The nitrogen- and non-nitrogen-contribution effect of ploughed grass leys on the following arable forage crops: determination and optimum use

摘要

From 1990 to 1998, we studied the N release from ploughed 3-year-old grazed grasslands in the subsequent three seasons of forage crops on a sandy loam soil. Silage maize in the ley-arable rotation outyielded continuous maize on permanent arable: plots by 85, 21 and 2% at mineral N fertilization rates of respectively 0, 75 and 180 kg N ha(-1). This decreasing yield effect with increasing N fertilization indicated that the ley-arable rotation effect was mainly a N-contribution effect. The N release was highest during the first year; it decreased during the second and third year following the grassland ploughing. Economically optimum N fertilization rates for silage maize in these years were respectively 2, 139 and 154 kg N ha(-1). Simultaneously, on permanent arable plots this was respectively 152, 191 and 183 kg N ha(-1). This resulted in comparable yields (19.75 Mg DM ha(-1) year(-1)) but with a possible saving of 231 kg of mineral N fertilizer ha (-1) in a 3-year silage maize period following the ploughed leys compared with continuous silage maize. The N uptake by silage maize on temporary arable plots following grasslands was higher than on permanent arable plots, owing to the higher yields but also to an increased N concentration in the crop on the temporary arable plots. Starting the arable forage crop sequence with fodder beet following the grassland ploughing and adjusting the N fertilization to the enhanced N release minimized the risks on high amounts of residual soil N and hence N leaching losses.