Phosphorus and Potassium Placement Effects on Early Growth and Nutrient Uptake of No-Till Corn and Relationships with Grain Yield

Early plant growth and grain yield of no-till corn (Zea mays L.) are usually lower than for conventionally tilled corn in the northern U.S. Corn Belt. Root-zone fertilization is likely to enhance early growth and increase yields. This study evaluated the effects of P and K placement on early growth and P and K uptake of no-till corn, and on relationships between these effects and grain yield response to placement. Ten long-term P and K trials (5 trials each, P and K) were established in 1994 at five research centers and were evaluated for 3 yr;, 11 1-yr P-K trials were established in farmers' fields (1994–1996). Treatments several P and K rates (0–56 kg P ha⁻¹; 0–132 kg K ha⁻¹) banded with the planter 5 cm beside and below the seeds and broadcast or deep-banded at a 13- to 18-cm depth before planting. Soil samples were collected before applying the treatments from the 0- to 7.5-cm and 7.5- to 15-cm depths. Soil-test P (0-15 cm) ranged from very low to very high across sites and soil-test K ranged from optimum to very high. Banded P (deep or shallow) increased early growth and P uptake more than the broadcast placement did at most trials. Phosphorus increased yields only in very low and low testing soils, and there was no response to P placement. Banded K (deep or shallow) seldom affected early growth, but usually increased K uptake. Potassium increased yields in several soils that tested optimum or higher in soiltest K, and yields were higher when K was deep banded. Planting onto a fall-applied coulter-knife track without applying P or K often increased early growth and nutrient uptake, but seldom increased yields. Early growth and nutrient uptake responses to banded P did not translate into higher yields. Small but frequent yield responses to deep-banded K were not related to increased early growth, but could be partly explained by increased K uptake. Judging potential effects of P and K placement on grain yields of no-till corn based on effects (or lack of effect) on early growth may be misleading for soils that are not extremely deficient in these nutrients. Iowa Agric. Home Econ. Exp. Stn. Journal Paper no. J-17688. Project 3233. Work supported in part by the Leopold Center for Sustainable Agriculture.