Subsurface gravel blind ditch increasing improved effects of takyric solonetz by desulfurized gypsum and yield of oil sunflower

Abstract: Takyric solonetz, is a kind of alkaline soil, which is quite unique in China and even in the world. In Northern Ningxia,China, this soil belongs to a kind of clay with a big soil bulk density and a badly structured physical property. So, after irrigation, dispersed soil particles in clay lead to low soil porosity, and poor permeability and salt is difficult to be quickly washed away. In order to explore the effect of different blind ditch spacing and gravel cushion thickness on the physical-chemical properties of takyric solonetz, salt ion concentration and oil sunflower yield, a field experiment was carried out in Pingluo County of Ningxia. A total of 3 kind of blind ditch spacing (3 , 6 , 9 m) and 3 gravel cushion thicknesses (25, 30, and 35 cm) were designed. Besides, the desulfurized gypsum (22.5 t/hm2) and leaching amount (4500 m3/hm2) were applied. Then, the soil physical and chemical properties, soil salt ion concentration and yield of oil sunflower of different treatments were measured to determine the amelioration effect of gravel blind ditch. The test items were permeability of soil, soil pH value, exchangeable sodium percentage (ESP), total salinity and salt ion concentration. The results showed that the gravel blind ditch could improve water permeability of soil and keep desalination by leaching. The desalination effect was closely related to blind ditch spacing and gravel cushion thickness. The smaller the blind ditch spacing and the gravel cushion thickness, the more significant the effect. In the soil layer of 0-40 cm under the gravel blind ditch treatment, the concentration of 4 ions (Na+, CO32-, HCO3-, Cl-) significantly decreased and the Ca2+ and SO42- concentration increased compared with those under CK. In addition, there was little variation for the concentration of Mg2+ and K+. The result of Person analysis showed that Na+ was greatly related to Cl- and SO42- and it was an important cation of takyric solonetz. The blind ditch spacing of 3 m and gravel cushion thickness of 35 cm decreased soil pH value, ESP, and total salinity in 0-40 cm by 11.7%, 32.3% compared to CK treatment in the first year. In the second year, the values of pH, ESP and total salinity decreased by 12.5%, 39.6%. Furthermore, the yield of oil sunflower was 2.87 and 3.44 times that of CK respectively in the first and second year. The hydrodynamic force was higher in the blind ditch nearby, where the water moved fast. In the upper soil of blind ditch, the soil salinity infiltrated into the blind ditch along with water. Furthermore, the blind ditch density and gavel straw bed could shorten migration distance of soil salinity so that the soil salinity could be more easily discharged by blind ditch. This could reduce the soil salinity effectively and accelerate the process of salt leaching. Thus we conclude that the subsurface gravel blind ditch is able to improve the newly reclaimed takyric solonetz land most effectively and increase the yield of oil sunflower. These results will also provide a technical support for the salt-water management of the newly reclaimed takyric solonetz farmlands, and a guide for the sustainable development and utilization of waste takyric solonetz land.