Abstract
The increasing soil salinity levels under reclaimed water irrigation have a negative effect on plant growth. Greenhouse experiments were conducted in 2018 and 2019 under reclaimed water–fresh water combined irrigation. After transplanting (Day 1), rice was irrigated with clean water (tap water) for 10 days to facilitate rice root colonisation. Subsequently, rice was irrigated with reclaimed water for 50 days (Day 11 to 60), and then irrigated with clean water. B. subtilis and S. cerevisiae were mixed with clean water (tap water) and irrigated into soil at Day 61. B. subtilis (20 billion colony-forming units/g) and S. cerevisiae (20 billion colony-forming units/g) were mixed at the following proportions: 5 g and 0 (J1), 3.75 g and 1.25 g (J2), 2.5 g and 2.5 g (J3), 1.25 g and 3.75 g (J4), and 0 and 5 g (J5), respectively; rice treated with reclaimed water (CK) and clean water (J0) with no microorganisms applied were also used. We measured NO3--N and NH4+-N concentrations and electrical conductivity (EC) in the soil at 0–5, 5–15, and 15–25 cm layers; root activity; and malondialdehyde (MDA), soluble sugar, superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and glutamine synthetase (GS) activity in leaves at Day 71. B. subtilis and S. cerevisiae combination could promote rice physiological indices, and B. subtilis had a greater effect than S. cerevisiae. There are obvious differences in the physiological performance and soil N between 2018 and 2019 due to the EC of reclaimed water. Redundancy analysis revealed that soil NO3−-N and the mass of B. subtilis applied were major factors influencing leaf physiological indices. Five grams of B. subtilis is recommended to facilitate rice growth after irrigation with reclaimed water. Our research provides a new agronomic measure for the safe utilisation of reclaimed water.
Highlights
In China, the exploitation of reclaimed water in agriculture is in its infancy, and extensive studies on its safe utilisation in agricultural activities, in addition to technological developments, are required
2018, soil electrical conductivity (EC) of J2 and J4 treatments was lower than J0, and in 2019, soil EC of J2–J5 was lower than J0, indicating that the application of microbial agents can further reduce soil EC
Of 0–5 cm and 15–25 cm layers was close, which indicated that the soil salinity increased significantly under the condition of high EC reclaimed water irrigation, which directly led to the effect of different years on soil EC exceeding that of microorganism treatments (Table 4)
Summary
In China, the exploitation of reclaimed water in agriculture is in its infancy, and extensive studies on its safe utilisation in agricultural activities, in addition to technological developments, are required. Calcium and hydrogen carbonate ions, in addition to N, P and potassium nutrients, among others, it poses soil salinisation risks [5] and could deteriorate soil physical and chemical properties [6]. Plant growth-promoting bacteria facilitate plant development by enhancing plant growth or influencing plant metabolism directly through their metabolic activities [9]. Bacillus spp. secrete exopolysaccharides and siderophores that inhibit the movement of toxic ions, facilitate ionic balance maintenance and water translocation in plant tissues, and inhibit pathogenic microbe growth [10]. Mohamed (2005) [17] observed that active foliar application of dry yeast improved plant growth and yield, and increased N concentrations in grain
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