Abstract
Over many decades there has been a global trend away from mixed farming and integrated crop-livestock systems to more-intensive single commodity systems. This has distorted local and global nutrient balances, resulting in environmental pollution as well as soil nutrient depletion. Future food systems should include integrated crop-livestock systems with tight nutrient budgets. For nitrogen (N), detailed understanding of processes, fluxes – including of gaseous forms – and budgets at a component level is needed to design productive systems with high N use efficiency (NUE) across the full nutrient chain. In Uruguay, a unique rice-livestock system has been practiced for over 50 years, attaining a high production level for rice (mean grain yields > 8 Mg ha−1) and an average level for livestock (120 kg liveweight gain ha−1 y−1). The aim of this study was to quantify the components of the N balance and NUE of this system, so as to understand its long-term sustainability, and draw conclusions for other regions. Analysis of country-level statistics for each component over the last 16 years shows tight N balances of +3.49, +2.20 and +2.22 kg N ha−1 yr−1 for rice, livestock and the whole system, respectively. Based on average values of N retained in edible food products, NUE values were 65.7, 13.2 and 23.1% for rice, livestock and the whole system, respectively. While NUE of livestock was unchanged over the period, NUE of the rice component decreased due to increasing fertiliser use. Further gains in N efficiency are possible by better integrating the system components. Actions to increase system level NUE include raising pasture and livestock productivity and controlling the increasing use of N fertilisers in rice. Tightly integrated crop-livestock systems can play a significant role in re-shaping global agriculture towards meeting food security, environmental and socioeconomic sustainability targets.
Highlights
The independent Scientific Panel on Responsible Plant Nutrition has recently outlined a food system approach to plant nutrition in which multiple socioeconomic, environmental and health objectives must be achieved (Scientific Panel on Responsible Plant Nutrition, 2020)
Many high-income countries outsource much of the environmental burden of their food production to other countries, who must ensure that their agricultural systems are both competitive and sustainable (Sun et al, 2020)
We calculated a simple N balance based on N inputs minus N outputs, and Nitrogen use efficiency (NUE) from outputs relative to inputs using a common N budgeting approach (Watson and Atkinson, 1999)
Summary
The independent Scientific Panel on Responsible Plant Nutrition has recently outlined a food system approach to plant nutrition in which multiple socioeconomic, environmental and health objectives must be achieved (Scientific Panel on Responsible Plant Nutrition, 2020). The fate of nitrogen (N) in crop and livestock production is central to this because of its global impacts on sustainable food production. Nitrogen use efficiency (NUE) – here defined as the ratio of N outputs over N inputs – tends to decline as countries intensify their agriculture through increasing fertiliser use. Large regional differences in N budgets and NUE exist, aggra vated by transnational nutrient transfers due to the separation of crop and livestock farming, as well as increasing global trade of crops and livestock products (Grote et al, 2008; Uwizeye et al, 2020). Many high-income countries outsource much of the environmental burden of their food production to other countries, who must ensure that their agricultural systems are both competitive and sustainable (Sun et al, 2020). Uruguay is a prime example of a country producing mostly crops and livestock for export
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