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 usuall y Lower than for conventionally tilled corn in the northern U.S. Corn Belt. Root-zone fertilization is likely to enhance early growth and increase yie lds. 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 effe cts 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' f ields (1994-1996). Treatments several P and K rates (0-56 kg P ha(-1); 0-13 2 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 samp les 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 h igh 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 broadc ast 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 soil-test K, and yields were higher when K was deep banded. Plant ing onto a fall-applied coulter-knife track without applying P or Ii often increased early growth and nutrient uptake, but seldom increased yields. Ea rly growth and nutrient uptake responses to banded P did not translate into higher yields. Small but frequent yield responses to deep-banded K were no t related to increased early growth, but could be partly explained by incre ased K uptake. Judging potential effects of P and K placement on grain yiel ds of no-till corn based on effects (or lark of effect) on early growth may be misleading for soils that are not extremely deficient in these nutrient s.