In many parts of the world, saline water collected from field drainage has been successfully used for irrigation (Grattan et al., 1994). However, plants may suffer from osmotic stress, ionic imbalance, and the inhibition of nutrient absorption when irrigated with saline water, with an adverse effect on fruit yield (Ben-Gal et al., 2008; Munns, 2002). To alleviate the effects of salinity stress on plants, the application of extra water for the leaching of salts (e.g., Na+, Ca2+, and Mg2+) from the root zone is a common method of reducing the salt content in the surface soil (Chen et al., 2016). An appropriate LF will maintain tolerable root-zone salinity (Dudley et al., 2008), in turn, enhancing the fruit yield.
Peppers (Capsicum annuum L.) are considered moderately sensitive to salt stress (Rameshwaran et al., 2016). The threshold-slope linear response model (Maas and Hoffman, 1977) and the sigmoidal-sharp salinity response model (Van Genuchten and Hoffman, 1984) are commonly used to describe yield–salinity relationship. The LF may affect the yield of peppers, but whether the LF also has an effect on the parameters of these models is unclear.
Irrigation with saline water may in many cases improve fruit quality. The fruit quality parameters of tomatoes (Solanum lycopersicum L.) including total acidity, TSS, sugar content, pigment content, and organic acid content were improved by saline water irrigation (Gough and Hobson, 2015; Plaut and Yehezkel, 2004). It also improved the quality of the melons (Citrullus vulgaris L.) by increasing Fn, dry matter, acidity, TSS, and total sugar content (Colla et al., 2006; Navarro et al., 1999). For peppers, however, there is limited literature that is mainly concerned with sweet peppers or bell peppers, and it is not inconclusive. Navarro et al. (2010) and Rubio et al. (2009) found that irrigation with saline water (3.0 dS·m−1 NaCl) had no effect on the TSS, Fn, and, pH of sweet peppers. However, Navarro et al. (2002) found that saline water irrigation (from NaCl or Na2SO4) decreased the quality of sweet peppers by reducing pulp thickness, Fn, TSS, and fructose, glucose, and amino acid contents. On the other hand, saline water irrigation improved the fruit quality of bell peppers giving higher TSS, VC content (ascorbic acid), total sugar content, and acidity (Patil et al., 2014), and improved the quality of sweet peppers causing a higher myoinositol, fructose, and glucose content (Rubio et al., 2009). The quantitative relationship between the fruit quality parameters of hot peppers and the ECe or evapotranspiration, which are useful relationship to know for the management of saline irrigation for high-quality hot pepper production, have not been documented. In addition, we studied Na+, K+, and Ca2+ concentrations and K+/Na+ ratio in hot peppers to further understand the mechanisms causing the effects of the ECiw and LF on yield and quality.
The objectives of this study are 1) to assess the effects of ECiw and LF on the yield, fruit quality, and ion content of hot peppers; 2) to study the responses of a total yield of hot peppers to salinity and to calibrate the yield indices of both a threshold-slope linear response model and sigmoidal-shape model; and 3) to establish the quantitative relationships between fruit quality, ion content, and ECe or seasonal evapotranspiration.
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