Phosphorous and Potassium Management for Soybean Production Under No-till and Strip-till.

Broadcast phosphorus (P) and potassium (K) applications in no-till can lead to vertical stratification and reduced availability of these nutrients. The objective of this study was to determine the impact of 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— no-till broadcast (NTBC), no-till deep placement at 15 cm (NTDP), and strip-till deep placement (STDP) — as the main plot, P rate (0, 28, 56, 84 kg P₂O₅ ha^-1 yr^-1) as the subplot, and K rate (0, 50, 100, 200 kg K₂O ha^-1 yr^-1) as the sub-subplot in a corn-soybean rotation. Soil P and K and root parameters were measured 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 and R3 development stages and continuously for soil-water from 2007 to 2009. At rates ≤56 kg P₂O₅ ha^-1yr^-1, STDP produced 3.1 Mg grain ha^-1 which was 13 and 15% greater than NTDP and NTBC, respectively. While water availability increase with depth and deep placement increased P and K levels at 10-20 cm depth at IR, overall 48% of the measured root surface area density (RSAD) was allocated to the top 5 cm. Within the 0-5 cm depth, NTBC had 47% greater RSAD than STDP. Under limited soil P fertility, STDP enhanced the growing environment and allowed soybean to more effectively access P with less energy expenditure to develop and maintain its root system.