Effect of treated sewage water on the concentration of certain nutrient elements in date palm leaves and fruits

Abstract

Leaflet and fruit samples were collected from 9‐year old palms irrigated with potable water and treated sewage water from two locations (the University and the city sewage effluent plant). After drying, ashing, and dissolution of ash by HCl, calcium (Ca), and magnesium (Mg) concentrations were determined by atomic absorption photometry; sodium (Na), and potassium (K) by flame spectrophotometry and chlorine (Cl) by titration. Results of the present study were then compared with those of 1993. Unlike the 1993 results, K, Ca, Mg, and Na concentrations did not show any significant differences in leaves or fruits. Potassium, Ca, and Mg in leaves and fruits irrigated with three types of water in 1995 showed higher concentrations than in 1993. Sodium was lower in leaves and fruits during 1995 than 1993 when treated sewage water was used, but with potable water it was higher in leaves and lower in fruits. The increase in K, Ca, and Mg and the reduction in Na were related to summer rains in 1995. Fruits irrigated with potable water contained higher Na and lower Cl than leaves, however, with treated sewage water (University plant), leaves and fruits contained similar amounts of Na, but higher Cl in fruits; whereas with city plant treated sewage water fruits had lower Na and Cl than leaves. Sodium in the fruits irrigated with potable water increased at a higher rate (3.8x) than in leaves (1.6x), but it decreased at higher rate in fruits (0.66x) than in leaves (0.24x) irrigated with treated sewage water. The increased rate was related to higher K rate (53x) whereas the reduction in Na was related to lower K rate (29x). The ratios of Ca/Mg and Na/Ca showed similar patterns in leaves and fruits irrigated with potable water or treated sewage water. Sodium/Ca ratio was always higher in fruits than in leaves, while Ca/Mg was always higher in leaves than in fruits. The ratic of K/Na tends to be greater in the leaves when their K concentration was equal to or greater than Na concentration. However, higher Na in the leaves resulted in higher K/Na ratio in the fruits, indicating that Na replaced K. The ratio Ca/K in the two seasons was higher in leaves than in fruits irrigated with potable water, but with treated sewage water, it was higher in leaves during 1995 and higher in fruits during 1993. This indicated that when either Ca or K was higher than the other in the leaves than fruits, their ratio in the leaves will also be higher. When their concentrations in the leaves were similar, then the ratio Ca/K would be higher in the fruits.