The Utility of Crotalaria juncea as a Cover Crop in a Temperate Climate

Final Report for ONE09-105

Project Type: Partnership
Funds awarded in 2009: $9,644.00
Projected End Date: 12/31/2011
Region: Northeast
State: West Virginia
Project Leader:
Dr. Gerald Leather
West Virginia University
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Project Information

Summary:

Field experimental plots were established with the assistance of two farmer cooperators (Shanholtz Orchards and Church View Farm) in Hampshire County WV to evaluate several cover crops in a young peach orchard and in vegetable cropping. This was a multi-year project to determine how sunn hemp (Crotalaria juncea), a tropical legume, compared to other cover crops for weed control, soil fertility, and nematode population reduction. Because of drought in the first summer season (2009) that resulted in poor cover crop emergence and growth, field plots were re-seeded with the same cover crops according to the experimental design. During the 2010 growing season, the area was under extreme drought with less than 7.6 cm. of rainfall from June to mid-October at the vegetable crop location, and less than 18 cm. rainfall at the orchard location. The greater amount of rainfall at the orchard location was due to a single thunderstorm on July 9th that produced 12.7 cm. of rain within a 2 hr. period.

Growth of the peach trees was not different among all treatments in 2009 with an average increase in trunk circumference at 24cm above soil level of 5.5cm. In 2010 under the severe drought, the increase was only 1.2cm and there was no difference among treatments for either year.

Results of the 2009 and 2010 cover crop growth, peach tree growth, and weed infestation in the orchard research plots were presented as seminars to the Hampshire County Fruit Growers Association. The orchard research area was part of Fruit Grower Demonstration Tours in 2009 and 2010.

Introduction:

Weed control is the biggest cost to certified organic farmers and gardeners. This cost for weed control is also a factor for others who wish to reduce the use of herbicides, especially in fruit and vegetable production for local markets. Crop rotation, mechanical cultivation, plastic mulching, and hand weeding are the most effective, but expensive methods for weed suppression now used by these producers. Chemical formulations approved for weed control in organic cropping are mostly “burn down-non selective” products that affect only the leaves and growing stems of the sprayed plant. More effective, less expensive methods of weed control are required to increase production and profitability of organic and sustainable farms and gardens.

Although cover crops are extensively used in sustainable agriculture, mostly as green manure and for over-winter soil protection, their effects on weed populations are limited.
In large tree fruit production, the additional problems are nematode populations that lead to stunted growth or death of fruit trees, and meadow vole (Microtus sp.) girdling of trees if the orchard floor provides winter shelter.

We proposed to evaluate the weed-suppressive benefits of hairy vetch (Vicia villosa), buckwheat (Fagopyrum sagittatum), and a tropical plant, Crotalaria juncea (sunn hemp), as cover crops in the temperate climate of West Virginia. Sunn hemp has been shown to grow well as far north as Pennsylvania but does not produce seed. Cover crops in common use within the temperate area of the northeastern United States such as rye (Secale cereale) and hairy vetch are allelopathic to some weeds. Hairy vetch is an important cover crop because it produces nitrogen that is available to succeeding crops. Buckwheat has been used in the northeastern states as a “smother” crop for control of quackgrass (Agropyon repens) and other weeds.

In tropical and subtropical climates, sunn hemp fixes high levels of nitrogen and reduces nematode and weed populations. This plant produces an allelochemical that is highly concentrated in its seeds and is readily leached into the soil by water and thus, may provide early weed control until it germinates and becomes established. No studies have evaluated the nematode suppressive effect of sunn hemp in Northeastern States.

Project Objectives:

1. To determine the overall production of buckwheat, hairy vetch, and sunn hemp and compare their suitability as a cover crop in orchard and vegetable farming systems.

The first year (2009) seeding of the cover crops at both farms was completed after the beginning of a drought season resulting in less than a satisfactory crop emergence of sunn hemp and hairy vetch at the vegetable farm. At the orchard location, sunn hemp and buckwheat emergence was reduced. In 2010, the severe drought began after emergence and reduced buckwheat growth at both locations.

2. To determine by soil sampling if there are differences among the cover crops and farming systems on total soil nitrogen, inorganic N, P, K, and nematode populations.

Initial soil samples taken before the first seeding of the cover crops had normal N, P, K, levels when the previous crops were considered. A few of the nematode species expected in orchard plots were not present in any of the initial samples.

