Improvement effects of subsurface pipe with different spacing on sodic-alkali soil

Abstract: According to the worldwide difficult problem of soda meadow alkaline soil improvement, the paper used the technology of subsurface drainage and desalination, and studied the effects of different spacing (L1 with 5 m, L2 with 10 m, L3 with 20 m and L4 with 40 m) on soil permeability, organic matter content and exchangeable sodium percentage (ESP), sodium adsorption ratios(SAR), and other physical-chemical characters of soda meadow alkaline soil. Supplementary measures contained applying farmyard manure (34 m3 / hm2) and modifier (15 t/hm2). Pipe spacing was obtained by the below three means of Dacey law，pipe spacing numerical method of experience and the relational expression between pipe buried depth and pipe spacing. The results showed that: 1)compared with CK (no subsurface drainage and no supporting measures), CK1 (no subsurface drainage but having supporting measures) improved the soil permeability significantly; compared with CK1, the soil permeability of L1, L2 and L3 was improved significantly; and the soil permeability coefficient （K10）of L1 treatment is higher than others; 2) compared with CK, the organic matter content, available potassium content and cation exchange capacity (CEC) of CK1 was increased significantly; compared with CK1, the organic matter content of L1, L2 and L3 was increased significantly, and the alkaline nitrogen content, available potassium content and CEC of L1 increased significantly; 3) the treatment of subsurface pipe being densely buried can decrease the soil pH, electrical conductivity (EC), total alkalinity (TA), ESP and SAR of soil. Effects of treatment L1 on the soil pH, EC, TA, ESP and SAR of soil were the most obvious among the treatments, and pH, EC, TA, ESP and SAR of L1 treatment were the minimum with 7.85, 0.15 mS/cm, 2.34 cmol/kg, 39.47% and 2.41 (mmol/L) 1/2 respectively. In general, under the conditions of subsurface drainage with burial depth 0.8 m, and the same rice-planting and supporting measures, subsurface drainage spacing of 5 m had the best improvement effect，and pH value of the surface soil dropped to below 8.0. This research preliminarily solved the problem of soda meadow alkali soil improvement, providing an important theoretical basis and technical support for ameliorating sodic soil, improving land capability and discussing the feasibility of subsurface pipe technology using for amelioration of sodic soil in soda saline-alkali soil region, and promoting the development, popularization and application of the subsurface drainage and desalination soil technology.