| Subsurface drip irrigation(SDI)is an advanced water-saving irrigation method.However,as a result of dripline being buried below the plow layer,large pre-emergence irrigation or sprinkler system are usually used to ensure crop germination,which will cause water leakage or investment increase.The difficulty of crop germination under SDI in spring-drought-prone areas is a worldwide problem that prevents the extension promotion and application of SDI.Therefore,to study the key technical is great scientific significance and practical value.In year 2015 and 2016,a series of field experiments was conducted in Chifeng City,in Eastern Inner Mongolia,China.A systematic experimental study and numerical simulation were carried out on exploring the suitable sowing method for spring corn under SDI,and the corresponding pre-emergence irrigation amount,irrigation and fertilization schedule,and design parameters.The main conclusions are as follows:(1)This paper proposed a new sowing method called alternative/row bed planting(AP)with 10 cm-deep trapezoidal furrow;seeds were then sown in 5 cm below the furrow.In comparison with the traditional flat planting(FP),AP significantly improved water environment around the seeds.Under the two dripline buried depths of 30 cm(D30)and 35 cm(D35),the soil moisture content in seeds increased by 20.0%?98.8%,and the emergence rate increased by 9.2%-25.1%after pre-emergence irrigation of 25 mm.(2)The effects of pre-emergence irrigation amount on the emergence rate were analyzed,and the quantitative relationships between the corn emergence rate and soil relative humidity and between the corn emergence rate and soil effective saturation around the seeds were obtained.When the initial soil water content before sowing was 40%-60%of field capacity,the emergence rate of AP increased first with the increase of pre-emergence irrigation amount and then decreased in sandy loam.When the pre-emergence irrigation amount was 45 mm,the corn emergence rate of APD30 can reach 100%.Under AP,the corn emergence rate and soil relative humidity(R24)around seeds 24 h after irrigation showed a quadratic relation,and the soil effective saturation(Se)around seeds right after irrigation showed a linear function relationship.If the emergence rate can reach 90%?95%,R24 should be 85%and Se should be 0.77.(3)In comparison with FP,AP can not only increase the emergence rate,but also store the rainwater.The soil water storage at corn root zone during the growth period increased by 1.5%-3.5%,the yield increased by 11.9%-40.9%,and the water use efficiency increased by 3.0%-25.8%.(4)The application amount of irrigation and nitrogen had significant effects on the dynamic change of soil nitrate-N.When the nitrogen application amount was 240 kg/hm2,the nitrate content in the growth period was fluctuating up and down around the initial value.The nitrate-N had spread out from the buried emitter(buried depth,30 cm)with soil water moving.The nitrate-N content near the emitter decreased with the increase of irrigation amount;hence,the nitrate-N content in 20?40 cm soil layer decreased with the increase of irrigating amount,whereas the nitrate-N content in 0?20 cm and 40?60 cm increased with the increase of the irrigating amount.When the irrigation quota increased from 70%ET' to 100%ET',the concentration position of soil nitrate-N at corn harvest season migrated from 20?50 cm to 50?110 cm,which would increase the risk of nitrogen leaching.(5)The increase of irrigation amount can promote nitrogen absorption and benefit for growth and yield.Based on the nitrogen fertilizer effective equation,in considering the utilization efficiency of water and nitrogen and the transporting distribution characteristics of soil water and nitrogen,the suitable nitrogen application amount for AP under SDI was 240?259 kg/hm2 and the irrigation quota was 85%ET'.When the irrigation quota was 70%and 85%ET',it would inhibit corn growth and also lead to yield reduction when the amount of nitrogen was more than 290 kg/hm2.When the irrigation quota was 100%ET',the yield increased with the increase of nitrogen(from 0 to 340 kg/hm2).Water use efficiency and nitrogen utilization efficiency of corn initially increased and then decreased with the increase of irrigation and nitrogen amount.The suitable combination of irrigation quota and nitrogen amount was 85%ET' and 240 kg/hm2,respectively,for water use efficiency and 85%ET'and 290 kg/hm2,respectively,for nitrogen utilization efficiency.(6)The HYDRUS-2D model for AP was developed and verified,and the effects of design parameters(furrow depth,dripline burial depth,and irrigation amount)on soil water at seeds under different conditions of soil and initial soil water content were studied.In considering the corn germination,soil texture,corn root distribution,mechanical operation,energy consumption,tillage depth,deep percolation,and initial soil water content,the dripline burial depth was recommended as 30?35cm,the furrow depth was 10-15cm and the range of irrigation amount should be 25-67mm. |
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