Living mulch

In agriculture, a living mulch is a cover crop interplanted or undersown with a main crop, and intended to serve the functions of a mulch, such as weed suppression and regulation of soil temperature. Living mulches grow for a long time with the main crops, whereas cover crops are incorporated into the soil or killed with herbicides.

Other benefits of mulches are slowing the growth of weeds, and protects soil from water and wind erosion. Some living mulches were found to increase populations of the natural enemies of crop pests (Hartwing N., H. Ammon 2002). Legumes used as living mulches also provide nitrogen fixation, reducing the need for fertilizer.

Benefits

When cover crops are turned over into the soil, they contribute nutrients to the main crop so that less chemical fertilizer is required (Brophy et al., 1987). The amount of the contribution depends on the biomass, which varies over time and depends on rainfall and other factors. The greater the biomass, the greater the nutrient turnover. Legume cover crops turn over nitrogen fixed from the atmosphere. Reports indicate that legumes in general have higher foliar nitrogen contents, from 20 to 45 mg g-1 (Lehman et al., 2000).

Bare soil resulting from intensive tillage can lead to soil erosion, nutrient losses, and offsite movemente of pesticides. In addition, weeds can germinate and grow without competition. A living mulches can reduce water runoff and erosion, and protect waterways from pollution. Living mulches have also been shown to increase the population of organisms which are natural enemies of some crop pests. (Hartwing and Ammon 2002)

Living mulches control weeds in two ways. When they are seeded before weed establishment, they suppress weeds by competition (Hartwing 1977). In some situations, the allelopatic properties of living mulches can be used to control weeds. For example, the allelopatic properties of winter rye (Secale cereale), ryegrasses (Lolium spp), and subterrain clover (Trifolium subterraneum) can be used to control weeds in sweet corn (Zea mays var rugosa) and snap beans (Phaseolus vulgaris) (DeGregorio and Ashley, 1986).

Populations of ground-dwelling predators were greater in a corn and soybean rotation with alfalfa and kura clover living mulches than without a living mulch (Prafiska et al., 2006). This situation was due in part to a change in the composition of vegetation in the agricultural system (Andow, 1991).

Drawbacks

Unfortunately, living mulches compete for nutrients and water with the main crop, (Echtenkamp and Moomaw, 1989) and this can reduce yields. For example Elkins et al (1983) examined the use of tall fescue (Festuca arundinacea), smooth bromegrass (Bromus inermis), and orchargrass (Dactylis glomerata) as living mulches They found that herbicides killed 50% to 70% of the mulches but corn yield was reduced 5% to 10% at the end of the harvest.

Although leguminous cover crops have large biomass production and turnover, they are not likely to increase soil organic matter (Barber and Navarro, 1994). This is because legumes used as living mulches have greater N contents and a low C to N ratio. (Lehmann et al, 2000). So when legume residue decomposes, soil microbes have sufficient N available to enhance their breakdown of organic materials in the soil.

Types

In the tropics, it is common to seed tree crops with living mulches such as legume covers in oil palm plantations (Broughton, 1976), coconut (Aldaba, 1995) and rubber (Watson 1989).

In Mexico, legumes used traditionally as living mulches were tested as nematode and weed suppressors (Caamal-Maldonado et al., 2001). The mulches included velvetbean (Mucuna deeringiana) jackbean (Canavalia ensiformis), jumbiebean (Leucanea leucocephala) and wild tamarindo (Lysiloma latisiquum). Aqueous extract of Velvetbean reduced the gall index of Melodoigine incognita in the roots of tomato, but suppressed tomato rooting as well. In addition, Velvetbean suppressed the radical growth of two local weeds Alegria (Amaranthus hypochondriacus) by 66% and Barnyardgrass (Echinochloa crus-galli) by 26.5%.

Nicholson and Wien (1983 ) suggested the use of short turfgrasses and clovers as living mulches to improve the resistance soil compaction. These authors established Kentucky bluegrass (Poa pratensis) and white clover (Trifolium repens) as living mulches since they did not caused reduction of yield corn (the accompanying main crop).

