Consecutive Applications of Mineral Fertilizer or Animal Wastes and Effects on soil Phosphorus after Thirteen Years of no-tillage

This study aimed to investigate the impact of long-term repeated applications of different animal waste types and mineral fertilizer on soil phosphorus (P) fractions and chemical nature of P species. A long-term field experiment was conducted for 13 years on a sandy Alfisol in Santa Maria, southern Brazil. The treatments consisted of pig slurry, dairy slurry, pig deep-litter, mineral fertilizer, and an unfertilized control. Soil samples were taken from the 0–4 cm layer in July 2017 and analyzed using sequential chemical P fractionation, P K-edge X-ray Absorption Near Edge Structure (P-XANES), and µ-fluororescence spectroscopies. The continuous application of pig slurry, dairy slurry, and mineral fertilizer resulted in P accumulation in soils beyond the levels required for adequate plant nutrition. Pig deep-litter promoted P accumulation in more labile fractions, above all in the inorganic P form, while pig slurry, cattle slurry and mineral fertilizer increased more stable P fractions. The P-XANES analysis showed the association of goethite-bound P (69–72%) regardless of the source added to soil, while the formation of secondary species such as Ca-P, P-kaolinite, and DNA varied among animal wastes. The relative proportion of organic P as DNA was higher in pig slurry. Pig deep-litter and mineral fertilizer promoted the accumulation of species of amorphous-Ca-P. The long-term application of different types of animal waste and mineral fertilizer led to the accumulation of P in soils, with each source promoting accumulation in different species.