Improving soil fertility

Advancing food security and environmental sustainability in farming systems requires an integrated soil fertility management approach that maximizes crop production while minimizing the mining of soil nutrient reserves and the degradation of the physical and chemical properties of soil that can lead to land degradation, including soil erosion. Such soil fertility management practices include the use of fertilizers, organic inputs, crop rotation with legumes and the use of improved germplasm, combined with the knowledge on how to adapt these practices to local conditions.

The Joint FAO/IAEA Division assists Member States in developing and adopting nuclear-based technologies for improving soil fertility practices, thereby supporting the intensification of crop production and the preservation of natural resources.

An integrated soil fertility management aims at maximizing the efficiency of the agronomic use of nutrients and improving crop productivity. This can be achieved through the use of grain legumes, which enhance soil fertility through biological nitrogen fixation, and the application of chemical fertilizers.

Whether grown as pulses for grain, as green manure, as pastures or as the tree components of agro-forestry systems, a key value of leguminous crops lies in their ability to fix atmospheric nitrogen, which helps reduce the use of commercial nitrogen fertilizer and enhances soil fertility. Nitrogen-fixing legumes are the basis for sustainable farming systems that incorporate integrated nutrient management. Use of nitrogen-15 lends understanding of the dynamics and interactions between various pools in agricultural systems, including nitrogen fixation by legumes and utilization of soil and fertilizer nitrogen by crops, both in sole and mixed cropping systems.

Soil fertility can be further improved by incorporating cover crops that add organic matter to the soil, which leads to improved soil structure and promotes a healthy, fertile soil; by using green manure or growing legumes to fix nitrogen from the air through the process of biological nitrogen fixation; by micro-dose fertilizer applications, to replenish losses through plant uptake and other processes; and by minimizing losses through leaching below the crop rooting zone by improved water and nutrient application.

The isotopes of nitrogen-15 and phosphorous-32 are used to trace the movements of labelled nitrogen and phosphorous fertilizers in soils, crops and water, providing quantitative data on the efficiency of use, movement, residual effects and transformation of these fertilizers. Such information is valuable in the design of improved fertilizer application strategies. The nitrogen-15 isotopic technique is also used to quantify the amount of nitrogen fixed from the atmosphere through biological nitrogen fixation by leguminous crops.

The carbon-13 isotope signature helps quantify crop residue incorporation for soil stabilization and fertility enhancement. This technique can also assess the effects of conservation measures, such as crop residue incorporation on soil moisture and soil quality. This information allows the identification of the origin and relative contribution of different types of crops to soil organic matter.