Effect Of Brackish Water Irrigation Mode On The Rule Of Soil Water And Salt Movement In Saline-Alkali Farmland

The research soil was taken from the cotton farmland of Kenli county,Dongying city, Shandong province, and it belonged to severe saline-alkali soil. In the laboratory, one-dimension vertical infiltration experiments were conducted on this soil to study under different irrigation water qualities, combination ratios and sequences between brackish and fresh water, the variation rules of cumulative infiltration, wetting front depth and infiltration rate with time; the vertical distribution feature of soil water and applicability of one dimensional algebraic model in simulating water content of soil profile; the vertical distribution law of soil salinity, desalination effect and influence of plough layer salinity on growth(full-grown stage) of main crops(winter wheat, summer maize, cotton and peanut)in northern Shandong plain. Main results showed that:(1) In the initial phase of infiltration, soil water movement was fast and cumulative infiltration, wetting front depth and infiltration rate were less affected by mineralization degree of brackish water, combination ratio and sequence between brackish and fresh water. As time went on, at the same time, cumulative infiltration, wetting front depth and infiltration rate of brackish water were significantly higher than fresh water, but the difference among brackish water that mineralization degree ranged from 2g/L to 5g/L showed unconspicuous; under different combination ratios between brackish and fresh water, with the ratio of fresh water accounting for irrigation quota increasing, cumulative infiltration,wetting front depth and infiltration rate gradually decreased; cumulative infiltration, wetting front depth and infiltration rate with brackish water being irrigated first were obviously greater than the opposite combination sequence. For the change rules of infiltration rate with time under different brackish water irrigation modes, the fitting results of the Kostiakov fomula were more conform to the real process of infiltration compared with Green-Ampt model and Philip model,besides coefficients of determination(R2) of regression equations were more than0.95.(2) Soil water content was maximal after the infiltration of brackish water,mineralization degree of 4g/L, being over, and it’s minimal after fresh water irrigation at the same depth; combination ratio between brackish and fresh water brought different effects on soil water content at different depths, but soil watercontent of combination irrigation was significantly greater than fresh water irrigation; compared with fresh water irrigation first, soil water content with brackish water irrigation first was higher in the whole soil layer. For moisture content of soil profiles under different brackish water irrigation modes, one dimensional algebraic model had high simulation accuracy, root mean squared error(RMSE) fluctuating from 1.0203% to 2.2927% and index of agreement(D)reaching above 0.9.(3) At the same depth, soil salinity content was basically positive correlated with mineralization degree of infiltration water. Soil salinity content of combination irrigation under different combination ratios between brackish and fresh water was obviously less than the direct irrigation of brackish water and essentially equal to fresh water irrigation within a certain depth range, but with soil layer depth sequentially increasing, soil salinity content of combination irrigation was far more than fresh water irrigation; soil salinity content with brackish water irrigation first was significantly lower than fresh water irrigation first in the upper layer and near depth of 60 cm of soil, but the change law was completely opposite in the middle and under layer of soil. For soil layer ranging from 0cm to 30 cm where crop roots are densely distributed, the greater mineralization degree of infiltration water was, the higher the mean content of soil salinity was, but coefficient of variation of salinity content on soil profile showed fresh water >brackish water of mineralization degree of 2g/L>4g/L>3g/L>5g/L; as the ratio of fresh water accounting for irrigation quota increased, the average of soil salinity content gradually reduced, however, coefficient of variation increased at first and then decreased; compared with brackish water irrigation first, the average and coefficient of variation of soil salinity content with fresh water irrigation first was higher.(4) Influence of brackish water irrigation mode on soil desalination depth was less, but on desalination rate within soil desalination depth significantly. The smaller mineralization degree of infiltration water was and the bigger the ratio of fresh water accounting for irrigation quota under combination irrigation between brackish and fresh water was, the higher soil desalination rate was as a whole.(5) The chief crops of five cities(Liaocheng city, Dezhou city, Binzhou city,Dongying city and Jinan city) in northern Shandong plain are winter wheat,summer maize, cotton and peanut. As long as mineralization degree of brackish water, combination ratio and sequence between brackish and fresh water weresuitable, plough layer salinity wasn’t harmful to crop growth in full-grown stage.