Rice soybean production system is the main sequential cropping system in the irrigated lowland of Chiang Mai Valley. Traditionally, the lowland farmers plant rainy season rice with minimum inputs for subsistence. The soybean introduced in the early 20th century, is planted following rice for cash in the dry season. The biological nitrogen fixing soybean provides average yield of 1.25 t/ha and is able to maintain rice yield at 2.8- 3 t/ha without chemical fertilizer. Thus soybean is considered by farmers as fertility conserving and regenerating crop in this low external input production system. In recent years, the lowland farmers use chemical fertilizer to increase rice productivity to over 3 t/ha. However, since the economic crisis in 1997, the price of chemical fertilizer has increased causing farmers to work for alternatives for improving soil fertility and increasing rice yield.

Sesbania rostrata has been introduced as green manure crop before rainy season rice in the rice soybean system. The legume is broadcasted in mid May and incorporated into soil after 55-60 days. Rice is then transplanted 7-10 days after Sesbania incorporation. The on-station studies and on-farm participatory experimentation show convincing results of increasing rice yield over 20%, which is equivalent to yield obtained by applying 54 kgN/ha. After two years of farmer participation, the area planted to Sesbania rostrata in the test site as green manure crop has been increased three folds.

The farmers, realizing the importance of Sesbania as a resource conserving and regenerating crop, have begun to organize a seed production unit within the community. In the 2001 season, the farmer group in the test site has been able to produce 120 kg of Sesbania seeds, which can be used to cover 40 rai (6.4 ha) (seeding rate 18.75 kg/ha). Seeing the real benefit of Sesbania, the farmers have organized themselves to produce Sesbania seed for community use. 

The reduction of production costs is an important production strategy for small rice farmers in Chiang Mai Valley. Therefore the use of low external inputs while maintaining stable rice yield is a practical solution. The benefit of green manure crops is observed in the long term, but the Sesbania rostrata in rice soybean system shows immediate positive result in increasing rice yield, resulting in farmer adoption. The contribution is due to its nitrogen fixing ability and its fast growing habits, producing dry biomass of over 3 t/ha at 55-60 days and with 3.5% nitrogen content.

The relatively lower C:N ratio (16-24) as compared to soybean residue (30) also makes it decompose easily. The growth of Sesbania rostrata fits the cropping calendar of rice-soybean system. It suppresses weed growth, thus reducing the use of herbicides in rice cultivation. It fits in the lowland ecological niche, particularly on the clay-loam soil. The heavy clay soil will cause poor seedling establishment.

As farmers see the benefit of Sesbania in improving system productivity, they adopt the technology and organize the community seed production, so that seed is available within the community. It is expected that with the increasing price of chemical fertilizer, use of Sesbania rostrata as green manure will continue, and it could have long term benefit to soil organic matter.  

Use Renewable Resources

Sesbania rostrata is a biological nitrogen fixing plant, used as an on-farm resource.

Conserve Resources

Incorporating S. rostrata increases soil nutrients and soil fertility without using chemical fertilizer.

Manage Ecological Relationships

Use of S. rostrata returns crop residues and manure to soils, controls weed.

Adjust to Local Environments

S. rostrata fits with lowland rice -soybean cropping patterns.

Empower People

This system enhances farmer participation in on-farm trial and encourages farmers to produce S. rostrata seed.

Manage Whole Systems

S. rostrata increases farm productivity and reduces the use of chemical fertilizer in the community.

Maximize Long-Term Benefits

Use of S. rostrata increases long term soil organic matter, reduces production cost and generates additional income.

Value Health

Sesbania and soybean in the whole production system maintain environmental health and provide a nutritive diet. 

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