Perennial forage-based fallows support long-term soil carbon and nutrient trajectories in smallholder rotations of the Peruvian Andes

Meza K.; Vanek S.; Olivera E.; Huaraca J.; Scurrah M.; Ccanto R.; Fonte S.J. · Agriculture, Ecosystems and Environment (2025) · DOI: 10.1016/j.agee.2025.109884

Resumen

Smallholder cropping systems of the Andean highlands are often characterized by complex rotations with a multi-year fallow period, where growth of natural vegetation helps to restore soil fertility and provide forage. Shortening of these traditional fallows in many regions threatens the long-term productivity of soils. Recent collaborative research with farmers in the Andean region suggests that replacing traditional fallows with seeded forage-based fallows (FBF) comprised of productive perennial grasses and legumes offers great promise to support forage production and restore soil health. However, the long-term implications for soil nutrient and carbon stocks remain unclear. To address this issue, a set of on-farm trials were established to support a modeling approach for comparing test six different FBF mixtures vs. a traditional fallow control. We evaluated forage productivity and impacts on soil fertility following 3 years of fallow. In addition, inputs and outputs of nitrogen (N), phosphorus (P) and potassium (K) were examined using a nutrient balance approach, while soil organic carbon (SOC) dynamics were evaluated using the DayCent model. We found that perennial FBFs produced twice as much forage as the traditional control, with no apparent negative impacts on soil fertility. While FBFs were associated with greater nutrient export, farmers compensated for these exports with greater manure inputs, resulting in minimal differences in nutrient balances between treatments. On average, N and K balances tended to be negative (−13.9, −7.5 kg ha−1 yr−1, respectively), with erosion losses being a major driver, while P balances were largely positive (15.1 kg P ha−1 yr−1). DayCent projections indicated that perennial FBFs are likely to increase SOC by 13.4 Mg ha−1 in the next 36 yr, while shortened traditional fallows or those planted with only annual forages are likely to lose SOC over time. Our findings suggest that FBFs offer considerable potential for regenerating soil health and enhancing the production of much needed forage in these high Andean crop-livestock systems.