The application of vegetable, fruit and garden waste (VFG) compost in addition to cattle slurry in a silage maize monoculture: nitrogen availability and use

In Flanders, vegetable, fruit and garden wastes (VFG) are collected selectively and composted. We studied the effects of the application of this VFG compost on silage maize on a sandy loam soil. A yearly application of 22.5 Mg of VFG compost ha-1, in addition to 42 Mg of cattle slurry ha-1 resulted in economical optimum dry matter yields with a substantial saving of mineral fertilizer N. During the 1st, 2nd, 3rd and 4th year of this compost+slurry application, an additional amount of mineral fertilizer N of, respectively, 94, 43, 22 and 12 kg N ha-1 was needed. Compared to a system with only mineral N fertilization, this implied savings of, respectively, 52, 92, 142 and 134 kg N ha-1. Silage maize N uptake and N concentration in maize were higher when compost was applied. Despite of the low N output/input rate with compost application, it did not result in an excessive amount of residual soil nitrate-N, provided that the additional mineral fertilizer N was adapted to the economic optimum level. Compared to slurry application, 4 years of VFG compost application resulted in significantly higher soil organic matter and total nitrogen concentrations.