Mineralization of C and N in Whey-Treated Soils and Absorption of N by Plants

Acid whey deriving from milk processing is a nutrient-rich organic residue, with high potential for use in agriculture. However, in order to establish adequate application doses, it is paramount to understand its mineralization dynamics in the soil. The aims of this study were to evaluate C and N mineralization in two soils fertilized with acid whey and compare the efficiency of distinct incubation methods with and without leaching techniques in predicting the potentially mineralizable N of this residue. Samples of two soils (Haplustox and Haplustult) were submitted to five acid whey doses (0, 80, 160, 240, and 320 kg N ha−1), and the mineralization of C and N was determined. A pot experiment was conducted with the same soils and doses, in order to determine growth and N absorption by maize. C mineralization increased in both speed and quantity with the application of acid whey. Similarly, the potentially mineralizable N was increased, displaying mean values of 79.7 and 68.2 mg N kg−1 in the methods with and without leaching, respectively. N mineralization had strong correlation with absorbed N (r = 0.97 and 0.96, in the methods with and without leaching, respectively). The correlation between net mineralized N and absorbed N was higher without leaching (r = 0.98), in comparison to the leaching method (r = 0.89). Acid whey causes net N immobilization at the beginning of incubation, resulting in low N availability during this period, and its mineralization was better evaluated by the method without leaching.