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Effects of Phosphorus, Calcium, and Hup^– and Hup⁺ Rhizobia on Pigeon Pea Yields in an Infertile Tropical Soil¹

Pigeon peas [Cajanus cajan (L.) Millsp. var. 64-28] were grown in the Republic of Panama in an infertile acid Oxisol (Bayano) in both greenhouse and field studies to determine if yield parameters could be increased by addition of P, Ca, and Rhizobium. In the greenhouse, P additions to the Bayano soil increased shoot and nocule weights, acetylene reduction activity, and hydrogen evolution, but neither inoculation with Rhizobium nor Ca additions had any effect on yields or N₂ fixing characteristics. Similar results were observed from field trials in the Bayano soil, where grain yields and plant N content were not increased after inoculation with Rhizobium strains P170 or P168, which were hydrogenase positive and negative, respectively. Strain P170 was a poor competitor with indigenous rhizobia as noted by the low recovery of antibiotic resistant rhizobia from nodules, while P168 was a superior competitor as noted by its recovery from nodules and by the higher production of H₂ from nodules than from the uninoculated control. Grain yields in the Bayano soil were considerably lower (245 kg ha^–1) in the absence of Ca and P and were increased progressively with P additions of 45, 90, 182, and 363 kg ha^–1. Addition of CaCO₃ (909 kg ha^–1) and P (90 kg ha^–1) gave grain yields (1407 kg ha^–1) comparable to the highest P level (1320 kg ha^–1) without additional Ca. With modest addition of Ca and P, pigeon peas in a less fertile acid soil could produce yields comparable to those in a more fertile and less acid soil.

Key Words: Nitrogen fixation • Nodulation • Hydrogenase • Cajanus cajan (L.) Millsp.

² Former graduate student and professor, Dep. of Soil and Environ. Sci., Univ. of California, Riverside, CA. The senior author is now professor, Facultad de Ciencias Naturales y Farmacia, Universidad de Panama, Panama City, Panama.

Received for publication September 14, 1984.