by Dr. Calvin Trostle, Extension Agronomy, TAMU Soil & Crop Sciences, Lubbock, (806) 723-8432, ctrostle@ag.tamu.edu

Producers across Texas are becoming more familiar with the concepts of cover cropping.  More farmers are asking about it, and some are trying cover cropping in some form.  Cover cropping across the U.S. and even in Texas takes many forms (Fig. 1).

Fig. 1. Cover crop combination mix drilled mid-August 2018, Mitchell Co., TX. Ample rains have occurred since planting. Sorghum/sudan + sudan at only 4.4% of a 20 lb. mix has generated substantial vertical growth. Rye* was 65% of the seed weight but is not prominent in the stand (hot conditions at planting for a cool-season grass?). Other species include cowpeas (a few are visible), hairy vetch,* rapeseed,* tillage radish,* buckwheat, sunflower, and flax. (*Anticipated to survive through the winter.)

In the Texas South Plains (general Lubbock region) we have over 1 million acres of cover cropping annually—the use of terminated rye or wheat to protect seedling cotton, mostly on irrigated (Fig. 2).

Fig. 2. Wheat planted on bed shoulders for eventual seedling cotton protection, Terry Co., Texas. Spring vertical growth will be terminated with glyphosate then cotton planted on top of the bed in the middle of the two wheat rows. The purpose is to control potential wind and blowing soil damage to fragile cotton seedlings.

Ironically, many cover crop advocates, likely from other areas, don’t view this terminated wheat system as a true cover crop (only one species, soil building not the purpose, etc.).  But it is.

Texas A&M Soil & Crop Sciences staff across the state are asked about cover crops on a regular basis.  Our answers vary widely depending on where we are located and the farmer’s goals.  For example, my reply to a typical question about cover cropping in the Texas High Plains, especially dryland (15-20” of annual rainfall) may differ considerably from my College Station colleagues, where rainfall is about double.  I am much more likely to be concerned about potential moisture use by a cover crop.

In fact, moisture loss is my primary concern for why cover cropping may NOT be a feasible endeavor for many producers, especially as you move further west across Texas.

Many claims about the potential benefits of cover crops need more data, especially long-term field trials of five years or more, to determine the pros and cons—and the economic impact—that cover crops might have.  There is certainly a major amount of observational conclusions and opinions about cover cropping and its effectiveness, and you will read about these in popular farm press or hear about them at numerous presentations on cover crops.  But being a member of a data-based educational institution, we in AgriLife don’t have a lot of Texas data to share with producers—yet.

Considerations Before you Implement Cover Cropping

Before you as a producer engage in cover cropping, especially if soil erosion protection is your goal, I urge you to consider two things:

• Can I achieve many of the benefits attributed to cover crops by instead by first focusing on reduction in tillage (no-till, strip till, reduced till)?
• Am I doing what I can to preserve the stubble and residues I have from my current cropping to address some of the same goals as cover cropping?

Changes in tillage can be difficult.  There are instances in West Texas where decreases in tillage have curtailed crop productivity to unacceptably low levels.  This doesn’t mean that tillage reduction can’t be done, but no-till/strip till/reduced till is not for everyone.  Some farmers are better at it than others.  Potential successes have included changes in equipment for strip-till or on the planter to allow you to plant into heavier residues or hard ground.  Also, some situations don’t lend themselves very well to some form of reduced tillage.  If you have tried tillage reduction but were not satisfied, ask yourself what you would do differently if you tried it again.  Do you have the right equipment?  Also, ask around for individuals in your region with similar soil type who use some form of reduced tillage for their “what works” ideas.

Here is a question I answered recently for a multi-state newsletter published in Kansas:

“Are we seeing any measurable improvement in the health of soils with cover crops?”

Writing from a Texas High Plains perspective, I replied:

• Limited data has been collected on most facets of cover cropping. Though I believe in time cover cropping will find a place in some cropping systems (overall available moisture a key factor), the very real concern among producers and university staff is the use of moisture by the cover crop in the overall cropping system especially in semi-arid regions.  “Can we afford the moisture use?”—whether we can or not (data needed!), we can not ignore the impact cover crops may have on moisture status.
• An emerging consensus among farmers and AgriLife Extension in the Texas South Plains and other similar drier regions is initial focus on cover cropping is not immediately soil health (defined in several different ways), but protection of the soil surface. This is especially important for wind erosion protection.  (Desired improvements in soil health attributes are dependent upon stopping wind erosion first.)

Desirable soil attributes that cover cropping can contribute to a cropping system include:

• Reduced soil erosion,
• Increased water infiltration rates and storage capacity,
• Gradual increase in soil organic matter,
• Better soil aggregation,
• Increased biological activity in the soil.

