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 th e effects of different fertilizer management on nitrogen status in soi l and plant response. Three different fertilizers, mineral (MN), miner al plus buffalo manure (MN+BM) and organo-mineral with peat (OMP), wer e 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 w ere analyzed for N by both the Kjeldahl method and the electro-ultrafi ltration technique (EUF). The soil Kjeldahl-N concentrations were scar cely affected by the different fertilizer treatments, while the EUF-N concentrations were closely correlated with the amounts of N added. Th e 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 lar gest proportions of EUF-Norg + NH4 were found in the untreated plots a nd in the plots treated with buffalo manure. The different fertilizer treatments significantly affected grain yield, which ranged from a min imum 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 ex hibited in the OMP treatment at the reduced rate. The grain yield was closely correlated with the total extractable EUF-N, but different rel ationships were found between the rate of N added, the level of EUF-NO 3-N in soil and grain yield for the different fertilizer treatments. ( C) 1997 Elsevier Science B.V.