| Freshwater scarcity and soil salinity increases are frustrating the sustainable developmentof agriculture worldwide,particularly in arid and semi-arid regions.Hetao Irrigation District in northwest China is typical arid and semi-arid region which is serious affected by two factors.To address the problems,some measures have been applied.Mulch-drip irrigation is considered asone of the best methods which can increase crop yields;reduced water application;decreased salinityand deep percolation.However,salinity increases with times under mulch-drip irrigation,which can decrease crop yields.Hence knowledge of soil water,heat and salt distributions in the zone is very important for understanding the rise of salt accumulation in crop field under long term mulch-drip irrigation.Maize is one of main cereal crops in the arid region of northwest China,where water shortage and soil salinity are major yield limiting factors.To reduce soil evaporation in the field and conserve water resources,soil surface mulched by plastic film has been widely adopted in recent decades in the region of northwest China.The combined effect of ridge tillage and film mulching method can not only reduce water loss from soil evaporation,but also changes the energy budget of the soil surface,accelerate crop development during the early stage by increasing soil temperature,improve crop water use and promote crop growth and yield.In order to investigate the effect of different tillage and film mulching method on saline-sodic soils water-salt condition and maize yield in Hetao Irrigation District,4 treatments based on the located observation in fields were complete random designed,including alternating ridge tillage and furrows with full film mulching(LQ),alternating ridge tillage and furrows with half-film mulching(LB),flat tillage with full film mulching(PQ)and flat tillage with half-film mulching(PB).Each treatment had four replicates with a plot of 4×12 m2.Soil surfaces were full or partial covered with clear plastic film with a thickness of 0.008 mm.The bare soil between plastic film of half-film mulching treatment was 60 cm.Maize was sown at 5.0 cm depth holes under the plastic film,where the crop spacing was 30 cm and row spacing was 20 cm(narrow)and 80 cm(wide).The maize cultivar “Ximeng 6” was sown on 24 April 2014 and 28 April 2015.The plots were harvested on 4 September 2014 and 5 September 2015,respectively.The results showed:(1)During the whole growing period of maize in 2014 and 2015,full film mulching treatment significantly improved the soil water storage of 0—70 cm soil layer,the soil moisture and soil temperature of LQ were higher than the LB,PQ and PB treatments.Compared to LB,PQ and PB,LQ increased soil moisture by an average of 14.7%,8.6% and 19.1% at seedling stage;At jointing stage,the difference of soil moisture between full film and partial film mulching treatment was significant both in ridge tillage and flat tillage mode.LQ enhanced soil moisture by up to 16.4%,5.4% and 19.6% than LB,PQ and PB respectively.The soil moisture of LQ were increased by 16.6%,5.1% and 20.3% than LB,PQ and PB respectively during heading stage.At maturing stage,soil moisture of each treatment were decreased,LQ increased soil moisture by 14.6%,5.1% and 19.1% compared to LB,PQ and PB respectively.The soil moisture of full film mulching treatment was significantly higher than partial film mulching treatment in 10 cm and 30 cm soil layers,however there was no significant different in 55 cm between each treatment.(2)The PB treatment has the lowest soil temperature during the maize growing stage in 2014 and 2015.The soil temperature of ridge tillage treatment significantly higher than that of flat treatment in 2014,LQ was increased by 2.07%,6.01% and 8.67% than LB,PQ and PB treatment respectively.Average soil temperature was significant higher in full film mulching than half film mulching in 2015.Compared to LB,PQ and PB,soil temperature of LQ was increased respectively 5.90%,1.33% and 8.96%,the soil temperature of PQ increased 7.53% compared with PB.The changes of soil temperature were tented to be steady with increasing soil depth.Ridge tillage with full film mulching method could significantly increase soil temperature,enhance the soil water content and has obvious effects on restraining the loss of heat.It is clear that the optimal mulch and tillage strategiesare beneficial toform better soil moisture and temperature environment and then increase crop yield.With the increasing of temperature and crop water consumption during growing period,LQ showed obviously effect on soil water conservation.In 2014 and 2015,the soil temperature was higher in LQ than in other treatments while the lowest value was recorded in the PB treatment.However,the soil temperature in LB was higher than in PQ in 2014;it is opposite that higher soil temperature was recorded in PQ compared with LB in 2015.It implied that tillage technology had a significant influence on average temperature compared with mulching mode under drought conditions in 2014.Conversely,mulching mode played a more important role in preserving thermal conditions than tillage technology during the humid year of 2015.Overall,ridge tillage efficiently transferred and accumulated heat from shallow soil to deeper layers.Additionally,the higher the soil surface temperature,the more significant the film insulation effect.(3)Soil salinity was redistributed after dripirrigation.The main desalination district was formed under dripper around 30 cm layer and salt accumulated towards to the outer side of humid area.The soil salinity of partial film mulching treatment are likely to build up on the surface of the un-filmed soil by evaporation,however,full film mulching treatment could effectively decrease the soil salt due to the effects of soil moisture.Under mulched drip irrigation,salt content of different horizontal position from drip irrigation zone showed the same trends ofelectrical conductivity curvevariation and the variation was decreased with the increase of soil depth.The soil salt content of each treatment changes greater at 40—70 cm soil layer than that of 0—40 cm soil layer during the growth period.Different treatment all played a certain role in desalination at 0—70 cm soil layer,the desalination capacity of half-film mulching treatment was much less than the full film mulching treatment.Full film mulching treatmentefficiently restrained soil water evaporationresulting in decreasing the upward movement trend of soil salt and created suitable environment for the growth of crops.(4)The maize in the LQ treatment enter the heading period 2-7 days earlier than other treatments,and matured 3 days earlier than that in half film mulching treatment.Additionally,the higher the soil surface temperature,the more significant the film insulation effect.LQ can not only enhance the number of rows per ear and grain number,but also conducive to the accumulation of dry biomass,promote the formation of maize yield under drip irrigation,and increase water use efficiency.Compared to PQ,PB and LB,the grain yield of LQ was increased respectively 9.15%,26.11%,42.64% and 2.14%,27.29%,41.66% in 2014 and 2015.The use of alternating ridge tillage and furrows with full film mulching method could optimize the soil moisture and temperature environment,decrease the soil salt content of arable layer,shorten the growth period of maize,and also increase crop yield considerably.The results could provide a technical basis for agricultural water-saving and high maize yield,and supply a suitable cultivation mode for efficient utilization of saline soil in Hetao Irrigation District.(5)The mathematical model was calibrated and verified using the field experimental data in 2014 and 2015.The results showed that the simulation values and the observation values were well fitted,HYDRUS-2D model could accurately simulate the effect of film mulching and tillage on soil water,heat and salt transfer under mulched drip irrigation in Hetao Irrigation District.In the case of insufficient experimental data,mathematical model could be used to simulate the soil water and salt transfer under different irrigation conditions,therefore,make up the shortage of field experiment.It can provide data support for optimization of irrigation system in Hetao Irrigation District. |
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