We as a society base a lot of our decisions on the numbers that support whether to adopt or reject our choices in life. When it comes to using cover crops in our cropping systems the numbers are growing. The largest number to support the adaptation of cover crops is 5,840 square miles. That number is the area in the Gulf of Mexico where shrimp and fish can’t live because the oxygen level is less than 2 parts per million. But why is the oxygen level so low? What’s happening is that excess nutrients in the form of nitrogen and phosphorus wash off of fields and enter the Gulf via the Mississippi River, which leads to hypoxia. Hypoxia occurs as a result of nutrient overload in the waters stimulating the excess growth of algae and phytoplankton. So much phytoplankton is produced that it can’t all be consumed, and it sinks to the bottom where bacteria decompose the remains and deplete the oxygen. This imbalance in the aquatic ecosystem now forms a “Dead Zone.” If you need oxygen to live and it’s no longer there, you suffocate and die, hence the name. The solution to the Dead Zone flows right back up the Mississippi River.
How can we reduce the runoff of excess nutrients and still produce enough food? The numbers that support cover crops might play a significant role in that reduction. When it comes to nitrogen, many fall planted cover crops reduce nitrogen loss by up to 60%. A late summer drilled radish with a grass cover crop can take up 120 pounds of nitrogen, preventing it from leaching, and hold on to it until spring. A well-established annual ryegrass can recapture up to 100 pounds of nitrogen after a corn harvest. Not only will crimson clover produce somewhere between 70 and 140 units of nitrogen, (with approximately ½ of that being available for the next crop), the rest is being used to build new organic matter. A 1% increase in soil organic matter can increase the water holding capacity by over 26,000 gallons per acre. Phosphorus loss is closely related to soil erosion moving off the field. Using cover crops with no-till will cut soil erosion by 90% compared to conventional tillage without cover crops. Fall cover crop establishment alone will reduce phosphorus loss by up to 60%. To put that reduction of phosphorus run-off into perspective, 1 pound of phosphorus can create 500 pounds of algae.
Cover crops increase nutrient uptake 10% over conventional cropping systems alone. There are many other benefits of cover crops as well, such as weed suppression and being a livestock feed source. You don’t have to start cover crops with a high management cover crop mix. Oats and radish broadcasted into standing corn or soybeans just before harvest or planted similar to a wheat crop would be a great start with no termination needed in the spring. However, more advanced cover crop mixes will add more conservation cropping benefits in your long-term farming operation. Adding wheat to your crop rotation opens another window of cover crop benefits. To maximize these benefits you need to think no-till or strip-till to reap all the potential that good soil health has to offer. The numbers that support the adaptation of cover crops might just be the best chance for the resurrection of the Gulf of Mexico’s Dead Zone, and in preserving our own soils close to home.
By: Woody Woodruff