Subsurface Phosphorus Placement Could Help Improve Water Quality
eKonomics News Team
There continues to be a growing concern about the impact of production agriculture and phosphorus fertilization on water quality. Phosphorus enrichment of water bodies have been blamed for algal blooms in Lake Erie. Many states in the Midwest have discussed nutrient management strategies to reduce the amount of P lost to surface waters.
“The dissolved form of phosphorus has the largest direct impact as a causal factor for harmful algal blooms,” said Dr. Tom Bruulsema, Vice President Americas and Research at the International Plant Nutrition Institute (IPNI).
Two factors that have been identified to contribute to eutrophication – nutrient enrichment of a water body – are fertilizer source and placement. There are as many as 20 potential causes for the increased soluble P finding its way into Lake Erie (Smith et al., 2015).
Considering the 4 R’s: Placement and Source Research
Several decades of phosphorus fertilizer placement research have been conducted throughout North America. Researchers have found less dissolved phosphate in runoff water when fertilizer is applied below the soil surface as opposed to surface broadcast.
Dr. Douglas Smith, a soil scientist at the Agricultural Research Service (ARS) Grassland, Soil and Water Research Laboratory in Temple, Texas, conducted phosphorus fertilizer placement research in the Western Lake Erie Basin region.
In 2015, Smith conducted an experiment to measure soluble P concentrations in water following various fertilizer application methods. Smith lined runoff boxes with landscape fabric and placed soil in them. He then simulated rainfall events. The amount of soluble P was collected and measured from each treatment.
Smith found P loss decreased when dry, granular monoammonium phosphate (MAP) were banded in the soil compared with surface application. The banded placement of MAP decreased soluble P loss by 98 percent.
When liquid ammonium polyphosphate (APP) was applied to the soil surface and banded subsurface, there were no differences in soluble P loss. However, the amount of P lost from APP application was significantly less than dry applications of MAP.
One way to combat these negative environmental effects is by placing P fertilizer below the soil surface. Placing liquid or dry fertilizers just a centimeter below the soil surface can dramatically decrease their loss potential (Smith et al., 2016). This translates into improved water quality and higher plant P availability.
The findings from these studies are leading to one conclusion: “Farmers and fertilizer applicators should use phosphorus placement as a way to reduce dissolved phosphorus in the water supply,” said Bruulsema.
In the spring of 2017, Bruulsema compiled an Issue Review on the 4R Phosphorus Management Practices. The publication discussed what placement farmers should use to decrease the chances of negative environmental impacts while supporting high crop yields. All of the cropping systems in the article recommend banding or incorporating phosphorus fertilizer in the soil as a way to improve water quality.
“In addition to improving water quality, subsurface phosphorus placement can produce higher yields in some soils,” Bruulsema said. “For soils testing above the optimum test level, phosphorus applied in a band near the seed can assure the fertilizer does not limit yields.”
With the research to back them up, Bruulsema said farmers can be confident that subsurface phosphorus placement can be used with the right source to improve water quality and potentially boost yields with greater plant P availability.