|Gallaher, R. n.|
Submitted to: Journal of Nematology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/1/2007
Publication Date: 1/1/2008
Citation: Wang, K., Mcsorley, R., Gallaher, R., Burelle, N.K. 2008. Cover crops and organic mulches for nematode, weed, and plant health management. Journal of Nematology. 10:231-242. Interpretive Summary: It has been well recognized that sustainable agriculture and pest management involve many different dimensions and interacting factors. Methods for management of plant-parasitic nematodes are no exception, and they are linked to other sustainable management practices including plant health, soil nutrients, and weed management. Several leguminous cover crops, such as ‘Iron Clay’ cowpea (Vigna unguiculata) and ‘Tropic Sun’ sunn hemp (Crotalaria juncea), provide viable and sustainable methods for nematode management. These cover crops not only suppressed plant-parasitic nematodes, but also enhanced beneficial nematodes that are either important in soil nutrient cycling, or are natural enemies to plant-parasitic nematodes. In addition to the nematode management and nitrogen provided by these nematode-resistant legumes, the crop residues may increase levels of soil organic matter, improving water-holding capacity and other soil properties. This multifaceted nematode management is referred to as ecologically based soil nematode management since its success relies on the understanding of other organisms in the soil ecosystem. Two field experiments were conducted in 2003 and 2004 to evaluate ‘Tropic Sun’ sunn hemp (Crotalaria juncea) and ‘Iron Clay’ cowpea (Vigna unguiculata) as summer cover crops and as organic mulches. ‘Iron Clay’ CP did not suppress root-knot nematodes in this experiment, possibly due to a mixed species population of Meloidogyne. SH as mulch was more effective than using SH as a cover crop in suppressing root-knot nematodes and weeds, as well as in enhancing free-living nematodes, crop nutrient content, and crop yield. A lasting suppressive effect of SH on root-knot nematodes was only significant in a less susceptible host such as turnip, but not on a very susceptible host such as lima bean, which quickly built up high population levels of root-knot nematodes. A negative relationship between root-knot nematode numbers and nematode community diversity suggests the importance of maintaining soil biodiversity. The presence of P. penetrans modified the relationship between crop yield and nematode community indices. In 2003 when root-knot nematode pressure was high, crop yield was strongly affected by root-knot nematode abundance, and root-knot nematodes were positively related to abundance of omnivorous nematodes and SI. However, in 2004, root-knot nematode pressure was low due to P. penetrans infestation, and nematode community structure was consistent with a top down regulation exhibited by a negative relation between root-knot nematodes and numbers of predatory nematodes. Under such conditions, nematode community indices followed the concept of organic enrichment where crop yield was positively related to EI and abundance of predatory nematodes, and negatively related to CI. In addition, N and K content in the crop were each positively related to EI, and negatively related to CI, indicating the enrichment opportunists play important roles in nutrient mineralization.
Technical Abstract: Two field experiments were conducted in 2003 and 2004 to evaluate ‘Tropic Sun’ sunn hemp (Crotalaria juncea) and ‘Iron Clay’ cowpea (Vigna unguiculata) as summer cover crops and as organic mulches. Both experiments were a 3 x 3 split-plot design in which the main plots were summer planting of sunn hemp, cowpea or fallow, and the subplots were organic mulch of sunn hemp, cowpea or no mulch. The summer cover crop was followed by turnip (Brassica rapa) and lima bean (Phaseolus lunatus) in the fall. A mixed population of Meloidogyne species hindered cowpea cover crop from suppressing root-knot nematodes. Using sunn hemp as a mulch suppressed root-knot nematodes more effectively than using it as a cover crop. Sunn hemp mulch only suppressed root-knot nematodes in a less susceptible host such as turnip, but not on a very susceptible host such as lima bean. While sunn hemp as a cover crop failed to enhance beneficial free-living nematodes, sunn hemp as a mulch enhanced free-living nematode population densities, especially when the mulch was chopped into finer form in 2004. Sunn hemp mulch also suppressed broadleaf weeds. Although sunn hemp and cowpea cover crops did not increase lima bean N and K content, their mulches increased the N and K content. Similar results were observed for turnip and lima bean yields. Population density of root-knot nematodes consistently had a negative relationship with nematode community diversity, but was positively related to abundance of omnivorous nematode and structure index in 2003, but negatively related to abundance of predatory nematodes and structure index in 2004. Lima bean yield in 2003 was strongly affected by root-knot nematodes, but was not affected by root-knot nematodes in 2004 due to development of indigenous Pasteuria penetrans which infected and controlled the root-knot nematode. Relationship between nematode community indices and plant health could be affected by abundance of plant-parasitic nematodes and potential nematode biocontrol agents. Lima bean yield was negatively related to structure index in 2003, but was positively related to enrichment index and abundance of predatory nematodes, while negatively related to channel index in 2004. Nitrogen and potassium contents of lima bean were also positively related to enrichment index and negatively related to channel index and maturity index in 2004.