Long‐Term P and K Applications: II. Effect on Corn and Soybean Yields and Plant P and K Concentrations

Abstract

Increasing emphasis on environmentally sound nutrient management requires an improved understanding of fertilizer P and K needs for profitable crop production. A 20-yr study was conducted on two glacial till soils to determine: (i) the effect of various P and K rates on corn (Zea mays L.) and soybean [Glycine max (L.) Merr.] yields and profitability during a 12-yr application phase and an 8-yr residual phase, and (ii) whether triennial applications of P and K produce crop yields equal to those from annual applications. Initial Bray P 1 and exchangeable K soil tests were 22 and 150 ppm, respectively, for the Webster clay loam (fine-loamy, mixed, superactive, mesic Typic Endoaquolls) and 10 and 228 ppm, respectively, for the Aastad clay loam (fine-loamy, mixed Pachic Udic Haploboroll). Phosphorus and K were applied annually for 12 yr at rates of 0, 50, and 100 lb P 2 O 5 /acre and 0, 50, and 100 lb K 2 O/acre while rates of 150 lb P 2 O 5 /acre and 150 lb K 2 O/acre were applied every third year. Yields were improved by the 50-lb P 2 O 5 rate in 6 of 12 yr when the soil test P (STP) was <22 ppm for the Webster soil and in 8 of 12 yr when the STP was ≤10 ppm for the Aastad soil. Yields were not improved further by the 100-lb P 2 O 5 rate on either soil. Yields from triennial P application were similar to those from annual P application in 23 of 24 site-yr. Annual application of fertilizer K increased yield only in 3 of 24 site-yr. During the 8-yr residual period, yields were increased above the eontrol in all 15 site-yr by carryover from the 50-lb P 2 O 5 rate. Corn yields were optimized at leaf K concentrations ranging from 1.14 to 2.29%, indicating the importance of knowing nutrient uptake characteristics of hybrids when assessing the K status of corn. Economic return was generally highest with the 150-lb P 2 O 5 rate applied every third year. Results from this study indicate that most profitable long-term returns can be obtained with broadcast applications of 150 lb P 2 O 5 /acre on a triennial basis and by monitoring STP and soil test K (STK) to take advantage of residual availability.