Monitoring nitrogen forms in soil/plant systems under different fertilizer managements. A preliminary investigation

A field experiment was carried out on maize (Zea mays, L.) to study the effects of different fertilizer management on nitrogen status in soil and plant response. Three different fertilizers, mineral (MN), mineral plus buffalo manure (MN + BM) and organo-mineral with peat (OMP), were added at the usual (140, 61 and 116 kg ha^?1) and the reduced (70, 31 and 58 kg ha^?1) rates of N, P and K. respectively. Soil samples were analyzed for N by both the Kjeldahl method and the electro-ultrafiltration technique (EUF). The soil Kjeldahl-N concentrations were scarcely affected by the different fertilizer treatments, while the EUF-N concentrations were closely correlated with the amounts of N added. The EUF also discriminated between the NO₃-N and the sum of the ammonium and the easily extractable organic N forms (EUF-N_org + NH₄). The largest proportions of EUF-Norg + NH₄ were found in the untreated plots and in the plots treated with buffalo manure. The different fertilizer treatments significantly affected grain yield, which ranged from a minimum of 6.3 t ha^?1 from the untreated plots, to a maximum of 11.9 t ha^?1 from those supplied with 140 kg N, 61 kg P and 116 kg K ha^?1 by OMP fertilizer. The highest agronomic efficiency index for N was exhibited in the OMP treatment at the reduced rate. The grain yield was closely correlated with the total extractable EUF-N, but different relationships were found between the rate of N added, the level of EUF-NO,-N in soil and grain yield for the different fertilizer treatments.