Humic acids are widely used in agriculture system for high quality plant production, but are these different source acids equally efficient. So, a pot experiment was carried out during two successive seasons (2016 and 2017) to study the effect of both individual and combined applications of different three sources of humic acids and either of Ca or Fe on growth and Ca and Fe utilization of sorghum plants (Sorghum Vulgare Var Saccharatum), under sandy culture condition. Used three humic acids isolated from different sources, i.e., clayey soil (HAS); podrite (HAP) and compost (HAC). Each HA was applied at rates of 0, 25, 50, 75 and 100 mg kg-1 refined sand. Either of Ca or Fe was added as acetate form (CH3COO) at rates of 0, 25, 50 and 100 mg kg-1 refined sand. The experimental design was a split-split plot design with three replicates.
Results showed that, applications of each three HA individually and in combination with Ca or Fe were associated by a significant increases of dry weights of shoots and roots of sorghum plants. The highest dry weights were found in the plants treated by HAC followed by those associated the treatments of HAP. So according the calculated RI (%) values for the mean treatments of different added Ca rates, the estimated dry matter yields of shoots and roots may be arranged as follows: HAC (137.02 and 179.08 %) > HAP (98.84 and 143.02 %) > HAS (98.04 and 84.31 %) respectively. While, thesis order with different added Fe rates were HAC (114.35 and 217.88 %) > HAP (108.82 and 148.23 %) > HAS (101.06 and 76.99 %) for shoots and roots dry matter yields, respectively. In addition, increasing application rates of HA and Ca or Fe were associated by an increases of Ca and Fe uptake by both shoots and roots. The found order of the used HA on the increase of Ca and Fe uptake by shoots and roots of sorghum plants was: HAC > HAP > HAS. Moreover, the uptake of Ca and Fe by shoots was higher than that uptake by roots. On the other hand, increasing application rates of Ca and Fe decreased their utilization rate by sorghum plants. While, increasing application rates of HA were associated by an increase in the utilization rate of Ca and Fe by sorghum plants.
Based on the obtained data, may be concluded that the fertilization program of sorghum plants must be include applications of HA especially HAC with Ca and Fe to obtained high quantity and quality of sorghum plants. Also, organic amendments must be used to increase Ca and Fe fertilizers efficiency.