Potassium-salinity interactions and their effect on growth, root water uptake and nutrient and physiological status of tomato

Alon Ben-Gal, Uri Yermiyahu, Hagai Yasuor, and Gilat Research Center, ARO

Background

Soil salinity is a major environmental factor limiting food productivity and has become a threat to sustainable development of agriculture, particularly in arid and semiarid regions (Singh, 2015; Devkota et al., 2007). Under saline stress conditions, cop water and nutrient uptake capacity are inhibited, photosynthesis and respiration are reduced, and ultimately, crop yield losses occur (Colla et al., 2012; Shaheen et al., 2013; Lucini et al., 2015; Neocleous et al., 2017). Therefore, the regulation and management of soil salinity and improvement of crop salinity stress tolerance are of current interest.

Potassium is the second most abundant macronutrient in plants, composing between 2 to 10% of plant biomass (Kaya et al., 2007; Nieves-Cordones et al., 2014). It plays a central role in the nutrient status of plants, especially via neutralization of negative charges, activation of enzymes, reducing excess uptake of ions such as Na and Fe, cell turgor maintenance and osmoregulation (Cakmak, 2005; Zheng et al., 2008; Aleman et al., 2009). Proper K supplement has been acknowledged to raise plant tolerance to salt stress. Positive effect of K nutrition on overcoming salinity stress has been reported in crops including tomato (Lopez and Satti, 1996; Fan et al., 2011), potato (Elkhatib et al., 2004), spinach (Kaya et al., 2001), melon (Kaya, et al., 2007), rice (Bohra and Doerffling, 1993), and strawberry (kaya et al., 2003). The effect of K has been assessed under different K concentrations（0-400mg L^-1）and salinity levels (30-130mM) (Plaut et al., 2013). Beneficial effects of increased K under saline conditions include: improving crop shoot growth and yield (Satti and. Lopez, 1994), hampering negative effects of NaCl on gas exchange and leaf area (Khayyat et al., 2009), and increasing photosynthesis (Psarras et al., 2008), the number of tillers and kernels per spike and yield of barley (Endris and Mohammad, 2007). Potassium may counteract the deleterious effects of Na by lowering Na uptake, and then improving K/Na ratio in shoots (Botella et al., 1993; kaya et al., 2001; Psarras et al., 2008). However, others found that there was no moderating effect of salinity stress on yield and growth of tomato, barely and corn, suggesting that K uptake is simply reduced by Na due to the competitive interaction between K and Na (Yurtseven et al., 2005). Yurtseven et al. (2005) reported that the positive effect of K application on overcoming salinity-induced tomato yield decrease only could be explained by a simple fertilizer effect. Salinity stress would be aggravated when K oversupplied. The quantified improvement of salinity tolerance on crop by supplying the K fertilizer still needs to be assessed and tools are needed to determine optimum rates of K fertilizer application under conditions of salinity.

Polysulphate is an evaporite mineral, a hydrated sulfate of K, Ca and Mg found in USA, China, UK and Russia with apparent large reserves (Zheng et al., 2015). Polysulphate contains 11.6% K, 12.2% Ca, 3.6% Mg and 19.2% S within the chemical formula K2Ca2Mg(SO4)4• 2(H2O) and has been suggested as a potential fertilizer to meet crop demands of these minerals (Yermiyahu et al., 2017). Polysulphate has been used as a potassium source for fertilizer production and has been directly applied after granulation or crushing (Zheng et al., 2015). Polysulphate has been shown to benefit biomass/yield production and quality of food in both pot and field experiments (Fraps, 1932; Barbarick, 1991; Satisha and Ganeshamurthy, 2016). There is no information regarding polysulphate under conditions of salinity.

Research objectives

1. To quantify the characteristic of the physiological response of tomato to supply rate of potassium fertilizer under conditions of salinity.
2. To quantify and understand mechanisms of the response of water and potassium uptake under single and combined salinity and potassium stresses.
3. To evaluate polysulphate as a potassium source under conditions of salinity.

We present a dual experimental-modeling approach to address the objectives. The experiments will provide data that will be used to calibrate and validate a predictive mathematical model for simulating water use and potassium uptake. Due to its economic importance and extensive database regarding salinity response, tomato will be used as a model crop for the study.