Effect of Mixed Manure on Selected Chemical Properties, and Phosphorus Adsorption Characteristics of Vertisols in Haramaya District, Eastern Ethiopia

The high phosphorus fixing characteristics of Vertisols and the lack of crop response to its application as a fertilizer is one of the major challenges leading to phosphorus deficiency. Its bioavailability is determined by adsorption and desorption characteristics. A Pot experiment was conducted to investigate the effect of mixed manure on phosphorus adsorption characteristics using the batch equilibrium method including selected properties of Vertisols. Four rates of mixed manure (0, 5, 10, and 15 t ha ) were added to the soil. Following 30 days incubation period, changes in selected soil properties, phosphorus adsorption, and desorption characteristics were studied. The data were analyzed using ANOVA. The results revealed a significant decrease in soil pH, and increase in soil organic carbon, total nitrogen, available phosphorus, and cation exchange capacity as compared to the control. The overall means of the amount and efficiency of adsorbed phosphorus were significantly decreased due to mixed manure. Besides, the interaction effect of mixed manure and added phosphorus concentration revealed a significant increase in both the amount and efficiency of adsorbed phosphorus. Both parameters revealed an increasing trend with increased rates of added phosphorus concentration but decreased with increased rates of mixed manure. Though all treatments were fitted well to both the Freundlich and Langmuir isotherms, the former one was used to due to its higher R value. Freundlich adsorption coefficient and intensity were found reduced significantly compared to the control. Therefore, mixed manure application has increased phosphorus availability by reducing its adsorption and related properties of Vertisols.