| Saline-alkali land in the Yellow River Delta is an important reserve land resource at the present stage in China,and as an important source of‘expansion,quality improvement and efficiency increase’of cultivated land in China.However,there are many problems such as poor soil,soil salt stress,shallow groundwater level and high salinity,and lack of fresh water resources in its development and utilization.The shortage of fresh water resources is an important factor for limiting crop yield.Wheat is subjected to drought stress during the critical period of water demand,which seriously affects the morphological development and yield of wheat.Therefore,in order to alleviate the pressure of agricultural water use and make rational use of saline water resources,it is of great significance to improve the quality and efficiency of crop growth and save fresh water resources in coastal saline-alkali land.In this study,a pot experiment was conducted to replace fresh water with saline water after drought stress at seedling stage.Different substitution ratios[W1(light:salt=5:1,salinity=2.27 g·L-1),W2(light:salt=4:2,salinity=4.54 g·L-1),W3(light:salt=3:3,salinity=6.81 g·L-1),W4(light:salt=2:4,salinity=9.07 g·L-1),W5(light:salt=1:5,salinity=11.34 g·L-1),W6(light:salt=0:6,salinity=13.4 g·L-1),CK1(no drought treatment,normal irrigation,salinity=0.22 g·L-1),CK2(drought treatment,fresh water=0.22 g·L-1)]were studied.The effects of different irrigation amounts（T1:45%of field capacity,T2:60%of field capacity,T3:75%of field capacity）on wheat growth and soil characteristics were determined to determine the optimal salt water replacement ratio and irrigation amount.Through field experiments,the effects of salt on soil water and salt transport were explored to find a suitable way to use salt water resources in the field,to achieve efficient cultivation of wheat in saline-alkali land,and to enrich the theory of water and salt transport regulation in coastal saline-alkali land.The main results are as follows:（1）The replacement ratio of brackish water was light:salty=5:1,salinity=2.27 g·L-1（W1）,light:salty=4:2,salinity=4.54 g·L-1（W2）,light:salty=3:3,salinity=6.81 g·L-1（W3）irrigation water were not reduced wheat dry weight,water use efficiency,leaf POD activity significantly;light:salty=2:4,irrigation water with salinity=9.07 g·L-1（W4）was not reduced wheat plant height,stem diameter,root-shoot ratio,root surface area,maximum fluorescence（Fm）,K+content in aboveground and underground parts,soil urease,sucrase and phosphatase activity significantly;when light:salt=1:5,salinity=11.34 g·L-1（W5）and 0:6,salinity=13.4 g·L-1（W6）,the growth of wheat was significantly inhibited.The irrigation water with fresh:salty=2:4,salinity=9.07 g·L-1（W4）made the soil salt content significantly greater than 64.93%of fresh water treatment（CK2）.Therefore,a comprehensive comparison of the effects of salt water irrigation on wheat and soil,light:salty=3:3,salinity=6.81 g·L-1（W3）can be used as the maximum salt water substitution ratio and irrigation water salinity threshold.（2）The stem diameter,total root length,projection area,surface area,Fo/Fm,H2O2,O2-and soil phosphatase activity of wheat increased with the increase of irrigation amount,while POD activity,SOD activity,chlorophyll content,Fv/Fo,Fv/Fo and soil p H decreased with the increase of irrigation amount.The average root diameter,Fm and Fv of wheat treated with 60%of field capacity（T2）were significantly higher than those of 75%of field capacity（T3）.There was no significant difference between T2 and T3 in plant height,stem diameter,root surface area,water use efficiency,GSH and soil invertase activity.The results of principal component analysis showed that the order of comprehensive effects of different water treatments of saline water replacing fresh water was:75%of field capacity（T3）>60%of field capacity（T2）>45%of field capacity（T1）.Considering that field experiments need to rely on irrigation to leach salt,75%of field capacity（T3）was selected as the best irrigation amount,so the comprehensive selection of saline water replacement ratio was light:salty=3:3,salinity=6.81 g·L-1,and irrigation amount was 75%of field capacity（W3T3）.（3）The soil salinity,base ions,electrical conductivity and SAR of saline water irrigation treatment were higher than those of fresh water irrigation treatment,while the p H decreased.Using light:salty=3:3,salinity=6.81 g·L-1,irrigation water is 75%of the field capacity of water for irrigation,soil salt content in the soil layer above 40 cm increased greatly,the overall increase after irrigation than before irrigation,rainfall before reaching the maximum,rainfall and decreased after the trend,and after rainfall than before irrigation of soil salt content in each soil layer was not significant,indicating that the soil salt can be recovered to the level before irrigation through rainfall leaching.（4）The yield and 1000-grain weight of wheat was not decrease significantly after a winter water irrigation.Therefore,under the premise of controlling soil salinity,wheat production was not significant reduced,the winter water irrigation was carried out with light:salty=3:3,salinity=6.81 g·L-1,and the irrigation amount was 75%of the field capacity.At this time,the water stress in the critical period of wheat water demand was alleviated and half of the fresh water resources were saved.Considering the effects of saline water irrigation on soil chemical properties and physiological growth indexes of wheat,this study preliminarily concluded that in the saline-alkali land of the Yellow River Delta where freshwater resources are scarce but saline water resources are abundant,wheat can be irrigated with freshwater:saline=3:3,salinity=6.81g·L-1,irrigation amount is 75%of field capacity after drought stress in the critical period of water demand. |
