Site-specific recommendations of cattle manure nitrogen and urea for silage maize

A novel decision support system (DSS) was developed to define site-specific cattle manure rates with the aim of increasing the stable pool of soil organic matter. A site-specific N balance model calculated urea rates for maize at side-dress. Inputs to the DSS were derived from geophysical methods (soil texture), near infrared spectroscopy (NIR; soil C) and multispectral images of the crop and yield maps (maize N requirement). The DSS was compared to farmer fixed N rate (170 kg manure N ha(-1) and 120-170 kg urea N ha(-1)) in a two-year field trial in Northern Italy. A replicated plot experiment was also established to study the effects of year, soil, and fertilizer rate on maize yield. Geophysical and NIR methods accurately mapped soil properties (errors < 20% for > 75% of the field compared to geostatistical mapping based on soil sampling and analysis). Site-specific application of manure and urea had high spatial accuracy (average error < 29 kg N ha(-1) for > 81% of the field). The great impact of year and soil properties on silage yield and N uptake suggested adjusting spatially the in-season target yield to prevent over-fertilization. Compared to the fixed N management, the DSS showed no reduction in yield and N uptake, and some potential environmental benefits, especially for the low-yielding zone of the field (-80 kg applied N ha(-1)). Future evaluation of other soil types and environments would provide the necessary information to upgrade the DSS at a farm scale.