Can Application of Dairy Liquid Manure over 10 Years into No-Tillage Affect Soil Phosphorus Lability?

Abstract

Long-term application of dairy liquid manure (DLM) can modify soil phosphorus (P) dynamics. P fractionation allows the identification of organic and inorganic P and its lability via procedures of lesser and greater power extraction. The aim was to evaluate the effect of successive DLM applications (10 years) in no-tillage on soil P fractions. The experiment was carried out in an Oxisol with a sandy clay loam texture. Treatments consisted of three DLM doses (60, 120, and 180 m³ ha⁻¹ year⁻¹) and the control (unmanured) (0 m³ ha⁻¹ year⁻¹) randomized in a complete block design with four replicates. The soil was sampled at three depths (0–0.05; 0.05–0.10, and 0.10–0.15 m), and sequential extractions were performed for each depth. DLM increased soil P concentrations in all fractions, mainly in the 0–0.05 m depth resulting in the following proportions of P (average of all DLM doses in 0–0.05 m depth): labile (29%), moderately labile (38%), low lability (17%), and residual (16%). In the unmanured treatment, the proportion was labile (18%), moderately labile (39%), low lability (22%), and residual (21%). DLM application resulted in a higher proportion of organic and inorganic labile P (water, resin, and NaHCO₃) indicating a greater plant availability but also a P water pollution risk by surface runoff.