All of these are desirable attributes, and you can improve many of them to some degree with reduction in tillage and better utilization of any remaining crop residues after harvest.  I encourage Texas farmers to consider how they can leave more—or all—of their stubble on the surface.  Let the roots be what improves soil structure and increases stable long-term organic matter; and use the stubble to protect the soil surface from wind and water erosion.  But these above five bullet points will not occur until first the soil surface receives a blanket (residue, whether from your cash crop like wheat, grain sorghum, and corn and/or a cover crop) likely coupled with a reduction in tillage.

I add that for many farmers plowing in stubble at least partially is a long-time practice.  But conservation tillage guidelines have always sought to retain at least 30% stubble on the surface.  Thus, you are planting into a higher level of stubble.  For many producers the challenge is not as great as it seems—I believe an important consideration is how you might re-equip your planter to plant into more stubble (Fig. 3).

Fig. 3. Standard planter unit with no specialized equipment planting into thin sorghum/sudan stubble, Lubbock Co., TX. In this instance the disk openers are doing a good job of cutting the stubble as the furrow is opened for cotton planting. Heavier stubble might require use of the trash whipper disks to clear a narrow band for planting.

Fall Cover Cropping

Many Texas producers have already implemented some form of cover cropping for this fall and winter.  There is a wide range of planting dates.  Ground that does not have a current cash crop may have been seeded to a cover crop mix as far back as mid-August.  Other fall cover cropping will not occur until this year’s crop is harvested, which could as late as Thanksgiving in the northern and western part of the state.  This right away highlights potential differences in cover cropping.  Early planted covers may include a blend of warm-season species to get substantial growth before a freeze (the sorghum/sudan in Fig. 1), then the species that are cold tolerant take over.  Later-planted cover crops will focus only on cold hardy species that can germinate, establish, and provide some growth over the winter.

Here are some practical guidelines for cover crop selection, including how many species you might consider planting.

• What are your goals? Do you need to curtail potential wind erosion?  If so, significant biomass might be your greatest need.  If you simply would like to have some cover growing to potentially improve your soil, then biomass may not be a concern.  My observations and limited testing suggest that for winter biomass which leaves a higher amount of residues next spring, I like rye.  Some years rye seems to grow better than wheat (at least in west Texas dryland), and the root system of rye is often more aggressive than wheat.  {For summer cover cropping, if biomass is again the goal, then I like conventional (non-BMR) sorghum/sudan as the core component of a cover crop.}
• Any cover crop species you plant should be adapted to the region. This may be hard to tell in some cases.  Generally, I find most radishes and turnips, other brassicas (mustards, canola), hairy vetch, Austrian winter peas, and of course your cool-season small grains are adapted.  Some of these species like small seeded brassicas, however, only survive the winter if established a month or more before the first freezes.  I find that clovers are sensitive.  Other species like flax, buckwheat, etc. I recommend you ask your seed provider.  Other than the small grains some varieties of many species will winterkill though that can be reduced if seeded as part of a cover crop mix where something like the rye is providing protection to winter susceptible cover crop species.  If you are planting early enough then fall growth may be sufficient for some warm season species, and a freeze will terminate them (and stop their moisture use, too), while other species take over through the winter.  But for later planted cover crops species I would insist on ensuring each species is winter hardy.  Otherwise, why pay for it.
• Do I need a mixed-species cover crop, and if so how many species? Again, for winter cover crops, the small grains could stand alone as a cover crop (revisit Fig. 1).  For a mix, it seems like some groups have focused on cover crop species in multiples of four.  An eight-way cover crop mix, or possibly 12, and even 16.  I think some of these high number multi-species mixes are overkill for several reasons as they drive up costs, and more likely some of the mix species won’t grow well (also see below).  Perhaps these high-number cover crop mixes take a “shotgun approach” (even the seed is “pretty”, Fig. 3.) assuming that depending on the year, at least some of them will grow.  Some cover crop seed providers and NRCS staff suggest that up to five species is enough (for fall/winter, a cool-season grass, a legume (hairy vetch, Austrian winter pea?), a tuber brassica like a turnip or radish, a small-seeded brassica (mustard, rapeseed), and maybe one more species.  University soil microbiologists in the Texas High Plains agree that a basic cover crop mix will likely accomplish your objectives, and that soil biological activity does not appear to be significantly higher or more diverse past a few different established species in a cover crop mix.
  

  Fig. 4. Multi-species cover crop mix with about a dozed species. This may be a shotgun approach in that the many species will ensure that some will grow well depending on the conditions. The colorful seed with different sizes might also generate a feel-good approach to cover cropping.

