Just about anytime I start talking about cover crops to a dryland farmer in western Kansas one of the first things I hear back from them is "we’re too dry for cover crops, I need to fallow to have enough moisture for the next cash crop".
Yes, fallow typically will provide some additional soil moisture for the next crop, but how much?
Research from USDA-ARS Great Plains Research Centers and Kansas State University Research and Extension show that on an average only 25% of the moisture received during a fallow period is captured and stored in the soil.
This varies depending on the type and amount of tillage done, weather conditions, soil type and so on.
The rest is lost through runoff, evaporation from the soil surface, transpiration from weeds and possible deep percolation below the root zone.
If we think about that a little bit, if a fallow field receives 20-inches of moisture, we only save 5-inches for the next cash crop and 15-inches is just lost.
The question then becomes can we grow a cover crop that will provide many soil health benefits, including less soil water evaporation, higher water infiltration, better water holding capacity and weed suppression on only the moisture that would have been lost anyway? I believe that we can, if the cover crop mix is properly designed and planted and terminated timely.
For a summer cover crop mix planted into wheat stubble I usually use low water low water use species, like millets, as the base of the mix.
They are very shallow rooted and grow and mature quickly once they are established. Because of the small seed size, they shouldn’t be planted more than about an inch deep.
Since the seed is small a few pounds go a long way in the mix, so they are very economical to use in a mix. I would also add one or two deep rooted species like radishes or sunflower. They are good at braking up compaction layers that almost all crop fields have.
A legume, like sunn hemp, could also be added if allowed to grow up to flowering stage so they have time to fix nitrogen. I prefer to plant these mixes as soon after harvest as possible if soil moisture is available to get the seeds to geminate and come up.
If not, the planting could be delayed up to mid-August.
Most of these mixes are designed to frost terminate but if conditions are dry in the early fall, I would recommend the cover crop be terminated early to limit its moisture use.
For cover crop mixes that would be planted after milo or corn. If the crop is harvested early enough and the cover could be planted prior to October 15th I would go ahead and get it in the ground.
Winter cereal grains like wheat, triticale, rye and barley would make up the base of the mix. I would also some turnips and radishes to help break up some compaction layers.
A legume, like winter peas, could be used to fix some nitrogen. If the mix can’t be planted prior to Oct. 15 I would delay the planting until early spring from mid-February to Mid-March and use oats as the base of the mix.
If growing conditions are favorable, I would delay termination of these mixes until the cereal grain is fully headed. If conditions become dry termination should be earlier.
Economics needs to be considered in any cropping decision. If you are thinking about incorporating cover crops into you cropping system push the pencil and figure your all your costs and returns.
It will cost money to establish a cover crop but most, if not all that cost, may be offset by less spray and/or tillage passes that you typically have during that fallow period.
Other economic gains can be made by potentially grazing the cover crop and the weed suppression that the cover crop provides.
Over time improving infiltration rates and increasing organic matter will also provide some economic benefit.
We have several producers in western Kansas planting cover crops in the fallow cropping systems and they have been very successful. As a rule, their cash crop yields haven’t decreased and some years they have had dramatic increases.
The key to their success is paying attention to detail, planting the right cover crop species and planting and terminating in a timely manner based on the weather and field conditions.