| This research selected different modes of rape-rice-rice rotation as the study object, setted six treatments:non-tillage and direct seeding of early season rice-no-tillage and broadcasted seeding of late rice (R1);non-tillage and direct seeding of early season rice-conventional tillage and broadcasted seeding of late rice (R2); conventional tillage and direct seedlings of early season rice and conventional tillage broadcasted seeding of late rice(R5);non-tillage and broadcasted seeding of early season rice-no-tillage and broadcasted seeding of late rice(R3);non-tillage and broadcasted of early season rice-conventional tillage and broadcasted seeding of late rice (R4)conventional tillage and transplanting of early season rice-conventional tillage and transplanting of late rice (R6). Rape seed was sowed after rice had been harvested. This research monitored crop growth and its development status, analyzed yields of different crops and relative indicators, studied carbon(C) emissions of cropland and the law of soil carbon sequestration, compared ecological and economic benefits of different treatments, so as to arrive at the optimal pattern of double-cropping rice, and provide a theoretical basis for the field production. The main results are as follows:During the growth stages of early season rice, comparing with direct seeding, treatments of broadcasted seeding (R3、R4) and transplanting treatment(R6) promoted the yield by18.6%(p<0.05); In terms of yield components factors, treatments of broadcasted seeding and transplanting treatment promoted the number of grains per spike, effective spikes, dry matter accumulation, by respectively15.3%(p<0.05)、5.5%(p<0.05) and12.3%(p<0.05); dry matter accumulation of R3was higher than R1、 R2、R4、R5、R6. by5.1%～16.0%(p<0.05),among which, R3was significantly higher than R1、R2、R4、R5(p<0.05). The experimental results show that, broadcasted seeding and transplanting treatments significantly increase yield of direct seeding by promoting the number of grains per spike, effective spikes, and dry matter accumulation; while cultivation methods make no difference on yields.During the growth stages of early season rice, comparing with direct seeding, treatments of broadcasted seeding (R3、R4) and transplanting treatment(R6) promoted the yields by18.6%(p<0.05); In terms of yield components factors, treatments of broadcasted seeding and transplanting treatment promoted the number of grains per spike, effective spikes, dry matter accumulation, by respectively15.3%(p<0.05)、5.5%(p<0.05) and12.3%(p<0.05); dry matter accumulation of R3was higher than R1、 R2、R4、R5、R6by5.1%～16.0%(p<0.05),among which, R3was significantly higher than R1、R2、R4、R5(p<0.05). The experimental results show that, broadcasting seeding and transplanting treatments significantly increases the yields of direct seeding by promoting the number of grains per spike, effective spikes, dry matter accumulation; while cultivation methods make no difference on yields.Among different modes of planting, C cumulative emission(CO2, CH4) in the rice growing period of non-tillage(R1、R3) was significantly lower than conventional tillage(R5、R6) treatment and semi-non-tillage(R2) treatment. In terms of soil C storage, R3、R1were the optimal treatment. When late rice was harvested in2002, R3was found to have promoted soil C storage by488kg.hm"2, which was higher than R4、R5and R6by3.8%～4.1%. The results show that cultivation methods make significant difference on CO2and CH4emissions. Thus, the ultimate main factor that affects field C emissions is the cultivation method. Comparing with conventional tillage, non-tillage can better maintain the stability of soil structure, reduce C emissions, and improve soil C pool.C emissions versus rice yield rate of different treatments ranged between0.82and1.12kg.kg-1. Among different planting patterns, the rate of R1、R3was significantly lower than R2、R4、R5、R6; R3was lower than R2、R4、R5、R6by24.4%-48.8%(p<0.05); no significant difference was found between R1and R3. The results show that, considering the ecological costs, Rl (non-tillage, direct seeding of early season rice, broad-casting seeding of late rice) and R3((non-tillage, broad-casting seeding of early season rice, direct seeding of late rice) are the best mode.Considering the economic effects, Rl、R2、R3、R4、R4was higher than R6by respectively18.1%(p<0.05)、15.2%(p<0.05)、32.9%(p<0.05)、27.4%(p<0.05)、-4.1%; R3、R4exerted the most eminent economic effects and did not present significant difference.In summary, having evaluated ecological effects, economic yields and C emissions versus rice yield rate, R3((non-tillage, broad-casting seeding of early season rice, direct seeding of late rice) is optimal among all the treatments with less demand of labors; it can better adapt to the current situation that China is short of labor in rural areas. Thus R3is convenient to be promoted and applied in production. Keywords:double cropping rice; direct seeding of early season rice and broadcasted seeding of late rice; carbon sequestration; carbon emissions; yields. |
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