Communications in soil science and plant analysis vol:31 issue:11-14 pages:2265-2272
Estimation of the nitrogen delivery of grassland in temperate regions is possible through measurement of the organic N content of the top layer. Organic nitrogen is built up under recently sown grassland until equilibrium is reached ('old' grasslands). Comparison of the actual soil organic N content with this equilibrium makes it possible to determine the nitrogen delivery (Hassink, 1995). To determine this equilibrium, the soil layers 0-6 cm, 0-15 cm and 0-23 cm of 40 unfertilised old grasslands in Belgium with different soil textures (clay, loam, sandy loam and sand) were analysed for their organic N-content and granulometric composition (9 fractions). From these fields it was found that the soil organic N-content correlated with the texture. For determination of the nitrogen delivery, 31 unfertilised experimental fields were set up, on which dry matter yield and nitrogen delivery were determined. NFNS (non fertiliser nitrogen supply, kg N/ha.yr) = 139.1 - 445.6 *Delta orgN (r(2)=0.63)(%, Delta orgN = orgN(eq) - orgN(act); sampling depth 0-15 cm and texture fraction 0-20 mu). The remaining variation in the data set may be partially explained by the water delivery capacity, as suggested by individual results. By taking into account N delivery capacity and probably also water delivery capacity, N fertiliser recommendations can be tuned to the specific characteristics of a field. Thereby, N-fertilisation may sometimes be increased for some fields, whilst for others a decrease of the N-fertilisation may be possible without loss of yield.