The Effect of Different Nutrient Sources and Switchgrass (Panicum virgatum L.) Harvesting Frequency On Soil Aggregate Stability and Mineral Nitrogen Distribution in the Profile.

In Oklahoma, confined animal farming produce tremendous amount of wastes in limited area challenging sustainability of this vital economic sector. Application of animal wastes together with increased harvesting frequency of switchgrass will have practical significance to improve soil structure and minimize nitrate leaching. Therefore, a field experiment was carried out to investigate the effect different nutrient sources and switchgrass harvesting frequency on wet soil aggregate stability and mineral nitrogen distribution in the profile in split plot design with four replications. The treatments included one and two times of harvesting assigned in the main plot. The subplot treatments were check, cattle manure, poultry litter, urea, NPK chemical fertilizer and legume crop planted between switchgrass rows. The result indicated that twice harvesting improved geometric mean diameter as a measure of wet soil aggregate stability and reduce nitrate amount deep in the soil profile than one time harvesting. Poultry litter and cattle manure improved soil structure and also resulted in more available nitrogen close to the root zone than chemical fertilizers thus contributing to minimize potential nitrate leaching. It can be concluded that the use of these animal wastes to improve soil fertility is a win-win situation to promote nutrient recycling and sustain benefit of confined animal farming.