Tropical Grasslands (2006) Volume 40, 222–230

Phosphate rock biofertiliser with Acidithiobacillus and rhizobia improves nodulation and yield of cowpea (Vigna unguiculata) in greenhouse and field conditions

N.P. STAMFORD, C.E.R.S. SANTOS AND S.H.L. DIAS

University Federal Rural of Pernambuco, Department of Agronomy, Recife, Brazil

Abstract

Biofertilisers produced with phosphate rock (PR) plus sulphur (S) inoculated with Acidithiobacillus can promote plant growth and increase available P in tropical soils. Pot and field experiments were carried out in a Brazilian tableland soil with low available P to evaluate the suitability of P biofertiliser at different levels as an alternative to soluble P fertiliser for cowpea, with and without rhizobial inoculation. In the pot experiment, P treatments were: PR — 800 kg/ha; PR plus S (S:PR = 100g/kg) — 800 kg/ha; biofertiliser (B) [phosphate rock treated with sulphur (S:PR = 100g/kg) plus Acidithiobacillus] — 200, 400, 600 and 800 kg/ha; and triple superphosphate (TSP) — 400 kg/ha. In the field experiment, P treatments were: PR — 800 kg/ha; biofertiliser — 300, 600 and 900 kg/ha; and triple superphosphate (TSP) — 400 kg/ha. A treatment without added P, S or Acidithiobacillus (P0) was added as the control in both experiments. Nodulation, plant dry matter yield, grain yield, N and P uptake, soil pH and available P increased when TSP and biofertiliser were applied. The best values for soil available P were obtained with application of P biofertiliser, especially with higher levels. Uninoculated cowpea nodulated with native rhizobia present in the tableland soil, although rhizobial strains selected for acid soils were more effective on inoculated plants. In pot experiments, rhizobial inoculation showed interaction with biofertiliser, although no significant differences were observed under field conditions. The results suggest that P biofertiliser may be used as an alternative to triple superphosphate in soils with low available P for fertilising tropical crops and pastures.

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