Quantification of phosphorus requirements of smallholder agriculture in tropical regions

Smallholder farms in the tropics can double their agricultural production by 2030 compared to 2015, according to a study to which José Mogollón (Institute of Environmental Sciences) contributed. But to achieve this, farmers need to increase phosphorus intake beyond what is currently expected. The study is published in Nature Sustainability.

Doubling smallholder agricultural production is one of the sub-goals of the Global Sustainable Development Goals, established by the United Nations in 2015. This requires that crops receive sufficient amounts of nutrients, including nitrogen and phosphorus are the most important. Nitrogen compounds available to plants can be produced from atmospheric nitrogen gas in unlimited quantities, but phosphorus is derived from rocks containing phosphate and global stocks are limited.

Revive depleted soils

In industrialized countries, phosphorus-based fertilizers have been used in profusion for decades, causing eutrophication of freshwater environments. But in many tropical countries with severely weathered soils, the situation is quite different. Fertilizers have hardly been used, soils are nutrient-poor and unproductive, and crop yields are below potential. Mogollón: “To increase production, farmers in these countries will have to increase the use of phosphorus-based fertilizers. And under realistic socio-economic scenarios, this is likely to happen. ‘

Together with colleagues, including scientists from the Netherlands Environmental Assessment Agency (PBL) and the University of Utrecht, he mapped to what extent phosphorus scarcity limits yields in tropical regions where there is mainly grows food crops and where smallholders dominate production. In addition, they studied how much phosphorus farmers would need to apply to meet the goal of doubling production by 2030.

José Mogollón: “We need to recycle phosphorus from waste and human urine.

More phosphorus is needed

When added to depleted soils, phosphorus binds to iron, aluminum, and clay minerals. After being fixed, it is less available to plants. Thus, the use of phosphorus will not fully translate into increased crop yields in the short term, but will also help saturate the soil.

Mogollón and his colleagues calculated that it is possible to overcome the phosphorus fixation process and achieve the goal of double production for the five regions studied: Sub-Saharan Africa, Middle East and North Africa, Central and South Asia. South, India and South Africa. -East Asia. But this possibility will not materialize when farmers continue on current trajectories. They need to increase their phosphorus use more than they anticipate.

Sub-Saharan Africa is the outlier

It is only in sub-Saharan Africa that the projected use of phosphorus is close to what is needed to double agricultural production. Mogollón: “In this region, phosphorus input and crop yields are low, so it is not very difficult to increase them. The researchers suggest that the goal of double production is too little ambitious for this region. It could be higher.

Important for recycling phosphorus

It can be difficult for developing countries to import the phosphorus they need, as prices are expected to be high in the coming months. Because China, one of the main producers of phosphorus, limits its exports. But not all the extra phosphorus has to come from rocks containing phosphate, said Mogollón: “It would be helpful to better recycle phosphorus from animal waste, food waste and also human urine. In a future with sustainable agriculture, this will certainly happen. ‘

Publication

Langhans, C., AHW Beusen, JM Mogollón & AF Bouwman, 2021. Phosphorus for Sustainable Development Goal targets to double the productivity of smallholders. Sustainability of Nature, November 22.

Text: Willy van Strien

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