A pot trial was carried out to assess the effect of three fertigation nutrient mixtures on the growth of Medjool date palm plants. The plants were grown either in river sand or in a 20% calcium carbonate - 80% river sand mixture to approximate desert soil conditions. Each fertigation solution comprised all of the elements required for healthy growth. The source of potassium of each solution differed. The fertilizer sources for the nutrients besides potassium were the same. The nitrate to ammonium ratio was markedly greater in the solution made up using KNO3. The concentration of each element in each solution was identical, except for a relatively small increase in the SO42- concentration in the solution made up with K2SO4 and a relatively small increase in Cl- concentration in the solution make up with KCl. These differences were unavoidable, being a consequence of the K source used. In addition, an equal amount of NaCl was added to each solution to render the solutions saline. The plants were fertigated three times a week. Growth was assessed in terms of plant height on a number of dates after planting, and top leaf-stem fresh weight, root fresh weight, number of compound leaves, or number of primary roots when the plants were lifted from the pots, two years after planting. The plants grew better in the sand-calcium carbonate mixture. No interaction was apparent with respect to medium type and fertigation solution. The plants fertigated with the solution made up with KNO3 grew better than those fertigated with the solution made up with KCl or K2SO4. They were of greatest height and showed prominence in the other growth parameters assessed. A difference in growth relating to whether KCl or K2SO4 was the K source was not clearly apparent. It was concluded that the growth of Medjool date palm plants could be expected to be better when nitrate predominates over ammonium in applying fertilizers. To maximize nitrate in a fertigation solution or fertilizer mix, the obvious option available is to use KNO3 as the K source in endeavoring to match solution nutrient concentrations with date palm nutrient demand. The use of nitric acid can also be considered.
