Increased Fertility Effects on Crop Yields in Corn/Soybean Rotations Grown with Twin-Row Production Systems.

Twin-row production has been an established practice in the Mississippi Delta more than 20 years for both corn and soybean production.  At the same time, crop rotations have regained their popularity among producers as grain crops have reappeared in a crop mix.  Multi-year field studies were established at the Delta Research and Extension Center to evaluate grain production in 1:1 or 2:1 (soybean:corn) rotation system planted in a twin-row configuration.  Twin rows were spaced 25 cm apart on bedded rows (102-cm centers).  Studies were implemented on sandy loam (favoring corn production) and clay (favoring soybean production).  A fertility component was included that evaluated 1) standard practice [SF] (soil test based) and 2) high fertility [HF] (increased nitrogen [N], phosphorus [P], and potassium [K]).  The SF included 246 kg N ha-1, 0 kg P ha-1, and 0 kg K ha-1 while HF included 290 kg N ha-1, 29 kg P ha-1, and 56 kg K ha-1.  All corn plots received 134 kg N ha-1 at planting with the other nutrients applied after stand establishment.  Cultural practices were maintained uniformly across both locations (managed independently) with the same cultivars.  At maturity, the center two rows of each plot were harvested and sub-samples taken for harvest moisture, test weight, and Seed Index (100-seed weight). For both locations, soil test P and K were in the medium to high or high+ range as determined by soil test analyses.  In general, there has been no significant yield increase from supplemental P and K applications especially on the clay soil site where soil test levels were very high.  Nitrogen responses have been measured in the corn in the rotation in some years.  The biggest response has occurred when conditions favor N loss during the season.