Winter Cover Crop Blends for Cotton Fields

Cotton Incorporated and the Missouri State Support Committee funded two experiments designed to provide information to farmers for  improving soil health in cotton fields.  The first study compares pure stands of winter cover crops to “cocktail” mixtures of cover crops on sandy at the MU Rhodes Farm and silt loam soils at the MU Lee Farm.  Test fields were bedded in the fall after cotton harvest and cover crops drill in the row middles. We are studying wheat, cereal rye, Austrian winter peas, crimson clover, tillage radishes and rapeseed.

Crimson clover mixed with winter wheat. 
Austrian winter peas mixed with cereal rye.
Austrian winter peas mixed with cereal rye.
Rapeseed mixed with cereal rye.
Rapeseed mixed with cereal rye.
Winter wheat, crimson cover and tillage radish blend.
Winter wheat, crimson cover and radishes.


Cotton yield increases from planting wheat in row middles to reduce blowing sand was reported in early studies at the Delta Center. The yield response varies from year to year depending on the severity of spring wind storms. In the last two years, we have not found a significant yield increase from using winter crops but numerically the highest yields compared to no cover controls have been with multiple cover crop blends.  The carbon:nitrogen ratio of the residue is reduced by mixing a legume such as crimson clover or Austrian winter peas with wheat or rye. This blend promotes mineralization rather than immobilization of N when the microbes decompose the residue.  It is a better diet for the microbes and ultimately the cotton plants. 

Blends versus Pure. One of the challenges of blends is knowing how much grass to mix with the legumes.  If too much wheat or rye is added to the blend, they may choke the legumes out. However, this is not a great concern. In cold winters, we observed that the grasses actually reduce winter kill in the legumes.  Cost is the biggest factor.  Since legumes seeds are expensive relative to grasses often the blend ratios are a economic decision.  

Solid versus Middles. In the fall,  farmers must decide whether to plant winter cover crops solid over the cotton rows or just in the row middles.  Pros and cons exist for selecting both systems.  The added mulch from planting cover crops solid helps suppress herbicide resistant weeds such as Mare’s tail and Palmer pigweed.  However, depending on spring rainfall, the solid cover crops deplete the moisture in the cotton seed bed and possibly delay cotton seed germination.  If you have center pivot irrigation be prepared to irrigate early if you broadcast cover crops across the cotton rows.

Termination Timing. Another decision that will be made in the spring is when to terminate the winter cover crop.  Before the Palmer pigweed problem developed less than 10 years ago, we always waited until after wheat stems jointed to allow the straw to develop enough stiffness to avoid a “melt down” .  But now some new pre-emergence herbicides have to be applied weeks in advance of cotton planting to avoid injury.   Crimson clover and Austrian winter peas produce most of the growth in a short time in early April.  Killing them early defeats the proposed of growth them in the first place. This is a challenge that I have not found a good solution.

Winter Kill.  In one out of four years, winter kill is a major problem with cover crops especially on the northern edge of cotton production. In 2013, we had a late cotton harvest due to below average temperatures.  This, in turn, resulted in late crop crop planting.  Coupled with a brutal winter, we had a weak stand of clover, peas, radishes, and rapeseed in the spring.  We might have been able to avoid this by flying on the seed before the cotton mature to give the cover crops time to establish before the winter freeze.   The downside of flying on seeds is that applying by airplane adds more cost.  Also broadcasting results in less soil to seed contact compared to a drill.

Crop Wind Protection

Matthew Rhine, research associate, has worked on the Cropping System project with Gene Stevens at the Delta Center for 10 years.

In the 1990’s, research at the University of Missouri-Delta Center at Portageville showed significant cotton yield increases from planting wheat cover crops in the row middles for wind protection (Stevens, et al, 1996).  Cover crops protect cotton seedlings from blowing sand and minimize replanting. The objective of our current study is to evaluate mixtures of cover crops including radishes and cereal rye for increasing rainfall and irrigation infiltration, enhancing nutrient availability, and reducing root knot nematodes.

