Adequate concentrations of available phosphorus in soil range between 21 and 30 mg dm−3 [18]. Thus, the content of the available phosphorus in the cultivated soil was below the optimal levels; however, plants showed no symptoms of phosphorus deficiency leading us to believe that the phosphorus from the cassava waste water supplied the plants with
the needed element. It was reported that the contribution of organic phosphorus to plant nutrition is 6% in fertilized soil and increases to 43% in soil treated with mineral fertilizer, which can promote the absorption of this element by plants [19]. In another study, it was observed that the amount of available phosphorus in soil decreases gradually as a function of the number of grown crops and the removal of this nutrient by plants [20]. Besides the uptake by plants, it is argued that a decrease in available phosphorus in soil may be related to the low solubility of phosphorus compounds in soil and the formation of non labile compounds in the soil after application of the waste [21].