| Guangdong Province is located in the subtropical and tropical humid monsoon region,with abundant light,water and heat resources,which is very suitable for the development of multi-crop cultivation.The "rice-rice-vegetable" triple cropping system is one of the major multi-crop systems in the Pearl River Delta of Guangdong Province.Previous studies have demostrated that soil fertility would declind in rice-vegetable rotation systems,which threaten the sustainable development of rice-vegetable rotation systems.In this paper,aiming at reveal the impacts of “rice-rice-vegetable” triple cropping system on soil fertility in Pearl River Delta and study the optimal improving soil fertility strategy,field experiments were carried out in two sites in Pearl River Delta.The typical early rice-late rice-green bean triple cropping system in Taishan City in the southwest of the Pearl River Delta,and the typical early rice-late rice-mustard triple cropping system in Aibei Town,Huizhou City,southeast of the Pearl River Delta were selected.The effects of the "rice-rice-vegetable" triple cropping system on soil fertility were discussed.And the influences of optimal annual nutrient management strategy,acid soil improvement measures,and organic fertilization measures on the growth of crops and soil fertility were tested.And a suit of fertilization measures for "rice-rice-vegetable" triple cropping system was established,so as to improve the soil fertility and support the sustainable development of the "rice-rice-vegetable" triple cropping system.The main findings are as follows:(1)The soil fertility under "rice-rice-vegetable" triple cropping system was tested.The yield and economical benefits of the "rice-rice-vegetable" triple cropping system were significantly higher than the "rice-rice" twice cropping system.Compared with the "rice-rice" twice cropping system,the total yield of the "rice-rice-vegetable" triple cropping system has increased by 395%-487%,and the annual economical income has increased by116%-448%.However,compared with "rice-rice" twice cropping system,the soil p H value under "rice-rice-vegetable" triple cropping system was significantly declinded,especially during winter vegetable season(soil p H was reduced by 0.37 to 0.52);but,the soil available N,P,and K increased significantly,especially during winter vegetable season(increased by30.84%,29.81%,and 51.43%);On the other hand,soil organic carbon and microbial diversity were significantly reduced,and the activities of soil catalase and dehydrogenase were significantly reduced.It can be concluded that,with the change of traditional "rice-rice" twice cropping system to "rice-rice-vegetable" triple cropping system in Pearl River Delta,the soil fertility also varied greatly with the following characteristics: a significant seasonal surplus of soil nutrients,and more acidification,decline in organic carbon and soil microbial diversity.(2)Research on nitrogen and phosphorus managements for "rice-rice-vegetable" triple cropping system.Results from this study demonstrated that the yield of LNP treatment,the fertilization schedule of which was normal fertilization for winter vegetable + reduced 20%N and P for early rice + normal fertilization for late rice,was higher than that of conventional fertilization treatment,and the soil alkaline nitrogen and available phosphorus during early rice season was reduced by 13.35%～16.76% and 8.29%～15.03% compared with conventional fertilization.OLNP treatment,the fertilization schedule of which was reduced 10% N and P for winter vegetable + reduced 10% N for early rice and reduced 10%P for late rice,can effectively reduce soil available nitrogen and phosphorus content during winter vegetable season and early rice season.But the yield of winter vegetable and total yield per year in OLNP treatment were lower than conventional fertilization.Therefore,reducing nitrogen and phosphorus for early rice in "rice-rice-vegetable" triple cropping system was better.It not only reduced the soil nitrogen and phosphorus nutrient surplus,but also had an positive impact on yield.(3)Study on acid soil improvement technology for "rice-rice-vegetable" triple cropping system.The application of lime and acidic soil conditioner can significantly increase the soil p H,but the increase differed among different season.Compared with CK treatment,soil p H in lime and acidic soil conditioner treatment was increased by 7.27% and6.37% during winter vegetable season,by 5.34% and 6.03% during early rice season,and by 2.88% and 2.09% during late rice season.At the same time,soil available phosphorus and acid phosphatase activities in lime and acidic soil conditioner treatments were also higher than CK treatment during winter vegetable season,and the yield of leafy vegetables was increased by 11.39% and 11.26%.But no significant differences in soil nutrient content and yield of crops among different treatments during early rice season and late rice season were detected.This indicates that winter vegetable season is the key period for acid soil improvement.(4)Study on reducing chemical fertilizer incorporated with organic matter for "rice-rice-vegetable" triple cropping system.The yield of crops in the organic amendimated treatments which reduced chemical fertilizer incorporated with organic matter(Bio-organic manure: BM,Peanut bran:PB)were significantly higher than CK treatment.The yield of winter vegetables,early rice and late rice increased by 12.82% and 14.32%,4.43% and5.04%,4.37% and 4.81% respectively.Soil p H and soil organic carbon in BM treatment were significantly higher than those of conventional fertilization treatment,and especially during winter vegetable season.During winter vegetable season,soil microbial biomass carbon in BM and PB treatments was significantly higher than that of conventional fertilization treatment,with an increase of 11.63% and 11.76%;and Soil Chao,ACE,and Shannon indexes were significantly increased in BM and PB treatment;and the abundance of eutrophic bacteria was increased in BM and PB treatment,such as Proteobacteria,Bacteroidetes,Actinobacteria;and the activities of catalase,dehydrogenase,invertase,β-glucosidase,urease and acid phosphatase was improved in BM and PB treatment.But there are no significant influence on soil microbial abundance and activities during early rice season and late rice season due to BM and PB treatment.(5)Integrated fertilization measures for "rice-rice-vegetable" triple cropping system.Based on the results of the above research,synthetical fertilization(SF)measures for "rice-rice-vegetable" triple cropping system were established: reduced chemical fertilizer incorporated with organic matter and acid soil conditioner for winter vegetable season +reducing nitrogen and phosphorus for early rice + conventional fertilization for late rice seaso.The plotexperiments indicated that the yield of winter vegetable and total yield per year in SF treatment was increased by 9.08% and 7.15% compared with CK treatment,and the soil alkaline nitrogen and available phosphorus decreased by 14.70% and 10.69%respectively in SF treatment than CK treatment.Compared with CK treatment,soil p H value in SF treatment was significantly increased,the increases during winter vegetable season,early rice season and late rice season were 19.24%,7.66%,and 4.58%,respectively.In addition,soil organic carbon and microbial biomass organic carbon were significantly increased,and soil bacterial community abundance and diversity were significantly increased in SF treatment.Therefore,the change of soil nutrient,acidity and soil microbial diversity caused by "rice-rice-vegetable" triple cropping system could be resumed through the integrated fertilization measures. |
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