Soil is in a steady state under natural conditions, but an inadequate management can cause degradation, mainly of the organic matter, impairing the sustainability of agricultural systems. The present study was undertaken in a six-year-old field experiment on a typic Hapludalf (Red Yellow Podzolic Soil), at the Department of Soil Science, UFSM, Santa Maria, Rio Grande do Sul state, Brazil, to evaluate the effects of plant successions on soil nitrogen dynamics, under no tillage system. The plant successions used were common vetch (Vicia sativa)/corn (Zea mays), blue lupine (Lupinus angustifolius)/corn, field peas (Pisum arvense)/corn, black oat (Avena strigosa)/corn and winter fallow/corn, associated to two nitrogen doses (0 and 80 kg ha-1) applied on corn. The soil was managed by the no-tillage system, and evaluations were made on the levels of N on the cover crops and on the surface plant residues, and of the soil nitrogen under total, mineral and organic forms, at three soil depths (0-2.5; 2.5-7.5 and 7.5-17.5 cm). The winter cover crop soil evaluations were made in areas without mineral N fertilizer. The use of soil cover crops, during six years under no tillage, induced significant increase of soil mineral, organic and total nitrogen. The crop succession caused differences only in 0-2.5 cm layer. The succession lupine/corn caused higher soil N improvement.
dry matter; crop succession; soil improvement