Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/1/2002
Publication Date: 5/1/2002
Citation: RAO, S.C., MACKOWN, C.T., BIDLACK, J.E. BIOMASS AND NITROGEN TRAITS OF SUMMER PIGEON PEAS AND WINTER WHEAT GROWN FOR THREE ROTATIONS IN CONTAINERS. COMMUNICATIONS IN SOIL SCIENCE AND PLANT ANALYSIS. 2002. v. 33. p. 897-912. 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. Pigeon pea, a summer drought tolerant annual legume that is suitable for forage and grain production, could serve as a legume cover crop rotated with winter wheat in the southern Great Plains. Productivity and potential N-fixation benefits of legumes can depend on the source of bacteria used for inoculation. We conducted a preliminary experiment using plants grown in 5-gallon containers. Performance of two cultivars of pigeon pea 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 following legumes was contrasted with winter wheat grown following summer fallow but fertilized with 0, 40, or 80 lb N/acre. Pigeon pea productivity (dry weight and N content) differed for the two cultivars, but was unaffected by the source of inoculum and was equivalent to the uninoculated control. After the first rotation, wheat productivity was enhanced following legumes, and an estimated 27 lb N/acre was derived from the legumes by the third crop of wheat. The favorable response of wheat to the pigeon pea rotation warrants development of field research into summer legume and winter wheat rotations for the southern Great Plains. These results will be useful to agronomist, crop consultants, and producers seeking to understand effective use of legume cover crops as a source of N for cereal crops.
Technical Abstract: Pigeon pea [Cajanus cajan (L.) Millsp.] cultivars, 'Georgia-1' and 'ICPL-87', were grown without inoculation and with Bradyrhizobium inoculation (multistrain, TAL 1127, or TAL 1132) to evaluate legume dry weight (DW) and N content, soil mineral N, and subsequent wheat (Triticum aestivum L.) productivity. Pigeon peas were grown during summer and 'TAM 101' wheat was grown during winter, along with summer fallow controls fertilized with 0, 45, and 90 kg N/ha, in 36-cm diam. 20-L pots from 1992 to 1995. Representative pigeon peas were harvested in the fall and remaining plants were incorporated into the soil. Wheat was planted and soil cores were collected at 35 to 48 d after pigeon pea harvest. Wheat was harvested the following spring. Factors affecting DW and N content of both crops included length of growing season, environmental variation, and contribution of residual N. Among pigeon pea cultivars, Georgia-1 occasionally demonstrated higher DW and N content compared with ICPL-87. Estimation of N provided by pigeon pea to the last wheat crop in the third sequence of yearly rotations was 30 kg N/ha. Pigeon pea treatments demonstrating highest DW, N content, and contribution to soil N generally produced winter wheat with higher yield and N content compared with other treatments. While yield and N content of winter wheat fertilized at 90 kg N/ha either decreased or stayed the same from 1993 to 1995, these same measurements in wheat following pigeon peas demonstrated a 3- to 4-fold increase over the same time period and warrant further research in field rotation systems of the southern Great Plains.