Overwinter Mineralization of a Biosolid and Composted Banana Residues in Humid Mediterranean Conditions

Abstract

The objectives of this work were to study nitrogen (N) release from a biosolid and a compost of banana wastes. The overwinter N decomposition was evaluated as the uptake by a cereal cover crop and the in situ losses from buried bags in a loamy sand (site 1) and in a calcareous silty clay loam (site 2). Organic materials were applied in two rates as sludge (1, 3.75 Mg ha−1; 2, 7.5 Mg ha−1) and compost (1, 3.29 Mg ha−1; 2, 6.58 Mg ha−1). Immediately after their incorporation in October, barley was planted as a cover crop. Its growth was negatively affected by the slow drainage of the silty clay loam, leading to greater N concentration in site 1 (21.18 g kg−1 of barley versus 14.35 g kg−1 of barley in site 2). Yet only 10% of the added N was intercepted by the cover crop in the fast-draining site 1. The ash-rich compost (N: 21.1 g kg−1; ash: 467 g kg−1) was comparable to the control. Within site 2, the biosolid treatments had a residual effect on a second barley crop, as N uptake was 1.99–2.13 times that of the control. The approach of in situ loss from bags incorporated in bare soil was repeated in two successive seasons. Nitrogen losses (% input) during the fall and winter months were comparable between sites 31.9 % (site 1) and 28.6 % (site 2). When the N fate was studied during the winter months only, the loss decreased slightly, suggesting the presence of a fraction liable to decomposition overwinter in Mediterranean conditions. Soil nitrate was determined 1 month after the incorporation of the cover crop in late spring. In the first season, only the sludge 2 treatment generated more nitrate than the control, whereas 19 months after the application of the organic products both sludge treatments had a positive effect. The soil properties influenced the amounts of N mineralized with site 1, yielding twice that of site 2. In the fast-draining soils, the presence of an active cover crop overwinter is necessary, while the N level of sludge 1 (164 kg N ha−1) was more acceptable.