Resumo

FLORES-LOPEZ, Hugo E. et al. Contributions of nitrogen and phosphorus from three agricultural systems of "El Jihuite" watershed, in Jalisco, México. Agrociencia [online]. 2009, vol.43, n.7, pp.659-669. ISSN 2521-9766.

The El Jihuite watershed has a reservoir with the same name, which is used for the inhabitants of Tepatitlán, in the state of Jalisco, México. However, the problem of eutrophication has been observed in the water of the dam and phosphorous as a limiting factor, although there is no knowledge on the processes taking place on the lands with agricultural use, in which the enrichment of this nutrient in this reservoir takes place. Nitrogen and phosphorous losses brought about by maize, tequila agave and grass crops were evaluated on a scale of field plot, in order to quantify the nutrients produced by these agricultural systems and identify the processes related to the eutrophication of the El Jihuite dam. Nitrogen loss was seen to be related to surface runoff, whereas phosphorous depended on the water erosion of the agricultural systems studied. The loss of inorganic nitrogen in tequila agave, maize, bare soil and native grass, for 2002, was of 7, 4.6, 3.9 and 3 kg ha^-1; in 2003 it was 14.9, 7.2, 8.6 and 2.4 kg ha^-1. Total loss of phosphorous in the same crops for 2002 was 3.7, 3.4, 1.7 and 0.1 kg ha^-1; in 2003 it was 10.8, 7.8, 4.3 and 0.0 kg ha^-1 . Phosphorous is a limiting factor in the eutrophication of the El Jihuite dam, and its correction will rely on the control of water erosion on lands with agricultural use; soil conservation practices should therefore be encouraged.

Palavras-chave : Nonpoint source pollution; El Jihuite watershed; phosphorous; nitrogen.

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