Using Cotton Straw Interlayer to Reduce Evaporation and Salt Migration From Groundwater to the Soil Surface

Abstract

【Background and objective】 Evaporation and its associated salt accumulation on the soil surface is an abiotic stress facing agricultural production in arid and semi-arid regions, and how to alleviate its detrimental impact is a topic that continues to attract interest from both researchers and practitioners. Cutting the capillary connection in soil is one technology and the purpose of this paper is to investigate the feasibility of burying a straw interlayer in soil to slow down evaporation and salt migration from groundwater. 【Method】 The experiments were conducted in columns filled with saline soil taken from a cotton field that has been watered by film-mulched drip irrigation in southern Xinjiang. The groundwater table was controlled at the depths of 1.0 m, 1.5 m and 2.0 m respectively, with a cotton straw interlayer buried at a depth between 15 cm and 60 cm from the soil surface. In each treatment, we measured water evaporation and salt accumulation on the soil surface. 【Result】 ①The cumulative evaporation and daily evaporation rate both decreased as the groundwater table depth increased, with the average daily evaporation rate being 1.73 mm/d, 1.12 mm/d and 0.49 mm/d, respectively, when the groundwater table was 1.0 m, 1.5 m and 2.0 m deep. The cotton straw layer reduced water evaporation with the reduction depending on its burying depth. The reduction was the highest when its buying depth was 15 cm, and the least when the burying depth was 30 cm. ②Salt accumulation in 0~30 cm soil layer decreased as the groundwater depth increased, with daily accumulation rate being 0.031 g/kg/d, 0.012 g/kg/d and 0.004 g/kg/d, respectively, when the groundwater table depth was 1.0 m, 1.5 m and 2.0 m without the straw layer. The efficacy of the straw layer in reducing evaporation was more noticeable in the early stage of the experiment, and was most effective when being buried at the depth of 15cm. When groundwater table was 1 m, 1.5 m and 2.0 m deep, burying the straw 15 cm deep reduced daily slat accumulation in the 0~30 cm of soil by 71.25%, 87.15% and 90.58%; 41.91%, 37.85% and 34.90%; and 20.45%, 26.63% and 33.33%, respectively, compared with that buying it at 30 cm, 45 cm and 60 cm deep. ③The accumulated salt in 0~30 cm soil increased linearly with soil water evaporation. 【Conclusion】 The accumulated salt on the soil surface and daily evaporation from groundwater both decreased as groundwater depth increased. Regardless of its burying depth, the cotton straw layer reduced groundwater evaporation and salt accumulation in 0~30 cm soil, but it was most effective when being buried at the depth of 15 cm. We also found that the accumulated salt in the 0~30 cm soil increased linearly with water evaporation.

Keywords

• groundwater evaporation
• cotton straw interlayer
• soil salt accumulation
• groundwater depth
• cumulative evaporation