Soil test phosphorus and phosphorus availability of swine manures with long-term application
Hao, X.J., Zhang, T.Q., Wang, Y.T., Tan, C.S., Qi, Z.M., Welacky, T., Hong, J.P. (2018). Soil test phosphorus and phosphorus availability of swine manures with long-term application. Agronomy Journal, [online] 110(5), 1943-1950. http://dx.doi.org/10.2134/agronj2017.07.0412
Plain language summary
Phosphorus is an essential nutrient required for agricultural production, however, its over application in animal manures due to uncertainty of availability to crops has largely contributed to eutrophication for nearby streams and lakes. Manure phosphorus crop availability varies with animal types (e.g. pig, cattle, poultry), manure forms (liquid vs. solid), and handling process (raw vs. composted). Manure phosphorus also builds up in soils with time. In order to develop effective nutrient management programs, the form-specific long-term effects of manure application must be assessed, with its phosphorus availability quantified. Using an innovative systems approach, this paper did so through an 8-year study in which three forms of swine manure (liquid, solid, composted) were compared with inorganic fertilizer and then scored based on crop utilization and the legacy effects on soil test phosphorus. The results demonstrated that for swine manure, long-term phosphorus availability is identical and equal to chemical fertilizer, regardless of form. Moving forward, this knowledge can help farmers improve manure management and maximize crop production in an environmentally sustainable manner.
Understanding the form-specific long-term effects of manure (liquid, solid, and composted) application on soil P is essential for nutrient management planning. This 8-yr study aimed to quantify changes in soil test P (STP, Olsen-P) with application of three forms of swine manure compared with inorganic fertilizer and to calculate the manure P source availability coefficient (PSAC) as the ratio of the specific manure form to inorganic P in providing crop P availability. The STP content increased linearly with both total and net P addition at the surface (0–15 cm) and subsurface (15–30 cm) soil depths, regardless of P source. The slope of STP vs. total or net P addition in the surface layer was steeper for liquid than for solid manure, whereas in the subsurface layer, composted manure showed a greater slope than either liquid or solid manure. The amount of applied P required to increase STP by one unit in the surface layer was 19.9, 15.7, 31.6, and 20.9 kg P ha–1 for inorganic fertilizer and liquid, solid, and composted manure, respectively. When increases in subsoil STP and grain P removal were considered, the net P additions of inorganic fertilizer and liquid, solid, and composted manure needed to increase STP by one unit were 12.2, 9.8, 16.1 and 10.7 kg ha–1, respectively. The PSAC values were 0.99, 1.08, and 0.97 for liquid, solid, and composted manure, respectively. The long-term availability of swine manure P was largely identical among forms and was similar to that of inorganic fertilizer.