Irrigation with Brackish Groundwater and Desalination Concentrate: Effect on Soil Microbial Properties, Plant Uptake, and Ion Deposition in Soil

Published Date:

September 2021

Authors:

Manoj K. Shukla, Akram Ben Ali, Sarah Cerra

Abstract:

Severe drought as a result of low precipitation, and high evapotranspiration rates in the southwestern U.S. including New Mexico have stressed variably brackish groundwater for irrigation purposes. Desalination using reverse osmosis (RO) produces both fresh water and highly saline byproduct. RO concentrate, a byproduct of brackish groundwater desalination, can be a source of irrigation water for salt tolerant crops. But in that event, issues related to soil health must be investigated due to the accumulation of salts in the soil. The objectives of this study were to: (i) identify salt deposition patterns due to the drip irrigation method, (ii) measure the plants’ ion uptake, changes in plants, and ion concentrations, and (iii) determine the impact of irrigation with brackish groundwater and RO concentrate on the soil microbial community and soil organic carbon.

In this three-year study, brackish groundwater and RO concentrate were Ca dominant and were used to irrigate two halophytic species: Atriplex canescens and Atriplex lentiformis. This study was conducted in Alamogordo, New Mexico at the Brackish Groundwater National Desalination Research Facility (BGNDRF). The drip irrigated field was divided into two blocks, North and South. The two blocks were planted with mixed Atriplex canescens and Atriplex lentiformis. Several measurements were taken on soil texture using the hydrometer method, soil water content using the gravimetric method, EC using an EC meter, evapotranspiration (ET) using Blaney-Criddle and Hargreaves models, stem water potential (SWP) using a pressure chamber, as well as plants’ ionic uptake, and soil microbial composition. The soil microbial biomass was measured using the fumigation-extraction method. Dissolved organic carbon C and nitrogen N were determined using a Vario-Cube analyzer. Soil, water, and plant samples were collected and sent to AgSource Lab, Nebraska for ion analysis.

No-significant differences were found for ET between the two models. Na and Cl concentrations in soil at a location 90 cm from the west side of the plant trunk were 2844 mg/l at 80% irrigation rates and 5236 mg/l at 60% irrigation rates. Na and Cl at a 60% irrigation rate at 25 cm depth were 1965 mg/l and 5877 mg/l, respectively. A somewhat bell-shaped curve distribution was observed with salt deposition at the edge of the wetting front. The SWP for Atriplex canescens was -27 bar. Na and Cl were 5.87 mg/l and 11.1 mg/l, respectively, in Atriplex canescens leaf sample. Soil pH was around 8. Soil nitrate produced a nitrogen content of 18.94 mg N/kg for soil at the surface on the north side. Soil ammonia was 0.49 mg N/kg for soil on the north side near the soil at the surface. Soil organic carbon was 3.15% at the soil surface. Microbial biomass was 221 mg C/kg soil at the surface and 140.6 mg C/kg soil at 40 cm soil depth. Glycosaminidase enzyme was 40.62 ug p-NP/g soil/h at 40 cm soil depth. The Shannon microbial diversity index was 3.58 H index at the soil surface and 1.94 H index at 40 cm soil depth. Atriplex canescens and Atriplex lentiformis showed high performance when irrigated with brackish water and RO concentrate. Future studies should use other Atriplex species and explore benefits including their potential as ornamental plants, nitrogen fixation, and other benefits.

Download:
Technical Report 397

Keywords:
desalination, brackish groundwater, halophytes, ion deposition, plant survival, soil microbial properties, concentrate management