Nitrogen mineralization after leys ploughed in early or late autumn
1993
Linden, B. (Sveriges Lantbruksuniv., Uppsala (Sweden). Inst. foer Markvetenskap) | Wallgren, B.
In order to study the nitrogen effects exerted on the subsequent crop by second- and third-year leys (grass, red clover, grass-clover) compared with cereals (oats and winter wheat), eleven two-year field experiments were performed in south and central Sweden during 1988-90. The trials comprised two ploughing times in the first experimental year; 1) in late August or early September ("early ploughing"), whereupon winter wheat was sown and 2) in late October or early November ("late ploughing"), followed by spring barley in the next year. Early ploughing of clover- and grass-clover leys caused distinctly increased net N mineralization during the autumn with larger accumulation of mineral nitrogen in the soil profile during this time than after cereals. This nitrogen was largely lost during the subsequent winter. After grass, less mineral N was accumulated than after cereals. By contrast, where leys were allowed to grow and take up nitrogen during the autumn, soil mineral N decreased, obiviously with reduced N leaching risks during the following winter, particularly after grass leys. Late ploughing after cereals also led to less soil mineral N in late autumn than early ploughing. Compared with early ploughing, late ploughing increased the net N mineralization during the subsequent spring and growing season. Following the cereal, grass, clover and grass-clover crops, the amounts of plant-utilized soil N, consisting of such released N and of the plant-available fraction of the mineral N present in the soil already in early spring, were 14, 7, 18, and 14 kg ha-1 larger after late ploughing. Compared with cereals, the grass-clover and clover leys increased the amounts of plant-utilized soil N by 30-40 kg ha-1, irrespective of ploughing time, whereas no additional nitrogen was available after grass leys.
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