Maximizing Soil Nitrogen Credits through Soybean Maturity Group Selection.

Arkansas crop production relies heavily on the soybean (Glycine max)- rice (Oryza sativa) rotation system for the benefits provided to both crops. One specific benefit is the N credits supplied to the rice crop. This reduction of fertilizer-N needs results in a large savings of input costs associated with the crop, helping the producer to maximize profitability as N fertilizer is often the largest input cost to a rice producer. Increasing the amount of soil-N available to the following rice crop may be accomplished through soybean maturity group (MG) selection and planting date. Different MGs of soybeans will produce a different yield and harvest index, thus returning differing amounts of N to the soil system. Planting date regulates the amount of time spent in vegetative growth stages; therefore, influencing the soil N credits generated. This study intends to determine which factor most heavily influences the soil-N credits generated: soybean grain yield or planting date. Nitrogen Soil Test for Rice (N-STaR) soil samples were taken at rice emergence to quantify the plant available-N within each soybean MG system. The 5.4 MG yielded the highest with 3,115 kg ha^-1, however this MG did not have the highest biomass N returned to the soil system. Maturity group 5.6 returned the most biomass N at 217.8 kg N ha^-1 while yielding only 2,799 kg ha^-1 on average. There was no significant difference (p-value= 0.8067) in plant available-N between previous MGs the following spring. The objective of this study is to determine the impact made on soil-N credits from different MGs of soybean and the influence on the following rice crop’s N fertilizer recommendation. The relationship between soybean characteristics and the amount of plant available-N for the following crop will allow producers to select the best possible aspects to maximize profitability while minimizing inputs.