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Core Ideas Wheat yields are greater following fallow than following crops.The most stable systems are WF(NT), WF(CT), and WMF.The least stable systems are WCMF, WM, and WCF.The probability of obtaining a yield less than 1500 kg ha‐1 is low for wheat after fallow.Risk‐averse farmers wishing to intensify a WF system should consider WMF. The winter wheat (Triticum aestivum L.)–fallow (WF) dryland production system employed in the Central Great Plains has evolved in the past 40 yr to include a diversity of other crops, with a reduction in fallow frequency. Wheat remains the base crop for essentially all cropping systems. Decisions to change a farming system benefit from information about average wheat yields, yield stability, and probabilities of obtaining a specified minimum wheat yield. The objective of this experiment was to quantify wheat yields, yield stability, and the probability of obtaining a specified minimum yield in eight dryland rotational systems varying in cropping intensity. The study was conducted over a 24‐yr period at Akron, CO. Yield stability was characterized with six stability measures. The probability of obtaining a yield less than 1500 kg ha−1 was also calculated for each rotation. Wheat yields were greatest in rotations where wheat followed a fallow period and least where wheat followed millet production. Rotations ranked from most stable to least stable wheat production (averaged over the six stability measures) were WF(NT), WF(CT), WMF, WCMP, WCM, WCMF, WM, and WCF. The probability of producing <1500 kg ha−1 was very low for rotations with wheat following fallow (about 0.03) and much higher for wheat following pea (0.35) or millet (0.48–0.58). The study results identified the WMF rotation as an intensified rotation with relatively high average wheat yields and yield stability.

Recent recommendations advocating the use of cover crop mixtures instead of single-species in semi-arid environments require rigorous scientific studies. One of those stated benefits is greatly reduced water use by cover crops grown in mixtures. The objectives of this study were to characterize soil water extraction patterns and determine water use of cover crops grown in single-species plantings and in a 10-species mixture and to compare cover crop water use to evaporative water loss from no-till fallow. The study was conducted at Akron, CO, and Sidney, NE, during the 2012 and 2013 growing seasons on silt loam soils. At each location there were a dryland treatment and an irrigated treatment. Soil water contents were measured by neutron scattering and time-domain reflectometry at six depths (0.0–1.8 m, Akron) or four or five depths (to 1.2 m or 1.5 m, Sidney). There were no consistent significant differences in soil water contents or growing season crop water use with the single-species plantings compared with the 10-species mixture. Cover crop water use (216 mm) averaged 1.78 times greater than evaporative water loss (122 mm) from the no-till fallow treatment with proso millet (Panicum miliaceum L.) residue. There appears to be no evidence from data collected in this semi-arid environment, even when irrigated to simulate higher rainfall environments, to support the conclusion that cover crops grown in multi-species mixtures use water differently than single species-plantings of cover crops.

In order to properly determine the value of charring crop residues, the C use efficiency and effects on crop performance of biochar needs to be compared to the un-charred crop residues. In this study we compared the addition of corn stalks to soil, with equivalent additions of charred (300 °C and 500 °C) corn residues. Two experiments were conducted: a long term laboratory mineralization, and a growth chamber trial with proso millet plants. In the laboratory, we measured soil mineral N dynamics, C use efficiency, and soil organic matter (SOM) chemical changes via infrared spectroscopy. The 300 °C biochar decreased plant biomass relative to a nothing added control. The 500°C biochar had little to no effect on plant biomass. With incubation we measured lower soil NO(3) content in the corn stalk treatment than in the biochar-amended soils, suggesting that the millet growth reduction in the stalk treatment was mainly driven by N limitation, whereas other factors contributed to the biomass yield reductions in the biochar treatments. Corn stalks had a C sequestration use efficiency of up to 0.26, but charring enhanced C sequestration to values that ranged from 0.64 to 1.0. Infrared spectroscopy of the soils as they mineralized showed that absorbance at 3400, 2925-2850, 1737 cm(-1), and 1656 cm(-1) decreased during the incubation and can be regarded as labile SOM, corn residue, or biochar bands. Absorbances near 1600, 1500-1420, and 1345 cm(-1) represented the more refractory SOM moieties. Our results show that adding crop residue biochar to soil is a sound C sequestration technology compared to letting the crop residues decompose in the field. This is because the resistance to decomposition of the chars after soil amendment offsets any C losses during charring of the crop residues.