Field trials at Portageville and Clarkton showed that achieving a clover stand and keeping it through a cold winter is easier on silt loam than on sandy soils.  Seedling survival was improved when clover was mixed with wheat. Generally, vetch was more winter hardy than clover.  On large-scale strip tests at Clarkton over three years, cotton with 40 lb N/acre after vetch cover crop was compared to cotton with100 lb N/acre after wheat. Each year, cotton yields were either higher or the same using vetch with 60% less N fertilizer.  However, vetch is difficult to kill and is a problem weed in wheat fields.

The Natural Resource Conservation Service is promoting soil quality programs with “cocktail” mixtures of cover crops.  The idea is to have some type of live root growing in the soil 12 months a year to provide uninterrupted favorable conditions for symbiotic fungi such as mycorrhiza and predators to nematodes. Widmer et al. (2002) summarized research on cover crops and soil health management to reduce plant-parasitic nematodes. Myers (2002) cited anecdotal evidence that compounds in canola residue suppress nematode growth. Canola is in the mustard family with turnips and radishes. In Burleigh County, North Dakota, farmers plant a mixture of cover crops for grazing and hay rotated in alternate years with row crops such as corn.   By minimizing soil disturbance with conservation tillage, farmers have created a healthy environment for microorganisms and earthworms.  Beneficial fungi also help with crop phosphorus uptake and nematode control. The mucous secretions from the soil organisms increase soil aggregate stability which helps rainfall percolation and reduces runoff. Over the long-term, the farmers are using less fertilizer.

This project is evaluating new crop cover management practices. In North Carolina, boot growth stage cereal rye was killed without herbicide by snapping the stalk with a roller.  Small seeded weeds such as pigweed often require light to sprout. The thick matt of rye residue laying on the soil surface helps prevent their germination. Radishes may be good cover crop for helping P uptake in cotton. It is easy to kill and produces good fall growth.  White and Weil (2011) found that available soil P is concentrated in soil surrounding radish holes left by decaying taproot roots. In Northeast Missouri radishes are being used in corn/soybean rotations.

We learned from past cover crops tests that small plots do not provide a good evaluation of the effects of wind protection.  Often “upwind” cover crop treatments have as much effect on the cotton seedling as the cover in the actual plot.

Plan of Work

Research is being conducted on sandy soil at Clarkton Missouri at the MU Rhodes Farm.  Cover crop seeds were broadcast in September before cotton defoliation  in wide strips across two ranges with the rows running with the prevailing southwest wind. A smaller test with radishes will be conducted beginning next fall on range which has high root knot nematode levels. Background and seasonal soil quality parameters will be measured for organic matter content, aggregate stability, water infiltration, soil CO2 respiration, bulk density, and residue cover. Soil pH, N, P, K and micronutrients and earthworms and nematode eggs will also be sampled.  Cover crops will include wheat, Abruzzi rye, crimson clover, rapeseed, tillage radishes, and Austrian winter peas. Some rye plots will be rolled and some left standing before planting cotton.   Strips will be maintained in the same location over the life of the study. Cotton plant population, growth stage dates, and yield will be recorded for each treatment.

Field Notes on March 20, 2012

Rainfall was low in September and October 2011 when we established the cover crops. This was our first experience with Austrian winter peas as a winter legume crop.  Pea seeds are much larger in size than clover.  They sprouted on the soil surface after a light rain but  had a difficult time rooting into the dry soil.  Ideally, they should be planted into the soil and covered rather than broadcast.  But, to our surprise, the winter peas produced a better stand with more growth than crimson clover. Plant height of the peas is 3 to 10 inches and clover is 1 to 3 inches. 

The winter of 2011/12 had above normal temperatures which probably helped the winter peas (left). Mid March is a rapid growth stage for winter cover crops.  The closer that we wait to kill the peas with burndown herbicides the more N they will fix from the atmosphere. But they will pull more moisture from the soil which may inhibit cotton seed germination.  Another potential problem is the vines on the pea plants could wrap around the planter row cleaners.

