Oct 13, 2021 5:05 PM

YOUNKER: Cover crops in dryland cropping systems

Posted Oct 13, 2021 5:05 PM
Dale Younker 
Dale Younker 

By DALE YOUNKER
Natural Resources Conservation Service

One of the biggest concerns I hear about cover crops in dryland cropping systems is that they use moisture that is needed for the next cash crop. I will concede that cover crops use moisture, just like any living, growing green plant. But do they use any more moisture than what is typically lost during the fallow period anyway.

Research from USDA-ARS Great Plains Research Centers and Kansas State University Research and Extension show that only about 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, transpiration from weeds and deep percolation below the root zone. Based on those losses, a field that receives 20 inches of moisture during the fallow period will only gain about 5 inches of soil moisture for the next cash crop and 15 inches is just lost.

The question then becomes, can we grow a cover crop on the moisture we are losing anyway to help decrease evaporation, improve infiltration rates, increase water holding capacity and provide other soil health benefits? I believe that we can If the cover crop mix is properly designed, and planted and terminated timely

Millets are a good base for summer cover crop mixes planted into wheat stubble. These low water use, shallow rooted species grow and mature quickly once they are established. Because of the small seed size, they need be planted no more than about an inch deep. With the small seed size a few pounds go a long way in the mix, so they are very economical to use.

Adding a pound or two deep rooted species like radishes or sunflower will help break compaction layers that most cropped fields have. A legume, like sunn hemp, could also be added if allowed to grow long enough to fix nitrogen.

I prefer to plant these mixes as soon after harvest as soon as possible if there is enough soil moisture to get the seeds to geminate and come up. If not, the planting can be delayed up to mid-August. Most of these mixes are designed to die after a hard freeze but if conditions become dry, or if a large flush of volunteer wheat comes up, the cover crop should be terminated earlier to limit its moisture use.

I like planting cover crops in the fall, behind grain sorghum and corn if they can be planted prior to November 1st. Winter cereal grains like wheat, triticale, rye and barley provide a good base for these mixes. Adding a pound or two of turnips and radishes will help break up compaction layers. A legume, like winter peas, or a vetch, could be added to help fix some nitrogen.

After November 1st I would delay the planting until early spring and use oats as the base of the mix. If growing conditions are favorable, and the field is going to wheat the next fall, I would delay termination of these mixes to about the early heading stage. If another fall crop is going to be planted that spring, or If conditions become dry, you may want to terminate earlier.

Consider the economics when incorporating cover crops into you cropping system and figure your all your costs and returns. It takes money to establish a cover crop, but that cost may be offset with less spray and/or tillage passes during the fallow period. Other economic gains can be made by potentially grazing the cover crop and increased weed suppression.

We have several producers in western Kansas successfully incorporating cover crops in their fallow cropping systems. As a rule, their cash crop yields haven’t decreased and some years they have seen dramatic increases. The key to their success is paying attention to detail, using the right cover crop mix, and planting and terminating in a timely manner based on the weather and field conditions.

For more information about this or other soil health practices you can contact me at [email protected] or any local NRCS office.

Dale Younker is a soil health specialist with the USDA Natural Resources Conservation Service in Jetmore.