Plain Language Summary
Phosphorus (P) is one of the essential nutrients that crops need to grow. As the global population increases, we need to use P fertilize at cropland continually. However, inappropriate use of P in agriculture will cause trouble for both the environment and society. First, the available amount of phosphate rock, which is the raw material for P fertilizer, is limited on earth and in short in many countries. Second, too much P lost to the environment can lead to bad water quality, causing the death of fish in waters and impairing human health. To address these challenges, we need to understand factors influencing the use efficiency of P, and how improvement in P use efficiency can alleviate P shortage and nutrient pollution problems. This study answers the two questions by examining historical P use data and projecting future P budget at cropland in different scenarios. Based on the study results, we suggest national and global P efficiency improvement goals to achieve by 2050 to produce enough food and reduce P pollution to an acceptable level.
1 Introduction
Phosphorus (P) is one of the nutrients critical for growing crops, which are fundamental for feeding the growing population (Tilman et al. 2002, Cordell et al. 2009, Cordell and White 2014). Consequently, the urge for more food production and higher yield is likely to drive up the demand for P inputs to cropland. By estimate, the total global consumption of P fertilizer at cropland has increased by almost four times from 1961 to 2013 (Lu and Tian 2017), and the demand may increase to 22-27 Tg P yr-1 by 2050, even assuming a sustainable future (Mogollón et al. 2018).
However, over and improper use of P results in excessive P leaching to adjacent water bodies, causing nutrient pollution (Foley et al. 2011, Bouwman et al. 2017, Fink et al. 2018, Mekonnen and Hoekstra 2018). Inorganic fertilizer use was the primary source (47%) of P going to the world’s largest 100 lakes between 2005-2010 and 1990-1994, and developing countries had a higher chance of P-stimulated eutrophication (Fink et al. 2018). Even after the reduction or cessation of fertilizer input, the large surplus of P accumulated in soil (known as legacy P) will continue to pollute surface waters, offsetting the benefits brought by nutrient abatement measures (Sharpley et al. 2013, Powers et al. 2016, Bouwman et al. 2017, McCrackin et al. 2018).
At the same time, many countries have concerns about P depletion. The reported phosphate rock reserves on a global scale may be adequate for the current food production need (Cordell and White 2014). However, there are debates on the abundancy (Edixhoven et al. 2014), and stocks of phosphate rock on a local scale in many countries are insufficient for agricultural production. Besides the uneven distribution of phosphate rock throughout the world, its non-renewable nature and inefficient management increase the P depletion concern (Cordell et al. 2009, Cooper et al. 2011).
One key solution to these two P challenges is to improve P use efficiency (PUE) at cropland (Cordell and White 2014, Bouwman et al. 2017, Heuer et al. 2017, Lun et al. 2018). The goal of improving efficiency goes beyond increasing production through intensification or extensification. It also emphasizes better managing inputs to reduce the negative impacts of agriculture on the environment and society. Improving efficiency is the critical pathway towards synergies between agriculture productivity, sustainability, and resilience (Coomes et al. 2019).
Improvement in PUE relies on not only an understanding of P use patterns but also its key drivers. Previous studies have examined cropland P budget (P inputs and output at cropland) and use efficiency on different temporal and spatial scales (Cordell et al. 2009, MacDonald et al. 2011, Cordell and White 2014, Chen and Graedel 2016, Bouwman et al. 2017, Lu and Tian 2017, Lun et al. 2018, Mogollón et al. 2018). However, no studies have evaluated enough socio-economic and agronomic drivers influencing PUE, or quantifying the impacts of PUE improvement on addressing the two P challenges. Besides, global and regional priorities of P management are still unclear, which are critical information for decision-makers to develop effective strategies. To fill the research and political gaps, we (1) evaluated the historical patterns of P budget and PUE at cropland by country and crop type between 1961-2014; (2) identified key socio-economic and agronomic drivers influencing global and national PUE; and (3) suggested global and regional priorities for addressing P challenges by 2050.
2 Data and Methods