Effects of composted and non-composted solid phase of pig slurry on N, P, and K contents in two Mediterranean soils

Improvement of organic matter content in Mediterranean soils is a main concern in soil management, especially in highly intensive agricultural areas and in degraded burned soils. Solid pig slurry is a good soil amendment, not only for its high organic matter content but also for the nutrient it can supply. The objective of this study was to estimate the influence of raw and composted application of a solid pig manure on the NPK content of two degraded soils. Two calcareous soils (Typic Xerofluvent, with highly intensive agricultural use, and Lithic Xerorthent, affected by forest fire) were incubated (aerobically, nonleached conditions, 87 days of incubation at 25 degrees C; soil moisture content 60% of WHC), with two manures derived from the solid phase of pig slurry (composted [CSP] and noncomposted [NSP]). The manures were mixed with the soils at two rates, adding 7 and 14 g organic C kg(-1) soil, respectively, in 300-g pots. The variations in N, P, and K contents in soils were investigated. Both manure amendments increased organic N in the soils. Mineralization of organic N was affected by the type of soil and the composting of manure. Moreover, significant interactions between manure and soil type were observed. Available P was increased by the amendments also, but large differences have been observed between soils. After manure amendment, a higher increase in available P occurred in the agricultural soil with respect to the burned soil. Both manure types caused a similar increase of available P, but efficiencies (increase in availability with respect to total P added) were greater for the composted manure. The increase in available K was related to its content in the manures, being greater for the noncomposted manure. As expected, an increase in application rate led to higher NPK contents. The use of the solid phase of pig slurry could be a successful practice for improvement of soil fertility, which in turn stimulates the rapid recovery of vegetation in burned soils.