Impact of Land-Use Change on Soil Fertility: A Case Study in the Peruvian High-Andean Puna Grasslands.

In the Peruvian Central Andes, high-Andean Puna grasslands (above 3800 m a.s.l.) used traditionally for livestock grazing are being converted to maca (Lepidium meyenii) croplands driven by its high international price during the last years. There is a local perception that maca cropping depletes soil nutrients leaving it degraded for subsequent agricultural or grazing activities. To test this perception, two soil fertility experiments were performed using dry biomass production of guinea grass (Panicum maximum cv. Tanzania 1) (GDP) growing in pots of different land-use soils. In the first experiment, soils from maca cropfields (n=21), long maca fallow fields (≥7 years) (n=11), and native grasslands (n=20) were used. In the second experiment, soils from long standing perennial ryegrass-clover mixture (pasture) and native grassland soils (n=20 each) were tested. Plant-available N (ion exchange resin membranes), P (Bray-extraction), and K (acetate-extraction) were also analyzed for each soil. In the first experiment, GDP showed significant differences between land-use and ranch location soils (two-way ANOVA). Unexpectedly, GDP, N, P and K in maca cropland soils were significantly higher than in native grasslands soils (Tukey’s test). The higher GDP in maca soils might be a result of higher N mineralization rates commonly found in plowed soils, as well as a result of the incorporation of organic amendments for maca production. In the second experiment, pasture soils showed a significant higher GDP than native grasslands soils (one-way ANOVA), but we did not find significant differences in N, P or K. However, soil pH was significantly lower in native grasslands soils, probably limiting plant nutrient uptake. This study suggests that reduced soil fertility is not a factor limiting ecological functionality of disturbed Puna grasslands. Further research is needed in order to understand how agricultural land-use change disturbs this ecosystem’s structure and functionality.