Summer fallow is the most common cultural practice in the northern Great Plains. With proper cultural management, however, annual cropping may be feasible and economical. Our objective was to determine crop and soil response to nontraditional annual cropping practices (till and no‐till) in lieu of conventional fallow‐crop rotation for the production of spring wheat (Triticum aestivum L.) and barley (Hordeum vulgare L.) in the in the northern Great Plains. The study, initiated in 1983, was on a Dooley sandy loam (fine‐loamy, mixed Typic Argiboroll) 11 km north of Culbertson, MT. Tillage practices on annually cropped treatments included sweep tillage in autumn and disk tillage in spring; sweep tillage in spring; and no‐tillage. Conventional fallow‐spring wheat rotations were included as the control. With three exceptions, there were no statistical differences among treatments in soil P, soil nitrate N, and pH. Phosphorus and N were nonlimiting in all years; pH decreased about 0.06 units per year in the 0‐ to 8‐cm layer because of N fertilization. Bulk density differences in the 0‐ to 10‐cm layer appeared after 7 yr, with the lowest bulk density for the no‐tillage annual crop treatment. Grain and straw yields with the no‐tillage treatment were both 80% of yields with the fallow‐crop treatment. Total water use efficiency, based on soil water differences between harvest of one crop and harvest of the next, was significantly greater with no‐tillage than with the fallow‐crop treatment. Soil organic C decreased nearly 0.4 g kg−1 per year with the fallow‐crop treatment; there was a negligible decline with the notillage annual crop treatment. No‐tillage annual spring wheat crop production was the most efficient crop and soil management practice from the standpoint of yield, water use efficiency, soil organic C, and bulk density.

N made available to crops that follow legumes in rotation. An estimate of soil mineralizable N is needed to determine crop While fertilization guides use total organic matter and needs for N fertilizer. The objective of this research was to estimate previous crop as indicators of N mineralization for the soil net N mineralization in soils maintained in continuous corn (Zea mays L.) (CC), corn-soybean [Glycine max (L.) Merr.] (CS), and coming season, a variety of direct and indirect lab methcorn-soybean-wheat (Triticum aestivum L.)/alfalfa (Medicago sativa ods may be used for more precise predictions (Fox and L.)-alfalfa (CSWA) rotations that have been managed since 1990 Piekielek, 1978; Hong et al., 1990). Laboratory tests with zero N (0N), low N (LN), and high N (HN) fertilization. Soil allow compositing and homogenizing soil samples to samples were taken from 0-to 20-cm depth in plots planted to corn decrease the standard deviation and required replicain 1998. In order to produce more realistic time-series data of net N tion. Aerobic incubation for 120 to 252 d is commonly mineralization, soils were incubated in filtration units in a variableused to estimate the size and decay rates of mineraliztemperature incubator (VTI) that mimicked field soil temperatures able N pools (Stanford and Smith, 1972; Cabrera and under a growing corn canopy. Rotation and N fertilization significantly Kissel, 1988). Temperature and matric potential of incuaffected net N mineralization in soil samples. Cumulative net N minerbated soils affect the rate and cumulative N mineralized. alized in a 189-d field temperature incubation averaged 133 Ϯ 6 kg ha Ϫ1 in CC, 142 Ϯ 5 kg ha Ϫ1 in CS, and 189 Ϯ 5 kg ha Ϫ1 in CSWA. Within ordinary field soil matric potentials from Ϫ1.85 Across rotations, average net N mineralized was 166 Ϯ 9 kg ha Ϫ1 in to Ϫ0.01 MPa, temperature has a greater influence on 0N plots, 147 Ϯ 10 kg ha Ϫ1 in LN plots, and 152 Ϯ 10 kg ha Ϫ1 in N mineralization than does matric potential (Zak et al., HN plots. Inclusion of a legume, particularly alfalfa, in the rotation 1999). Most N mineralization laboratory experiments increased net N mineralized. Generally, more net N was mineralized are incubated at 35ЊC, considered the ideal temperature from plots receiving no fertilizer N than from soil with a history of for maximum N mineralization. Nitrogen mineralized N fertilization. Variable-temperature incubation produced realistic in laboratory incubations at 35ЊC represents potential time-series data with low sample variability.

