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Plant Species and Defoliation Efects on Soil Nitrogen Mineralization in a Semiarid Rangeland of Argentina


The objective of this study was to evaluate the efects of moderate defoliation and grass species on soil nitrogen (N) mineralization in a semiarid grassland of northeastern Patagonia, Argentina. Studied species were Poa ligularis and Nassella tenuis (desirable/preferred by cattle) and Amelichloa ambigua (undesirable/non preferred). Two defoliations were made to a 5 cm stubble height during the growing season. Hypotheses were that (1) net N mineralization and N availability in the soil are increased by a moderate defoliation and greater species forage quality, and (2) potential N mineralization is higher in the soil beneath the desirable than undesirable species. In 2013 and 2014, in situ net N mineralization was estimated using the tube incubation technique under feld conditions. Potential N mineralization was estimated by long-term laboratory incubations. Defoliation treatments did not afect the soil inorganic N dynamics. The soil under A. ambigua showed a greater in situ net N mineralization than other species, but only in 2013. Poa ligularis presented the highest initial inorganic N and potentially mineralizable N values. However, the opposite was recorded in this specie for the mineralization constant rate. These results demonstrated that moderate defoliations did not afect soil N availability, and presence of the desirable perennial grasses increased the potential N mineralization pool. Sustainable management practices that promote the persistence of these species in plant community are important to maintain soil fertility on semiarid grasslands.

Palabras clave
Poa ligularis
Nassella tenuis
Amelichloa ambigua
Perennial grasses
Inorganic soil N

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