Investigating the potential use of mono-potassium phosphate (MKP: 0-52-34) applied through fertigation as a method to improve salinity tolerance of tomato plants

Tomato is a moderately sensitive crop to salinity. High salinity alters vegetative growth and production leading to economic losses. The study here investigated the potential use of mono-potassium phosphate (MKP: 0-52-34) as a method to increase salt tolerance on tomato (Solanum lycopersicum L. ‘Valouro’) plants irrigated with saline solutions (NaCl+CaCl2) of EC: 6, 8, 10 and 12 dS m‑1 and fertigated with different doses of MKP: 0, 2, 3 and 3.5 g L(‑1). Results of PCA analysis showed that plant growth indicators (i.e. plant height and leaf number), flowering (number of clusters and flowers), fruit set and production (fruit number, individual fruit weight, and fruit yield) were negatively affected by increasing salinity while indicators of fruit quality (titrable acidity, total soluble solids, fruit firmness and pH) were improved. Plant height and yields were reduced by 22, 31, 39, 40% and 76, 87, 90, 95% under the effect of 6, 8, 10, and 12 dS m(‑1) respectively, while improvement in TA, TSS, firmness and acidity peaked at EC=12 dS m(‑1). Salinity induced a shorter growth cycle and earlier flowering, fruiting and fruit maturity dates. The beneficial effect of MKP in mitigating salinity effect was the most obvious at EC=6/MKP=2 and EC=8/MKP=2 inducing best averages of vegetative and productive parameters compared to EC=6/MKP=0 and EC=8/MKP=0. Leaf and stem composition were also affected by MKP application. The highest N and P contents in stem were observed at EC=10/MKP=3.5 (1.79 and 0.25%, respectively) and K content was the highest at EC=6/MKP=3.5 (3.07%). N content in leaves was the highest in the control (2.38%), while P and K peaked respectively at EC=8/MKP=2 (0.19%) and EC=6/MKP=3.5 (2.99%). Results of polynomial model predicted an optimal use of MKP as fertilizer when applied with a dose of 2 g L(‑1), while a non-beneficial use of MKP on salt-tolerance was predicted at EC>10 dS m(‑1).