When it comes to nutrient loss, no-till practices sometimes get the blame. But a study out of Iowa found that tillage also contributes to nutrient runoff.
The Iowa Soybean Association (ISA) and the University of Iowa’s IIHR—Hydroscience & Engineer college evaluated water monitoring data from Agriculture’s Clean Water Alliance, and the ISA On-Farm Network fertilization data collected from 1994-2014, and discovered that soil nitrates were immediately vulnerable to leaching following incorporation of soybean residue.
They say leaching potential was greatest when soil nitrates were readily available and plant uptake wasn’t available, especially in tiled fields. They found nitrates from incorporated soybean residue would remain susceptible to runoff so long as the ground was unfrozen to the depth of tile drainage.
It just goes to show that using tillage to incorporate residue or fertilizer doesn’t guarantee protection from nutrient runoff.
But that doesn’t mean no-till alone is the solution. Adding cover crops to your management system can help prevent nutrient runoff even further, experts say. According to the Iowa Nutrient Reduction Strategy, cover crops can reduce nitrogen (N) loss by 31% on average and phosphorus (P) loss by 29% on average.
Here are some species to consider if you’re looking to scavenge and retain nutrients:
- Annual ryegrass. Whatever residual N is in the field, annual ryegrass will take it up. You can have 60%-85% N returned to the following crop if it’s terminated before it’s jointing in the spring, says agronomist Mike Plumer.
- Cereal rye. This is another grass option for holding and returning N. The key to getting N back is to make sure it’s 10 inches tall or less when it's terminated, Plumer says. He explains that as it starts jointing, the plant becomes high in cellulose and lignin and requires a lot of N to break down.
- Winter wheat. University of Maryland research found that winter wheat seeded in September took up 40 pounds of N per acre by December. It can also scavenge and hold P and potassium (K) for the next crop.
- Sweet clover. Widely adapted to temperature and rainfall zones, this species of clover is credited with mining nutrients like K and P from deep in the soil profile, and the mycorrhizal fungi that surrounds its roots also increases P availability, says Dale Mutch, a retired Michigan State University Extension cover crop specialist.
For more information on these species and others that can protect nutrients, you can download our free eBook, “The Pluses and Minuses of Today’s Most Popular Cover Crops.” If you’re looking to take your cover crop program a step further, check out our new special report, “Covering Up, Part 3: Branching Out With Your Cover Crop Program.”