There is significant variability within plots in the stands of tillage radishes and rapeseed plants. Both brassica (mustard) species are flowering now.  The radishes are 3 to 24 inches tall and the rapeseed is 3 to 38 inches tall. Although the radishes have long roots, part of the tap roots are above the soil surface and will not help loosen the subsoil.











The radishes roots that we cut with knives were hollow in the centers. We don’t know it this was caused by a pest or is normal for the crops. The above ground foliage looked healthy.


Some radish roots are completely dead in the middle of  and others just had necrosis in the centers of the roots.



No nitrogen fertilizer has been applied to the cover crops other than residual N from last year’s cotton crop.  Abruzzi rye is hardier and producing more biomass than the winter wheat.  The rye is 7 to 32 inches tall versus wheat that is 4 to 9 inches tall.

In a multi-species cover crop mixture, domination of the grass crop at the expense of legumes and mustards may not be a good thing. Peas produce vines and can climb on rye or wheat which clover cannot do.  We had a hard time finding the small clover crops in mixtures with grass species.

 Austrian winter peas growing with Abruzzi rye.

Crimson clover, wheat, rapeseed mixture.

Because of the large, open fields, cotton farmers typically plow as little as possible to prevent loose soil from blowing in the spring. Ridge-tillage is a common practice.  To improve drainage and soil temperature in the seed furrow, fields are typically hipped (rebedded) in the fall when wheat cover crop seeds are broadcast. In the current test, we not disturb the  beds in the fall from the 2011 season.  This helped promote a natural stand of henbit cover in our untreated check plots. We are looking at alternative management practices that will keep the height of the beds by running strip tillage equipment at planting or light cultivation in the row middles during the season.


Stevens, G., B. Phipps, and J. Mobley. 1996. Managing cotton for reduced wind damage with ridge till systems. In P. Dugger and D.A. Richter (ed.) Soil Management and Plant Nutrition Conf., Proc. Beltwide Conf., Vol. 2, p. 1403-1405. Nashville, TN, Jan 9-12, Natl. Cotton Council, Memphis, TN.

Myers, R. 2002. Canola-an emerging oilseed alternative. Jefferson Institute. Columbia, MO

White, C. and R. Weil. 2011. Forage radish cover crops increase soil test phosphours surrounding radish holes. Soil Sci. Society of America 75:121-130.

Widmer, T. N. Mitkowski, and G.S. Abawi. 2002. Soil organic matter and management of plant-parasitic nematodes.  J. Nematology 34:289-295.


Soil moisture and rice roots


One of the fun parts of working at Ukulima Farm in South Africa is the exchange of ideas between the research partners. Claire Lorts and Larry York, PhD grad students from the Penn State University Root Lab, went the extra mile and offered to sample and examine rice roots from our small plot rice variety test. Their advisers are Kathleen Brown and Jonathan Lynch. Information about the PSU root lab can be found at Shown with me, left to right, collecting root core samples in the rice plots are students Jacob Mtladi, Rodney Managa, Claire Lorts (holding hammer), and Tsitso Mokoena.  .

Sprinkler irrigation was applied during the season based on ET calculations except in early January when a supply line broke between the pump at the river and the center pivot.  Several days were required to find the location of the break and fix the pipe. During that time (Jan 2 to 14), soil moisture in the 0 to 20 cm depth became very dry causing many small tillers to turn brown and die on the rice plants.

Although this was unfortunate for the overall rice yields, it gave us an unexpected opportunity to see which rice varieties had the least damage from water stress. The variety showing the least visual above ground plant stress was Cardi 70-3 from Cambodia.

The Penn State root scientists  used a technique called “shovelomics”  which is the act of digging up roots and phenotyping them. Shown below are root balls from healthy rice plant (top) compared to a plant variety that showed severe vegetative water stress (bottom).

Also, evaluated by the root biologists was the angle of the roots.  Generally, plants with roots growing in a downward angle extract soil water deeper and withstand short term periods without water better than plants with shallow roots.




