Effects Of Three Water Management Models On Soil Quality And Rice Yield In Paddy Fields

The southern hilly region is the main rice planting area in China.The rice fields are distributed in cascades because of the terrain,and the water resources in the fields are also different.Due to the different water conditions in paddy fields,various water management measures are employed in these areas.Water management can alter soil physical and chemical properties as well as soil microbial community,ultimately leading to the changes of soil quality and rice yield.To explore the effect of water management on soil quality and rice yield,three water managements including flooding-rainfed(F-RF),flooding-midseason drying-flooding(F-D-F)and continuous flooding(CF)in Taoyuan Agro-ecology Experimental Station was selected for the study.The soil physical and chemical properties,microbial biomass,and bacterial community in early rice,late rice and fallow stages were measured,and the soil quality index(SQI)was calculated.Using high-throughput sequencing technology,the effect of water managements on soil bacterial community were analyzed,and the factors that driving the bacterial community composition and structure were identified.Linear regression analysis was used to determine the quantitative relations between soil quality and rice yield at the early and late rice stages,respectively.The results will provide theoretical references for proper water management in rice planting.The main findings were as follows:(1)Generally,soil water content(SMC)was lower in F-RF than that in F-D-F and CF.Total nitrogen(TN),total phosphorus(TP)and available phosphorus(AP)were significantly different among the three water managements(p<0.05),which were much lower in CF than F-RF and F-D-F.The lowest pH but the highest dissolved organic carbon(DOC)were observed in F-D-F.Although water management altered soil physical and chemical properties,its effect was highly different at early rice,late rice and fallow stages.The influence of water management on SOC was more obvious at the early rice stage compared to the late rice and fallow stages.However,SMC and DOC were more sensitive to water management at the late rice stage in contrast to the other two stages.(2)There were significant differences in soil microbial biomass carbon(MBC)and soil microbial biomass nitrogen(MBN)in different water managements(p<0.05),and the highest was found in F-RF,followed by F-D-F,and the lowest was in CF.Soil bacterial diversity was distinct among different water management,especially at the late rice stage,the Shannon-Weiner index,Chao1 index and Shannoneven index were significantly lower in F-RF than F-D-F and CF.Proteobacteria(24.23%～44.22%),Firmicutes(5.87%～33.55%),Acidobacteria(3.96%～8.83%)and Chloroflexi(2.27%～10.23%)were the dominant bacterial phylum in paddy soils,but their relative abundances varied with water managements.For example,the relative abundance of Acidobacteria was in the order of F-RF>F-D-F>CF,whereas those of Firmicutes and Chloroflexi were reverse.RDA analysis revealed that there were tight linkages between bacterial communities and soil quality indicators,and MBC,MBN,SMC,TN,TP,AP and NO3--N were the key factors driving the composition and structure of soil bacterial community.(3)Water management altered soil quality,while its impact was distinct at different stages.The calculated SQI was the highest in F-D-F at the early stage,which was 60.98%significantly higher than that in CF(p<0.05)but was not remarkably different from FRF.At the late rice stage,the SQI of F-D-F was 0.87,which was significantly higher than that of F-RF and CF by 0.31 and 0.28,respectively(p<0.05).At the fallow period,the influence of water management on SQI turned weak,and no significant difference was observed among R-RF,F-D-F and CF(p>0.05).Compared different water management SQIs and combining with correlation analysis,it can be seen that Bradyrhizobacteria,Ruminobacteria and Sphingomonas were of great significance to the improvement of soil quality.(4)The effect of water management on rice yield was similar at the early and late rice stages,with the pattern of F-D-F>CF>F-RF.The rice yield of F-D-F was 5303 kg·ha-1 at the early rice stage,which was 14.18%and 0.67%higher than that of F-RF and CF,respectively.The rice yield was 6726 kg ha-1 in F-D-F at the late rice stage,which was 53.13%significantly higher than that of the F-RF(p<0.05).No significant difference was observed between F-D-F and CF irrespective of growth stage(p>0.05).Compared with the early rice stage,the impact of water management on rice yield was more obvious at the late rice stage.Linear regression analysis revealed a significant positive correlation between rice yield and soil quality(p<0.05),indicating that the improvement of soil quality increased the rice yield.Collectively,at the early and late rice stage it is suggested that F-D-F is a better water management that can maintain both rice yield and soil quality in south hilly area.At the fallow stage,F-RF is a more reasonable water management that can maintain soil quality in the south hilly area.