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Prasert Songmuang and Damri Tawonmas
Soil Science Division, Department of Agriculture, Ministry of
Agriculture
and Co-operatives, Chatuchack, Bangkok 10900, Thailand
Introduction
Thailand has the total land area about 51.4 million ha. Rice is regarded as the main crop occupying 9.6 million ha. While paddy area about 4.8 million ha is located in the Northeastern Region where poor soil fertility and uncertain rain fall are major constraint of rice production. Moreover, about 80 % of arable land is under rainfed condition that causes rice production always run the risk of flood in rainy season and water shortage in dry season. Naturally, Northeastern region is the main area of produced very famous rice variety Khao Dawk Mali 105 (KDML). Rice production conventionally increase by proper use of fertilizer and introduction of new improved varieties which highly respond to nitrogen fertilizer. Chemical fertilizer is neccessary and widely used by the Thai farmer. However, rates of chemical fertilizers applied by the farmer is still low than the rate of recommendation due to the high cost of fertilizers that farmer can't afford. So, the nation average paddy yield is rather low compared with other rice producing countries (Table 1). The organic fertilizer also plays vital role for better production and becomes the alternative source of essential plant nutrients Therefore, the need for increase paddy yield by using chemical fertilizer and organic fertilizer were recommended .
Rice varieties
Thailand, normally there are two types of variety, photoperiod-sensitive and the photoperiod-insensitive variety. The characteristic of the photoperiod-sensitive varieties are generally tall in excess of 150 cm, vigorous growing, leafy, profuse tillering, late maturing, lodging susceptible and poorly responsive to nitrogen fertilizer. It can be grown only in traditional wet season rice system and most of them are limited yield potential. However, they still have ability to produce a moderate but stable yield under adverse conditions such as relatively drought, in saline soil, deep water and intense weed competition. There are plenty of local varieties with palatable taste of the farmer especially in the Southern. While, photoperiod-insensitive variety are mostly high yielding and nitrogen responsive. They have early vegetative vigor, relatively high tillering ability, erect growing leaves, short sturdy stems that resit lodging. These variety are also possible for increasing the total rice production by double cropping in the dry season under irrigation.
Fertilizer application
Presently, chemical fertilizers are widely used for rice production in Thailand. Paddy yield show the best response to nitrogen fertilizers. The response of rice varieties to various rates of N fertilizer is recommended to different types of paddy soils. Nammuang C. (1996) reported the quadratic response of paddy rice yield to fertilizer N, indicating the higher rate of N substaintially increased the rice yield. The maximum yield received from each variety depended upon the fertility of soil types. The results also showed the maximum yield from clay and clay loam soil which was greater than sandy loam respectively.
Effect of organic fertilizer on paddy yield
A number of our experiments had been carried out in Thailand over 20 years (19760996) to study on the effect of chemical fertilizer and rice straw compot on rice yield. The tend of response was found that yields were much the same for all treatments in the short term, but rice straw compost repeatedly applied brought about a gradual improvement in soil properties which raised paddy yield significantly. Also, a comparative study of soil properties under rice straw compost and chemical fertilizer were carried out in long-term. The soil in plot received rice straw compost had not only low bulk density, but also had high organic matter content, ext. P and S remarkably (Songmuang et al, 1990). Long-term experiments indicated that compost application in wetland rice field cause an increase in the organic C, N, P and grain yield (Ponnamperuma 1984)
References
