fertilizer was placed in a 5‐ by 5‐cm band, corn plants had 185 kg root−1 pull resistance, 0.26 g shoot−1 P accumulation, and 10.5 Mg ha−1 grain yield. However, when P and N fertilizers were applied to the soil surface, corn plants had significantly less root pull resistance (151 kg root−1), P accumulation (0.22 g P shoot−1) and grain yield (10.1 Mg ha−1). Added K fertilizer decreased shoot dry weight (added K = 97 g shoot−1, no K = 103 g), decreased P accumulation (added K = 0.22 g P plant−1, no K = 0.25 g), increased shoot N concentration (added K = 19.3 mg N g−1, no K = 19.0 mg), and had no significant effect on K concentration or accumulation. We conclude that, although planting‐time fertilizer placement was important for optimum corn growth and yield production in irrigated no‐till systems, added K fertilizer did not interact with fertilizer placement to improve yield on the high‐K‐testing soils used in this study.

Hansen, M. J., Owens, V. N., Beck, D. and Sexton, P. 2013. Suitability of cover crop monocultures for late-season forage in South Dakota. Can. J. Plant Sci. 93: 589–597. Cover crops provide many agronomic benefits and can produce large amounts of forage that is suitable for grazing. The objectives of this study were to determine (1) suitable cover crop forages based on yield and nutrient values; and (2) changes in feed value and yield of these crops through the late fall. Five cover crop monocultures consisting of lentil (Lens culinaris Medikus), cowpea (Vigna unguiculata L.), foxtail millet (Setaria italica L.), oats (Avena sativa L.), forage radish (Raphanus sativus L.), and a mixture of these crops were planted after winter wheat (Triticum aestivum L.) harvest in 2010 and 2011 in central and southeastern South Dakota. Forage data were collected on approximately Oct. 01, Nov. 01, and Dec. 01 each year. Yields increased after the first harvest date at both sites, both years. Oats, radish, and the cover crop mixture all yielded >4000 kg of dry matter per hectare on the second harvest date in 2011 in central South Dakota and radish and oats yielded >4000 kg ha−1 in southeastern South Dakota on the second and third harvest dates, respectively. Forage quality tended to decrease after each harvest date. Radish in central South Dakota in 2010 had the highest protein values for the study (194–313 g kg−1) whereas oats in southeastern South Dakota had the lowest protein concentrations (63–108 g kg−1), both years. All cover crops except cowpea were viable forages through the late fall when they had good establishment with the potential need for protein supplementation with oats, foxtail millet, and the cover crop mixture, depending on animal requirements.