Abstract
In Japan, the highest salt concentration in irrigation water for sugarcane cultivation has been reported to be above 2500 mg L−1, which may cause harmful effects to the crops; however, little information is available on the relationship between the salinity of irrigation water and sugarcane. To investigate its effects on agronomic and physiological traits, a Japanese cultivar, Saccharum spp cv. NiF8, was grown with 0, 200, 500, 1000, 2000, and 3000 mg NaCl L−1 under pot conditions. The treatments significantly lowered leaf area; however, NaCl levels up to 500 mg L−1 did not greatly reduce culm weight and juice sugar concentration. These traits were impaired when the tested cultivar was grown with 1000 mg NaCl L−1 or higher, indicating that salt concentration is desired to be lower than 1000 mg L−1. CO2 assimilation rate was inhibited mainly due to stomatal closure caused by salt stress. The treatments significantly altered Na+, Cl−, and K+ concentrations in juice but not those in leaf, suggesting that juice analysis is an effective method to estimate its salinization status. Culm weight and juice sugar concentration were severely affected as juice conductivity exceeded 900 mS m−1; thereby, sugarcane plants of NiF8 possessing conductivity above this level could be considered salt-stressed where water salinity is a concern.
Highlights
Salt stress is a major factor limiting crop productivity in arid and semi-arid regions
It is likely that there is a threshold of lowered leaf area index that does not significantly affect biomass production since defoliation resulted in only small differences in total dry mass [22] and agronomic parameters [23]
Our study demonstrates that salt concentration in irrigation water is desired to be kept lower than 1000 mg L−1 to prevent any loss in sugar yield by salt stress; the threshold salinity level may be variable among cultivars and other major cultivars in Japan must be tested for resistance to salt stress
Summary
Salt stress is a major factor limiting crop productivity in arid and semi-arid regions. Most crops are sensitive to salinity that is caused by high concentrations of salts in the soil [1]. Apart from natural salinity, a significant proportion of newly cultivated agricultural land has become saline due to inappropriate irrigation, which causes water tables to rise and salt to build up in the root zone [2]. According to the Food and Agriculture Organization (FAO), 45 million ha, which accounts for 19.5% of global irrigated lands, are salt-affected soils [3]. The cost of soil salinization on agriculture is estimated to be US$ 12 billion per year, and this value is expected to further increase [4].
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