With a global population expected to reach nine billion people by 2050, improved management of key essential soil nutrients such as phosphorus will be necessary to boost crop yields and stay ahead of steeply rising food demand.
Studies suggest this could be a problem in U.S. Corn Belt states as the International Plant Nutrition Institute (IPNI) suggests phosphorus is being under-applied in rather significant portions of that region.
The lowest soil test phosphorus levels in North America are generally found in the Great Plains, but many farmers there are responding to that and slowly building those levels up by increasing phosphorus use relative to crop-removal rates.
Phosphorus is present as phosphate in every cell of our bodies. It is a nutrient required by all living things for basic life-sustaining processes, such as energy storage. Global supplies of phosphate are finite, and most of the largest phosphate reserves are in areas of the world that are prone to political instability, such as Africa and the Middle East.
The phosphorus situation is also challenged by many agricultural soils with insufficient levels of plant-available phosphorus, and some soils with a high capacity to fix applied phosphorus in slowly available forms due to reactions with calcium, magnesium, aluminum or iron. Crops grown in these soils are not able to obtain sufficient phosphorus to meet their needs and cannot reach their full yield potential.
If an applied rate of phosphorus is less than optimum for a crop under existing conditions, and a practice such as fertilizer placement is changed that increases nutrient use efficiency, yield will usually increase, at least in the short term. However, in other cases, nutrient-use efficiency can increase with no effect on yield if a rate exceeding optimum levels is reduced to optimum.
In such cases where soil fertility levels are less than optimum, an increase in phosphorus application rates is called for, even though that rate increase will likely reduce nutrient use efficiency. In other cases, the summary shows phosphorus is being over applied and use reductions would be appropriate and would increase nutrient use efficiency without reducing yield.
In contrast, states in the central and eastern Corn Belt generally have higher soil test phosphorus levels today than in the Great Plains, but soil levels are either stable or slowly declining due to application of less phosphorus than what is being removed by crops.
Farmers there have been to a degree living off phosphorus that was built up in their soils from past fertilization. In some cases in the same region, phosphorus levels were higher than the optimum range, and they are now moving down into the optimum range, which is good for both economic and water quality reasons.
“The key to producing higher yields and feeding the growing world population is not simply applying more fertilizer, as one might think,” said Kenneth Avery, chief executive officer at Verdesian Life Sciences. “Rather, it is finding sustainable solutions for nutrients such as phosphorus to be used more efficiently and effectively to produce more food.”
“Increased plant uptake of phosphorus translates into less of that nutrient being left in the soil, where it is subject to off-site movement into waterways,” Avery said. “It also allows farmers to be good stewards of the land and help minimize the environmental footprint left by phosphorus applications.”
Unlike nitrogen, which is subject to a great amount of movement within the soil, air and water, phosphorus generally stays put once applied.
The biggest quantity of phosphorus loss is usually by soil erosion. If phosphorus sources like fertilizer or manure are left on the soil surface without enough time for retention or if the soil surface is over-enriched in phosphorus, the soluble phosphorus lost in run-off can contribute significantly to water quality problems.