Below are preliminary results from the plant and root measurements and rice grain yields in the small plot variety test.  Rice is normally flood irrigation. These lines were identified from aerobic screening research in Texas and Missouri as possibly being able to withstand water stress better than other rice varieties.  Values for tillers and roots are numbers per plant.

  • Rice variety            # tillers       #roots    yield, bu/acre
  • Best 2000                   8.0          133          12
  • Cirad 141                   9.8           187          15
  • Nerica 6                      6.0          181           33
  • Zhe 733                       9.3         196            20
  • Wells/Nerica 4           10.5         175           53
  • IAC 201                      9.3           160           30
  • Cardi 70-3                  6.0           117           79
  • Nerica 4                     9.8           189           52

We observed “hollow” areas in the center of root balls that were caused either by a “die off” of roots in  due to water stress in early January or that some rice varieties just naturally stop growing new roots in the parent plant in the center when tillering begins.  The root diameter measurements are still being processed.

Cardi 70-3 had the least number of tillers and roots per plant, but produced the highest grain yield.  This is the opposite of what one might expect. Perhaps this variety partitioned more energy into growing fewer but larger roots to grow deeper in the soil. Shown below are photos of Larry York and Dominik Mtladi scanning rice roots to evaluate diameter and branching.

Rice Harvest at Ukulima Farm

Below are photos from the rice harvest last week at the Ukulima Farm in South Africa.

Soil differences and slope in the field had a greater impact on rice yields than our irrigation rate treatments.  The test field drains to the center from the north and south ends. The highest rice yields were recorded in the test blocks in the middle.

Cropping history was also an important factor in rice yields across the field.  One half of the field was fallowed in the previous growing season and the other half was planted in corn.  Rice grew more vigorous and competed with weeds better where we did not have corn last year.

Weed control was satisfactory but not perfect.  In areas where corn was grown in 2010/11, rice plants produced fewer tillers and weeds began to emerge at mid season.

Most of the rice irrigation treatment plots produced 40 to 50 bushels per acre.  But a “bell ringer” four acre block in the center of the field averaged more than 90 bushels per acre.

Most farmers in South Africa are not familiar with rice production. The total amount of rice harvested and loaded into the bin for storage was 1,215 bushels.

We planted an area of the field cirlce in cowpeas as a legume rotation crop for rice next year.  The field workers on the farm were allowed to pick the peas and take them home for their families.

Rice Heading

Most of the rice in the irrigation experiment is at the boot stage or is already heading. Some parts of the field are maturity faster than other areas. The variety is Nerica 4 from AfricaRice  in Benin.

This is one of places in the field that the rice has already headed.

Another view of the rice field at Ukulima Farm in South Africa.

Progress on South Africa Rice Research

It is the last half of the rice growing season in South Africa. I came here for 10 days in October with Matt Rhine, and Jim Heiser to help plant rice under Pivot 8 at the Ukulima Farm near Alma in the Limpopo Province.  Matt and Jim stayed and worked with the farm crew to fertilize and apply herbicides for weed control.  When Matt left before Christmas, he observed that a few of the rice plants were in the early stage of reproduction called internode elongation .  Earl Vories came and worked until the second week of January and now my wife and I are here until mid-March.

We still do not have propanil and quinclorac rice herbicides. But, with the help of the farm manager, we were able to find alternative chemicals this year which are used on other crops in South Africa.  I am finding small wandering jew and nutsedge plants between the row drills and in areas where the rice stand is thin. But the rice is already past the safe growth stage for applying herbicides. In case the weeds come up through the rice canopy, I have ordered sodium chlorate which can be applied right before harvest to dry the vegetation down to run through the combine.

One of the lessons that we learned last year is that an atomizer is needed to promote mixing of the injected liquid fertilizer in the irrigation water.  Last year the rice was dark green at the pivot, then became light green and yellow the farther you went from the center. Pictured below is the outside of the atomizer which was screwed into the injection port at the center pivot.  The rice is more uniformly green across the field this year.

