Raising Soybean Yield Potential in Dry Seasons: Increased Rooting Depth and Greater Soil Water Extraction with Deeper Depth to the Fragipan

The primary goal of this research is to raise soybean yield potential, in dry seasons, on fragipan soils. Fragipan soils occupy a significant portion of Kentucky’s crop land. The most significant limitations associated with soybean production on fragipan soils are excessive wetness in the spring and increased probability of crop moisture stress in the summer. Both limitations are due to the presence of the fragipan and both limitations become more severe as the depth to the fragipan lessens (becomes shallower). Work at the Princeton Research and Education Center suggests that poultry litter amendment might cause the fragipan depth to increase (Figure 1). The work reported in Figure 1 resulted from a chance observation, must be verified, and a valid mechanism/explanation found. If the fragipan depth is lowered, is it merely dissolving (fragipans contain a cementing agent) or is it dissolving and reforming, at a deeper depth? Additionally, the subsoil above the fragipan is often very acid (pH values of 4.0 to 5.0). Work in other regions indicates that gypsum application can significantly reduce the impact of subsoil acidity on root growth and soil moisture extraction by corn. No such comparable information exists for soybean. There is interest in determining whether application of poultry litter and/or gypsum would enhance soybean root development, soil moisture availability, and raise soybean yield potential in dry summer seasons. Recently, work by Karathanasis, Matocha and Murdock suggests that sodium (Na) could assist with dispersion and break-up of the fragipan. This caused these investigators to consider an added sodium treatment to evaluate any field response. As sodium chloride (NaCl), road salt, is the cheapest form of soil-mobile Na, this source will be added in the field trial. The major goal of this work is to determine whether any of these two amendments (poultry litter, gypsum, NaCl) will result in greater soybean yield potential on fragipan soils – and then to determine the mechanism behind that increased yield potential so as to extend the results of the experiment to other soils. In 2012 and 2013, which were very dry and very moist, respectively, poultry litter has resulted in a positive soybean yield response, albeit small (Table 1, below). Gypsum has not benefitted soybean yield. This proposal is to fund the third of three years of the field research work.