Core Ideas Crops differ in depth of soil water extraction. Crops did not differ in lower limit of water availability. Wheat ends the growing season with a drier soil profile. Proso millet ends the growing season with a wetter soil profile. Extractable available soil water may aid in designing successful rotational sequences. Dryland cropping decisions would benefit from information about soil water extraction by various candidate crops. The objectives of this experiment were to: (i) quantify average soil water extraction by depth in the soil profile for winter wheat (Triticum aestivum L.), corn (Zea mays L.), proso millet (Panicum milliaceum L.) , and dry pea (Pisum sativum L.), and (ii) verify previously published values of drained upper limit (DUL) and lower limit (LL) of water extraction for each crop grown on a silt loam soil in northeastern Colorado. Soil water contents at planting and physiological maturity were measured over a 21‐yr period. Average ending soil water was least at all measurement depths for wheat and greatest for millet. The greatest total profile water extraction was seen for wheat (141 mm) and the least for pea (46 mm). Soil water extraction occurred, on average, from the 0‐ to 180‐cm profile for wheat, 0‐ to 150‐cm profile for corn, 0‐ to 120‐cm profile for millet, and 0‐ to 90‐cm profile for pea. When soil water was plentiful at planting and followed by dry growing season conditions, millet extracted soil water from the entire 0‐ to 180‐cm profile. Crop rotational sequences utilizing shallow rooted crops (such as millet and pea) that do not fully extract soil water at lower depths will allow for greater soil water availability to subsequent crops such as wheat and corn that are able to explore the lower soil profile more effectively for soil water.

Crop production systems in the water-limited environment of the semiarid central Great Plains may not have potential to profitably use cover crops because of lowered subsequent wheat (Triticum asestivum L.) yields following the cover crop. Mixtures have reportedly shown less yield-reducing effects on subsequent crops than single-species plantings. This study was conducted to determine winter wheat yields following both mixtures and single-species plantings of spring-planted cover crops. The study was conducted at Akron, CO, and Sidney, NE, during the 2012–2013 and 2013–2014 wheat growing seasons under both rainfed and irrigated conditions. Precipitation storage efficiency before wheat planting, wheat water use, biomass, and yield were measured and water use efficiency and harvest index were calculated for wheat following four single-species cover crops (flax [Linum usitatissimum L.], oat [Avena sativa L.], pea [Pisum sativum ssp. arvense L. Poir], rapeseed [Brassica napus L.]), a 10-species mixture, and a fallow treatment with proso millet (Panicum miliaceum L.) residue. There was an average 10% reduction in wheat yield following a cover crop compared with following fallow, regardless of whether the cover crop was grown in a mixture or in a single-species planting. Yield reductions were greater under drier conditions. The slope of the wheat water use–yield relationship was not significantly different for wheat following the mixture (11.80 kg ha–1 mm–1) than for wheat following single-species plantings (12.32–13.57 kg ha–1 mm–1). The greater expense associated with a cover crop mixture compared with a single species is not justified.