In one study (Echtenkamp and Moomaw, 1989), chewing fescue or red fescue (Festuca rubra) and ladino clover (Trifolium repens) were effective living mulches for controling weed growth. Unfortunately, these cover crops also competed with corn for water which was particularly problematic during a dry period. These authors also mentioned the possibility of using ladino clover (Trifolium repens) as a potential living mulch. However, this clover was difficult to kill with herbicides in winter.

Management

Because they compete with the main crop, living mulches may eventually need to be mechanically or chemically killed. (Brandsaeter et al. 1998, Tharp and Kells, 2001)

It is important to judiciously select the appropriate herbicide rate for burning down a living mulch. Echtenkamp and Moomaw, 1989 found that herbicide rates were inadequate to suppress all the living mulches. Therefore, the mulches competed with the main crop for resources. In some cases, the clover could not be killed at the first herbicide application, so a second application was needed. For another treatment, rates that were so high that they caused the cover crop to be kill to rapidly, so that broadleaf weeds invaded the corn. This study suggested that the timing and dosage of herbicide should be carefully considered.

Living mulches were tested in a no till corn-production systems with two methods for establishing grass and legume living mulches (grass and legume) between corn rows (Echtenkamp and Moomaw, 1989). In 1985, there was no difference between drilling and broadcasting seeds by hand seeds the seeds by hand in that study. However in 1986, drilling resulted in higher populations (97 plants m-2) than broadcasting (64 plants m-2) likely because precipitation levels. Precipitation should be considered because farmers have no control over it.

Beard (1973) recommended chewing fescue (red fescue) (Festuca rubra var commutata var shadow FESRU) as a good living mulch because it adapts to the shady conditions under corn and soybean. This grass is also well adapted to dry and poor soils.

Plant nutrition

Lehman et al (2000) noted that legume cover crops have important positive effects on the nutrient cycling of tree crops. They concluded that leguminous living mulches work in three ways:
* Fixing the atmospheric N2 that is important for the main crop,
* Recycling soil nutrients, and
* Enhacing soil nutrient availability for the main crop. Lehman et al (2000) measured the above ground biomass accumulation of Pueraria phaseoloides, which is a living mulch used in tropical tree crops. They found that pueraria accumulated 838 mg of dm (dry matter) ha-1 as compared with 4.4 mg dm ha^-1 for Theobroma grandiflorum, and 1.4 mg dm ha-1 for Bactris gasipaes. These latter two speies are native cultivated species from the Amazon.

Control of erosion

Vegetative cover as living mulches protect soil against wind and water erosion. Plants should form a mantle or thick mulch that protect soil from detachment. Living mulches intercept raindrops and reduce runoff. The protection that such vegetation provides against wind is influenced mainly by the amount of biomass that covers the ground (differs with each spp), plant geometry and row orientation. (Trohen and Hobbs, 1991).

In one experiment (Hall et al , 1984), water runoff and soil loss on a 14% slope was compared for rototilled (RT), no-till with corn stover mulch (NTCMS) , no-till in CSM+ birdsfoot trefoil living mulch (NT-BFT) and no till in CSM and crownvetch living mulch (NT-CV). The results indicated that the water runoff was 6,350 L ha-1 for NT-BFT, 6,350 L ha-1 NO-CSM, 5,925 L ha-1 for NT-CV, and 145,000 L ha-1 for RT. The soil loss for the RT was 14.22 t ha-1 while with the other treatments it was less than 0.5 tons ha-1. The least soil loss was obtained with NT-CV 0.02 tons ha-1. The reduction of water runoff and erosion is one of the greatest advantages of having a cover crop. Soil can be easily eroded with no vegetative ground cover or plant residue. Ideally soil erosion should be less than 4 to 5 tons/ha/year (Pimentel et al., 1995).

