Grain Yields in Twin-Row Planting of Soybean/Corn Rotations - Increasing Nitrogen, Potassium and Phosphorus Fertility.

Twin-row (TR) planting has gained in popularity and is now an established practice in the Mid-South USA for both corn and soybean production. Over the past two decades, crop rotations have regained their popularity among producers and grain crops have replaced cotton. Field studies were established iin 2012 to evaluate grain production in 1:1 or 2:1 (soybean:corn) systems planted in a TR configuration. Twin rows were spaced 10 inches apart on 40-in (on center) bedded rows. Studies were designed and implemented on both sandy loam soil (favoring corn production) and clay soil (favoring soybean production). A fertility component was included to evaluate 1) a standard (SP) practice (soil test based) and 2) high (HF) fertility (increased nitrogen [N], phosphorus [P], and potassium [K]). The SF practice included 220 lb N/acre, 0 lb P/acre, and 0 lb K/acre while the HF practice included 260 lb N/acre, 26 lb P/acre, and 50 lb K/acre. Plots received uniform N at planting (120 lb N/acre) with the other nutrients applied after the stand was established. All cultural practices were maintain across each location (managed independently) with the same cultivars. At maturity, the center two rows of each plot were harvested with sub-samples taken to determine harvest moisture, test weight, and Seed Index (100-seed weight). Grain yields for corn (15.5%) and soybean (13.0%) were adjusted to a uniform moisture content. Results have varied from year to year with some response N response on the wetter years. On the clay site, where soil test P and K are high, the addition of extra fertilizer has not led to increased yields. Following soil test recommendations, especially under high yield environments is essential for economic yields. Rotation benefits for corn following soybean are again evident to some extent and economics should drive the type of rotation.