MYCORRHIZAE, PHOSPHORUS ABSORPTION, AND YIELD OF MAIZE IN RESPONSE TOTILLAGE

Maize (Zea maps L.) in the early season in no-till (NT), compared with conventional tillage (CT), has reduced dry matter due to cooler tempe ratures near the seed, in spite of increased plant P absorption caused by more effective mycorrhizae in the less-disturbed soil. We grew mai ze under NT and CT in a soil with 1.6 mg kg(-1) NaHCO3--extractable P, adding 0, 25, 50, or 100 kg P ha(-1). A rotary cultivator (ROTO) soil -disturbance treatment gave plots more severe disturbance than CT, and a no-till hand-plant (NTHP) treatment gave plots with minimal soil di sturbance. Early season P uptake and mycorrhizal colonization Here sti mulated in the NT and NTHP treatments. The reverse was true for shoot dry mass. Early season responses to tillage treatments were the same a t each of the fertilizer rates. Yields increased with increasing ferti lization. At all rates of P, yields with the CT and ROTO treatments we re similar to each other, as were yields with the NT and NTHP treatmen ts. At low soil-P fertility, NT and CT gave similar yields. However, a t and above 50 kg P ha(-1), yields in CT exceeded those in NT by 1000 kg ha(-1). We expect that under P-limiting conditions, NT could give i ncreases in yield over CT, or similar yields could be achieved in NT a nd CT but at lower soil-P availability in NT, but only if the early se ason growth depression in NT can be overcome.