Abstract:
Abstract: Subsurface drip irrigation (SDI) is an advanced water-saving irrigation method. Alternate row/bed planting is a sowing technique with a 10 cm deep trapezoidal furrow; seeds are then sown in 5 cm deep soil below the furrow bottom. It can significantly improve the germination of spring maize under subsurface drip irrigation. To optimize this technology, 2-year field experiments were performed in Chifeng, Inner-Mongolia, China to study the relationship between the emergence rate of spring maize and soil effective saturation of soil at the location of the seeds after different pre-emergence irrigation amounts from 15 to 60 mm. A HYDRUS-2D model was established to obtain soil effective saturation when seed germination rate reached 90% and then to investigate effect of furrow depth, dripline depth, and irrigation amount in the conditions of different soil texture and initial water content on soil effective saturation in order to obtain best technique parameters combination for seed germination. The irrigation amount was 15, 25, 45 and 60 mm; the furrow depth was 0 and 10 cm; the dripline depth was 30 cm. The germination rate was obtained when the seed germination kept stabilized. The results showed that the maize germination rate increased linearly with soil effective saturation (R2=0.70,P<0.01). The HYDRUS-2D model simulation results had a high agreement with the measured soil water content with the root mean square error of 0.024-0.035 cm3/cm3). The soil effective saturation was not less than 0.77 for 90% of germination rate. The simulation results showed that the soil effective saturation increased with the increase of furrow depth and decreased with the increase of dripline depth. The required irrigation amount to meet the effective saturation of 0.77 decreased with the increase of soil clay content due to the larger hydraulic conductivity of the fine textured soil. The required irrigation amount to meet the effective saturation of 0.77 also decreased with the increase of initial soil water content and furrow depth, and increased with the increase of dripline depth. When the initial water content of the surface soil was 40%-60% field water holding capacity, the required irrigation amount to meet the effective saturation of 0.77 decreased by 15-20 mm for sandy loam, by 6-15 mm for silty loam and by 7-18 mm for silty clay respectively, with the increase of furrow depth by 5 cm. When the dripline depth increased from 30 to 35 cm, the required irrigation amount to meet the effective saturation of 0.77 increased by 16-21 mm for sandy loam, and by 4-14 mm for silty loam and silty clay. Under the different furrow depths and dripline depths, when the initial water content of surface soil increased from 40% to 60% of the field capacity, the required irrigation amount to meet the effective saturation of 0.77 decreased by 9-14 mm for sandy loam, and decreased by 9-19 mm for silty loam and silty clay. Considering the spring maize root distribution, cultivation and deep percolation, the dripline depth should be 30 and 35 cm; considering the soil texture, mechanical operation and energy consumption, the furrow depth should be 10 and 15 cm. Within the range of furrow depth and dripline depth mentioned above, the optimal irrigation amount was 25-67 mm. The study gives agricultural managers a guideline to determine the optimal combination of the 3 parameters.