Tillage, Crop Rotation, and Nitrogen Management Strategies for Wheat in Central Montana

Conventional tillage is gradually being replaced by no‐till or minimal tillage. Our objectives were to investigate: (i) winter wheat (Triticum aestivumL.) yield, and nitrogen uptake efficiency (NUE), as affected by surface‐applied N and crop rotation in no‐till and tilled fields; and (ii) N availability and uptake as affected by tillage history and crop rotation. A study was imposed on adjacent long‐term no‐till (LTNT) and long‐term sweep‐tilled (LTST) fields for 6 yr. Wheat yield, N uptake, and soil NO3–N were measured for fallow (F)–winter wheat (WW), spring pea (Pisium sativumL.) (SP)–WW, spring wheat (SW)–WW, and winter pea (WP)–WW rotations with four N rates (0, 45, 90, or 135 kg ha−1). From fall to spring, soil NO3–N increased in F–WW, SP–WW, and WP–WW rotations, but not with SW–WW rotation. After spring application of urea to the soil surface of the LTNT field, WW biomass growth was greater in SP–WW than in SW–WW at lower N levels, but no differences were found between the SP–WW and SW–WW rotation at higher N rates. In the LTST field, no difference in biomass was found between the SP–WW and SW–WW rotations except for the 0 N rate. Winter wheat in rotation with pea greatly increased wheat yield, N uptake, and NUE. Lower WW yield and NUE in SW–WW rotation apparently resulted from less over‐winter N release and the unavailability of surface‐applied N.