Abstract. Modern restructuring of agricultural landscapes, due to the expansion of monocultures and the resulting elimination of non-crop habitat, is routinely blamed for rising populations of agricultural insect pests. However, landscape studies demonstrating a positive correlation between pest densities and the spatial extent of crop monocultures are rare. We test this hypothesis with a data set from 140 subsistence farms in the Andes and find the inverse correlation. Infestations by the Andean potato weevil (Premnotrypes spp.), the most important pest in Andean potato agriculture, decrease with increasing amounts of potato in the landscape. A statistical model predicts that aggregating potato fields may outperform the management of Andean potato weevils by IPM and chemical control. We speculate that the strong pest suppression generated by aggregating potato fields may partly explain why indigenous potato farmers cluster their potato fields under a traditional rotation system common in Andean agriculture (i.e., ''sectoral fallow''). Our results suggest that some agricultural pests may also respond negatively to the expansion of monocultures, and that manipulating the spatial arrangement of host crops may offer an important tool for some IPM programs.

Land use change and intensification in agricultural landscapes of the Andean highlands have resulted in widespread soil degradation and a loss in soil-based ecosystem services and biodiversity. This trend threatens the sustainability of farming communities in the Andes, with important implications for food security and biodiversity conservation throughout the region. Based on these challenges, we sought to understand the impact of current and future land use practices on soil fertility and biodiversity, so as to inform landscape planning and management decisions for sustainable agroecosystem management. We worked with local communities to identify and map dominant land uses in an agricultural landscape surrounding Quilcas, Peru. These land uses existed within two elevations zones (low-medium, 3200-3800 m, and high elevation, 3800-4300 m). They included three types of low-medium elevation forests (eucalyptus, alder, and mixed/native species), five pasture management types (permanent pasture, temporal pasture [in fallow stage], degraded pasture, high-altitude permanent pasture, and high-altitude temporal pasture [in fallow stage]) and six cropping systems (forage crops, maize/beans, and potato under four types of management). Soil fertility was evaluated in surface soils (0-20 cm) with soil physicochemical parameters (e.g., pH, soil organic matter, available nutrients, texture), while soil biological properties were assessed using the abundance and diversity of soil macrofauna and ground cover vegetation. Our results indicated clear impacts of land use on soil fertility and biological communities. Altitude demonstrated the strongest effect on soil physicochemical properties, but management systems within the low-mid elevation zone also showed important differences in soil biological communities. In general, the less-disturbed forest and pasture systems supported more diverse soil communities than the more intensively managed croplands. Degraded soils demonstrated the lowest overall soil fertility and abundance of soil macrofauna, but this may be reversible via the planting of alder forests. Our findings also indicated significant covariation between soil physicochemical parameters, soil macrofauna, and ground vegetation. This suggests that management for any one of these soil properties may yield unintended cascading effects throughout the soil subsystem. In summary, our findings suggest that shifts in land use across the landscape are likely to have important impacts on soil functioning and biodiversity.