3. To evaluate the weed populations in all control and cover crops during each growing season.

Total percent weed cover was the most significant data collected and was best correlated with total crop cover as influenced by lack of rainfall on emergence or growth during both seasons.

4. To determine the production of vegetables planted in the cover crop residues by weight at harvest and growth of the young peach trees by trunk circumference increase.

The drought in both years resulted in nearly complete vegetable crop failure. Growth of peach trees was 80% less during the second growing season than in the first season. Early spring rains during the first year enabled good growth of the deep rooted peach trees.

Cooperators

Click linked name(s) to expand
  • Rakesh Chandran
  • James Kotcon
  • Steve Martin
  • Kane Shanholtz

Research

Materials and methods:

Site # 1: Young (2 yr.) peach tree orchard. The experimental design was a randomized block with 4 treatments and replicated 4 times. Each treatment was a plot 3m x 8m, and contained 2 trees. The treatments were: Fallow control; Seeded sunn hemp at 62 kg/ha; Seeded hairy vetch at 40 kg/ha; Seeded buckwheat at 56 kg/ha. Plots were seeded on July 9, 2009 and June 6, 2010.

Soil samples were taken from each plot before planting of the cover crops and at the end of the growing season to determine the nematode populations and nitrogen, phosphorus, and potassium levels. Weed species dominance was determined as the percent of soil area covered by each weed and crop species. Data are reported as the total average percent weed or crop cover by all species recorded in each treatment. Data were analyzed by ANOVA and multiple range tests.

Site # 2: Fall and spring vegetable production. The experimental design was a randomized block with 4 treatments (5 treatments for spring) replicated 4 times. Each treatment was a plot 3m x 3m with 1 m buffer between plots.

The treatments were:

Fallow control with mowing following stem counts to prevent weed seed formation;

Seeded sunn hemp at 62 kg/ha and mowed 2 mo. after sowing and planted with fall vegetables 2 wk. after cutting;

Seeded hairy vetch at 40 kg/ha and mowed 2 mo. after sowing and planted with fall vegetables 2 wk. after cutting;

Seeded buckwheat at 56 kg/ha and mowed 2 mo. after sowing and planted with fall vegetables 2 weeks after cutting.

The cover crops were seeded on July 9, 2009 and June 10, 2010. Weed control with fall vegetable planting and standard cultural practices included hand weeding. The treatments for spring planting were: Fallow control; Sunn hemp and buckwheat sown August 25, 2009 for winter kill, and rye and hairy vetch sown September 29,2009 for spring mowing. The fall crop planted into the cover crop mulch was Swiss chard (Bata vulgaris cicla). The spring crop was tomato (Lycopersicon esculentum) and green bean (Phaseolus vulgaris). Weed populations were analyzed as those at site # 1 and soil samples taken before cover crop planting, and after vegetable crop harvest. The end-of season soil samples was to allow us to determine if the nematode suppressive effect of the cover crops persists during growth of the vegetables. Crop plant growth and production, nematode populations, and soil analysis data were analyzed by ANOVA and multiple range tests.

Research results and discussion:

The average crop cover at the vegetable farm for the 2009 growing season was 26% for sunn hemp, 90% for buckwheat and 38% for hairy vetch. Note that hairy vetch has limited growth if seeded in late spring until the following early spring. The average total weed cover was 211% in control, 194% in sunn hemp, 105% in buckwheat, and 206% in the hairy vetch (see footnote for measurement explanation). In the 2010 growing season the average percent coverage of the crops at the vegetable farm was 74% for sunn hemp, 86% for buckwheat, and 68% for hairy vetch. The average total weed cover was 146% in the fallow control, 66% in sunn hemp, 34% in buckwheat, and 107% in the hairy vetch.

At the peach orchard site in 2009, the average crop cover was 57% for sunn hemp, 60% for buckwheat and 43 % for hairy vetch. The average total weed cover was 166% in the fallow control, 87% in sunn hemp, 101% in buckwheat, and 116% in hairy vetch. In the 2010 growing season in the orchard the average percent coverage of the crop was 85%
for the sunn hemp and 50% for the buckwheat. The hairy vetch sown in 2009 in the orchard was mulched at bloom and provided weed free plots until mid-summer. Percent weed and crop cover was determined the 1st week in September, 2010. The average percent weed cover was 132% in the fallow control, 21% in sunn hemp, 58% in buckwheat, and 129% in hairy vetch.

