Srinivas C. Rao

NODULATION, NITROGENASE ACTIVITY, AND DRY WEIGHT OF CHICKPEA AND PIGEON PEA CULTIVARS USING DIFFERENT BRADYRHIZOBIUM STRAINS

Chickpea [Cicer arietinum (L.)] and pigeon pea [Cajanus cajan (L.) Millsp.] were grown outside in large clay pots from 1992 to 1995 in Edmond, Oklahoma. Plants were studied to evaluate nodulation, nitrogenase activity, and shoot dry weight (DW) of ‘ICCV-2’ and ‘Sarah’ chickpea inoculated with multistrain, TAL 1148, and TAL 480 Bradyrhizobium, as well as ‘Georgia-1’ and ‘ICPL-87’, pigeon pea inoculated with multistrain TAL 1127, and TAL 1132 Bradyrhizobium. Following wheat [Triticum aestivum (L.) emend. Thell.] harvests in the spring, legumes were planted in the summer and harvested at three successive dates during the following months. Leaves and stems from remaining plants were incorporated into the soil after the last harvest. Across year, chickpea measurements were sensitive to temperature and precipitation whereas pigeon pea measurements were sensitive to length of growing season as well as climate. Pigeon pea consistently demonstrated higher nitrogen-fixing capacity and shoot DW compared with chickpea. Nodule and shoot DW of both species increased with plant age whereas nodule count and nitrogenase activity generally increased with plant age and leveled off or decreased at flowering. Sarah chickpea demonstrated higher nodule count and nodule DW than ICCV-2, as did the Georgia-1 pigeon pea compared with ICPL-87. Shoot DW of Georgia-1 pigeon pea was generally higher than that of ICPL-87. Multistrain inoculum improved nodulation and shoot DW of chickpea, and TAL 1127 improved nodulation of pigeon pea compared with other treatments. These results indicate that specific chickpea and pigeon pea cultivars, along with appropriate Bradyrhizobium strains, may improve nitrogen fixation and DW of these species.

Biomass and nitrogen traits of summer pigeon peas and winter wheat grown for three rotations in containers

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 nitrogen (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− 1, 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− 1. 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− 1 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.

Dry Weight and Nitrogen Content of Chickpea and Winter Wheat Grown in Pots for Three Rotations

ABSTRACT Chickpea [Cicer arietinum (L.)] cultivars ‘ICCV-2’ and ‘Sarah’ were studied along with a control, multistrain, TAL 1148, and TAL 480 Bradyrhizobium strains to determine the effect(s) of cultivar and inoculum on dry weight (DW) and nitrogen (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 prior to wheat planting, and soil cores were taken at 35 to 48 d after chickpea harvests. Additional summer fallow treatments for the winter wheat part of the experiment received 0, 45, and 90 kg N ha−1 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.