From our experiences in flood irrigated rice in Missouri, we knew that rice needs to be rotated with a non-grass crop to interrupt disease and insect cycles.  In our current field, maize was planted in part of the field and the other part was fallow.  The rice is shorter and not as green where maize was last year. The best rotation crop for rice is a legume such as soybeans. Soil nematodes are a major problem here, especially on soybeans.  Planning for next year, we planted one-half of the pivot circle with cowpeas because they are more resistant to nematodes. In Missouri, people call them purple hull or black-eyed peas. Although cowpeas originated in Africa, most of the local people do not know what they are.  My wife and I looked for black-eyed peas at the grocery in Modimollie but could not find them. Farmers here mainly grow cowpeas for livestock feed and do not use them for human food. This is unfortunate, because cowpease go great with cornbread and they are a good source of protein in diets. Below is a photo of the cowpeas in one-half of the circle.  They are a hardy crop that requires little water to produce large amount for nitrogen and crop residue of building soil organic matter.














Last year some of our biggest challenges were getting rice seeds through the import permit process and into the country and controlling volunteer corn from the previous crop in the field.  This year, we are having problems repairing hail damage to the variable rate irrigation equipment which we use to apply treatments. We are having to use a backup system which applies alternating irrigation rates of 9 and 12 mm in 30 degree intervals (3 replications).  Shown below is the controller system at the center pivot point.

In October, I helped Matt and Jim plant a small plot variety/hybrid rice test. Most of the lines are not growing as well as the Nerica 4 that we planted in the big irrigation test.  But there are a few lines that are obvious improvements such a Nerica x Wells cross provided by Dr. Anna McClung, USDA-ARS. Cardi 70-3 from Cambodia is also looking good.





Below are dates of events

  • 10/17/11 – Planted rice and cowpeas
  • 10/18-10/19/11 – Planted small plot rice trial
  • 10/20/11 – Watered rice and cowpeas 12mm
  • 10/21/11 – Sprayed 0.2lb/ac clomazone + 2pt/ac paraquat (rice)
  • 10/22-10/23/11 – Watered cowpeas and rice 12mm
  • 10/25/11 – Cowpeas 0.5 oz/ac halosulfuron + 1.5 pt/ac pendimethalin
  • 10/25/11 – Rice 0.75 oz/ac halosulfuron + 1.5 pt/ac pendimethalin
  • 11/2/11 – Replanted poor stand areas Not in small plots (rice)
  • 11/3/11 – Starter Fertilizer (4-4-4) applied with 12mm water (rice)
  • 11/4/11 – Replanted 3 reps of tests 1 and 3. Watered in Starter fertilizer with 8mm water (rice)
  • 11/7/11 – Watered Rice 12.7 mm
  • 11/8/11 – Basagran (24 oz/ac) + halosulfuron (0.5 oz ai/ac) applied to Rice.
  • 11/11/11 – H20 Rice and cowpeas 12.7 mm
  • 11/14/11 – KNO3 fertilization (10.2 lb K/ac, 3.5 lb N/ac) 5% solution to Rice in 12 mm H20
  • 11/14/11 – Washed in Fertilizer with 5.6 mm H2O
  • 11/14/11 – First Signs of first tiller activity (10 % of Rice)
  • 11/16/11 – H20 cowpeas and rice 12mm
  • 11/17/11 – Ronstar (2 L/ha) application to rice
  • 11/19-11/20/11 – 35 # N/ac AN (18% N) applied in 12 mm H2O
  • 11/25/11 – 20 # N/ac ASN (18% N) applied in 6 mm H2O, additional 6 mm H20 to wash in
  • 11/25/11 – Sprayed cowpeas Basagran (1.16 L/ha) Imazamox (0.87 L/ha) Permit (40 g/ha) + NIS
  • 11/28/11 – H20 Rice and Cowpeas 12mm
  • 12/1/11 – 20 # N/ac ASN applied in 6 mm H2O, additional 6 mm
  • 12/5/11 – 12 mm H2O applied to rice and cowpeas
  • 12/8/11 – 20 # N/ac ASN applied in 6 mm H2O, additional 6 mm
  • 12/12/11 – Grandstand applied to rice at 0.5 L/ha
  • 12/17/11 – 12.7 mm fertigation, rice only
  • 12/18/11 – Clincher applied to rice
  • 12/19/11 – 12.7 mm irrigation, rice & peast
  • 12/21/11 – 12 mm (47%) irrigation, rice only
  • 12/23/11 – 5.7 mm (100%) fertigation (50 L/ha injector), rice only
  • 12/29/11 – started 12.7 mm, rice only, rained out (did not include in scheduler)l
  • 12/31/11 – 12 mm (47%) irrigation, rice only
  • 1/2/12 – 8.1 (70%) mm irrigation, rice only
  • 1/3/12 – 7 mm (80%) on pea; 12.7 mm on rice
  • 1/10/12- 12 mm (0.47 inch) irrigated on rice
  • 1/12/12- 9 mm (0.35 inch) irrigated on rice
  • 1/14/12- 9 mm (0.35 inch) irrigated on rice
  • 1/16/12- 9 and 12 mm (0.35 and 0.47 inch) irrigated on rice
  • 1/19/12 – 9 and 12 mm (0.35 and 0.47 inch) irrigated on rice(EZ Plan A reverse)
  • 1/21/12- 9 and 12 mm (0.35 and 0.47 inch) irrigated on rice (EZ Plan A forward)
  • 1/22/12- Last year I saw blank panicles early that I attributed to poor pollination from feeding from yellow and black spotted beetles.  But this year I am not finding beetles in the field. But many of the first head to come out have incomplete grain set.
  • 1/23/12- first big rain in six weeks.  The weather station recorded 0.38-inch yesterday evening and 0.44-inch after mid-night.  I measured 1.1 inches in the gauge at the Rice Cottage.

