Effects Of Irrigation And Rainfall On Soil Salt And Nutrients In Coastal Saline-alkali Farmland

As an important ecological economic zone in my country,the Yellow River Delta has abundant land resources.However,due to the influence of the formation process,geographical location,environmental conditions and other factors,the saline soil has become its main soil type.Restricted by conditions such as insufficient local freshwater supply and severe salinization,the coastal agricultural areas of the Yellow River Delta mainly use a single flood irrigation method with a large fixed amount of water to press salt and wash salt in spring to ensure timely spring ploughing of saline-alkali farmland.However,the large-scale irrigation and salt pressure will not only reduce the salt content in the soil,but also wash out the nitrogen and phosphorus nutrients in the soil,causing the nutrients to enter groundwater,lakes,oceans and other water bodies,resulting in agricultural non-point source pollution.However,the effects of irrigation and rainfall on the migration of soil salt and nutrients in the coastal saline-alkali farmland of the Yellow River Delta and the migration of salt nutrients in the soil environment and drainage ditches are still unclear.This paper uses farmland fixed-point observations combined with indoor soil column simulation experiments to study the migration law of salt nutrients in farmland-ditch during spring irrigation and rainy season rainfall and the effect of different irrigation amounts on the migration of salt nutrients in saline-alkali land,in order to provide information for efficient ecological management of saline-alkali land in the Yellow River Delta.References and rationale.The main findings are as follows:(1)Farmland irrigation and rainfall in the rainy season both produced the leaching phenomenon of farmland salinity,which had a greater impact on the 0-40 cm soil layer salinity leaching.In both irrigation and rainfall periods,the desalination rate was the highest in the 0-20 cm soil layer,reaching 26.51%and 31.87%,respectively.However,the soil layer affected by leaching caused by rainfall is deeper,and the desalination rate is higher than that caused by irrigation in the soil layer of 60-100 cm.Both irrigation and rainfall in the rainy season will cause the leaching of nitrogen and phosphorus in farmland,which has a greater impact on the leaching of nitrogen and phosphorus nutrients in the 0-20 cm soil layer.The leaching rates of nitrogen are 8.72%and 11.81%,respectively;were 29.34%and 24.30%.However,the nutrient leaching caused by irrigation will accumulate in the 80-100cm soil layer.On the whole,continuous rainfall has a more obvious effect on the leaching of salt and nutrients,and a single irrigation will cause the accumulation of salt and nutrients in the deep layer.(2)During the rainy season,the leaching rate of ammonium nitrate in the surface layer 0-20 cm soil layer was lower than that during the irrigation process,but the leaching rate of NO₃^--N and NH₄⁺-N in the 20-100 cm soil layer during the rainy season were higher than those during the rainy season.The leaching rate of ammonium nitrate nitrogen and soil NO₃^--N during irrigation were higher than that of NH₄⁺-N.(3)The total nitrogen(TN)and total phosphorus(TP)of water quality in farmland ditches gradually decreased along the direction of the ditches,and the removal of nitrogen and phosphorus nutrients from the water bodies showed obvious differences in different grades of ditches.After the observation data of the whole year,the removal rates of total nitrogen and total phosphorus in the agricultural ditch are 13.74%and 21.40%respectively;the removal rates of total nitrogen and total phosphorus in the Dougou ditches are 8.76%and 13.13%respectively;The removal rates of total nitrogen and total phosphorus by the ditches were 8.09%and 2.73%,respectively.At the same time,with the increase of drainage days,the concentration of nitrogen and phosphorus is gradually decreasing,while the changes of NO₃^--N and NH₄⁺-N are fluctuating,and there is a trend of pooling from upstream to downstream,and the peak value gradually increases from agricultural ditch to bucket and branch.On the whole,the variation range of nitrogen and phosphorus concentration in agricultural ditch is higher than that in dougou and branch ditch.(4)In the soil column test,the contents of TS,TN,AP,NO₃^--N and NH₄⁺-N decreased significantly after all irrigation under the three different irrigation amounts of 200 mm(S1),300 mm(S2)and 400 mm(S3),and the distribution pattern of soil layer was similar to that before and after field irrigation.The nutrient stripping rate increased gradually with the increase of irrigation amount.Both low irrigation amount S1 and medium irrigation amount S2 had nutrient accumulation in the bottom soil.The nutrient accumulation occurred in the 60-80 cm soil layer in S1 and 80-100 cm soil layer in S2,and the accumulation degree of S1 was greater than S2,while leaching occurred in the whole soil layer in S3 with high irrigation amount.(5)Under three different irrigation water processing,the soil nitrogen and phosphorus leaching solution concentration over time,rendering the change trend of decrease after increased first,and irrigation water,the greater the higher the concentration of nitrogen and phosphorus in leaching solution,the leaching process,the 400 mm total phosphorus content in leaching solution irrigation water processing showed higher than the other two water treatment,significant difference(p<0.05).The irrigation amount of 300 mm can effectively reduce soil surface salinity and reduce the risk of nitrogen and phosphorus loss.(6)The multivariate analysis of variance showed that the main influencing factor for the significant change of ditch nitrogen concentration was ditch type;Different ditch type,different ditch location and time all have significant influence on the phosphorus concentration in the ditch,and the ditch type is the most important factor affecting phosphorus concentration.Correlation analysis showed that soil salinity was significantly positively correlated with soil nitrogen and phosphorus nutrient migration(P<0.01),but negatively correlated with soil bulk density(P<0.01).