Traditional Processing of Black and White Chuño in the Peruvian Andes: Regional Variants and Effect on the Mineral Content of Native Potato Cultivars. Farmers in the high Andes of central to southern Peru and Bolivia typically freeze-dry potatoes to obtain chuño. Processing of so-called black chuño follows tending, treading, freezing, and drying. The making of white chuño is generally more complex and involves exposure of tubers to water. Regional variants exist for each of these processes, yet their influence on the nutritional composition of native potato cultivars is little known. Tubers belonging to four distinct cultivars and produced in a replicated trial under uniform conditions were processed into four types of chuño following standard traditional procedures (farmer-managed). These regional variants were documented, and the dry matter, iron, zinc, calcium, potassium, phosphorus, magnesium, and sodium content of the four resulting different types of boiled chuño determined at the International Potato Center's Quality and Nutrition Laboratory (Lima, Peru). Content values were compared with those of boiled (unprocessed) tubers from the same experiment. Regional variants of processing are to a large extent determined by tradition, environmental condition, and market demand. The zinc, potassium, phosphorus, and magnesium content of all types of chuño decreases in comparison with unprocessed tubers. Concentrations of these same minerals decrease more drastically for white as compared to black chuño. The effect of the four regional variants of freeze-drying on the dry matter, iron, calcium, and sodium content of chuño differs by process and/or cultivar.Procesamiento tradicional de chuño negro y blanco en los Andes Peruanos: Variantes regionales y efecto sobre el contenido de minerales en cultivares nativos de papa. Los agricultores de la zona Alto Andina del centro al sur del Perú y Bolivia someten a la papa a un proceso de congelado-secado para obtener chuño. El procesamiento del chuño negro involucra tender, pisar, congelar y secar. Por lo general la elaboración del chuño blanco es más compleja y requiere que los tubérculos se remojen en agua. Existen variantes regionales para cada uno de los procesos. Sin embargo, la influencia de estas sobre la composición nutricional de cultivares nativos es poco conocida. Tubérculos de cuatro cultivares distintos y producidos en un ensayo replicado bajo condiciones uniformes fueron procesados en cuatro 'tipos' de chuño siguiendo procedimientos tradicionales estándar (manejo de agricultor). Se documentaron las variantes regionales y se determinó el contenido de materia seca, hierro, zinc, calcio, potasio, fósforo, magnesio y sodio de los cuatro diferentes 'tipos' de chuño en el Laboratorio de Calidad y Nutrición del Centro Internacional de la Papa (Lima, Perú). Se compararon los valores de contenido del chuño con los de tubérculos hervidos (sin procesar) provenientes del mismo experimento. Los variantes regionales de procesamiento se determinan principalmente por tradición,...

SU MMARYIn the Central Peruvian highlands, potatoes are commonly cultivated by smallholder farmers in fields between 3500 and 4300 m asl. Severe climatic conditions, marginal soils and limited access to inputs and infrastructure define these challenging agro-ecological environments. To prepare an adequate seed bed for the potato and mitigate climatic, topographic and labour constraints, Andean farmers have developed distinct footplough-based tillage systems: barbecho, chiwa and chacmeo. A series of field experiments was conducted in 2005/06 and 2006/07 at four different locations to investigate the effect of three different tillage systems on potato tuber yield, varying factors such as cultivars and types and amounts of fertilizer applied. The objective was to improve understanding of the effect of these factors on potato yield and study the potential advantages and disadvantages of each tillage system.The study showed that the type of tillage influenced a great variety of factors. Farmers often use a combination of tillage systems as a strategy to diversify possible risks, considering trade-offs regarding productivity v. yield stability, internal v. external resource use, labour requirement during peak times v. more uniform distribution or extensive v. intensive production. The chiwa and to some extent the chacmeo tillage systems resulted in relatively constant and stable yields for different environments and genetic materials, whereas the more intensive barbecho system sought to optimize growth conditions for the potato crop but was more liable to stress and required external resources. Currently, farmers often use the barbecho system to produce commercial cultivars for the urban markets investing the greatest share of internal and external resources. They use the chiwa and chacmeo systems to produce diverse native cultivars for their home consumption, valorizing their taste, cooking qualities and lower resource requirements.

Soils of the Andean highlands are under threat from cropping system intensification. Improved forage-based fallows offer great promise to address this issue, but research is needed to better understand the potential of species mixtures vs. monocultures to support multiple farmer objectives, especially forage production and soil conservation. We used a pot study to quantify above- and belowground biomass production as well as the total N uptake of grass–legume pairs between five grasses: (1) oat (Avena sativa), (2) ryegrass (Lolium multiflorum), (3) festulolium (Lolium × Festuca genera), (4) brome grass (Bromus catharticus), and (5) orchard grass (Dactylis glomerata), and four legumes: (1) vetch (Vicia dasycarpa), (2) red clover (Trifolium pratense), (3) black medic (Medicago lupulina), and (4) alfalfa (Medicago sativa) relative to the performance of each species in monoculture within two soils from the central Peruvian Andes. Grass–legume bicultures demonstrated significant overyielding, producing 65% and 28% more total dry biomass and total N uptake on average than monocultures. Aboveground biomass of bicultures was significantly influenced by the species of legume present, while belowground biomass was more affected by the grass species in the mixture. When evaluating the growth of each species separately, our findings indicate that overyielding was driven more by the enhanced growth of grasses relative to legumes. Our findings indicate that combining key functional groups (e.g., grass and legume, annual and perennial) offers great promise for developing improved fallows for supporting soil health and productivity in Andean agroecosystems.