CONICET | Buscador de Institutos y Recursos Humanos

Aboveground Net Primary Production (ANPP) is an indicator of ecosystem functioning and a key variable for the sustainable and efficient management of pastoral livestock systems. Overseeding legumes in natural grasslands coupled with phosphorus fertilization (IG) is an intensification technology extensively used in pastoral livestock systems in Uruguay to increase ANPP. The effect of this practice has been scarcely evaluated beyond punctualcontrolled condition experiments. In this study we used Enhanced Vegetation Index (EVI) time series, a spectral index closely related to the amount of intercepted radiation and therefore to ANPP, to analyze the effect of this technology in livestock commercial farms under production conditions. We used EVI time series of 4 years before and 9 years after intensification of 20 natural grassland (NG) and IG paired paddocks under the same grazingconditions. Both treatments were compared in terms of both EVI magnitude and intra-annual and interannual coefficient of variation (CV) using factorial repeated measures ANOVA and Tukeys test adapted for multiple comparisons. Annual EVI mean of the IG was 4% higher than the NG (P=0.0003 and F1,19=18.88); the difference were concentrated in the June-November period where they reached 7.5%. NG were slightly more stable thanIG both intra-annually (19% vs 21%, F1,19=24.14, P<0.0001) and interannually (15.8% vs 17.1%, F1, 19=14.80, P=0.0011). Our results confirm that this technology generates an increase in ANPP concentrated in the period of greatest forage deficit in NG of Uruguay (winter-early spring), while showing a decrease in system stability, potentially associated with the loss of plant species diversity.

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