Abstract: Decomposed rice straws were applied on a lettuce field in an attempt to reduce fertilization.Along with the mechanical rice harvesting,a decomposition agent was added to the straws to optimize the application.The results showed that,in comparison with the control,the treatments increased the lettuce production by 833.40-1 633.35kg·hm-2,or 1.42%-2.79%.The lettuce plant height and stem girth increased,and the soil nutrient profile improved.The seasonal soil organic matter content increased by 0.2-0.5g·kg-1(0.65%-1.61%)with a reduction on the amount of fertilizer used.The lettuce yield under Treatment 3was the highest among all with 60 000.30kg·hm-2,an increase of 2.79% over the control.The organic matter content of the lettuce under Treatment 2was the highest(i.e.,31.5g·kg-1),and the available P was the highest as well(98.3mg·kg-1) among all.And,the lettuce treated by Treatment 3contained the most alkali-hydrolyzable nitrogen(i.e.,120 mg·kg-1).As a result,it was concluded that,with the straw decomposition agent,the optimal addition rate of dry straws to the field was 4 500kg per hectare,while a 10%reduction on nitrogen and phosphate and 10%to 20% on potash fertilization was achieved.