Study On Water-salt Balance And Water Requirement Of Salt-leaching Of Drip Irrigation Under Mulching For Cotton Field

Drip irrigation is not able to generate deep permeability. The salt in soil can not be removed by leaching of irrigation water. Considering the sustainable development of irrigation agriculture in oasis, long-term drip irrigation under mulch may induce potential ecological risk. Therefore, the sustainable development of oasis agriculture is concentrated on the water and salt balance under the condition of drip irrigation below mulch and quantity of the salt-leaching water.Based on characteristics of water and salt transport of farmland, water and salt model, water and salt balance and leaching water quantity, the dynamics and balance of water and salt under the condition of drip irrigation under mulch were reviewed. Previous studies showed that soil salt accumulated gradually in drip irrigation under mulch, and the mode, salt-leaching water quantity and suitability assessment under such conditions were scarce. Therefore, through three-year field experiment on the water and salt dynamics and balance, the response of root system and aboveground biomass accumulation of cotton to soil moisture, the effects of water-saving and salt-leaching in drip irrigation under mulching and the salt-tolerant index of cotton were analyzed by which the water-saving mechanism of drip irrigation under mulching was revealed .Water dynamics and balance in cotton field under the condition of drip irrigation below mulch were studied. The results showed that the horizontal distribution of soil water content followed the order: width row land > narrow row land > bare land. The effects of drip irrigation on soil water content was limited within top 100 cm soils below which soil water content are similar. The wetting front was able to reach 100 cm in depth with the drip irrigation amount between 3926 and 4265 m3/hm2, and 60 cm between 2947 and 3600m3/hm2, 40 cm for 2618 m3/hm2. The growth period of cotton under the condition of drip irrigation below mulch in South Xinjiang.required 543.2 mm water. The water requirement in seedling, budding, flowering and bolling accounted for 10.0 %, 15.4 %, 53.0 % and 21.6 % of the total, respectively, minimum in seedling period and maximum in flowering and bolling period. The water consumption in fallow period was 238.1 mm. The optimal water consumption ranged between 506.0 and 536.7 mm. The cotton yield reached the highest, 6361 kg/hm2, when irrigation amount was 3464 m~3/hm~2.The root biomass under different irritation treatments was mainly distributed at mulched area, occuping 60.7 %-73.5 % of the total and correspondingly, 39.4 %-26.6 % at inter-mulch areas. Water stress increased the rooting depth, root biomass and the extent of lateral rooting. The maximum root length density is 26.5 mm/cm3, appearing at 24.1 cm away from the plants, 12.9 cm under the mulch. Over-irrigation increased the height, width of the inverse-fourth leaf, amounts of branch and square, thus accelerating the biomass accumulation rate. It also increased the root/shoot ratio and the proportion of biomass allocated to vegetative organs. However, over-irrigation increased the rate of fruit abscission and therefore reduced the economic yield. These results suggested that both excessive soil moisture and water stress could affect the biomass accumulation and allocation in different organs in various life stages. Under the conditions of the current experiments, 3600 m3·hm-2 seemed to be the optimal irrigation amount.Soil salt presented a Y-shaped distribution in space. The soil salt content under mulch was less than inter-mulch lands, presenting a characteristic of'low at two ends and high at the middle'within of the soil profiles. Differently, it increased gradually from the lower soil layers to soil surface at inter-mulch lands. The peak position of soil salt under mulch moved downward with the increases of drip irrigation amount. The average salt content in 0-60 cm and 0-100 cm soil layer decreased after drip irrigation. The desalinization rate increased with the increase of drip irrigation amount. In 0-60 cm soil layer, desalinization rate ranged between 6.0 % to 34.8 %. Soil salt of inter-mulch lands trended to accumulate, with the accumulation rate decreasing with the increase of drip irrigation amount. The average salt content in 0-60 cm soil layer increased with the time of drip irrigation. Based on water-salt balance, estimation method of salt content-dependent water requirement of salt-leaching was proposed, which was applied in current study. Furthermore, preliminary index system for suitability assessment of drip irrigation under mulch was established.