Experimental And Simulation Research On The Characteristics Of Soil Salt Ion Transport Under Drip Irrigation

Saline-alkali land is an important reserve strategic resource of arable land in China.Rational development,utilization and protection of saline-alkali land play an important role in agricultural development and ecological environment protection in China.Drip irrigation under mulch has remarkable effects on increasing temperature,preserving soil moisture and inhibiting salt,which is one of the successful techniques for improving coastal saline-alkali soil.Mathematical models are now considered as an important tool for optimal planning of agricultural systems and play an increasingly important role in modern sustainable agricultural production.Four irrigation treatments(LI₁₀(conventional drip irrigation with quota 10mm),LI₂₀(conventional drip irrigation with quota 20mm),FI₁₀(mulched drip irrigation with quota 10mm),FI₂₀(mulched drip irrigation with quota 20mm))were applied.The transport process of soil salt ions under different drip irrigation conditions was studied.The HYDRUS-2D model was used to simulate the migration and transformation of salt ions in farmland soil of saline-alkali land in this region,and the distribution characteristics and spatial-temporal variation of salt ions in farmland soil during maize growth period under different drip irrigation methods were studied The main conclusions are as follows:(1)The results showed that the K⁺/Na⁺in 0?60 cm soil layer with larger irrigation amount were larger than those with smaller irrigation amount under different irrigation treatments.Ca²⁺/Na⁺was larger in all soil layers of 0?60cm under mulch drip irrigation with the same irrigation amount,The dry biomass accumulation in the whole growth period and the correlation coefficient of the 0?20cm soil layer(K⁺/Na⁺)/Ca²⁺secondary fitting were all above 0.90,under the same(K⁺/Na⁺)/Ca²⁺condition,the dry matter accumulation in FI₂₀treatment was always the maximum and that in LI₁₀treatment was always the minimum.When(K⁺/Na⁺)/Ca²⁺>1.72,the dry matter accumulation of each treatment increased with the increase of(K⁺/Na⁺)/Ca²⁺.(2)The soil Ca²⁺,Mg²⁺and Na⁺concentration of 0?60cm soil layer significantly decreased of conventional drip irrigation and mulched drip irrigation treatments after irrigation.After irrigation,LI and FI treatment 0?20cm soil layer soil total salt decreased by25.2%and 32.6%,while 0?20cm soil layer soil Na⁺concentration decreased by 37.3%and57.7%respectively.Both LI and FI treatments had a significant positive correlation with soil Na⁺concentration,and a significant negative correlation with soil K⁺concentration.Using soil Na⁺as an indicator to evaluate the effects of irrigation and prelipitation on improving crop rhizosphere salt is more accurate.(3)The K⁺/Na⁺and Ca²⁺concentrations in the root layer soil of the conventional drip irrigation treatment have a greater impact on the root K⁺/Na⁺compared with the drip irrigation treatment under the mulch;The increase of Ca²⁺in the root layer soil by conventional drip irrigation and drip irrigation under mulch can inhibit the increase of root K⁺/Na⁺by inhibiting the increase of root layer soil K⁺/Na⁺.(4)The main soluble salt cations in the soil profile of each treatment were Na⁺and K⁺,which accounted for 51.72%and 25.90%of the total cations,respectively.The main anions were HCO₃^-(53.77%)and SO₄^2-(29.24%).For the same irrigation quota,the mulched drip irrigation reduced the number of potential salt-forming ion pairs in the soil,and the sulfate content gradually decreased.Na Cl was the main factor causing soil salinization,the main factors affecting the characteristics of farmland soil salinity were Na⁺,total salinity,SAR,alkalinity,CL^-,and HCO₃^-,respectively.(5)The main objective of this study was to use measured major ion concentrations collected from drip irrigation farmland in coastal saline-alkali land to calibrate the variably saturated water flow model HYDRUS(2D/3D)coupled with the reactive transport model UNSATCHEM.The results demonstrated that the model performed reliably in the simulation of water and salt transfer under field conditions different drip irrigation methods.Drip irrigation under mulch can delay the time of salt ion accumulation to the peak,but the Na⁺concentration is larger than the conventional drip irrigation with the same irrigation amount when the irrigation amount is small.At the end of the simulation,the average SAR of the soil profile in 0?60 cm soil layer under different drip irrigation methods ranged from 9.8 to 13.1,the treatment of large irrigation amount of drip irrigation under plastic film is beneficial to reduce soil SAR.