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Agriculture in the Central Andes of Peru is performed mostly by small farmers in mixed crop-animal production systems. Farmers are usually organized in collaborative social structures named Farm communities, in which complex mechanisms for access to land, labor and inputs can be found. Although the region is not unknown for Peruvian and International research institutions, most of the research in the past has focused on social aspects of the production systems or on specific physical and biological topics (climate, soils, biodiversity), with limited integration to the existing social structures. This work aims to develop a holistic view of the farming systems in four farm communities in the Mantaro Valley (Central Andes of Peru) by investigating all biophysical inputs and outputs at the field level on quantitative scales, and providing information for future implementation of strategies to increase the farm technical sustainability.The present work was developed from 2004 to 2008, in the research sites of Colpar, Quilcas, Aramachay, Sincos, Molinos and Quero. The experimental data were collected using participatory research methodologies and structured interviews of farmers combined with farm visits and intensive measurement of selected pilot-plots. The climate during the experimental period was measured through semi-automated weather stations.The crop cycles managed in 38 plots along three crop seasons were categorized in terms of use of organic and inorganic nutrient inputs. The inorganic fertilizers used were measured and the organic matter sources were chemically characterized. With these data, the production of biomass and the inputs and removals of carbon, nitrogen, phosphorus and potassium were measured, and nutrient balances were calculated. The use of labor, animal traction and machinery were measured per plot. The amount of animals raised per farm was recorded at the beginning of the study. Biomass production and C- and N-balances were further calculated for the main rotations identified, and data were integrated at the farm level for selected families in Colpar, Quilcas and Aramachay.The precipitation in Mantaro Valley is concentrated in a well-defined rainy season extending from October to March. The dry season is colder, but the diurnal variation of temperature is much wider than the yearly variation. The major climatic risks during the crop season are the occurrence of drought periods and frosts. The risk of frosts is highest in Aramachay, resulting in the replacement of corn by barley in the crop rotations. The overall climate is adequate for annual crops, but without irrigation to overcome the dry season it is impossible to establish permanent crops.Two main groups of soils were indentified in the studied zones: soils located on hillsides, which are fine-textured, moderately fertile, high in organic matter and acidic; and soils located on the valley floor, which are coarse-textured, chemically fertile, low in organic matter and of neutral to alkaline pH. The unfavorable chemical properties in the soils identified can be remediated with regular soil management practices. Soil fertility can be increased through the application of organic matter and rational use of inorganic fertilizers. Phosphorus and potassium deficiencies did not seem to be critical. As strongly acidic soils are common, liming could result in increased yields for barley and legumes. In general terms, soil chemical properties are not strong limiting factors for the production systems.Crops included potatoes, cereals, corn, grain legumes and native tubers. Potatoes received the highest amounts of external inputs (organic and inorganic) but yields obtained varied widely in relation to the inputs applied. In general, the C- balances were variable and the N-, P- and K-balances were positive, indicating that, in certain cases, potato plots were overfertilized. Barley and wheat were cultivated with fewer inputs compared to potato, while corn and faba bean fertilization consisted mainly of farmyard manures. C-balances in cereals and corn were strongly negative, and nutrient-balances depended on the amount of fertilizers applied. C- and nutrient-balances were positive for faba bean. Crop production systems in Colpar are oriented to organic matter use while in Molinos production is based on inorganic fertilizers. Quilcas, Aramachay and Sincos have mixed-input systems.Livestock included cows, oxen, sheep, donkeys, guinea pigs and poultry. Animals are fed with natural pastures during the rainy season and with fodder and crop residues during the dry season. Crops fertilization depends on farmyard manures, thus crop production is strongly related to animals. Most of the farmers prepare farmyard manure according to one traditional procedure. Manure accumulates during the dry season, when most of the animals stay in the stable.In all the zones, land is split in small units to diversify cropping and diminishing climatic risks. The plots are usually larger in the flat areas. The availability of land per farm is markedly lower in Colpar and Quilcas compared with other zones. Human labor, especially obtained from family members, is the main source of energy for crop cultivating activities. Exchanged labor was more frequently observed in Colpar and Quilcas and contracted manpower was used more in Molinos. Both male and female laborers had the same importance for crop management, although they could be divided according to specific activities. Animal traction was used extensively for soil preparation and transport, especially in high altitude zones. The use of machinery was limited to low and flat areas where plots were larger and accessible. Crop production in Colpar was totally dependent on human and animal labor, while Molinos used more machinery.Monocultures of cereals or corn and rotations with potato were negative in C-balances, but the N-balances were positive. The inclusion of faba bean in the rotation resulted in positive C- and N-balances. Fallow periods could restore C and N in the system,but their contribution was lower than that for legumes. Partial transfer of inputs from potato to barley and replacement of fallows with grain or forage legumes are proposed as strategies for increasing sustainability of rotations.At the farm level, C-balances in Aramachay and Quilcas were negative and N-balances were positive, while in Colpar, both were positive. The production per farm indicated a higher capacity of farmers in Aramachay to orientate towards markets, compared with Colpar and Quilcas. This may indicate more poverty in the last zones.Soil liming and inorganic fertilization increased grain yield of barley, indicating that transferring fertilizers from potato could result in a better use of nutrients within the rotations in farm communities in the Mantaro Valley.