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In agriculture, a living mulch is a cover crop interplanted or undersown with a main agriculture, and intended to serve the purposes 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 protecting soil from water and wind erosion. Some living mulches were found to increase populations of the natural enemies of crop pests.Hartwig N.L., H.. Ammon 2002 Cover crops and living mulches Weed Sci. 50: 688-699 used as living mulches also provide nitrogen fixation, reducing the need for fertilizer.
Bare soil resulting from intensive tillage can lead to soil erosion, nutrient losses, and offsite movement of pesticides. In addition, weeds can germinate and grow without competition. 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.
Living mulches control weeds in two ways. When they are seeded before weed establishment, they suppress weeds by competition.Hartwig N.L 1977 Nutsedge control in no-tillage corn with and without a crownvetch cover crop. Proc. Northeast. Weed Sci. Society 31: 20-33 In some situations, the allelopathic properties of living mulches can be used to control weeds. For example, the allelopathic 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).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
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 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 This situation was due in part to a change in the composition of vegetation in the agricultural system.Andow 1991. Vegetational diversity and arthropod population response. Annu. Rev. Entomol. 36: 561- 586.
Although leguminous cover crops have large biomass production and turnover, they are not likely to increase soil organic matter.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 This is because legumes used as living mulches have greater N contents and a low C to N ratio. So when legume residue decomposes, soil microbes have sufficient N available to enhance their breakdown of organic materials in the soil.
In Mexico, legumes used traditionally as living mulches were tested as nematode and weed suppressors.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 The mulches included velvetbean ( Mucuna pruriens) jackbean ( Canavalia ensiformis), jumbiebean ( Leucaena leucocephala) and wild tamarindo ( Lysiloma latisiliquum). Aqueous extract of Velvetbean reduced the gall index of Meloidogyne incognita in the roots of tomato, but suppressed tomato rooting as well. In addition, Velvetbean suppressed the radical growth of the local weeds Alegria ( Amaranthus hypochondriacus) by 66% and Barnyardgrass ( Echinochloa crus-galli) by 26.5%.
Nicholson and Wien (1983) suggested the use of short and as living mulches to improve the resistance soil compaction. These authors established Smooth Meadow-grass ( Poa pratensis) and white clover ( Trifolium repens) as living mulches since they did not cause reduction of yield corn (the accompanying main crop).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
In one study, chewing fescue or red fescue ( Festuca rubra) and ladino clover ( Trifolium repens) were effective living mulches for controlling weed growth. Unfortunately, these cover crops also competed with corn for water which was particularly problematic during a dry period. The possibility of using ladino clover ( Trifolium repens) as a potential living mulch was also mentioned; however, this clover was difficult to kill with herbicides in winter.
It is important to judiciously select the appropriate herbicide rate for burning down a living mulch. In 1989, Echtenkamp and Moomaw 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 killed too 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. In 1985, there was no difference between drilling and broadcasting 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 of 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.Beard, J. 1973 Turfgrass: Science and Culture Prentice-Hall Inc. Englewood Cliffs, NJ This grass is also well adapted to dry and poor soils.
In one experiment, water runoff and soil loss on a 14% slope was compared for rototilled (RT), no-till with corn stover mulch (NT-CSM), 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 NT-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.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 Reducing water runoff and erosion is one of the most significant 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 D., C. Harvey, P. Resosudarmo et al., 1995 Environmental and economic costs of soil erosion and conservation benefits. Science 267: 1117-1122
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