by Piyaporn Hawiset
19 December 2000
Planting crops purely to enrich soil boosts rice yields
The idea of growing plants that enrich the soil for major crops is catching on, with once-sceptical Northern farmers of Thailand now true believers. Experiments involving the planting of African Dhaincha (Sesbania rostrata) were proving successful, with the plant seeds also becoming another source of farm incomes. The International Rice Research Institute recommends the plant as a "green-manure" crop for rice cultivation, because of the species' ability to boost nitrogen content of the soil, rapid growth and tolerance of floods.
Phrek Gypmantasiri, chairman of the agricultural systems program at Chiang Mai University, said farmers in the North had problems with poor quality soil because they did not know how to maintain soil fertility. As a result, crop yields were low and production costs were increasing.
The centre made trial plantings of African Dhaincha between 1994 and 2000 in the Northeast and found that paddy yields had increased 20%. At the same time, annual use of nitrogenous fertiliser had been reduced by 8.4 kilogrammes per rai (1 rai=1,600 m3), saving 300 baht (US$1=43 baht) per rai. Because farmers in the North had been sceptical, he said, the current focus was on convincing them of the merits of the program.
In 1998, the research team recruited a total of 50 farmers from three districts in Chiang Mai who agreed to set aside one rai of their respective plantations for African Dhaincha. The farmers now realised that the plant helped increase crop yields, reduced costs and was also no threat to their health, he said. The quality of paddy improved to the extent that each crop provides rice seeds for future planting. The seeds are also sold to farmers in the province at 12 baht per kilogram, three baht less than at the local state-run agriculture extension centre.
Chamnong Lakueng, chairman of a seed-gathering group in Ban Muagtue sub-district, said farmers wanted the local administration to help market the rice seed because farmers had no resources to do so. The group of 21 farmers hoped to build up a business selling rice seed in the area, he said.
Before harvesting their one-rai plots, the farmers jointly survey each other's fields three times to ensure that only one variety of seed is present. If not, the crop is not harvested for rice seeds.
Mr Chamnong said that farmers used chemical fertilisers and insecticides before joining the project but now they had switched to using natural traps to kill the insects.
"We use yellow glue to lure the insects. Although we cannot eliminate them 100%, we can reduce our costs," he said.
The best time to plant African Dhaincha is late May, sowing three kilograms of seed per rai. Usually, the plants are ploughed into the soil between late July and early August. To fell the two-metre-tall plants, farmers normally use a lightweight mechanised plough, known locally as a walk-behind tractor or khwai lek (literally iron buffalo). Farmers can sow rice seed about three days after felling the African Dhaincha, as the plant yields maximum emission of nitrogen within the following 28 days, the period during which paddy most needs nutrients for growth.
Mr Phrek said African Dhaincha could be left to grow longer than two months with a view to harvesting the seeds as late as November. The yield, about 200 kilograms per rai, could be sold to other farmers at 30 baht a kilogram, providing additional income.
He said the university would ask the Land Development Department to buy the seed from farmers at 16 to 20 baht a kilogram, as the department had the resources to distribute the seed to farmers in other areas. The department already buys small quantities of seed from farmers in the Northeast and supplies it to farmers in areas where the plant has reduced soil salinity.
Mr Phrek, who wants to see Thailand's diverse strains of rice remain commercial prospects, said farmers planting African Dhaincha grew varieties of rice including fragrant glutinous, red jasmine, luengyai, pha and bird rice.