Effect of Phosphorus and Potassium Rate and Placement on Corn Development in Conservation Tillage.

In conservation tillage systems, like no-till (NT) and strip-till (ST), phosphorus (P) and potassium (K) typically become vertically and/or horizontally stratified in the soil.  This stratification has the potential to make P and K less available and to limit corn yield.  The objective of this study is to determine the influence of tillage and P and K placement and rate on soil P and K content, soil water status, root and shoot development, and grain yield of corn.  The experiment was arranged in a split-split-block design with three replications in a corn-soybean rotation. Tillage/placement— NT broadcast (NT-BC), NT deep placement at 15 cm (NT-DP), and ST deep placement (ST-DP)— as the main plot, P rate (0, 23, 46, and 68 kg P₂O₅ hectare^-1 year^-1) as the subplot, and K rate (0, 41, 82, and 164 kg K₂O hectare^-1 year^-1) as the sub-subplot. Soil and plant samples were collected through the season. Soils P and K concentrations decreased with increasing soil depth.  Corn grain yield was not influenced by tillage-placement method or K rate.  The 68 kg P₂O₅ hectare^-1 produced  690 kg ha^-1 increase in grain yields over the control (no P added), with the greatest response in NT-BC.  Soil water was not influenced by treatment, but at the end of the season, the in row positions had more soil water compared to the between rows position.  Dry matter accumulation at R3 development stage was increased by 1,214 kg ha^-1 with the highest K rate compared to no K application and by 2985 kg ha^-1 in NT-BC compared to NT-DP.  Root analysis indicates no influence of treatment on root distribution in the soil profile.  There was a two-fold decrease in root length density for each successive depth increment from the 0-5, 5-10, 10-20, and 20-40 cm depths.