Nitrogen and potassium requirements of chinese cabbage (Brassica rapa L.) on oligotrophic peat

A.C. Leong* and H. Salbiah**

Abstract

In 1998, Malaysia’s net import of fresh and chilled vegetables was RM781 million, with chinese cabbage accounted for RM14 million. There is a need to reduce the loss in foreign exchange, especially so when the crop can be grown locally. Chinese cabbage is traditionally grown in the cool climate of the highlands in Sabah, Sarawak and Peninsular Malaysia. Suitable heat tolerant varieties have been identified but there is no local information on chinese cabbage production in the lowlands. The two identified varieties were further evaluated at three rates of nitrogen (N) and potassium (K) on peat. The replicated 2 x 3 x 3 factorial experiment was laid out in a RCB design, under netted structure, in MARDI Research Station, Kelang in late 1998 and repeated in 1999. The Tropic Queen variety recorded a significant higher yield in the first crop but no varietal yield differences were detected in the second crop. The response to N was linear in the first crop. In the second crop, a higher N rate was added to confirm the results of the first crop. It was noted that the yield (31.7 t/ha) at the highest N rate of 300 kg N/ha, was lower than the yield (32.8 t/ha) obtained at 250 kg N/ha, though no distinct cubic relationship was noted. Nitrogen rate at 250 kg/ha is therefore the most appropriate rate for chinese cabbage on peat. No yield differences were detected between the various K rates in both crops. Potassium at 150 kg/ha can be recommended for chinese cabbage on peat. All the treatments and their second and third factor interactions were non-significant. Foliar analysis carried out only in the first crop, showed no differences in percentage N and percentage K for the different N and K rates. This confirmed the yield results obtained. Based on an average yield of 29 t/ha, the estimated net returns/ha at an ex-farm price of RM0.50/kg and RM0.90/kg were respectively RM7 740.60 and RM19 340.60 per hectare.

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