Carbon and Nitrogen Mineralization From a Gelatin Industry Biological Sludge.

The impact of agro-industrial organic wastes in the environment can be reduced by its use in agricultural systems and from the point of view of soil fertility increasing the soil organic matter content and providing nutrients to the plants are desirable. The objective of this study was to evaluate carbon and nitrogen mineralization from gelatin industry biological sludge in Ultisol. The experiments were carried out under laboratory conditions, in a completely randomized design with six biological sludge rates (zero; 100; 200; 300; 400 and 500 m³ ha^-1) and three replicates. The gelatin industry biological sludge showed: solids = 1.59%; pH 8.3; EC = 4.13 mS cm^-1; total-N; NH₄⁺-N; NO₃^--N and organic-C concentration in dry weight, equal to 67.8; 13.9; 0.2 and 140.6 g kg^-1, respectively, and the C/N ratio = 2.1. Carbon mineralization was evaluated by the amount of CO₂ trapped by 1 mol L^-1 NaOH solution and nitrogen by NH₄⁺-N and NO₃^--N content in soil. Carbon mineralization fraction was greater than 100%, indicating a "priming effect" at the end of 193 days of incubation. With the largest biological sludge rate (equivalent to 500 m³ ha^-1) was mineralized 0.1 g kg^-1 of C from native soil organic matter. Considering the initial C content of 10.4 g kg^-1, the application of biological sludge promoted a decrease of about 1% of soil organic carbon. Nitrogen potentially mineralizable (N₀) increased with biological sludge rates, ranging from 33.92 to 181.90 mg kg^-1. Nitrogen mineralization fraction in 126 days was greater than 74% and the half-life averaged 8.7 days, indicating that the nitrogen in the biological sludge is readily available to the plants.