Optimizing fertilizer use: challenges and solutions

Several factors influence crop productivity, and can be classified as biotic, related to living beings involved in the production process, as well as abiotic factors, among which climate, physics and soil fertility stand out. Of the latter, soil fertility is the most easily managed, and the use of fertilizers, soil conditioners and amendments to provide a better production environment is undeniable.

However, Brazil imports approximately 85% of the approximately 41 million tons of fertilizers it consumes annually. Among the essential macronutrients, we import 90% of nitrogen (Russia, China and the Middle East), 75% of phosphate (China, Morocco and Russia) and 90% of potassium (Belarus, Canada and Russia). It is worth noting that, fortunately, our main agricultural commodity, soybeans, does not depend on nitrogen fertilizer, a result obtained through intensive research into biological nitrogen fixation (BNF).

This external dependence, a matter of national security and sovereignty, is extremely uncomfortable for a player of our importance in global agriculture, mainly because a significant part of these fertilizers comes from politically unstable regions, which facilitates the action of speculators and has caused sudden increases in their prices.

Among the fertilizers consumed in larger quantities, phosphorus (P) and potassium (K) depend exclusively on mineral reserves, but nitrogen (N) can be obtained from natural gas or from a process that fixes atmospheric N, the latter with a large consumption of electrical energy.

It is important to highlight that this uncomfortable situation does not occur in relation to limestone (acidity corrector) and agricultural gypsum (soil conditioner), in which we are self-sufficient.

Actions to partially reverse this external dependence on fertilizers, aiming to reduce it to 50% by 2050, include prospecting for deposits, encouraging increased domestic production and addressing environmental and logistical issues, as detailed in the National Fertilizer Plan, prepared by an Interministerial Working Group, which recently had its goals revised. Also close to this line of action, we can mention the use of mineral or organic waste from industrial or agro-industrial chains as fertilizers, which also provides a tangible opportunity to reduce the generation of greenhouse gases and to recycle nutrients that would otherwise be destined for landfills.

Another approach to addressing this problem is to reduce the amount of fertilizer required, resulting from increased efficiency in the use of this input, without compromising productivity. It has been observed that after the advent of mineral fertilizers, the way crops are fertilized remained practically unchanged for decades: soluble sources of N, P and K are still applied to the soil, often with a low rate of utilization by crops. For example, it is estimated that only 50% of the nutrients applied are effectively utilized by plants, with losses due to fixation in the soil (P), leaching (N and K) and volatilization (N).

Fertilizer use efficiency

Increasing the efficiency of fertilizer use requires different strategies, the most commonly used being to synchronize the release of nutrients with crop development, so as to make them available as the plant cycle progresses, reaching maximum demand during the grain filling phase. The most notable example involves nitrogen, in which techniques are used to physically encapsulate fertilizer granules and/or use chemical or biochemical retardant substances, which is widely used with urea, the most common source of N on the market.

The most widely used natural source of P is phosphate rock (calcium phosphate), which must undergo acid treatment to increase its solubility in the soil. However, highly soluble forms, such as MAP (monoammonium phosphate), when applied to tropical clay soils, are subject to P fixation in oxides, quickly becoming unavailable to plants. As a result of this process, although our agricultural soils already have high levels of phosphorus due to the long history of fertilization, a significant portion of this element is not accessible to plants. To solve this problem, biological products have recently been developed that can make part of this phosphorus available, reducing the need for fertilizers.

The approaches mentioned above were obtained after years of Research, Development and Innovation (RD&I) by Embrapa, universities and other public and private research institutions and do not dispense with solutions that involve the use of more efficient plants, biostimulants and improvements in production systems. Just to give an example, the use of cover crops can reduce some of these nutrient loss processes by providing a cycle between the deeper layers and the soil surface, indicating that combined strategies can be more efficient for increasing fertilization efficiency.

Therefore, it is understood that to maintain the successful history of our agriculture, with consistent increases in productivity, constant advances in soil fertility and plant management technologies are necessary, providing greater efficiency, lower costs and less environmental impacts.

*Per Walder Antonio Gomes de Albuquerque Nunes e Adriana Marlene Moreno Pires, from Embrapa Agriculture West