The synergistic effect of biochar and poly(2-ethyl-2-oxazoline)/poly(2-hydroxyethylmethacarylate)/chitosan) hydrogels on saline soil properties and carrot productivity

Abstract

Background: Soil salinity is one of the most important factors limiting crop production. Furthermore, with the increasing population and saline soil worldwide there is no choice but to utilize saline soil to increase the agricultural regions. Therefore, to improve carrot productivity under saline conditions, it is necessary to provide good management such as applying hydrogels and biochar for improving soil properties. Methodology: Hydrogels (PEtOx-HEMA-CS) were synthesized from poly (2-ethyl-2-oxazoline), 2-hydroxyethyl methacrylate (HEMA as crosslinker) and chitosan (CS) via exposure those to gamma irradiation dose; 30 kGy of dose rate 0.9 kGy/h and obtained three types of hydrogels according to concentration of chitosan used. The PEtOx-HEMA-CS hydrogels were enhanced water holding capacity for agriculture purposes. The chemical structures of obtained hydrogels were characterized by FTIR, XRD and SEM. The swelling (%) and gelation (%) were determined. Biochar (BC) as an active substance was physically mixed with those hydrogels at various ratios (0/100, 0.5/99.5, 1/99 and 100/0 (g/g) biochar/hydrogels). BC, PEtOx-HEMA-CS and the mixture of PEtOx-HEMA-CS-BC were mixed with saline soil at ratio 0.05% and 0.1% w/w of obtained materials/soil. A pot experiment was conducted to mitigate the salinity hazards on carrot productivity using biochar with and without hydrogels. Mean maximum temperature, minimum temperature, precipitation, relative humidity and wind speed from September to December in the studied region are 28.66 ℃, 15.76 ℃, 0.01 mm, 58.81%, 5.94 km/h, respectively. Findings: The obtained data referred that there is a significant decrease in soil salinity and exchangeable sodium percentage and increase in organic matter, cation exchange capacity, field capacity, permanent wilting point and available water especially at (PEtOx-HEMA-CS5)0.1-BC1. The highest increment percentage of nitrogen, phosphorous and potassium were 36.36%, 70% and 72%, respectively. In addition, the relative increase of carrot productivity was 49.63% at the highest rates of biochar and hydrogels. However, the highest value of water use efficiency was observed at the mixture of biochar and hydrogels at (PEtOx-HEMA-CS5)0.1-BC1. Conclusions: Finally, applying biochar combined with (PEtOx-HEMA-CS5) could be recommended as a good approach to improve carrot productivity and water use efficiency under saline soil conditions. Graphical Abstract: [Figure not available: see fulltext.].