Soil restoration using composted plant residues: Effects on soil properties

Organic soil amendments are increasingly being examined for their potential for soil restoration. In this paper, different composted plant residues consisting of leguminous (red clover, Trifolium pratense L) (TP) and non-leguminous (rapeseed, Brassica napus L) (BN) plants and the combination of both plant residues (red clover + rapeseed, Trifolium pratense L. + Brassica napus L. at a ratio 1:1) (TP + BN) were applied during a period of 4 years for restoring a Xelloric Calciorthid soil located near Seville (Guadalquivir Valley, Andalusia, Spain). The effect of the organic soil amendments on plant cover, soil physical (structural stability, bulk density), chemical (C/N ratio), and biological properties (microbial biomass, soil respiration and enzymatic activities (dehydrogenase, urease, beta-glucosidase, phosphatase and arylsulfatase activities)) were determined. Organic amendments were applied at rate of 7.2 and 14.4 t organic matter ha(-1). All composted plant residues had a positive effect on soil physical properties. At the end of the experimental period and at the high rate, soil structural stability was highest in the BN (28.3%) treatment, followed by the TP + BN (22.4%) and the TP (14.5%) treatments and then the control. Soil bulk density was higher in the BN (30.9%), followed by TP + BN (26.2%) and TP (16.1%) treatments with respect to the control. However, soil biological properties (biomass C and the enzymatic activities) were particularly improved by the TP + BN treatment, followed by TP, BN and the control. After 4 years, the percentage of plant cover increased 87.2% in the TP + BN amended soil with respect to the control, followed by TP (84.1%) and BN (83.8%). These differences were attributed to the different chemical composition of the composts applied to the soils and their mineralization, controlled by the soil C/N ratio. The application of TP + BN compost with a C/N ratio of 18. resulted a more favourable soil biological properties and plant cover than the application of TP (C/N ratio = 8.8) and BN (C/N ratio = 47.7) composts. (C) 2008 Published by Elsevier B.V.