Energy beets in Missouri

In the 1960’s, Great Western Sugar Company had plans to build a processing facility in Southeast Missouri.  For eight years, field research was conducted at the University of Missouri- Delta Center in Portageville to provide farmers with local information on sugar beet varieties, weed control, soil fertility, row spacing, plant population, fumigants, fungicides for control of Cerocospora leaf spot, and Rhizoctonia root rot. This research was directed by Jim Roth, Harold Kerr, Armon Keaster, and Charles Baldwin.  Beets were planted in the spring and harvested in the fall. Renewed interest in growing to beets in Missouri has developed because beet varieties are now available for biofuel production.

Jake Fisher, recently retired superintendent at the Delta Center, managed most of  the plot work for the scientists from 1963 to 1970. Sugar beet yields at the Delta Center varied from 8.4 to 36 tons per acre.  To read the full report, click  Sugar Beet Research in Southeast Missouri 1970. Most years, they found the highest yields occurred on clay soils. Deep cultivation after emergence of sugar beets improved penetration of the the irrigation water. Variety tolerance and foliar fungicide sprays were effective in controlling Cerocospora leaf spot.

In 1970, six farmers in Southeast Missouri grew sugar beets on a commercial scale. The Great Western Sugar Company had a field man in the area to assist the growers. Unfortunately, growers had problems harvesting their beets because the weather was extremely wet.  Even though beets grew well on gumbo soil, field drainage, especially on clay, was important for harvesting in the fall.Despite the problem with commercial scale harvesting, Jim Roth concluded that sugar beets can be economically produced in southeast Missouri.

Over the course of their research, the most evident problem was the damage caused by root rots that sometimes reduced the stand of beets. They also observed that harvesting techniques needed to be improved because

beets grown in Missouri protruded above the ground more than they do in other areas. Machinery used in western states was not acceptable because many beets were pushed to the side and did not enter the harvester.  They concluded that less power is required for harvesting than beets growing in the soil to the depth of the crown.