In 2009, the dominate weed species in the vegetable crop experiments were spiny amaranth (Amaranthus spinosus), common ragweed (Ambrosia artemisiifolia), and common lambsquarters (Chenopodium album) as determined by percent soil cover. In 2010, there was a slight shift in dominance with spiny amaranth, fall panicum (Panicum dichotomiflorum), and common ragweed in order of percent soil cover. At the orchard site in 2009, the dominate weed species were green foxtail (Setaria italica), dandelion (Taraxacum officinale), and lambsquarters. In 2010, the orchard site dominant weeds were green foxtail, lambsquarters, and hemp dogbane (Apocynum cannabinum).

Growth of the peach trees was not different among all treatments in 2009 with an average increase in trunk circumference at 24cm above soil level of 5.5cm. In 2010 under the severe drought, the increase was only 1.2cm and there was no difference among treatments for either year. When the total growth over the 2-year period was analyzed, there were no differences among treatments.

FOOTNOTE Each species of plant is quantified by the number of stems and by the % ground cover. Thus, a single species could have 100% but with more species, the total is more than 100% ground cover. In fact, without drought, the total weed cover (adding all species) in the control plots would have approached 500%. Think about a dandelion and a broadleaf dock growing side by side, where both cover the same amount of space but at different vertical places. This is how plant ecologists determine species dominance.

In soil sampling for nematodes, 5 species were identified in those taken before the first year planting. However, samples taken in the fall of 2009, spring 2010, and fall 2010 were nearly devoid of nematodes due to dryness of the soil to a depth of 15cm.

There were no significant treatment effects on soil chemistry (percent carbon and nitrogen, pH, mg/kg of calcium, magnesium, phosphorous, and potassium)at either site after two years of cover crop growth. However, Ca, Mg, P, and K increased equally in all treatments, including the control, at the orchard site while an almost equal amount of decrease of these minerals were measured at the vegetable site. At both sites, pH remained the same over the 2-year treatment time. There were no differences in cultural practices at the two sites but differences in soil texture may explain the differences in soil chemistry that occurred during the two years of cover crop growth.

Research conclusions:

In 2009, the dominate weed species in the vegetable crop experiments were spiny amaranth (Amaranthus spinosus), common ragweed (Ambrosia artemisiifolia), and common lambsquarters (Chenopodium album) as determined by percent soil cover. In 2010, there was a slight shift in dominance with spiny amaranth, fall panicum (Panicum dichotomiflorum), and common ragweed in order of percent soil cover. At the orchard site in 2009, the dominate weed species were green foxtail (Setaria italica), dandelion (Taraxacum officinale), and lambsquarters. In 2010, the orchard site dominant weeds were green foxtail, lambsquarters, and hemp dogbane (Apocynum cannabinum).

Growth of the peach trees was not different among all treatments in 2009 with an average increase in trunk circumference at 24cm above soil level of 5.5cm. In 2010 under the severe drought, the increase was only 1.2cm and there was no difference among treatments for either year. Likewise, when the growth over two years was analyzed, there was no difference among treatments.

Participation Summary

Education & Outreach Activities and Participation Summary

Participation Summary:

Education/outreach description:

May 2009 - Seminar presented at the Hampshire County, WV Tree Fruit Growers Meeting. Background and objectives of experiments to be conducted with cover crops were outlined.

June 2009 - Demonstration Tour of orchard cover crop field plots was conducted as part of the meeting of the Hampshire County, WV Tree Fruit Growers.

March 2010 - Seminar presented at the Hampshire County, WV Tree Fruit Growers Meeting. Results of the 2009 experiments on cover crops were shown.

August 2010 - Poster presentation of cover crop research and chemical information on the allelochemical found in the seed of sunn hemp at the International Society of Chemical Ecology.

September 2010 – Review of cover crop research presented at the semi-annual meeting of the WVU Agriculture and Natural Resources Extension Faculty.

March 2011 – Presented the results of the 2010 cover crop experiments at the Hampshire County, WV Tree Fruit Growers Meeting.

Project Outcomes

Project outcomes:

No economic analysis performed.

Farmer Adoption

As a result of the research conducted on the vegetable farm, the cooperating farmer used rye cover crop (spring vegetable experiment) to roll down for weed control in his 2011 transplanted tomato crop. He also strip planted buckwheat to enhance honey production in his bee colonies.

Assessment of Project Approach and Areas of Further Study:

Areas needing additional study

Sunn hemp grew well during the two seasons of drought but additional studies need to be performed to determine longer term aspects of influence on weed and nematode control.

Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the view of the U.S. Department of Agriculture or SARE.