NITROGEN LOSSES BY LEACHING IN A MIXED GRASSLAND GRAZED IN TEMPERATE CLIMATE

Abstract

Nitrogen losses by lixiviation in grazing grasslands are important because they may represent low N use efficiency in the production system and cause negative impact on underground water. Nitrogen lixiviation losses and the effect of excreta of grazing animals were estimated in a mixed grassland of alfalfa (Medicago sativa L. cv. ‘Valenciana’) and orchard grass (Dactylis glomerata L. cv. ‘Potamac’) in the east of the Valley of México. For assessment of the inorganic N (N-NO₃- y N-NH₄+) present in drainage water, lysimeters receiving urine, feces and a control (without excreta) were utilized. Total N-content in excreta, net herbage production, the amounts of N ingested by the animals and inorganic N concentration (N-NO3- y N-NH4+) in soil were estimated in this study. Inorganic N concentrations in the upper 60 cm of soil were high (70 to 80 mg kg^-1). During the rainy season, 10 rain events caused drainage below that soil layer, with high inorganic N concentrations in lixiviates (48 mg L^-1). As a consequence of both factors, 40 kg N ha^-1/year were lixiviated. Such an amount might be considered high, but within the range of values reported in the literature, and it only represented 7 % of the total N input of the system. The presence of animal excreta did not affect N losses.