Pasture production and tree growth in a young pine plantation fertilized with inorganic fertilizers and milk sewage in northwestern Spain

The use of organic waste materials such as milk sewage as an organic fertil izer could have the dual advantages of organic-waste disposal and reduced d ependence on inorganic fertilizers. The effects of fertilization with (1) c onventional mineral fertilization, (2) milk sewage sludge at 40 kg N ha(-1) target rate and (3) no fertilization on pasture production and tree growth were examined in an experiment consisting of two pasture mixtures under a one-year-old Pinus radiata plantation with a density of 2500 trees ha(-1). The two pasture mixtures were: (1) Dactylis glomerata L. var. saborto (25 k g ha(-1)) + Trifolium repens L. group Ladino (4 kg ha(-1)) + Trifolium prat ense L. var. Marino (1 kg ha(-1)); (2) Lolium perenne L. var. Tove (25 kg h a(-1)) + Trifolium repens L. group Ladino (4 kg ha(-1)) + Trifolium pratens e L. var. Marino (1 kg ha(-1)). The experiment began in the spring of 1995 using a randomized block design with three replicates in Castro Riberas de Lea (Lugo, Galicia, north-western Spain). Plot size was 12 x 8 m(2), with a 1 m buffer strip between plots. Two-year data showed that fertilization wi th either material had a positive effect on pasture production, with no sig nificant difference between the two fertilization treatments. Tree growth i n the milk sewage sludge plot was significantly higher than in the control plots. Inorganic fertilization increased pasture production, but affected t ree growth negatively. The results show that milk sewage sludge could be us ed as a fertilizer in silvo-pastoral systems.