Effect Of Alternate Wetting And Drying Irrigation On Soil Properties,Root Growth And Yield Formation

Rice is one of the important food crops in China,and more than 65%of the population feeds on rice in China.Although a lot of progress has been made in the study of root morphology and physiology and soil properties,there were few studies on the effects of paddy soil properties on rice root growth and development.In this study,under the condition of pot experiment,5 different types of rice varieties,Yangdao 6,Nanjing 9108,Yangliangyou 6,Changyou 5 and Yongyou 2640,were used as materials.The treatments,alternate wetting and drying irrigation,panicle fertilizer and straw returning were set up to observe the effects of these treatments on rice yield,root morphology and physiology and soil properties,in order to clarify the effects of soil properties on the growth and development of root system,and to propose cultivation techniques to improve rice yield by regulating root system and soil properties and provide the theoretical and practical basis for high yielding and water saving cultivation.The main results are as follows:1.Compared with CI(conventional irrigation),WMD(alternate wetting and moderate soil drying irrigation)increased the rice yield to varying degrees except for the slight decrease of the yield of Nanjing 9108 during the tillering stage;WSD(alternate wetting and severe soil drying irrigation)reduced the yield.Under the same irrigation method,HN(halving the panicle fertilizer)reduced the yield of rice,but HN+WMD((halving the panicle fertilizer combined with alternate wetting and moderate soil drying irrigation treatment)could have a similar yield level as the NN(normal panicle fertilizer).SR(straw returning)significantly increased the rice yield compared to the treatment without straw,and it was beneficial to further increasing rice yield combined with WMD.2.Compared with CI,WMD significantly improved the main morphological characters of root and increased root vitality except for the decline of root main morphological and physiological traits of Nanjing 9108 at the tillering stage;WSD decreased root morphological characters such as root dry weight,root length,root volume,and root vitality.Compared with CI,root aeration tissue is more developed under mild water stress.Compared with NN,HN reduced the root dry weight,root length,root surface area,root volume and root vitality during the panicle initiation stage.The root shoot ratio slightly increased and the root diameter did not change significantly under the two panicle fertilizer treatment.There was no significant difference in root main morphological and physiological characters between CI+NN and WMD+HN.Compared with the treatment without straw,SR improved the root weight,root length,root volume and root vitality during the panicle initiation stage significantly,and it would further promote root growth combined with WMD.3.Compared with CI,WMD significantly increased the contents of nitrate nitrogen and soil organic matter,improved soil urease,sucrase and hydroxylamine reductase activities,reduced the content of ammonium nitrogen,decreased the nitrate reductase and nitrite reductase activities;WSD reduced the contents of ammonium nitrogen and soil organic matter,decreased the soil urease,nitrate reductase,nitrite reductase and hydroxylamine reductase activities,while the content of nitrate nitrogen was higher.Compared with NN,HN reduced the contents of nitrate nitrogen and ammonium nitrogen in soil,and decreased soil urease and invertase activities.Compared with the treatment without straw,the contents of nitrate nitrogen,ammonium nitrogen and organic matter in soil were higher than SR;SR improved the soil nitrate reductase,nitrite reductase and hydroxylamine reductase activities,while the soil urease activity decreased.The contents of nitrate nitrogen and ammonium nitrogen,urease activity in rhizosphere soil under the same water treatment,panicle fertilizer and straw treatment were lower than those in bulk soil;the content of soil organic matter,the activities of soil invertase,nitrate reductase,nitrite reductase and hydroxylamine reductase were higher than bulk soil.Compared with CI,WMD increased the species diversity of ammonia-oxidizing bacteria and reduced the species diversity of denitrifying bacteria during the panicle initiation stage.4.Correlation analysis showed that root oxidizing power at the tillering stage was significantly and positively correlated with soil invertase activity.Root surface area and root volume were significantly and negatively correlated with soil invertase activity.Root aeration tissue was significantly and positively correlated with the content of nitrate nitrogen in soil,and significantly and negatively correlated with soil invertase activity.The main characters of root morphology(root weight,root length,root surface area,root volume,root aeration tissue)were positively correlated with the content of nitrate nitrogen,organic matter and enzyme activities in rhizosphere and bulk soils to varying degrees during the panicle initiation and grain filling stage.The main characters of root morphology negatively correlated with the content of ammonium nitrogen in rhizosphere and bulk soils to varying degrees.To a certain extent,the morphological and physiological traits of root system are closely related to the rhizosphere and bulk soil properties,and there were differences in their correlation during different growth period.By regulating the soil water and nutrients,improving the soil environment and rice root morphological and physiological traits,it is conducive to increasing rice yield while reducing irrigation water volume,to achieve green,high-yield and efficient cultivation.