Study On Soil Water And Salt Transport Characteristics In Brackish Water Drip Irrigation

The way of agricultural irrigation combines brackish water with drip irrigation can give full play to superiority of both, save water and increase production. Based on the high levels of salt content of brackish water, it is easy to form soil salinization if we use the water for a long time and affect normal growth of crops, so the study on salt and water movement is particularly important. In this paper, we combine brackish water with drip irrigation and have a simulation experiment in laboratory. The instrument is a rectangular plexiglass box. We studied four alternate modes of drip irrigation(saline-fresh; fresh-saline; saline-fresh-saline;fresh-saline-fresh)and emitter discharge, salinity, emitter spacing for a single point source and two points under water and salt transport characteristics and conditions. The main conclusions are as follows:(1) Emitter discharge has greater impact on the soil moist body characteristics. In single point source infiltration conditions, emitter discharge is more significant in the wetting front,especially in the horizontal direction. In the same time, the greater the dripper flow, horizontal wetting front advance faster. In the conditions of two points, the wetting front becomes a horizontal straight line after the two wetting front meet. To the distribution of water, water gathered more in the Upper layer of soil; impact on salinity distribution mainly in vertical section, a large emitter flow rate on soil salt leaching have some effects.(2) Consider the mineralization of water effects together with the contribution from the sodium from water in soil, different mineralization of water on the wetting front advancing processes of change can be divided into two cases: when the salinity of water is less than 3g/L,the greater the salinity the smaller the horizontal wetting front advance distance and vertical wetting front advancing the greater distance; when the salinity of water is greater than 3g/L,the greater the salinity horizontal wetting front promoting greater the distance, but vertical wetting front advance distance smaller. Distribution of soil moisture in order to deal with the most uniform D8.Soil conductivity and salinity have a significant positive correlation and D8 give optimal environment of water and soil.(3) Two point source infiltration, the smaller of emitter spacing the sooner the wetting front meet, and with the extension of time the distance promote farther, the wetting front close to a horizontal line; on soil water distribution main at the intersection of the surface, emitter spacing decreases, the same position have a high moisture content, in the horizontal direction,the two profile have similar moisture content. Spacing set at 30 cm,the horizontal direction in nearby the intersection salt content reaches the maximum, spacing is set at 20 cm,the horizontal direction salt distributed more evenly, no significant difference.(4) The impact of freshwater and saltwater in different alternate order, the impact of the wetting front advancing in a single point source is mainly reflected in the initial irrigation0-30 min,freshwater moves faster in the horizontal direction and saltwater is faster in the vertical direction; the influence in soil moisture is mainly in the 2-6cm depth layers, the order of saline-fresh-saline keeps highest moisture content, the order of saline-fresh is second. The first step of the order plays an important role to form the soil macropore, the influence of the subsequent infiltration on the soil moisture distribution have a relationship with time. Effects of different alternating order in soil salinity distribution is mainly in the 2-6cm depth. The order of fresh-saline and saline-fresh-saline is smaller in salt in 2-6cm but the order of fresh-saline-fresh, there is a mutation in values and finally drip fresh water can effectively leach salt gathered in the surface. For two points source, as the formation of the wet zone, the impact of different alternating order on the soil wetting front showing a one-dimensional variation to depth, the impact on soil moisture and salinity is mainly in the depth as same as a single point source, the application of freshwater and saltwater in different alternate order can retain soil moisture and effectively leach salt.