Plant a cover crop to reduce your soil erosion

Tuesday, August 5, 2014

These past few springs, there have been too many areas where blowing soil occurred. This can be lessened with cover crops

by PAT LYNCH

The purpose of cover crops is to cover the soil so as to reduce erosion. They have come a long way in the last four or five years. You need a minimum of 30 per cent cover. The forage shortage three years ago was a great help in showing how we can grow crops in summer and fall. We grew those crops for forage and they also served as cover. But we have a way to go in Ontario, both in covering more acres and in how we handle cover crops.  

Soybean ground has the biggest potential for cover crops. Soybean stubble does nothing to cover the ground in the following spring, when soils are most vulnerable to erosion. On top of this, many soybean fields are worked in the fall after harvest. No one has shown any benefit to working soybean ground after harvest, but that is another discussion.  

Soybeans neither improve soil structure nor add organic matter. Some crops are positive or neutral for improving the soil, but soybeans are negative in both cases. Soybeans are a big negative for Ontario soils. In fact, the soybean crop is putting a lot of Ontario's soil at risk. This year we will have the biggest soybean crop ever in Ontario. The amount of soil that will be exposed next spring is phenomenal. If we can grow a cover crop after soybeans, this will help reduce the risk.

You can do something to make soybeans a less negative crop. You can plant a cover crop either into or after soybeans. You could also broadcast seed just before the leaves drop or seed right after harvest.

The first choice of cover crops after soybeans is a cereal. I like oats. They will produce top growth that will reduce erosion next spring. Seed is economical and oats do not have to be burnt off the following spring. They add root mass to help soil structure. And, according to Peter Johnson, cereal specialist at the Ontario Ministry of Agriculture, Food and Rural Affairs, oats do not generate as many cereal root diseases and other negative factors (for winter wheat) as does winter wheat, rye or winter barley.

If you are on lighter soils, the root problem associated with winter wheat or winter rye cereal is not as huge as on heavier soils. If you opt for winter rye cereal, you must burn it off early next spring. Many growers let it go too long and suffer a yield loss from the allelopathic effect of rye cereal. (Allelopathy is the term used to describe the harmful affect one plant has on another.)

Another option is seeding winter canola, which could be broadcast early in September. Canola likes to reach a certain stage in order to overwinter. But since you do not care if the canola overwinters, you just want the soil covered since growth quantity is not a big factor.

Looking at all these options would be a nice long-term project for either the Ontario Soil and Crop Improvement Association or for individual growers. One of the factors to measure is the effects of these various cover crops on long-term wheat yields.

Cover crops in corn are a waste of time. If you leave corn stalks on top of the ground, that is all the cover you need. Whether you no-till into this cover or use conservation tillage, the ground will be well covered.

In some places, attempts are being made to improve soil structure by interseeding grasses into corn. This is different. For most of Ontario, we don't need to do this.

Red clover is another option but there are problems with red clover. Often, there are areas in a field where the stand is less than 100 per cent. For those areas, seed oats immediately after wheat harvest. Growers have tried seeding crimson clover in August but, so far, the results have only been fair. Nonetheless, keep trying. Accounting for nitrogen credit in a variable stand is an issue. But generally you can see next spring where there was no red clover and you can add extra nitrogen to those areas.

Tillage of red clover is also a concern. There is no reason why you have to moldboard-plow a red clover cover crop. Conservation tillage is a good way to handle red clover. This year, at Canada's Outdoor Farm Show, there will be a massive demonstration showcasing conservation tillage to handle red clover.

These past few springs, there have been too many areas where blowing soil occurred. This can be lessened with cover crops. It's up to you to do something. Plant a cover crop. BF

Consulting agronomist Pat Lynch, CCA (ON) formerly worked with the Ontario agriculture ministry and with Cargill.