EFFECT OF TIMING OF APPLICATION OF MUNICIPAL SOLID-WASTE COMPOST ON NAVAILABILITY FOR CROPS IN CENTRAL SPAIN

To calculate the correct nitrogen fertilizer rate for crops and the po ssibility of using municipal solid waste (MSW) compost as an organic a mendment, nitrogen mineralization rates were studied by laboratory inc ubation and field measurements in a soil in central Spain. Nitrogen mi neralization rates were studied in a 250-day laboratory soil incubatio n with two treatments: with and without compost, incubated at 28 degre es C and a moisture content of 70% of field capacity. Three phases are described: (1) no increase in the mineral nitrogen content, (2) a lin ear increase in the mineral N fraction and, finally, (3) a linear, par allel increase in both mineral N and easily mineralizable organic N fr actions. Incubation data were fitted to three different equations. The exponential model proposed by Stanford and Smith (1972) was selected to predict field N mineralization rates. The field experiment was perf ormed using a crop of maize with three treatments: compost applied in February (before sowing), compost applied during sowing and a control (without compost application): sampling was carried out over 14 months . Soil water content was measured periodically. Soil with compost appl ied in February showed 1.9 and 1.4 times more available nitrogen than soil without compost and compost at sowing, respectively, for the mont h of maximum accumulation. These results suggest that compost amendmen ts must be applied before sowing. Compost applications were shown to s upply the available nitrogen for spring crops. A simulation model show ed satisfactory agreement with field data, after correction for soil t emperature and water content.