On-Farm Evaluation of Double Crop Fertility Management in Oklahoma.

Many producers in Oklahoma choose to plant summer crops following the harvest of winter crops to increase farm revenue, while limiting costly inputs to reduce risk. This study aims to determine whether there is potential for producers to increase yields of double crops due to additional fertilization, and evaluate the ability of a soil test to predict crop response. This project is an extension of the work done by Oklahoma State University in 2012-2013 on winter wheat production. Nutrient rich strips of nitrogen (N), phosphorus (P), potassium (K), and sulfur (S) were applied at 30 sites across Oklahoma in 2016, on 3 different double crops (soybean, grain sorghum, sunflower), with varying environmental conditions. Nutrient rich strips were applied at a rate of 257.6 kg ha^-1 of product on top of farmer practice to a 1.8 by 45.7 meter strip in producer fields. Urea (46-0-0), triple super phosphate (0-45-0), potash (0-0-60), and gypsum (0-0-0-19) were used for sources of nitrogen, phosphorus, potassium, and sulfur, respectively. Composite surface (0-15 cm) and subsurface (15-45cm) soil samples were taken prior to application of product for soil nutrient recommendations. At maturity, three one m² subplots were hand harvested from each strip, as well as three one m² subplots from the producer practice outside of the plot. Of 30 locations and 120 comparisons, eight positive responses were recorded. Of these responses, one was a response to N, one was a response to P, six were responses to K, and there were no responses to S. Out of the eight responses recorded, four responses were in the areas that were expected to see a response from, based on prior soil test; one was a response to N, one was a response to P, and two were a response to K. This study is still underway for its second year.