In addition to cover crop species adaptation, here are some further considerations for simplifying cover crop multi-species mixes:

• If you are planting in a drier region where rainfall is less frequent, you may need to plant a cover crop mix 1.5” or even 2” deep to get established. Small seeded species like clovers, some brassicas, and other species may not emerge if planted too deep.
• Do you have a residual herbicide on the field? If so, that may eliminate the need to even consider planting some species if they likely won’t grow.  So, don’t spend the money on them.
• If you expect that weeds will become a problem in the field you are planting a cover crop mix in, will those weeds have time to go to seed (Fig. 5)? Would you possibly need to spray them?  If so, then that would eliminate susceptible cover crop species.  If this might be the case in your situation, then move away from potentially susceptible dover species in case you need to spray.
• Legumes by themselves can nicely diversify a cover crop mix.  But we cannot assume that root infection with the right N-fixing species-specific Rhizobium/Bradyrhizobium bacteria strain will occur.  They may not be present in the soil.  Or it is difficult to add an inoculant to the cover crop seed mix.  If an inoculant is used, I recommend a seed-applied inoculant already on the seed so that you do not have to deal with it (which most likely would be a seedbox powder inoculant, which AgriLife trials show are relatively ineffective at infecting and nodulating on numerous crops).
  

  Fig. 5. Dryland cover crop mix planted in mid-August 2018, Mitchell Co., TX. Along with the cover crops (visible in this image: sorghum/sudan, mustard, buckwheat, rye; there were six more seeded) is maturing pigweed seed. Avoiding pigweed going to seed is an important aspect of weed control, but to spray in this case for the pigweed would injure or eliminate most of the cover crop species

   

• Cover crop seed costs. How much is too much?  The economic value of the potential benefits may be found in your next cash crop as well as potential long-term improvements in your soil’s productivity (changes in aggregation, if tillage is reduced; wind erosion protection; soil biological activity and improved nutrient cycling; etc.)   But these are hard to quantify, at least on an annual basis.  Some cover crop mixes can exceed $40/acre.  I have a problem with that, especially in drier regions of Texas.  One farmer in the Lubbock region says he might be willing to try some cover crops, but he won’t pay more than $15/acre (irrigated) for seed.  A dryland Stanton Co. farmer showed me a prescription he received from an online cover crop seed planning tool which recommended a 12-species mix at $38/acre.  That is too much.

   Until data, practice, and experience demonstrates readily identifiable benefits to cover cropping, I recommend keeping cover crop seed costs down.  One idea I have—which colleagues agree might be a feasible approach to costs—is that cover crop seed costs should not exceed $1 per acre per each inch of average rainfall (+ irrigation, if used).  This limits cover crop seed costs in the drier western regions of Texas to no more than $16-18/acre.  With a limited amount of money that you would be willing to spend, what can you get in terms of pounds of cover crop species per acre?  If you want some biomass, you can get that for low cost using sorghum/sudan (~perhaps 5 lbs./acre) in the summer or rye/wheat in the winter (~10-20 lbs./acre).  What would you add to it?  If you are buying cover crop seed, factor in some of the considerations above, and then consult the seed supplier and get their “best bet” recommendation to give you a modest level of cover crop seed diversification for limited cost.

Consider this article as a guideline in your thinking on cover crops.  I encourage growers to tinker a bit and experiment.  But again, as noted earlier, don’t neglect consideration of how you might alter (reduce) tillage and make use of your existing crop residues to effect similar outcomes in your cropping.

Texas A&M AgriLife would like to learn from your experience and observations with cover cropping.  Contact your local and regional staff and let us know what you are doing.  The following Soil & Crop Sciences/Texas A&M AgriLife staff are some of the individuals who are working with cover crop research and educational programs.

Corpus Christi:  Dr. Joshua McGinty, jmcginty@tamu.edu, 361.265.9203

College Station:  Dr. Clark Neely (cool-season), cbneely@tamu.edu, 979.862.1412; Dr. Ron Schnell (warm-season), ronschnell@tamu.edu, 979.845.2935; Dr. Jake Mowrer, jake.mowrer@tamu.edu, 979.845.5366

Vernon:  Dr. Paul DeLaune, pbdelaune@ag.tamu.edu, 940.552.9941

San Angelo:  Dr. Reagan Noland, Reagan.noland@ag.tamu.edu, 325.653.4576

Lubbock:  Dr. Katie Lewis, katie.lewis@ag.tamu.edu; Dr. Wayne Keeling, wkeeling@ag.tamu.edu; Dr. Calvin Trostle, ctrostle@ag.tamu.edu; all at 806.746.6101

Amarillo:  Dr. Jourdan Bell, jourdan.bell@ag.tamu.edu, 806.677.5600

Inquire of your regional AgriLife staff about cover crop research and education in your area.  For the Texas South Plains consult https://lubbock.tamu.edu/cover-crops/