Resumo

CASTRO, Carlos; COUTINHO, João  e  MOREIRA, Nuno. Soil inorganic nitrogen evolution in cereal crop rotations. Rev. de Ciências Agrárias [online]. 2009, vol.32, n.2, pp.43-55. ISSN 0871-018X.

This work summarizes results of the final year of a rehearsal of rotations, that were elapsed for ten years in Vila Real Town (Trás-os-Montes), abording inorganic nitrogen evolution at 40 cm depth. The rehearsal included the traditional rotation of the conditions of dry of the area, cereal-fallow (TA), and rotations alternative that can be adopted in these conditions, cereal-legume (TL), cereal-cereal-forage mixture (TC) and cereal- cereal-rainfed pasture (TP). They were determined, and presented on other papers, the grain productions, straw and aerial biomass of the several cultures, parameters of quality of the grain of cereals and the parameters of the soil, pH, organic matter and the tenors of P₂O₅, K₂O and change bases were analyzed. This paper reports the results of one of the years when the evolution of the tenors of inorganic nitrogen of the soil of the several rotations was accompanied in the depth up to 40 cm. As main conclusions we can refer: a reduced influence of the rotations in the production and quality of the several cultures; the fallow year and the forage mixture leave the soil with the highest levels of inorganic nitrogen (9.4 mg N kg^-1 average nitrates in September). Thereafter, the value falls (0,95 mg N kg^-1 observed value in the case of cereal that follows fallow) at a time when it cannot be captured by the next crop, recently seeded, indicating serious risk of losses at the beginning of the wet season.

Palavras-chave : Inorganic nitrogen; soil; rotation experiments; rainfed agriculture.

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