| Mulched drip irrigation with brackish water has been widely used in arid areas for salt-tolerant crops irrigation.In order to use brackish water efficiently,we must not only take into full account the advantages and disadvantages of brackish water,but also the nutrition demand and principle of salt-tolerance of crops.It is important for theoretical and partical significance to prove up proper irrigation regime for brackish water,and to coordinate soil moisture,soil salinity,nutrient and trace element for promoting crop growth and yield while avoiding harm the soil ecological environment.There are still some dificiences concering about the study of cotton root growth dynamic under mulched drip irrigation,soil moisture and soil salinity distribution and transfer rules in the root zone,the combined effect of salinity and trace element in irrigation water on cotton(Gossypium hirsutum L.)growth though comprehensive reviews have been obtained,including(1)The dynamic and detail distribution of cotton roots are difficult to study,there are very few published study which evaluate if the minirhizotron technique can provid as an areliable,nondestructive for directly viewing and studied the growth of cotton fine root.(2)The effect of cotton root growth on the trancfer rules and spatial distribution of soil moisture and soil salinity reminds unclear.(3)Till now,there have been no previous studies which combine the corresponding soil-root-cotton growth parameters to predict cotton root length and yield efficiently.(4)Alought salinity and trace element concentractions in irrigation water and their independent effects on cotton growth and yields have been investigated extensively,the response of cotton to the combined stress of salinity and trace element remines unclear.Two-year field experiments were carried out in a cotton field under mulched drip irrigation with brackish and fresh water at the Bazhou Irrigation Experimental Station.In order to study the spatial distribution of soil moisture,soil salinity and their relationship with cotton roots growth,the monolith method and minirhizotron were used to accurately monitor the dynamic and spatial distribution of cotton roots,meanwhile,multiple methods and technologies were used to accurately monitor the soil moisture,soil salinity,cotton above-ground growth and yield.Moreover,three-year pot experiments containing different concentrations of salinity and trace element in irrigation water were conducted to study the combined effect of salinity and trace element on cotton growth and nutrition element uptake.The main conclusions were obtained as follow:(1)The distribution of cotton root length under mulched drip irrigation was increased with the increase of soil depth between 0-30 cm,then decreased with the increased of soil depth between 30-50 cm.Cotton roots were mainly concentrated in the 0-30 cm soil layer.The equation of liner regress could be used to estimate the actual root length growth parameter after we acquired the root length growth parameter with minirhizotron.(2)The soil moisture content was affected by the mulched drip irrigation mainly in the shollow soil layer(0-60 cm),while excess salts could not flush below the deepper soil and concentrated in the root zone.The average soil moisture content and soil salinity in the root zone were higher for brackish water irrigation treatment(BWT)than for fresh water irrigation treatment(FWT).Immediately after irrigation,the root zone showed its maximum soil moisture content and minimum soil salinity for both BWT and FWT.Then,soil moisture content decreased due to root water uptake;simultaneously,salt concentration increased,especially in regions where root length density was relatively high.The average root length density,shoot dry weight and yield for BWT were observed to be lower than those of FWT as a result of the elevated soil salinity associated with BWT.(3)Cotton root length could be predicted efficiently with the easily-measured root mass alone.Root growth parameters provided better predictions of cotton lint yield than the height and stem diameter.(4)Under salt stress,moderate concentrations of trace element in irrigation water would promote cotton growth and yield.There was an antagonistic relationship for the combined effect of salinity and trace element on cotton growth and yield.The ratios of K/Na and Ca/Na in cotton leves generally decreased as Na Cl concentration in irrigation water increased.This led to lower tolerance of cotton plants to salt stress and possibly inhibited cotton growth and yield. |
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