DataSheet1_Nutrient stocks, flows and balances for the Bolivian agri-food system: Can recycling human excreta close the nutrient circularity gap?.xlsx

Analysis of the current state of nutrient stocks, flows, and balances of a territory is necessary to inform strategies that can transition the agri-food sector to a circular economy model. In this study, we quantified the nitrogen and phosphorus budgets for the Bolivian agri-food system at national and regional scales by way of agro-ecological zoning. We performed nutrient balances to calculate indicators for sufficiency (extent of nutrient deficit/surplus) and circularity (proportion of nutrients recirculated). We also evaluated the potential of renewable stocks (human excreta and livestock manure) to meet nutrient deficits in the system. Our results showed that there are apparent deficits of 32 kt N and 8 kt P in the system that cannot be accounted for using available data. We estimate the real deficits required to bring yields of 45 crops grown in Bolivia to parity with those of neighbouring countries to be 110 kt N and 33 kt P. About 44% of nitrogen and 74% of phosphorus is currently recirculated in the system, with the major nutrient inputs being biological nitrogen fixation, livestock manure, and crop residues. However, nutrient recycling is likely to decrease in the future because the national strategy to address nutrient deficits is to increase domestic production of synthetic fertilisers. Our analysis also shows that there is a sufficient stock of nutrients already available in human excreta (39 kt N and 5 kt P) to cover 100% of the nitrogen deficit and 64% of the phosphorus deficit. The low-altitude zone of Chiquitania-Pantanal alone accounts for 65% of cultivation and 80% of the nutrient demand in the country. Here, export-oriented crops like soybean and sorghum are grown, but less than 25% of the nitrogen is recirculated. In contrast, there are nutrient surpluses of 41 kt N and 34 kt P in agro-ecological zones like the Valleys and Altiplano where traditional agriculture is practiced, and the majority of food is grown for local consumption. Overall, we find that recycling of human excreta, combined with transfer of regional nutrient surpluses, could be an effective strategy to reduce the overall nutrient deficit in the system.

对某一区域的养分储量、流动与平衡现状开展分析，可为推动农业食品部门向循环经济模式转型的战略制定提供科学依据。本研究通过农业生态区划（agro-ecological zoning）方法，在国家与区域尺度上量化了玻利维亚农业食品系统的氮、磷收支情况。本研究通过养分平衡核算，计算了养分充足性（养分亏缺/盈余程度）与循环性（养分循环回用比例）两类指标。此外，本研究还评估了可更新养分储量（人类排泄物与畜禽粪便）填补系统内养分亏缺的潜力。研究结果显示，当前系统存在32千吨氮素与8千吨磷素的表观亏缺，且现有数据无法对该亏缺作出合理解释。若要使玻利维亚境内45种作物的单产水平达到邻国同等标准，本研究估算所需的实际养分亏缺量为110千吨氮素与33千吨磷素。当前系统内约44%的氮素与74%的磷素实现了循环回用，主要养分输入来源包括生物固氮、畜禽粪便与作物秸秆。然而，由于该国应对养分亏缺的国家战略是提升合成肥料的国内产能，未来系统内的养分循环率或将出现下降。本研究的分析还表明，人类排泄物中蕴含的养分储量（39千吨氮素与5千吨磷素）足以完全覆盖氮素亏缺，并填补64%的磷素亏缺。仅奇基塔尼亚-潘塔纳尔（Chiquitania-Pantanal）低海拔区域就占据了全国65%的耕地面积与80%的养分需求。该区域种植大豆、高粱等出口导向型作物，但氮素循环回用率不足25%。与之相反，在山谷区与阿尔蒂普拉诺高原（Altiplano）这类以传统农业为主、多数作物为本地消费种植的农业生态区划中，系统内存在41千吨氮素与34千吨磷素的盈余。总体而言，本研究发现，将人类排泄物养分回用与区域养分盈余转移相结合，可有效降低系统整体的养分亏缺水平。