INVESTIGATIONS ON THE ADJUSTMENT OF NITRO GEN SUPPLY FROM DIFFERENT NSOURCES TO THE N UPTAKE OF MAIZE

A two years field experiment was conducted tb study the effects of the nitrogen fertilizers: wheat swill, BASAMMON (NH4 + nitrification inhi bitor DCD) and calcium ammonium nitrate (CAN) applied at N rates of 0, 60, 120 or 180 kg N/ha on yield, N uptake and soil mineral N residues of maize for silage or grain production. CAN was either broadcast or placed in the maize rows, with or without the addition of an Azospiril lum-biopreparation (AZOGREEN). Due to initially high soil mineral N co ntents (50-70 kg N/ha) and a high mineralization from the soil (unfert ilized: 100-170 kg N/ha), neither effects of fertilizer type, nor inte ractions between fertilizer type and N rate on biomass production and N uptake of maize were observed. The economically optimum total dry ma tter production and grain yield were obtained with a fertilization of 60-120 kg N/ha. In contrast to the biomass production the soil mineral N was considerably influenced by fertilizer type and N rate. The nitr ate content of the soil increased during the early developmental stage s of maize after an early application of swill or BASAMMON, and also d uring the ripening period after a late high dose of CAN. Though the pl acement of CAN was reflected in the soil, the soil nitrogen content pe r unit area could not be much reduced by row fertilization The effects of AZOGREEN were only small. The results were greatly influenced by t he high mineralization potential at the experimental site.