Soil Science Society of America Journal Soil Sci. Soc. Am. J. 82:463–474 doi:10.2136/sssaj2017.09.0309 Received 3 Sept. 2017. Accepted 12 Jan. 2018. *Corresponding author (joseluis.rolandob@gmail.com). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA. All Rights reserved. Land Use Effects on Soil Fertility and Nutrient Cycling in the Peruvian High-Andean Puna Grasslands Soil & Water Management & Conservation Expansion of crop production into high-altitude native grasslands is occurring in the Peruvian High-Andes due to climate change and agricultural intensi- fcation, with little understanding of the consequences to the ecosystem. The objective of this study was to determine the impact of land-use chang- es on soil fertility and nutrient cycling to guide future land management. Comparisons were made between native grasslands and two alternative farm- ing systems; the frst was a system in which native grassland was replaced by an annual cash crop, maca (Lepidium meyenii Walp.), followed by a long fallow and the second was a long-standing perennial cultivated pasture. There was greater N mineralization, extractable Bray-1 P, and K + in recently con- verted maca soils relative to adjacent native grassland soils most likely caused by tillage-induced nutrient mineralization and by incorporation of manure and native grassland residue during the frst year of land preparation prior to planting maca. Soil fertility, as determined by an ex situ pot trial to mea- sure plant yield, was correlated with plant cover, soil total organic carbon, and water stable aggregates (WSA) under fallow following maca, suggesting that soil erosion might be an issue in the long term. In cultivated pastures, we found an increase in long-term fertility driven primarily by the build-up of soil N and improved soil structure in the perennial grass-legume mixture compared with adjacent native grassland. Responsible management of the Puna agroecosystem requires restoration of plant cover after annual cropping of maca or the establishment of mixed perennial cultivated pasture. Abbreviations: AG, aboveground; BG, belowground; CEC, cation exchange capacity; CVA, canonical variates analysis; TOC, total soil organic carbon; TN, total soil nitrogen; WSA, water stable aggregates. I n the Peruvian Andes, Puna natural grasslands dominated by Calamagrostis, Festuca, Poa and Stipa grass species have traditionally been used for grazing live- stock (Wilcox et al., 1986). Until recently, cultivation at this altitude (above 3800 m asl) was limited to growing Andean tubers (e.g., Tropaeolum tuberosum Ruiz & Pav., Solanum spp., Oxalis tuberosa Molina) in small-holder farms of less than 2.5 ha (Dixon et al., 2001). An intensification of market-oriented cropping systems, an increasing export demand, and climate change have elevated the altitudinal limits for these systems such that row cropping is now encroaching into Puna native grass- land (Zimmerer, 2003; de Haan, 2009; Postigo, 2014; Rolando et al., 2017b). A case that represents this process is the land conversion from native grasslands to maca (Lepidium meyenii Walp.), a member of Brassicaceae family that is native to this re- gion and cropped for its edible expanded hypocotyl (Flores et al., 2003). The increase in land area used for maca production corresponds to an increase in export demand, largely from China, with no signs of slowing in the near future. The Junin region is the main maca producer in Peru, and between 2014 and 2015 its cropping area tripled to 6500 ha at the expense of native grasslands (Gobierno Regional de Junin, 2015a; MINAG, 2015). The land of native grass- Jose L. Rolando* International Potato Center (CIP) Apartado 1558, Lima 12, Peru and Univ. of Florida North Florida Research & Education Center Marianna, FL 32446 Jose C. B. Dubeux, Jr. Univ. of Florida North Florida Res. & Education Center Marianna, FL 32446 David A. Ramirez International Potato Center (CIP) Apartado 1558, Lima 12, Peru and Key Lab. of Aridland Crop Science Crop Genetic & Germplasm Enhancement Agronomy College Gansu Agricultural Univ. Lanzhou 730070, China Martín Ruiz-Moreno Univ. of Florida North Florida Research & Education Center Marianna, FL 32446 Cecilia Turin Victor Mares International Potato Center (CIP) Apartado 1558, Lima 12, Peru Lynn E. Sollenberger Univ. of Florida Dep. of Agronomy Gainesville, FL 32611 Roberto Quiroz International Potato Center (CIP) Apartado 1558, Lima 12, Peru Core Ideas • A short-term increase in fertility and greater N mineralization were found in agricultural lands. • Low plant recovery and soil degradation were found in fallow soils correlated with erosion indexes. • In grass-legume mixture pastures, improved soil structure and N build up increased soil fertility. • P was found as the limiting nutrient in the studied agroecosystem. Published online March 22, 2018