References

* Aldaba F.R., 1995. Coconut production in the Philippines: problems and prospects. Plantatios, Recherche, Developpement Sept-Oct:15-18
* Andow 1991. Vegetational diversity and arthropod population response. Annu. Rev. Entomol. 36: 561- 586.
* Barber, R.G., and F. Navarro 1994. The rehabitation of degraded soils in eastern Bolivia by subsoiling and the incorporation of cover crops. Land Degr. Rehab. 5:247-259
* Beard, J. 1973 Turfgrass: Science and Culture Prentice-Hall Inc. Englewood Cliffs, NJ
* Brandsaeter, L. J. Netland, and R. Meadow 1998 Yields, weeds, pests and soil nitrogen in a white cabbage living mulch system , in Biol. Agric. Hortic. 16: 291-309
* Brophy L. S., G. H. Heichel and M.P. Russelle. 1987 Nitrogen transfer from forage legumes to grass in a systematic planting design Crop Sci 27: 753-758
* Broughton W.J., 1977. Effects of varios covers on soil fertility under Hevea brasiliensis and on growth of the tree. Agro-Ecosys. 3:147-170
* Caamal-Maldonado J.A.,Jimenez J.J., Torres A., Anaya A. 2001. The use of allelopathic legume cover and mulch species for weed control in cropping systems. Agron J. 93:27-36
* De Gregorio R. E. and R.A. Ashley. 1986. Screening living mulches/ cover crops for no-till snap beans. Proc. Northeast. Weed Sci. Soc. 40:87-91
* Echtenkamp, G. W, and R. Moomaw 1989 No-till corn production in a living mulch system Weed technology 3: 261-266
* Elkins, D., D. Frederking, R. Marashi, and B. McVay. 1983. Living mulch for no-till corn and soybeans. J. soil Water Conserv, 38: 431-433
* Hall J, L. Hartwing, and L. Hoffman 1984 Cyanazine losses in runoff from no-tillage corn in “living mulch” and dead mulches vs. unmulched conventional tillage. J. Envoron. Qual 13: 105-110
* Harwig N.L 1977 Nutsedge control in no-tillage corn with and without a crownvetch cover crop. Proc. Northeast. Weed Sci. Society 31: 20-33
* Hartwig N.L., H.. Ammon 2002 Cover crops and living mulches Weed Sci. 50: 688-699
* Lehmann J, J.P. da Silva, Jr. L. Trujillo, K. Uguen 2000 Legume cover crops and nutrient cycling in tropical fruit tree production Acta Horticulturae 531: 35-72.
* Nicholson, A.G., and H.C. Wein. 1983. Screening of turfgrasses and clovers for use as living mulches in sweet corn and cabbage . J. Am Soc. Hort. Sci. 108:1071-1076
* Prafiska J. R, N. P Schmidt, and K.A Kohler, 2006 Effects of living mulches on predator abundance and sentinel prey in a corn-soybean-forage rotation Env. Entomology 35: 1423-1431
* Pimentel D., C. Harvey, P. Resosudarmo et al, 1995 Environmental and economic costs of soil erosion and conservation benefits. Science 267: 1117-1122
* Tharp, B. e., and J. J. Dells. 2001 Delayed burndown in no-tillage glyphosate-resistant corn (Zea mays) planted into soybean (Glycine max) residue and a wheat (Triticum aestivum) cover crop. Weed Technol. 15: 467-473
* Trohen F and J.A. Hobbs 1991 Soil and water conservation 1991 4:83-84 and 5: 108-109 Prentice Hall Inc. Englewood Cliffs, NJ

See also

* mulch
* plastic mulch

External links

Neutral articles

* [http://www.greenharvest.com.au/seeds/living_mulch.html living mulch and Cover Crops]
* [http://www.cals.ncsu.edu/sustainable/peet/cover/l_mulch.html living mulch by Dr. Mary Peet, NCSU]
* [http://www.gardenorganic.org.uk/organicweeds/weed_management/show_wman.php?id=18 Living mulch]
* [http://www.ag.ndsu.nodak.edu/oakes/2004Report/cblm04pic.htm CABBAGE LIVING MULCH STUDY, 2004]

Positive studies

* [http://www.ars.usda.gov/research/publications/publications.htm?seq_no_115=197400 Alfalfa living mulch advances biological control of soybean aphid]

Negative studies

* [http://bioengr.ag.utk.edu/Extension/ExtProg/Vegetable/year/VegInitReport03/8use_of_living_mulch_and_companio.htm Cucumber Production reduced yields]