Effect of Tillage on Fertilizer Requirements for Corn on a Silt Loam Soil1

Abstract Corn (Zea mays L.) yields less with no‐till or reduced tillage than with conventional tillage on medium and fine‐textured soils in Ontario, Canada. This study was undertaken to determine whether rates of N, P, or K above those normally recommended could increase the no‐till yields. Annual rates of 120 and 240 kg N/ha, and initial rates of 95, 475, and 1,260 kg P/ha and 95, 665, and 1,330 kg K/ha were applied to a silt loam soil (Albaquic Hapludalf) in combination with four different tillage treatments (fall moldboard plow, spring disc; fall mulch plow with heavy duty cultivator, spring disc; fall ridge; no‐till). Corn was grown, harvested for grain, and stover returned to the soil over a 6‐year period. Increasing N, P or K applications gave similar response patterns on each tillage treatment. There was no indication that the higher nutrient applications could overcome yield depressions associated with reduced tillage. Adequate N, P, K levels in corn tissue further substantiated an adequate nutrient supply with each tillage treatment. Resistance to penetration measurements on soil suggested that mechanical impedance might be more critical than nutrient supply in growth performance and explain the lower yields with reduced tillage. Soil tests for available P and K, combined for increments of the upper 30 cm of soil, tended to be higher with no‐till than with the plow treatment.