Organic Amendments Combined with Plant Growth-Promoting Rhizobacteria (Azospirillum Brasilense) as an Eco-Friendly By-Product to Remediate and Enhance the Fertility of Saline Sodic-Soils in Egypt

ABSTRACT

In Egypt, the total area of agricultural land is 3.36 million acres, which is 3.8% of the country entire territory. One of the main obstacles to agricultural production in Egypt is soil salinization and degradation. Therefore, saline-sodic soil reclamation in arid regions is highly relevant. This study aimed to use Azospirillum inoculation with eco-friendly organic wastes for free remediation of saline-sodic soils. In this work, nine treatments included two levels of spent grain (S1 and S2), two levels of compost (C1 and C2), a mix of both sources (C1S1), Azospirillum (A1), a mix of both sources with Azospirillum (A1S1 and A1C1) and untreated control. The treatments were previously incubated with soil at field capacity for five months under laboratory conditions at 28°C. The most relevant chemical and biological parameters were analyzed every month for five months. Results indicate that Azospirillum inoculation with spent grain increased soil organic carbon (TOC), dehydrogenase and urease enzymes, micro-nutrients iron (Fe²⁺), zinc (Zn²⁺), manganese (Mn²⁺), copper (Cu²⁺), and boron (B⁺), and macro-nutrients nitrogen (N), phosphorus (P) and potassium (K); while decreased exchangeable sodium percentage (ESP), pH and EC, by 75%, 12%, and 43% respectively, compared to initial conditions. A significant variation was observed in chemical and biological properties among all treatments in the order of S2 ≥ A1S1> A1 > C2 > C1S1 > A1C1 > C1 > control > initial. In conclusion, the addition of Azospirillum with the spent grain is highly recommended for the saline-sodic soil amelioration. It is more effective than compost to remediate and enhance saline-sodic soils fertility.

Graphical abstract

KEYWORDS:

• Azospirillum
• soil amelioration
• spent grain
• saline-sodic
• incubation

Highlights

1. Spent grain is a costless by-product which can be used for saline-sodic soil reclamation.

2. The combined application of Azospirillum with spent grain decreased the EC and ESP in soil.

3. TOC, pH, and Dehydrogenase were the main factors affecting ESP and then influencing, CEC and Ex-Na⁺.

4. Variable-rate compost application was more expensive than the spent grain and Azospirillum treatments for saline-sodic soil remediation.

Acknowledgments

We thank the Colleagues of Department of Soil Science and Soil Ecology, Institute of Earth Sciences of St. Petersburg State University, Saint Petersburg, Russia, Colleagues of Department of Land and Water Technologies, Arid Lands Cultivation Research Institute, City of Scientific Research and Technological Applications, Alexandria, Egypt, and Cultural Affairs and Missions Sector, Ministry of Higher Education and Scientific Research.