DIFFERENCES AMONG MAIZE CULTIVARS IN THE UTILIZATION OF SOIL NITRATE AND THE RELATED LOSSES OF NITRATE THROUGH LEACHING

In a 2-year field experiment conducted on a Gleyic Luvisol in Stuttgart-Hohenheim one experimental and nine commercial maize cultivars were compared for their ability to utilize soil nitrate and to reduce related losses of nitrate through leaching. Soil nitrate was monitored periodically in CaCl2 extracts and in suction cup water. Nitrate concentrations in suction water were generally higher than in CaCl2 extracts. Both methods revealed that all cultivars examined were able to extract nitrate down to a soil depth of at least 120 cm (1988 season) or 150 cm (1987 season). Significant differences among the cultivars existed in nitrate depletion particularly in the subsoil. At harvest, residual nitrate in the upper 150 cm of the profile ranged from 73-110 kg N ha-1 in 1987 and from 59-119 kg N ha-1 in 1988. Residual nitrate was closely correlated with nitrate losses by leaching because water infiltration at 120 cm soil depth started 4 weeks after harvest (1987) or immediately after harvest (1988) and continued until early summer of the following year. The calculated amount of nitrate lost by leaching was strongly influenced by the method of calculation. During the winter of 1987/88 nitrate leaching ranged from 57-84 kg N ha-1 (suction cups) and 40-55 kg N ha-1 (CaCl2 extracts), respectively. The corresponding values for the winter of 1988 / 89 were 47-79 and 20-39 kg N ha-1, respectively.