Precipitation storage efficiency (PSE) is the fraction of precipitation received in a given time period that is stored in the soil. Average fallow PSE for Great Plains wheat (Triticum aestivum L.)-fallow (W-F) production systems have ranged widely (10–53%). Study objectives were to compare PSE in conventionally tilled (CT) and no-till (NT) W-F systems over 10 seasons at Akron, CO, against published values and to identify meteorological conditions that may influence PSE. Soil water measurements were made four times during each fallow period, dividing the fallow season into three periods (first summer, fall–winter–spring, second summer). Precipitation was measured in the plot area and other meteorological conditions were measured at a nearby weather station. The 14-mo fallow PSE averaged 20% (range 8–34%) for CT and 35% (range 20–51%) for NT, much lower than previously reported for NT at Akron. During the second summer period, PSE was not different between the two systems. The largest PSE difference between the two systems was seen during the fall–winter–spring period (32 vs. 81%). Fallow soil water increased an average of 111 mm under CT and 188 mm under NT. The PSE during the three fallow periods was related to tillage, precipitation, air temperature, vapor pressure deficit, and wind speed, but sometimes counter-intuitively. A simple linear regression using inputs of tillage system, percentage of fallow precipitation events with amounts between 5 and 15 mm, and percentage of fallow precipitation events with amounts > 25 mm can be used to estimate PSE and fallow period water storage.

Soil loss through wind and water erosion is an ongoing problem in semiarid regions. A thin layer of top soil loss over a hectare of cropland could be corresponding to tons of productive soil loss per hectare. The objectives of this study were to evaluate the influence of beef feedlot manure, tillage and legume grass mixtures on changes in soil quality and nutrient components. The study was initiated in 2006 on an eroded site near Akron, Colorado, on a Norka-Colby very-fine sandy loam (fine-silty, mixed, mesic, Aridic, Argiustolls). Tillage treatments were no-tillage, shallow tillage (sweeps operations with V-blade) and deep tillage (DT; moldboard plow operations). In one set of plots, DT was implemented biannually (DT-2); and in another set the DT was done once at the initiation of the experiment in 2006. Amendments consisted of beef manure and urea (46-0-0), N fertilizer. Both amendments were added at low and high rates. A control treatment, with no fertilizer or manure added, was included with no-tillage and shallow tillage only. Six years of manure addition and tillage significantly altered soil chemical properties compared with fertilizer and grass legume mixtures. Across all the tillage treatments, at the 0-30 cm depth, soil pH from 2006 to 2012, was reduced 1.8 fold with high-manure compared with high-fertilizer treatment. Soil EC, Na, and SAR increased by 2.7 fold while soil P increase by 3.5 fold with high-manure treatment compared with low-manure from 2006 to 2012 across all the tillage treatments at the surface 0-30 cm. Soil organic carbon associated with high-manure was 71% higher than low-manure and 230% higher than high-fertilizer treatments in the 0-60 cm depth. Similar patterns were observed with soil total N. Overall, manure amendments greatly improved the soil nutrient status on this eroded site. However, the legume grass mixtures showed little effect on improving soils chemical properties. The micronutrients supplied by manure improved the soil nutrient status compared with inorganic fertilizer, the grass, and the grass-legume treatments. We concluded that more than six years are needed to measure significant improvements in soil quality from specific treatments, specifically fertilizer, grasses, and grass-legume mixtures in such eroded crop land.

