Biomass production and nutrient yields of four green manures and their effect on the yield of cucumber


P. Vimala, C. C. Ting, H. Salbiah, B. Ibrahim and L. Ismail


Four leguminous crops, i.e. Centrosema pubescence, Calopogonium mucunoides, Calopogonium caeruleum and Pueraria javanica were evaluated on acid sulphate soils as green manures. At 7 weeks from sowing, C. pubescence, C. mucunoides and P. javanica achieved a canopy coverage of over 80%, while the canopy coverage for C. caeruleum was 63%. Fresh biomass production when harvested at 12 weeks were 39, 37, 31 and 29 t/ha for C. mucunoides, P. javanica, C. caeruleum and C. pubescens respectively. The corresponding dry weights were 8.7, 6.4, 7.0 and 6.1 t/ha. Nitrogen contents were 1.4–1.7% in the roots, 1.8–2.5% in the stems and 4.0–4.5% in the leaves. The green manures also contained 0.2–0.3% P, 0.4–2.2% K, 0.2–1.0% Ca and 0.1–0.5% Mg. Micronutrient contents were 14–68 ppm Mn, 8–47 ppm Cu, 24–48 ppm Zn and 11–46 ppm B. Nutrient yields were 196–263 kg N/ha, 14–22 kg P/ha, 111–163 kg K/ha, 23–43 kg Ca/ha and 11–23 kg Mg/ha. Incorporation of the crops as green manures plus additional inorganic fertiliser application gave higher cucumber yields than those given by poultry manure at 4.4 t/ha plus inorganic fertiliser. Yields obtained with green manure alone were however only 6.1 kg and 5.3 kg/4.5 m2 plot, for the first and second crop respectively compared with 15.1 kg and 14.9 kg when the green manures were supplemented with NPK 12:12:17:2 at 0.6 t/ha. Yields increased significantly to 21.1 kg and 18.9 kg when NPK 12:12:17:2 was increased to 1.1 t/ha. It is concluded that green manures alone are not sufficient to sustain yields of cucumber crop on acid sulphate soils. Incorporation of green manures plus inorganic fertiliser was however effective in producing higher cucumber yields than incorporation of poultry manure plus inorganic fertiliser.

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