Evaluating Long‐Term Nitrogen‐ versus Phosphorus‐Based Nutrient Management of Poultry Litter

Environmental concerns are driving manure management in many areas from a traditional nitrogen (N) basis toward phosphorus (P)‐based nutrient management plans. We investigated how changing nutrient management from an N to a P basis affected crop yields and soil properties in high P soils over a 7‐yr period. Three sites were established on farmers' fields, and at each site the same six treatments were applied for 6 or 7 yr. These treatments were (i) no P; (ii) poultry litter applied on an N basis; (iii) inorganic P, equal to the P applied in treatment 2; (iv) poultry litter applied on an estimated annual crop P removal basis; (v) inorganic P, equal to the P applied in treatment iv; and (vi) poultry litter applied once every 2 or 3 yr at a 2‐ or 3‐yr crop removal P rate. All treatments received the same rate of plant‐available N. Yields, P balance, soil pH, Mehlich 1 P, and water‐soluble P (WSP) were monitored during the experiment. Over the course of the experiment, litter had the beneficial effect of raising soil pH relative to the inorganic treatments. After 7 yr, Mehlich 1 P and WSP were greatest in soils under the N‐based treatments, smallest in the no P treatment, and intermediate in the P‐based treatments. For example, at the Shenandoah site, Mehlich 1 P decreased by 35 mg kg −1 under the no P treatment and increased by 36 mg kg −1 under the inorganic N‐based treatment. There were no significant differences between inorganic fertilizer and poultry litter nutrient sources. The results of this study show that soil test P can be decreased in high‐P soils over a few years by changing from an N‐based to a P‐based nutrient management plan or stopping P applications without negatively affecting yields.