Manure Management Strategy to Reduce Phosphorus and Salts.

Achievement of a balance between the amount of nitrogen (N) supplied through animal manure to meet crop N requirements without overloading phosphorus (P) in the topsoil is a key to sustainable manure management for crop production. The objectives of the study were, (i) to determine the optimum water to manure leaching ratio to be used for leaching excess N, P, and K from poultry manure, and (ii) to determine whether leaching nutrients from poultry manure influences changes in EC, and to use different Magnesium sources to isolate and recover P as struvite and determine suitability for use as fertilizer. A laboratory experiment was set in a completely randomized design to determine the optimal volume of water required for leaching nutrients in manure. In the first experiment, a sample of 200 g air-dried poultry manure was leached with deionized water of 0.5, 1.0, 1.5, and 2.0 ℓ in leaching columns, and treatments were replicated three times. The second experiment evaluated the effectiveness of MgO and MgCl₂ as Mg²⁺ source in precipitating, isolating, and recovering of P as struvite, and the usability of the product as fertilizer based on nutrient content. The MgCl₂ treatment precipitated more P, while MgO produced more struvite. However, there a significantly higher nutrient imbalance for the product to be used as fertilizer. The regression analysis in experiment 1 showed that a 1.5 ℓ volume of water leached significantly higher (P≤0.05) amount of NO₃-N + NH₄-N (plant available N) in manure, and significantly lower levels of P and K. There was a significant reduction in electrical conductivity, which is soluble salts, from 7.3 dS m^-1 in poultry manure to 1.15 dS m^-1 in a 1.5 ℓ treatment. Higher plant usable N and lower P, K, and EC in manure are considered a goal of a balanced manure management plan. Apparently, a 1.0 to 1.5 ℓ of water to 200 g of poultry manure could just be the solution to solve a long existing problem of P accumulation and soluble salts loading in the topsoil when poultry manure is applied.