Abstract
Tomato and cucumber plants grown in the greenhouses require relatively high levels of potassium (K) regimes for optimum growth, yield and fruit quality. Greenhouse managers and farming industry owners who established their projects under the arid conditions of Saudi Arabia are applying K fertilizers to tomato and cucumber plants without taking into consideration the actual plant requirements of this essential element. Therefore, four levels of K fertilizer as potassium sulphate (100, 150, 200 and 250 ppm) were applied in fertigation method to both tomato and cucumber plants grown the in greenhouses at the Experimental Station of College of Agriculture and Veterinary Medicine, Qassim University, Qassim, Saudi Arabia; to evaluate their agronomic performance in response to various levels of K fertilizer. Results revealed that increasing potassium levels resulted in a significant increase in leaf K concentration and chlorophyll content. Both tomato and cucumber fruits produced from plants received high level of K (250 ppm) showed superiority over those produced from plants received low level of K (100 ppm) regarding percentage of total soluble solids contents and firmness. Moreover, there was a direct proportional relationship between the level of applied K fertilizer and studied fruit quality parameters (percentage of total soluble solids, firmness). In addition, our data in the present study revealed that under the suggested K regimes investigated, the marketable yield increased linearly with increasing K levels. In conclusion, increasing K rate to 250 ppm statistically increased leaf K concentration and chlorophyll contents of tomato and cucumber plants. While increasing K rates did not affect TSS% and firmness of tomato and cucumber fruits.