Precipitation, Temperature and Tillage Effects upon Productivity of a Winter Wheat–Dry Pea Rotation

Winter wheat (Triticum aestivum L.) is grown in rotation with fresh pea (Pisum sativum L.) in the wetter (≥450 mm) zones of the inland Pacific Northwest, and with summer fallow in the drier (<450 mm) zones. Typically, this cropping system has been tillage‐intensive. Summer fallow deleteriously affects soil properties, while fresh pea markets have decreased for decades. Alternative wheat‐based cropping systems are needed. The objective of this 6‐yr study was to evaluate the agronomic viability of a winter wheat–dry pea rotation under four tillage systems. Primary tillage operations for wheat and pea residue, respectively, were: (i) fall disk and chisel plow (Fall D‐CH); (ii) fall moldboard plow and moldboard plow (Fall MBD‐MBD); (iii) spring moldboard plow and moldboard plow (Spring MBD‐MBD); and (iv) fall sweep and skew‐tread (Fall SWP‐SKW). Spring precipitation strongly influenced dry pea yield, but tillage had little to no effect. Pea yield could be predicted well by a model combining precipitation distribution with a heat stress index. Wheat yield was more influenced by winter than spring precipitation, and was ∼400 kg ha−1 less for the Fall SWP‐SKW treatment. Wheat protein content was also reduced in the Fall SWP‐SKW tillage treatment. The probable reason for lower wheat yield is poor weed control. Dry pea is agronomically viable as a rotation substitute for summer fallow or fresh pea. The apparent yield decline of wheat yield in the minimum tillage system needs to be evaluated in terms of tillage costs, and improved technologies for weed, residue, and N management.