Nitrogen (N) cycling in rangeland soils could potentially be controlled by water supply, stocking rates, or a range of other variables, such as ecosystem N stocks. To gauge the relative importance and elucidate possible interactions among these factors, we measured many abiotic variables to identify first-order controls of δ15N for Patagonia's rangeland soils under contrasting historical grazing intensities. The results showed that δ15N values declined as water availability increased. The effects of precipitation and stocking rate on soil δ15N values were additive, and the effect of precipitation far outweighed the effects of grazing pressure. The soil N stock was a weak predictive variable for modeling variation in δ15N of the soil. Earlier assumptions about an inflection point for N cycling and δ15N values related to aridity were not confirmed. We conclude that variation in water ...

In the last decades, the intensive use of nitrogen fertilizers in annual and perennial crops has increased in Peru. These fertilizers are quickly available to plants by converting to nitrates, increasing crop yields. However, nitrogen fertilizers are very volatile and are also lost easily by leaching. This lost nitrogen (N) implies economic costs and leads to environmental problems such as eutrophication. Biochar, a new soil amendment, has been suggested as a solution to these problems; however, there has been little research on the subject in Peru. The objective of this study was to evaluate the effect of biochar application on corn yield and nitrogen balance in soils (Entisols with alluvial deposition) in San Ramon (Peru). Biochar was produced from green waste and pig manure. The research design considered five treatments: Control (T1), 7 t·ha-1 of pig manure (T2), 17.5 t·ha-1 of bio...

Guano de isla (seabird guano) is a strategic organic fertilizer in Peru, reserved primarily for economically vulnerable smallholder farmers. However, its availability is declining due to ecological pressures on seabird populations, creating an urgent need to improve its use efficiency. This study tested the hypothesis that biochar can enhance the nutrient use efficiency of guano de isla, allowing reduced application rates without compromising yield or profitability. A randomized complete block experiment (n=10 replicates per treatment) was conducted in sandy soil in Lurín, Peru, to evaluate lettuce (Lactuca sativa) yield under eight fertilization treatments, including inorganic fertilizer (NPK), guano de isla (400 kg ha⁻¹), biochar (3 t ha⁻¹), and combinations thereof. The biochar+guano de isla (BG) treatment applied 200 kg ha⁻¹ of guano de isla (50% of the standard rate). Econ...

Peru is the eighth largest producer of cacao beans globally, but high cadmium contents are constraining access to international markets which have set upper thresholds for permitted concentrations in chocolate and derivatives. Preliminary data have suggested that high cadmium concentrations in cacao beans are restricted to specific regions in the country, but to date no reliable maps exist of expected cadmium concentrations in soils and cacao beans. Drawing on >2000 representative samples of cacao beans and soils we developed multiple national and regional random forest models to develop predictive maps of cadmium in soil and cacao beans across the area suitable for cacao cultivation. Our model projections show that elevated concentrations of cadmium in cacao soils and beans are largely restricted to the northern parts of the country in the departments of Tumbes, Piura, Amazonas and Lore...