Deep and shallow banding of phosphorus and potassium as alternatives to broadcast fertilization for no-till corn

Proper P and K management for no-till crops is uncertain. Potential problems include inappropriate extrapolation of soil test interpretations and fertilizer recommendations from conventional tillage, inappropriate soil sampling techniques, and inefficient fertilizer placement. This study compared broadcast, deep-hand, and planter-band P and K placements for no-till corn (Zea mays L.). Long-term P and K trials were established in 1994 at five Iowa research centers and were evaluated for 3 yr. Eleven short-term P-K trials were established in farmers' fields during the same period. Treatments were various P (0 to 56 kg P ha(-1)) and K (0 to 132 kg K ha(-1)) rates broadcast, banded with the planter 5 cm beside and below the seeds, and deep-banded at the 15- to 20-cm depth before planting. Soil samples were collected from the 0- to 7.5-cm and 7.5- to 15-cm depths prior to planting. Soil-test P (PST) at the 0- to 15-cm depth ranged from very low to very high across sites; soil-test K (K-ST) ranged from optimum to very high. There were grain yield responses to fertilization at several sites, but no significant differences between the P or K rates and no interactions between rates and placements. Phosphorus increased yields only in soils testing very low or low, and there was no response to P placement at any site. Potassium increased yields in several soils that tested optimum or higher in K-ST, and yields were higher when K was deep-banded. High rates of broadcast or planter-banded K did not offset the advantage of deep-banded K. Responses were better related with deficient rainfall in late spring and early summer than with K-ST. Current soil-test P interpretations and P fertilizer recommendations based on chisel-plow tillage are appropriate for most Iowa soils managed with no-tillage. Further work is needed to better characterize and predict responses to deep-banded K. Because yield response was small, the cost-effectiveness of deep-band K will be determined largely by application costs.