Increasing nutrient use efficiency in farming systems

Increasing nutrient use efficiency in farming systems
Tom Bruulsema¹, Rob Norton²

1. International Plant Nutrition Institute, Guelph, Ontario, N1G IL8, Canada. Tom.bruulsema@ipni.net
2. International Plant Nutrition Institute, Horsham, Victoria 3400, Australia. rnorton@ipni.net

Nutrient use efficiency is directly and indirectly implicated in numerous performance metrics currently being proposed for global sustainability initiatives. These initiatives include the contributions of several United Nations agencies toward proposed Sustainability Development Goals, and those of the private sector corporations that form the food supply chain. The complete assessment of performance for the management of crop nutrition encompasses a wide range of social, economic and environmental indicators. The International Plant Nutrition Institute has worked closely with stakeholders to develop a range of nutrient performance indicators that reflect the diversity of impacts that come from nutrient best management practice. This paper aims to explain and provide support for the use of specific forms of nutrient use efficiency in the context of other indicators relevant to the enabling, monitoring, and impact assessment of best practices in nutrient stewardship.

The use of fertilizers is fundamental to feeding the global population, with around half of current food production made possible by balanced crop nutrient input. At the same time, there are parts of the world where fertilizers are under-used so that food security is threatened, or where they are overused to the point of contributing to environmental pollution. Selecting the most appropriate form of system nutrient use efficiency can be a helpful tool in prioritizing areas for improvement, for some but not all environmental impacts associated with nutrient management. Nutrient use efficiency emphasizes rate, but 4R Nutrient Stewardship includes considerations of source of nutrients, timing and place of application as well, since these can be crucial to managing several large-impact nutrient loss processes.

Selecting the most appropriate performance measure requires a detailed understanding of the processes involved in acquisition, residence time, allocation, remobilization and losses within plants. The acquisition or uptake efficiency and then remobilization or utilization efficiencies are important to plant breeders as they look for traits that can be used in selecting more efficient genotypes. Responses can be expressed as agronomic efficiencies or apparent recovery efficiencies, but both require a nil fertilizer application treatment to estimate the extra yield in response to added nutrient. Of a wide range of potential methods to assess nutrient use efficiency, partial nutrient balance (PNB; nutrient removal to use ratio) and partial factor productivity (PFP; crop yield per unit of nutrient applied) offer the benefits of being readily assessed at a range of scales including fields, farms, regions or nations. To fully represent the contribution of crop nutrition to sustainable production, however, any metric of nutrient use efficiency requires complementary metrics to reflect crop productivity and soil fertility. Nutrient use efficiency is a useful, complex, and incomplete metric of crop nutrition performance.