Nitrogen, Phosphorus, and Potassium Availability in Three Compost Derivatives from the Wine Industry and Two Fertilizers

Organic production worldwide shows ongoing advances in agronomic management. Compost is mainly used for nutritional management and its benefits in biological activity and soil construction are well known; however, there are questions regarding nutrient supply. The present experiment was conducted under controlled laboratory conditions to evaluate the dynamics of nitrogen (N), phosphorus (P), and potassium (K) delivery along with the real N supply of three composts made from residues of the wine industry and two fertilizers (organic fertilizer and conventional liquid fertilizer) in two soils with contrasting characteristics (clay loam and sandy loam). There were five incubation times (0, 7, 28, 56, and 112 d), five treatments for each soil with rate of 100 mg kg−1 of total N, including a control, three composts, and one fertilizer with three replicates and a split-plot experimental design. Results indicated that the composts generated P and K contributions, whose amounts were different in both soils; however, there was no net N contribution as available N. Both the organic and conventional fertilizers provided important N contributions, which differed in magnitude depending on the characteristics of each fertilizer and each soil. In addition, the three composts generated slight changes in pH and electrical conductivity (EC). The organic and liquid fertilizers produced moderate (36.1%) and high (65.2%) net N availability values for clay loam soil and sandy loam soil, respectively. For agronomic management decisions involving the use of these composts as a nutritional source, it is suggested that the present study be complemented with field experiments.