The Efficacy of Acidified Drip Irrigation for Reducing Soil pH in Remediating Heavy Saline Coastal Soils

Abstract

【Background】 Heavy saline coastal soil is a valuable land resource but its high salt content and sticky texture, along with its high sodium adsorption ratio and shallow groundwater table, makes it difficult to remediate. Previous studies had shown that the pH of coastal saline soil increased during its remediation, which could alter physical, chemical and microbiological properties of the soil for crops to grow. Common methods to alleviate these side effects include application of organic fertilizers, desulfurized gypsum, biochar and other additives. But they are expensive and not applicable to large-scale soil remediation. As such, more efficient methods are needed. 【Objective】 The aim of this paper is to present a simple and low-cost, yet green and efficient method to control soil pH in remediating heavy saline coastal soils by acidifying the drip irrigation water. 【Method】 The experiment was conducted in laboratory columns. It consisted of five treatments with the irrigation water pH controlled at 6 (S1), 6.5(S2), 7(S3), 7.5(S4) respectively. Without acidification (pH 8.2~8.5) was taken as the control (CK). In each treatment, we measured spatiotemporal variation in electrical conductivity of the saturated soil paste (EC), and its associated pH after the soil was leached by 60 mm, 120 mm, 180 mm and 240 mm of water respectively. 【Result】 Desalination occurred in the soil below the emitter first and it then expanded gradually; soil salinity decreased logarithmically with the amount of irrigation water. In all treatments, the temporal changes in salt leaching pattern and leaching rate were similar, while the change in soil pH differed. After 240 mm of water was applied, the average soil pH in 0~55 cm of soil under S1—S5 treatment was 7.73, 7.78, 7.86, 7.92, 7.92, respectively. Soil pH in the non-saline area (<4 dS/m) in S1—S3 treatment increased first followed by a decline, while the pH in S4—S5 treatment continued to increase, as time elapsed. It was found that the change in soil pH depended on acidity of the irrigation water.; the lower the pH of the irrigation water was, the sooner it took the soil pH to peak, and faster for it to fall back to constant. 【Conclusion】 Acidifying drip irrigation water to a pH in the range of 6~7 was effective to avoid soil pH increase during remediating heavy saline coastal soil. This can be achieved by adding industrial phosphoric acid to the irrigation water to create a suitable soil environment for plants to grow during the remediating processes while in the meantime controlling the soil pH not exceeding a critical value.

Keywords

• saline coastal saline soil
• column experiment
• soil ph
• salt leaching