Description

[Synopsis]

Soils in Northeast Thailand are characterized by a sandy texture and being low in capacity for nutrient supplying. These inherited characteristics typical of a poor fertile soil are the major limiting factors for crop productivity. One possible way to improve soil fertility may be to use locally available nutrient resources such as crop residues and animal feces more efficiently. In order to identify the available resources, it is necessary to quantify nutrient cycle through agricultural activities such as crop and livestock production in the region, and clarify limiting factor for effective utilization of the nutrient resources. In this report emphasis is placed on nitrogen as it is a major nutrient element.
A complete picture of the nitrogen cycle for agricultural production in Khon Kaen province was developed based on data from crop yields, chemical fertilizer application rate, animal feed supply, human food supply, production and usage of crop residues, animal and human feces and garbage, etc. These data were collected from agricultural statistics (1990-92), research reports, study reports, field observation, interview with farmers, and information from Thai researchers.
The nitrogen left as crop residues amounted to 52 kg ha^-1 yr^-1 , out of which 12 kg was fed to animals, 29 kg emitted to the environment by burning, and 11 kg returned to farmland. It is speculated that although crop residues were the main nitrogen resource in the area, the rate of recycling back to the farmland was limited. Animals received 23 kg ha^-1 yr^-1 of nitrogen from the weeds as feeds besides the crop residues and provided 22 kg ha^-1 yr^-1 of nitrogen to the farmland as feces, which was 80 % of nitrogen produced as animal feces. The nitrogen withdrawal as crop harvests (30 kg ha^-1 yr^-1 ) was more than the nitrogen amendment as animal feces, suggesting that it was not feasible to fulfill the crop N demand only through application of the animal feces because of limited animal husbandry activities in the area. Chemical fertilizer application was limited only to 18 kg ha^-1 yr^-1 of nitrogen, clearly indicating that local farmers have applied no or low rate of chemical fertilizer to most of the crops even in the recent years. The nitrogen losses through denitrification, leaching, erosion and emission, and nitrogen gains through atmospheric N₂ fixation, irrigation and rainfall were also roughly estimated to draw a nitrogen balance sheet that consequently showed a negative value of 40 kg ha^-1 yr^-1 . Considering that there is still 58 kg ha^-1 yr^-1 of nitrogen deficit to the farmland, more efficient utilization of available organic resources should be necessary in order to reduce negative value in the nitrogen balance.