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 pr oblems include inappropriate extrapolation of soil test interpretation s and fertilizer recommendations from conventional tillage, inappropri ate soil sampling techniques, and inefficient fertilizer placement. Th is study compared broadcast, deep-hand, and planter-band P and K place ments for no-till corn (Zea mays L.). Long-term P and K trials were es tablished in 1994 at five Iowa research centers and were evaluated for 3 yr. Eleven short-term P-K trials were established in farmers' field s 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 plan ter 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 rate s and placements. Phosphorus increased yields only in soils testing ve ry low or low, and there was no response to P placement at any site. P otassium increased yields in several soils that tested optimum or high er 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 lat e spring and early summer than with K-ST. Current soil-test P interpre tations and P fertilizer recommendations based on chisel-plow tillage are appropriate for most Iowa soils managed with no-tillage. Further w ork is needed to better characterize and predict responses to deep-ban ded K. Because yield response was small, the cost-effectiveness of dee p-band K will be determined largely by application costs.