For years, growers in northwest Ohio have battled claims that farm runoff of phosphorus (P) is the cause of the extensive algae blooms that develop most years during the summer months in western Lake Erie.
These concerns are becoming more serious as Ohio voters earlier this year approved a Bill of Rights for Lake Erie, which allows citizens to sue on behalf of the lake when this large body of water is in danger of being harmed.
Considerable no-till is done in the areas around Toledo, where rivers and streams flow into Lake Erie. While no-till and cover crops have helped reduce erosion and runoff, there are still serious concerns about the impact P is having on expansion of the lake’s algae blooms, which more than tripled in size in 2018 when compared with previous years.
Need More Than No-Till
Since P is tied to soil particles, there’s a belief among many educators that no-till is an excellent way to reduce P loss in lakes and streams.
As reported in an article on the Corn & Soybean Digest website, a comprehensive analysis of 85 research studies conducted between 1985 and 2016 indicated no-till needs to be combined with other conservation strategies such as cover crops to overcome the growing concerns with increased amounts of dissolved P.
Three researchers on the Indiana University-Purdue University Indianapolis staff — Pierre-Andre Jacinthe, Lixin Wang and Stefani Daryanto — reviewed those studies, \which delved into soluble and particulate P concentration losses. These studies directly compared no-till with more intensive tillage such as discing, chiseling, and moldboard plowing.
While the analysis indicated that particulate P loss is significantly less with no-till, researchers found the amount of dissolved P actually increases due to increased water infiltration and leaching. This is happening even though no-till is credited with dramatically reducing soil erosion and runoff when compared with more intensive tillage practices.
The researchers found no-till significantly reduced both the load and concentration of particulate P, as well as the total amount of P transferred to lakes and streams. But unfortunately, no-till led to higher concentrations and loads of dissolved P, especially during wet years.
While the results varied with climate, rainfall, topography, crop species and the number of years of reduced tillage, no-till was most effective at reducing particulate P loss on less than 3% slopes. While steeper slopes produced similar concentrations of dissolved P with all tillage systems, no-till produced a much larger dissolved P load.
Water Quality Benefits
When it comes to improving water quality, the reduction in concentration and load of particulate P may be among the most important water quality benefits of no-till.
Even so, these positive impacts are often offset by increased dissolved P loads in long-term no-tilled fields. It’s because these long-term no-tilled soils may contain higher soil organic matter content, retain more soil moisture and have a larger and more active community of soil microbes. While these are certainly positive impacts for soil, they can lead to higher P mineralization and higher dissolved P concentrations with no-till.
No-Till Nitrate Worries
When the scientists looked at nitrate concentrations with no-till, the results were not good for improving water quality. While no-till increases infiltration, which is important for reducing erosion and runoff, nitrate losses due to underground leaching were higher with no-till than with the use of more intensive tillage practices.
The change in nitrate loading in runoff from conventional tillage to no-till ranged from a slight increase to as much as a 35% reduction. Unfortunately, loading due to leaching increased by 3% to 22% with no-till.
What’s the Answer?
While most growers believe no-till is good for water quality since it reduces erosion and fertilizer runoff, it’s much more complicated when it comes to tackling nitrate and P concerns.
Since no-till definitely reduces concerns with P and nitrates in areas such as western Lake Erie, the Indiana researchers recommend combining no-till with other conservation management practices — including cover crops to scavenge residual P, intercropping, using reduced or split nitrogen applications, injecting rather than broadcasting fertilizer and rotating perennial crops with no-tilled corn, soybeans and wheat.
Stakeholders in agriculture, especially those working in target watersheds such as Lake Erie, must continue to focus on encouraging cover crops and pushing further use of no-till. Not only will this help growers remain profitable, it will let the general public continue to enjoy our lakes, rivers and streams.