Precipitation controls the annual net primary productivity in sown pastures across a precipitation gradient in dry subtropical Chaco

Abstract

Exotic pasture species are increasingly replacing native vegetation in subtropical areas because of their potential to increase forage yields. However, there is a scarce analysis of the relationship between forage yield and mean annual precipitation across regional gradients. We analyzed at a regional scale the temporal relationship between the aboveground net primary productivity (ANPP) and the precipitation for different sown grasses for several growing seasons across Dry Chaco, Argentina. We compiled biomass harvest data for seven cultivars of Megathyrsus maximus and Cenchrus ciliaris at eight different sites across a gradient of mean annual precipitation (MAP; 200 mm–1100 mm). We found positive relationships between ANPP and precipitation for most of the cultivars. The strong relationship between annual ANPP and MAP found implies that the high temporal variability in MAP translates into ANPP variability. The regional slope between annual ANPP and MAP was 11.12 kg DM.ha−1.year−1.mm−1. The ratio between the temporal and the spatial models ranged from 0.26 to 1.35. Precipitation use efficiency ranged between 3.9 and 24.1 kg DM.ha−1.year−1.mm−1. These models are robust enough to estimate the ANPP of specific pastures from MAP data. This represents a breakthrough, in grazing systems planning and defining conservation policies for natural resources.