Broadcast and Deep-Band Placement of Phosphorus and Potassium for Soybean Managed with Ridge Tillage

The efficiency of broadcast and band P and K placement methods for ridge tilled soybean [Glycine Max (L.) Merr.] has not been extensively researched. This study evaluated grain yield, early plant growth, and nutrient uptake (V5-V6 stages), and soil-test responses to broadcast and deep-band (15-20 cm below the ridge surface) placements in 14 trials. Fertilizer rates were 0, 14, and 56 kg P ha^(-1) and 0, 33, and 132 kg K ha^(-1). A randomized complete-block design was used. Soil-test P (STP) was 7 to 61 mg kg^(-1) (Bray-P1 test, 15-cm depth) and soil-test K (STK) was 100 to 197 mg kg^(-1) (ammonium acetate test). Phosphorus increased yield (P =<0.1) at four sites. Band P was better at one site (30 kg ha^(-1)) and broadcast P was better (40 kg ha^(-1)) at another site. Both P placements increased dry weight (DW) at two sites. Yield and DW responses to P were observed when STP was <19 mg kg^(-1). Phosphorus increased plant P uptake at eight sites, and band P was better than broadcast P at three sites. Potassium increased yield at two sites, and only band K increased yield at one of these sites. Potassium increased DW at four sites, and increases were always larger for band K. Band K increased K uptake at 10 sites and broadcast K increased K uptake only at two sites. Soil-test P in ridges predicted P sufficiency better than mean STP from ridges and valleys at two sites. Although K fertilization seldom increased yield in this study, increased plant K uptake with banding compared with broadcasting suggests that banding may be more efficient for grain production in other conditions.