Impact of Conservation Tillage and P and K Management On Rain-Fed Soybean Production.

Reduced tillage and broadcast phosphorus (P) and potassium (K) applications can lead to accumulation of these nutrients in the soil surface. The objective of this study was to determine the impact of conservation tillage (no-till and strip-till) and rate and placement of P and K on soybean production. The experiment was arranged in a split-split-block design with three replications with tillage/placement— NT broadcast (NTBC), NT deep placement at 15 cm (NTDP), and ST deep placement (STDP) — as the main plot, P rate (0, 28, 56, 84 kg P₂O₅ ha^-1) as the subplot, and K rate (0, 50, 100, 200 kg K₂O ha^-1) as the sub-subplot in a corn-soybean rotation. Soil samples were collected from the 0-5, 5-10, 10-20, and 20-40 cm depth increments from the in-row (IR) and between-row (BR) positions at R1 in 2007 and V5 and R3 development stages in 2008 from plots receiving P-K rates of 0-0, 84-0, 0-200, 84-200, and 56-100 kg P₂O₅-K₂O ha^-1 to measure soil P and K, root parameters, and soil water content. STDP significantly increased yields both years and in 2008 NTDP increased yield compared to NTBC. NTBC had similar soil P and K concentrations at both positions and decreased with increasing depths. Deep placement increased P and K levels at 10-20 cm depth compared to broadcast at IR while P and K levels were uniform for NTBC at IR and BR. Deep placement reduced P and K levels in the soil surface. Larger root length density (RLD) in 2007 than 2008 likely resulted from drier conditions in 2007. Soil water content generally increased with increasing soil depth in both seasons and greater water and RLD were present at the IR position. Increasing yield with STDP while reducing soil surface P levels indicates STDP maybe advantageous for soybean production and environmental protection.