Establishing an ecological forest system of salt-tolerant plants in heavily saline wasteland using the drip-irrigation reclamation method

Abstract

Salinization in the low-lying edges of the Yinchuan plain, in northwest China, is a threat to productive farmland. An experiment, adopting “drip irrigation + high ridge + salt tolerant plant” reclaiming pattern, was conducted to develop a method of forest construction. The drip irrigation was scheduled by soil matric potentials (SMPs) monitored by tensiometers at both 20 cm and 50 cm depths exactly under drip emitters. There were five treatments marked as S1–S5, with their corresponding SMPs controlled higher than − 5, − 10, − 15, − 20 and − 25 kPa. Two salt-tolerant plants, the Elaeagnus angustifolia and the Astragalus adsurgens, were planted on ridges for reclamation. Results showed that low salinity zones formed quickly under drip emitters and the average electrical conductivity of saturated soil paste extracts (ECe) within 60 cm depth increased as SMP thresholds decreased. The 3-year average ECe values were 1.8, 4.6, 6.0, 7.1 and 7.7 dS m−1 for S1–S5, respectively, reduced by 93.4%, 83.1%, 77.9%, 73.9% and 71.7% compared with initial values. Soil salt was progressively leached and reached to an equilibrium state when SMP was kept above − 10 kPa within one growing season. Two growing seasons were required to reach a similar equilibrium for SMP threshold between − 15 and − 25 kPa. The soil pH increased 0.25, 0.11, 0.09, 0.05 and 0.07, and the soil sodium adsorption ratios declined by 59.3%, 36.2%, 37.8%, 44.9% and 42.7% in S1–S5, respectively, indicating a dealkalizing soil environment in all treatments. Plant growth indicators decreased as SMP thresholds declined and a threshold of − 20 kPa was important to maintain plant survival rates and growths. Therefore, keeping SMP higher than –10 kPa in the first two years was important to ensure desalinization and that higher than –20 kPa in the third year was essential to maintain salt balance and plant growth. A method consisting of agronomic practices and a four-stage drip-irrigation schedule based on the key SMPs is recommended for constructing a forest system.