Abstract
Salinity is a major impediment to crop production. This study was undertaken to compare the effect of seaweed extract, humic acid, and potassium sulfate nanoparticles in alleviating salt stress in Alfalfa (Medicago sativa L.). Seeds of ten alfalfa genotypes were germinated in a growth chamber at five salt concentrations (0%, 0.5%, 1.0%, 1.5%, and 2.00%). Salt concentrations above 1% reduced seed germination by more than 70% in most genotypes. One salt tolerant genotype (Mesa-Sirsa) and one salt sensitive (Bulldog 505) were selected and planted in greenhouse pots containing 2 kg of sand and subjected to two salt levels (10 and 15 dS· m-1). Four treatments consisting of 1) control (Hoagland solution, no-salt), 2) seaweed extract at 4 Kg·ha-1, 3) humic acid at 28 L· ha-1, and 4) potassium sulfate at 300 Kg· ha-1. Plant biomass was reduced under both salt concentrations in both genotypes, with a greater magnitude in the salt sensitive genotype. Application of seaweed extract resulted in higher relative water content and proline under both salt concentrations (10 and 15 dS·m-1) in the salt sensitive genotype, and lower electrolyte leakage in both salt tolerant and salt sensitive genotypes, under both salt concentrations. Seaweed extract also resulted in higher catalase and SOD activities in both genotypes under 10 dS·m-1. Catalase and SOD activities were associated with significantly (p < 0.01) reduced electrolyte leakage and increased shoot dry weight. Overall, seaweed extract seemed to have a positive effect in alleviating salt stress in alfalfa.
Highlights
The germination percentage under NaCl salt solution decreased at a faster pace in all genotypes with increasing salt concentration compared to the mixed salts solution (Table 3)
Application of plant growth stimulants to one salt tolerant and one salt sensitive genotype grown under two salt levels (10 and 15 dS·m−1) resulted in overall changes in soil properties relative to the no-salt control
Application of humic acid improved the growth of the salt-tolerant genotype under both salt concentrations, while seaweed extract and potassium sulfate were more effective in the salt sensitive genotype under 10 and 15 dS·m−1
Summary
Salinity is one of the most limiting factors to crop production in arid and semiarid regions of the world. It affects an estimated 6% of the world’s land area or 12,780 million hectares (Mha), in addition to an estimated 20% of irrigated land impacted by secondary salinization resulting from irrigation [3] [4]. Salinity reduces plant growth and production by affecting physiological processes, including disruption of ionic equilibrium, water status, mineral nutrition, stomatal behavior, and photosynthetic efficiency [5]. Disparity in Osmotic potential leads to water deficit, reduced leaf area expansion and stomatal closure, which reduces photosynthesis and plant growth [6]. The ionic disequilibrium causes excessive accumulation of Na+ and Cl− in the older leaves, leading to their premature senescence [6] [7], in addition to creating an ionic imbalance that reduces the uptake of beneficial ions such as K+, Ca2+, and Mn2+ [8] and inhibits photosynthesis and enzyme activities [9]
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