An Investigation On The Salt-Water Coupled Transport And Crop Responses In Saline And Sodic Soils Under The Influence Of Irrigating Water Quality

The lower infiltration rate and therefore the lower crop yield are the main problem for saline soil. To resolve this problem, increase water use efficiency with sufficient and efficient leaching and to control groundwater table are of great importance for the sustainable development of agriculture in the areas.Soil hydraulic conductivity is closely related to the movement of water and salts in soil profiles and is highly affected by solution salt concentration and its composition. The effects of water quality, aging and hydraulic gradient, on the saturated hydraulic conductivity (HC) of disturbed smectitic silt loam were studied with the laboratory experiments. Two hydraulic gradient (4.55 and 0.3) and solutions with four SAR (Sodium Adsorption Ratio) values (SAR of 30, 20, 10, and 2) were used in the study. The soil were packed in 10 cm long columns and were consecutively leached with 10 pore volumes of 0.5, 0.08, 0.04, 0.02, 0.01, and 0.002MC1- solutions and distilled water. The soil infiltration characteristics curves were obtained under different conditions and the relation of water quality-aging-hydraulic gradient was established. At the same time, hydrodynamic dispersion coefficient was obtained by the Analytical solution of the one dimensional convectional-dispersion, breakthrough curves from the experiments and the pore velocity of flow in different time with the Golden-Section Search method. The analytical solution of 1-D convectional-dispersion differential equation with the hydrodynamic dispersion coefficients so determined can very well simulate the salt and water movement processes in the soil columns.Water movement in saline soil body under drip emitters and its characteristic parameters, the horizontal and vertical advance distances as related to time, are of importance in designing drip irrigation systems. A series of laboratory experiments were conducted to quantify the influences of irrigating water salinity, discharge rate, and soil salinity on the patterns of the wetted soil column and the wetting front dynamics. Two soils, a saline silt loamy soil and an alkaline silt clayey loamy soil, 3 discharge rates (2, 3.4, 8 1/h), 5 saline levels of irrigating water (4 different combinations of SAR = 20 and 2 and C = 80, 20 meq/l, as well as distilled water, DW), were used in the experiments. The results indicated that drip irrigation of different flow rates with different quality of irrigating water had its significant influences on the wetted patterns, higher discharge rate produced higher lateral or horizontal movement of soil water. Irrigation with DW yielded very lower vertical infiltration and the horizontal water advance was much faster, which is not good for salt leaching and may cause surface runoff. Irrigation with saline water produced faster horizontal water movement initially and with irrigation went on, vertical infiltration tended to increase as compared with the lateral movement.Drip irrigation experiments of watermelons and honeydew melons with saline water were conducted in the Hetao Region, China, in order to reduce ground water level and soil salinization. Saline groundwater, ranging in salinity from 3.3dS/m in the early season to 6.3dS/m at the harvest time was used. Four irrigation treatments (control, 30,60, and 90% of evaporation from Chinese Evaporation Pan) were used in the experiments. The control treatment was not irrigated through out the season, as is the local practice. The yields of watermelons and honeydew melons were dramatically increased and thequality improved under drip irrigation, as compared with control. And the crop water requirement coefficients based on Chinese Evaporimeter and the Crop Coefficients Kc were estimated accordingly.Surface irrigation can also obtain the good effect under the good management method. Field experiments were conducted to investigate the effects of (surge and continuous) furrow irrigation (as compared with flood irrigation), and the conjunctive use of quality Yellow River water with 0, 10, and 20% of the local saline groundwater on salin...