Green manures (GM) may offset inorganic N needs and improve soil quality. Study objectives were to determine effects of green manure on soil-N fertility, water use, soil quality, and yield of spring wheat (Triticum aestivum L.). On two treatments, lentil (Lens culinaris Medikus cv. Indianhead) was green manured in a green manure-spring wheat rotation. Lentil was killed by disking (GMMF) or chemicals (GMCF). Additional treatments were annually cropped wheat (AW) in a mechanical fallow (MF) or chemical fallow (CF) sequence. No inorganic N was used on GMMF and GMCF. Experiments were started in 1991 on a Williams loam (fine-loamy, mixed Typic Argiboroll) near Culbertson, MT. Green-manure treatments used 56 mm more water than fallow treatments when lentil was grown to lowerpod set. When lentil was killed at full bloom, there were no differences in water use among GM and fallow treatments. There were no differences among treatments in soil water at wheat planting. Wheat yield was 25% less on GM than on MF and CF. Soil NO 3-N (0-0.6 m) was 35% less on GM than MF and CF rotations. There were no differences in soil quality indicators of bulk density, organic C, pH, electrical conductivity, and deep NO 3-N (0.6 -1.8 m) among treatments after two cycles of GM. Potentially mineralizable N was 66% greater on GM treatments than on fallow treatments. Short-term results (5 yr) show that available N limited wheat production more than did soil water on the GM treatments. Soil improvement using green manures may require many additional cropping cycles.

Soil management and cropping systems have long-term effects on agronomic and environmental functions. This study examined the influence of contrasting management practices on selected soil chemical properties in eight long-term cropping system studies throughout the Great Plains and the western Corn Belt. For each study, soil organic C (SOC), total N (TN), particulate organic matter (POM), inorganic N, electrical conductivity (EC), and soil pH were evaluated at 0-7.5, 7.5-15, and 15-30 cm within conventional (CON) and alternative (ALT) cropping systems for 4 years (1999)(2000)(2001)(2002). Treatment effects were primarily limited to the surface 7.5 cm of soil. No-tillage (NT) and/or elimination of fallow in ALT cropping systems resulted in significantly (P < 0.05) greater SOC and TN at 0-7.5 cm within five of the eight study sites [Akron, Colorado (CO); Bushland, Texas (TX); Fargo, North Dakota (ND); Mandan, ND; and Swift Current, Saskatchewan (SK), Canada]. The same pattern was observed with POM, where POM was significantly (P < 0.05) greater at four of the eight study sites [Bushland, TX, Mandan, ND, Sidney, Montana (MT), and Swift Current, SK]. No consistent pattern was observed with soil EC and pH due to management, although soil EC explained almost 60% of the variability in soil NO 3 -N at 0-7.5 cm across all locations and sampling times. In general, chemical soil properties measured in this study consistently exhibited values more conducive to crop production and environmental quality in ALT cropping systems relative to CON cropping systems.

Knowledge of complex relationships between soils, crops, and management practices is necessary to develop sustainable agricultural production systems. Objectives were to determine how maize (Zea mays L.) would respond to monoculture (C‐C), 2‐yr rotation (C‐S) with soybean [Glycine max (L.) Merr.], or 4‐yr rotation (C‐S‐W/A‐A) with soybean, wheat (Triticum aestivum L.), and alfalfa (Medicago sativa L.) under different N input levels. We evaluated N fertilizer input (8.5 or 5.3 Mg/ha yield goal, or no N) and crop rotation (C‐C, C‐S, or C‐S‐W/A‐A) treatment effects on soil minerals (N, P, K, S, Ca, Mg, Fe, Mn, and Zn) and their subsequent effect on shoot dry weight and mineral concentrations, grain yield, and grain composition (oil, starch, and mineral concentrations) using univariate and multivariate statistical tests. Soil under C‐S‐W/A‐A rotation had greater NO3–N and less extractable P than other rotations. Significant input × rotation interactions revealed that shoot concentrations of N, Ca, and Mg were less while P, K, and Zn were greater at no N input for the C‐C rotation compared with other N input/rotation treatments. Increased soil NO3–N, increased plant Ca concentration, and increased grain N and grain S concentrations were most important in differentiating C‐S‐W/A‐A rotation from C‐C and C‐S rotation treatments. No N input resulted in less yield and kernel N concentration within the C‐C and C‐S rotations but not C‐S‐W/A‐A. Thus, growing maize in extended rotations that include forage legumes may be a more sustainable practice than growing maize in either monoculture or 2‐yr rotation with soybean.