IN THE FIELD
PHOSPHORUS AND WATER QUALITY:
WHERE WE’VE BEEN AND WHERE WE’RE GOING It will take multiple practices and collaboration to protect our waterways from phosphorus runoff. by Ryan Heiderman
T
he agriculture community continuously adapts to fulfill the ever-growing desires and needs of society. This willingness to try innovative practices that protect soil and water resources, while maintaining the productive capacity of the land, is essential to sustainable agriculture. A thorough understanding of the complex interactions between nutrients, water, and plant growth is necessary to meet the growing environmental pressures placed on the farming community. According to the USDA Census of Agriculture, from 2007 to 2017, the amount of commercial phosphorus (P) fertilizer applied and manure P generated continued to increase in many states. At the same time, farm acreage was shrinking. Overapplication of P contributes to both economic inefficiencies and environmental concerns, including harmful algal blooms and eutrophication of water bodies. Although much effort has been put into conservation adoption and implementation to reduce the amount and impact of particulate P (moves with soil, Figure 1) lost from cropland, there continues to be issues with dissolved P (moves with water) entering waterways.
The impact of legacy phosphorus Buildup of P in fields, whether due to overapplication of manure, unrealistic 6 | Journal of Nutrient Management | May 2022
F3 6-8 May 2022 In the Field.indd 1
Figure 1: Phosphorus is found in two forms. Phosphorus loss mitigation strategies may vary based on the form needed to be addressed.
yield goals, or legacy accumulation of nutrients from fertilizers or manure, is causing negative impacts on streams, rivers, and lakes across the country. Accumulation of P in the surface soil is common in soils that receive surface applied fertilizer and manure. This accumulation, as indicated by high surface soil test results, can happen over years or even decades, and P can continue to mobilize even after additional inputs cease. The mobility of legacy P in the dissolved form can act as a long-term source to surface waters. This unused P, which can leave fields dissolved in runoff, not only degrades water features but also represents an economic loss to producers. Residual P can persist for many years with the only significant drawdown coming from crop removal at rates of 3 to 5 ppm per year, or worse, from runoff and soil loss. The impacts of this legacy P are visible even
after aggressive steps are taken to reduce P inputs and losses.
Long-term changes The National Oceanic and Atmospheric Administration’s (NOAA) National Climatic Data Center shows from long-term monitoring that Midwest states have seen a modest rise in both total precipitation and extreme precipitation events. With extreme precipitation events comes the potential for enhanced water runoff. The majority of annual nutrient and sediment runoff can occur during a few, or even just one, of these large events if proper precautions aren’t in place. Although Discovery Farms monitoring has seen extreme weather events occur, fields with appropriate conservation practices in place have been resistant to detrimental losses during these outlier events. Timing of these large precipitation events, and whether or not there is cover on the soil, will jofnm.com
5/12/22 12:00 PM
