Silage maize (Zea mays L) ripening behaviour affects nitrate leaching over following winter

For economical and environmental reasons nitrogen management is of major importance in growing silage maize (Zea mays L). However, studies to improve N management are often restricted to fertilization measures. Therefore we investigated management effects besides fertilization on nitrogen utilization in two field experiments over two years on an eutrophic sandy soil. Experiment 1 examined the effect of row distance (0.35 m and 0.70 m) and harvesting time (premature, mid September; common practice, beginning of October, late harvest, end of October) in a two-way factorial design. In experiment 2 five maize varieties, differing in habitus and characteristic of ripening, were grown using a one-way factorial design. Nitrate leaching over winter was determined by the suction cup method. The row distance showed no significant effect neither on the soil mineral nitrogen content (SMN) in autumn nor on the amount of nitrate leaching. However, SMN and nitrate leaching were affected by the harvest time with significantly lower values for the early harvest. In the second experiment significant differences among genotypes were found with nitrate leaching rates between 52 and 77 kg NO3-N ha(-1). We conclude that the effects of harvesting time and variety on nitrate leaching were related to the stage of maturity of silage maize at harvest. Nitrate leaching during winter was lower when maize plants where prevented from sustained metabolic activity in autumn, either by premature harvest as shown in experiment 1 or by enhanced physiological ripening as in experiment 2.