Effects on soil of the application of compost in a super-intensive olive grove: organic residues and permanganate oxidizable carbon

Abstract

The application of composted organic by-products to the soil is a paradigmatic practice of the Circular Economy. Results of a 2-year trial of application of compost in a super-intensive olive grove (var. “Cobrançosa”), in Monforte, Portalegre, are presented, aiming to evaluate short-term effects on organic residues and soil organic matter. The compost was produced with sheep manure and leaves and sprigs from cleaning the olives. Application rates T0 (0 kg m^-2), T1 (2.5 kg m^-2) and T2 (5,0 kg m^-2) were tested in complete randomized blocks (3 treatments, 3 replications, total of 9 plots). The dry mass at 65ºC of organic residues (>1 mm) on the soil surface and permanganate oxidizable carbon (POX-C) were determined in composite soil samples from layers 0-5, 5-15 and 15-30 cm. Two years after application (i) the mass of organic residues at the soil surface decreased to 1/2 to 1/3 of the value 5 months after application, (ii) POX-C in layer 0-15 cm is still higher than control, especially in T2, which suggests an increase in stable organic matter, (iii) the methods used allowed the detection of short-term effects on soil, resulting from compost application.