Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/2/2006
Publication Date: 1/15/2007
Citation: Bidlack, J.E., Mackown, C.T., Rao, S.C. 2007. Dry weight and nitrogen content of chickpea and winter wheat grown in pots for three rotations. Journal of Plant Nutrition. 30:1541-1553. Interpretive Summary: Legume cover crops can be grown as a green manure to provide a source of nitrogen (N), the primary limiting nutrient for cereal crops. Chickpea is a summer drought tolerant annual legume that is suitable for forage, grain production, and green manure in a rotation with winter wheat grown in the southern Great Plains. Productivity and potential N-fixation benefits of legumes can depend on the source of bacteria used for inoculation. A preliminary experiment was conducted using plants grown in 5-gallon containers. Performance of two cultivars of chickpea was evaluated for three bacteria (two specific and one multistrain) inoculation treatments and a control that was not inoculated. Also, productivity of winter wheat grown over three cycles of rotation after legumes was contrasted with winter wheat grown following summer fallow but fertilized with 0, 40, or 80 lb N/acre. Chickpea productivity (total dry weight and N content) was similar but distribution between vegetative and reproductive plant parts differed for the two cultivars. Overall chickpea productivity was unaffected by the source of inoculum and was equivalent to the uninoculated control. Total dry weight and N content of wheat grown after the early maturing chickpea were unaffected because pods were removed resulting in less legume N incorporated into the soil. Compared to fallow wheat receiving no added N, only some of the other chickpea cultivar treatments enhanced wheat productivity. These results demonstrate that incorporation of primarily vegetative chickpeas as a green manure into a wheat-legume cropping system may provide some benefit. These results will be useful to agronomists, crop consultants, and producers seeking to understand effective use of legumes as a source of N for cereal crops.
Technical Abstract: Chickpea [Cicer arietinum (L.)] cultivars ICCV-2 and Sarah were studied along with control, multistrain, TAL 1148, and TAL 480 Bradyrhizobium strains to determine the effect(s) of cultivar and inoculum on dry weight (DW) and N content of the legume, as well as soil mineral N, DW, and N content of wheat [Triticum aestivum (L.) emend. Thell.] in a continuous wheat-legume rotation. Chickpeas were planted during the summer and harvested in the fall of 1992, 1993, and 1994. Vegetative growth from chickpeas was incorporated into the soil before planting wheat, and soil cores were taken at 35 to 48 days after chickpea harvests. Additional summer fallow treatments for the winter wheat part of the experiment received 0, 45, and 90 kg N/ha each year. Wheat plants were removed the following spring and stubble was incorporated into the soil before planting chickpeas in the summer. Sarah chickpeas accumulated about the same or more shoot DW and shoot N compared to ICCV-2; whereas ICCV-2 generally produced more pod DW and pod N compared to Sarah. Inoculum had no significant effect on chickpea DW or N content. Wheat DW and N following legumes increased marginally after growing Sarah chickpeas, as evidenced by higher values of some treatments. Only the multistrain or absence of inoculum in Sarah chickpeas resulted in significantly greater wheat DW or N content compared to the fallow wheat receiving no added N fertilizer. The contributions from ICCV-2 chickpeas to wheat DW and N content were not significant. Soil mineral N, as well as wheat DW and N content, fluctuated or increased during this three-year study, which demonstrated some benefit from incorporation of chickpeas into a wheat-legume cropping system.