Yield responses of vegetables to organic fertilizers

P. Vimala, H. Salbiah, T. Zahrah and M. Ruwaida

Abstract

The main objective of the paper is to obtain yield response data to organic sources and rates and subsequently to provide guidelines for organic vegetable cultivation in Malaysia. Three experiments were conducted to investigate the effect of organic fertilizers on vegetables. In the first experiment, poultry manure (PM) at 0, 13.3, 26.7, 39.9, 53.2 and 66.5 t/ha were applied to tomato (Lycopersicon esculentum), cabbage (Brassica oleracea var. capitata) and brinjal (Solanum melongena) grown on peat. Inorganic fertilizer (N:P₂O₅:K₂O:MgO =12:12:17:2) at 2 t/ha was used as control. Tomato yield increased from 4 t/ha to 31 t/ha when PM was increased from 0 to 66.5 t/ha. A linear yield response to PM was obtained, represented by the equation, Y= 9.70 + 0.35 PM where Y=yield and PM=poultry manure in t/ha. Applying 2 t/ha inorganic fertilizer gave tomato yield of 24 t/ha. To get this yield under organic farming, 40 t/ha of PM need to be applied. For cabbage, yields increased from 6 t/ha to 25 t/ha when PM was increased from 0 to 53.2 t/ha. The yield response was quadratic represented by the equation, Y= 6.02 + 0.61 PM - 0.01 PM2. Applying inorganic fertilizer at 2 t/ha gave cabbage yield of 28 t/ha. Brinjal yields increased from 3 t/ha at 0 PM to 46 t/ha at 66.5 t/ha PM. A linear yield response represented by the equation, Y = 8.95 + 0.58 PM was obtained. Yields obtained with inorganic fertilizer at 2 t/ha, was 37 t/ha. To get yields equivalent to the inorganic application, the organic grower has to apply 48 t/ha PM. In the second experiment comparing processed (PPM) and unprocessed poultry manure (PM) at 6.7, 13.4 and 20.1 t/ha on Amaranthus (bayam) grown on peat, no significant yield difference was obtained between PM and PPM. A linear yield response to rate of organic fertilizer applied was obtained. Yields obtained at 20.1 t/ha PM was 20 t/ha for the first crop and 14 t/ha for the residual crop. In the third experiment, on lettuce grown in Cameron Highlands on clay loam soil, PM was superior to three other compost evaluated, namely wormcompost, PM + sawdust compost, and PM + sawdust + rice husk compost. It is concluded that PM whether processed or unprocessed is the most suitable organic fertilizer presently available for organic vegetable cultivation. Recommendations would be about 40–50 t/ha for tomato, cabbage and brinjal on peat soil, 20 t/ha for Amaranthus on peat soil and 20 t/ha for lettuce in Cameron Highlands on clay loam soil.

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