Effect of stubble height on collectable amount of rice straw under different cultivation patterns

There has been a significant inconsistency in research results regarding the effects of stubble height on collectable amounts of rice straw under different cultivation patterns. This study was therefore investigated 23 rice cultivars (including 19 Japonica rice and 4 Indica rice) with desirable yield and widely cultivated in Jiangsu Province. The effects of varietal genotype, planting pattern and yield on resource availability and collectable amount of rice straw under different stubble heights (5 cm, 15 cm, 20 cm and 25 cm) were determined. The results showed that straw amounts of Japonica rice were 11.4% higher than that of Indica rice. The amounts of straw from Japonica and Indica rice were 7 874.17 kg·hm^-2 and 7 066.83 kg·hm^-2, respectively. For different planting patterns, mechanical transplanting yielded the highest amount of rice straw. Hand planting ranked the second, and parachute transplanting had the least straw yield. The yield of rice straw for mechanical transplanting was 34.2%, 23.7% and 18.5% higher than those of parachute transplanting, direct seeding and hand planting, respectively. The collectable amount of rice straw in high yield field was more than that in low yield field. However, no significant difference was noted between high and low yield fields. There were no significant differences in straw/grain ratios for yields with 6 750~9 000 kg·hm^-2. However, significant differences existed among fields with grain yields below 9 000 kg·hm^-2 and above 9 000 kg·hm^-2. Under similar stubble height, the effects of yield levels and varieties on ratio of collectable straw to total straw were insignificant. However, there were significant differences among different planting patterns, and parachute transplanting exhibited the least collectable straw ratio. Under different cultivation patterns, the variation in collectable straw ratio changed with increasing stubble height. Collectable straw ratio was 0.815~0.868 for 5 cm stubble height, 0.668~0.732 for 15 cm stubble height, 0.600~0.669 for 20 cm stubble height, and 0.533~0.618 for 25 cm stubble height. In conclusion, collectable rice straw ratio under the same stubble height was mainly driven by planting pattern. Yield and varietal differences had little effect on collectable rice straw ratio. It suggested that collectable amounts of rice straw should be estimated based on planting pattern, and the stubble height.