Localized Salt Accumulation Decreases the Cotton Root Length during Advanced Growth Stages under Drip Irrigation with Mulch Film in a Saline Soil

Xinjiang is a typical irrigated agricultural area in arid and semi-arid regions of China. Drip irrigation with mulch film (DI) technology, as an effective water-saving measure, is widely used in Xinjiang in recent years. Meanwhile, as in many other arid irrigated regions, the soil in Xinjiang also shows high salinity. Soil salinity caused by the distribution of irrigation water often has a more significant impact on crop growth compared to other soil factors under the condition of high soil salinity.

Roots are in direct contact with the soil, and thus are the first plant organ to encounter soil salinity, and potentially suffer damage from salt stress. Root length is more scientifically meaningful for evaluation of plant root function. Because collection of whole root systems under field condition is difficult, there are few studies of root length, and even fewer in which a species has been grown on the same site over several seasons.

To identify the salinity dynamics under DI in saline soil and determine the effects of salt salinity on cotton root length, Dr. MAI Wenxuan et al. conducted field experiments in saline soil based on a monolith method using flooding irrigation with mulch film (FI) as a control at the Korla Experimental Station of the Xinjiang Academy of Agricultural Sciences, China in 2009 and 2010.

Based on the field experiments and laboratory analysis, the results showed that the total cotton root length decreased 120 days after sowing (DAS) under DI, and was mainly centered in the 0–30 cm soil layer and at distances of 30–70 cm from the drip-lines. There was almost complete overlap in the area of root length decline and salt accumulation. In the soil depth of 0–30 cm and at distances of 30–70 cm from the drip-lines at 110 to 160 DAS in 2009 and 171 DAS in 2010, the electrical conductivity (EC) in all soil samples was at least 3 mS/cm and in some cases exceeded 5 mS/cm under DI treatment. However, EC barely exceeded 3 mS/cm and no reduction in root length was observed under FI treatment.

Correlation analysis of soil EC and root length density indicated that the root length declined when the soil EC exceeded 2.8 mS/cm. The main reason for the decrease of root length in cotton under DI was localized accumulation of salinity. The result was published in Journal of Arid Land in 2014.