Long‐term conservation tillage improves soil quality by enhancing soil structure, improving water availability, and reducing soil erosion. We investigated the effect of tillage intensity on soil organic carbon (SOC), organic carbon fractions, particulate organic matter (POM), and wet aggregate‐size distribution after 39 yr of management. The data reported here were taken from a long‐term tillage study initiated in 1967 near Akron, CO. Treatments sampled were conventional tillage (CT), moldboard plow (MP), no‐tillage (NT), and reduced tillage (RT). In 2006, soil samples were collected from the 0‐ to 5‐, 5‐ to 10‐, 10‐ to 20‐, 20‐ to 30‐, and 30‐ to 60‐cm depths in winter wheat (Triticum aestivum L.)–summer fallow (WF). Soils were fractionated for aggregate mass and POM–mineral‐associated carbon (C) to evaluate the form and stability of SOC. On a fixed‐depth basis, NT and RT had 21% more SOC, at the 0‐ to 30‐cm depth than CT and MP. However, on equivalent mass basis (ESM), SOC was greater with NT, MP, and RT by 11% compared with CT. Conservation practices, NT and RT, had more macroaggregation and consequently greater soil stability compared with CT and MP. Tillage practices significantly impacted whole SOC distribution between POM‐C and mineral‐associated organic matter C (MAOM‐C). The POM‐C vs. MAOM‐C component of the whole SOC was 23 vs. 77% at 0 to 5 cm and 10 vs. 90% at 5‐ to 20‐cm depth. The POM‐C associated with NT and RT, accounted for 17% of SOC where POM‐C accounted for 12% of SOC with CT and MP at 0‐ to 20‐cm depth. Redistribution and stratification of SOC, POM, and POM‐C were observed especially with MP. Over all, we found the application of conservation tillage practices to be crucial for maintaining soil quality and soil C stock in the WF systems of the central Great Plains.

Climate in the semiarid central Great Plains is expected to become warmer and drier in coming decades, with potentially greater variability in precipitation and temperature. Cropping systems that include forages and allow flexibility for determining if a crop should be planted and which crop to plant (based on available soil water at planting) may provide the opportunity to maintain economic viability in a changing climate environment. The objective of this study was to compare cropping system productivity and profitability of flexible rotations that incorporate forages against grain‐based cropping systems that are set rotational sequences. Yield and net returns for five set rotations and three flexible rotations were compared at Akron, CO, over 5 yr. Winter wheat (Triticum aestivum L.) yields were reduced by 57% when the fallow period prior to wheat production was replaced with crop production. Average net income was greatest for the continuously cropped all‐forage set 3‐yr rotation followed by the flexible 3‐yr rotations that included wheat and forage phases. The lowest net returns were seen for the set grain‐based rotations and the flexible wheat–grain crop rotation. Incorporating forage production as a phase in dryland wheat rotational systems can add profitability and sustainability to the production system in the face of climate variability. Core Ideas Including forages in semi‐arid dryland cropping systems increases profitability. Using flexible rotations based on soil water at planting can reduce fallow frequency. Continuously cropping with an all‐forage rotation maximizes net returns. Flexible rotations with forages may mitigate negative effects of climate variability.

Breeding superior bread wheat (Triticum aestivum L.) genotypes requires sufficient genetic variation to obtain high grain yield and adequate grain protein concentration. This study was conducted to determine variation for nitrogen use efficiency (NUE) and grain protein deviation among 20 hard winter wheat genotypes in one season and for two recently released cultivars (Snowmass and Byrd) in a second season, under five N application rates (0, 28, 56, 84, 112 kg ha−1). Among these genotypes, the proportionate contributions of component traits to total variance for NUE ranged widely: N uptake efficiency (57–89 kg kg−1) and N utilization efficiency (11–43 kg kg−1). Across all genotypes, N utilization efficiency contributed the most to variance for NUE under moderate to high N supply while N uptake efficiency contributed more under N limiting conditions. Increased NUE promotes high grain yields, but may result in decreased grain protein concentration through the commonly observed negative correlation of these traits. Analysis of residuals from regression of grain protein concentration on grain yield, or “grain protein deviation”, identified one genotype (Brawl CL Plus) that had 6.7 g kg−1 higher grain protein concentration than the average for all 20 genotypes. These results for a representative sample of a breeding population suggest that sufficient variation is available to improve NUE and grain protein deviation through breeding. Core Ideas We assessed variation available to improve N use efficiency and grain protein deviation through breeding. We determined variation for N use efficiency component traits in 20 breeding lines and cultivars. Nitrogen utilization efficiency contributed the most to variance for N use efficiency under moderate to high N. Nitrogen uptake efficiency contributed the most to variance for N use efficiency under N limiting conditions. Grain protein deviation varies among these genotypes; the highest was 6.7 g kg–1 above the mean.