Effect of sewage sludge and liming on productivity during the establishment of a silvopastoral system in north‐west Spain

Abstract

Silvopastoral systems are recognised as a sustainable means of increasing forest land through recovery of abandoned agricultural land. Establishment of agroforestry systems is currently promoted by the new EU regulations through direct farmer payments. This can fulfil Agenda 21's economic, cultural and social principles better than simply planting forest. An interesting fertilisation option for silvopastoral systems is sewage sludge, in view of the need to manage this product in environmentally acceptable ways. The present study aimed to evaluate the effect of three sewage sludge application rates (0, 160 and 320 kg ha‐1 per year of total N) and two liming rates (0 and 2.5 t ha‐1 of CaCO3) on pasture production and tree growth in a Populus x euramericana silvopastoral system, during the 5 years from planting. The silvopastoral system was established in autumn 2001, in Lugo (north‐west Spain), on a piece of abandoned agricultural land. A pasture mixture (25 kg ha‐1 of Dactylis glomerata var. ‘Artabro’ and 4 kg ha‐1 of Trifolium repens var. ‘Huia') was sown and Populus × euramericana saplings were planted at a density of 400 trees ha‐1. Liming (main plots) was applied before pasture was sown in autumn 2001, and sewage sludge (subplots) was applied homogeneously in the spring of 2002 and 2003. The results indicate that there was a significant liming × fertilisation interaction, and that initial pasture production could limit tree growth. The high sewage sludge rate when no lime was applied and the low sewage sludge rate after liming increased tree height and diameter because of the soil pH increment 6 years after establishment.