Tropical Grasslands (2000) Volume 34, 91–98

Relative responsiveness of some tropical pasture legumes to molybdenum

T.G. SCHWENKE1 and P.C. KERRIDGE2

1The University of Queensland, St Lucia
2CSIRO, Division of Tropical Crops and Pastures, Cunningham Laboratory, St Lucia, Queensland, Australia

Abstract

A glasshouse pot trial was conducted in Brisbane, Queensland, Australia, from March–June 1989. Legumes were grown in a molybdenum (Mo)-deficient red podzolic (Dr 2.21) soil. Sodium molybdate, at 6 rates from 0–200 g/ha Mo, and basal P, K, S, Zn, and Cu were mixed through the soil. Differences in growth potential between species made dry weight an unsuitable basis for comparing responsiveness. Using N concentration in plant tips and N2 fixed when no Mo was applied, relative responsiveness to Mo was categorised as follows:
least responsive — Stylosanthes scabra cv. Seca (Seca stylo); intermediate responsiveness — Macroptilium atropurpureum cv. Siratro (siratro), Aeschynomene americana cv. Glenn (Glenn jointvetch), Aeschynomene falcata cv. Bargoo (Bargoo jointvetch) and Chamaecrista rotundifolia cv. Wynn (Wynn cassia); most responsive — Neonotonia wightii cv. Tinaroo (Tinaroo glycine) and Desmanthus virgatus CPI 38351. Arachis pintoi cv. Amarillo (pinto peanut) grew well with no added Mo due to large Mo reserves in the seed. Further research is needed to determine its relative responsiveness after seed reserves have been depleted.
Mo-fertiliser recommendations for D. virgatus CPI 38351 would be expected to be similar to the highly responsive glycine (100 g/ha Mo, effective for only 2 years on a strongly adsorbing soil). Residual values of applications (100 g/ha Mo) for Glenn jointvetch, Wynn cassia and Bargoo jointvetch should be similar to those for siratro (3–5 years on a strongly adsorbing soil), while residual value for Seca stylo should be similar to that for lotononis (5 years on a strongly adsorbing soil).
Pod development of Bargoo jointvetch and flowering of Glenn jointvetch and siratro were delayed at the lower rates of Mo application. Maturation of Wynn cassia was not affected by application rate. Other species had not flowered prior to harvest. Insufficient Mo may be involved in lack of persistence of some legumes.

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