Crop response to phosphorus (P) application is often erratic in most acidic soil types. The main processes for P losses from agricultural fields are fixation, crop removal, erosion, surface runoff, and subsurface leaching. The purpose of this experiment was to evaluate adsorption properties of selected soils, determine the external phosphorous requirements (EPRs) of the soils, and identify factors contributing to P sorption in two soils in North Ethiopia. In this experiment, separately weighed 1 g soil samples were equilibrated with KH2PO4 at rates of 0.5, 5, 10, 20, 30, 40, and 50 mg PL−1. The P sorption data were fitted well with both Langmuir and Freundlich models with average r2 values of 0.91 and 0.88, respectively. The adsorption maximum (Xm) of the Langmuir isotherm ranged from 588.20 mg P kg−1 soil in Luvisols to 833.3 mg P kg−1 soil in Nitisols. The EPRL values ranged between 86.20 to 93.28 mg P kg−1 for soils of the study area. Among the soil properties, clay content and Ex. Al were positively correlated with Xm. The path analysis revealed that clay, pH, and Av. P had a direct effect on P sorption parameters. The EPRL of the studied soils was 3.44 to 3.6 times greater than the blanket P fertilizer rate recommendation. It is concluded that P sorption models can effectively be used to discriminate soils based on P fixation ability. The result further indicates that the current P fertilizer application rate of 50 kg P ha−1 being practiced across all soil types should be revised after validating the models and EPR values estimated in this study for each soil both under greenhouse and in-the-field conditions.

A greenhouse pot experiment was conducted to determine effects of vermicompost, inorganic fertilizers and their combinations on nutrient uptake, yield and yield components of wheat. A factorial combination four levels (0, 2, 4 and 6 tha-1) of vermicompost and four levels (0, 33.33, 66.67 and 100% ha-1) of the recommended NPK fertilizers was laid out in RCB design with three replications. Bread wheat variety, Kekaba was used as a test crop. Main effect results indicated that both vermicompost and NPK fertilizers significantly increased yield components, yield and nutrient uptake of wheat. Vermicompost applied at 2, 4 and 6 tha-1 increased grains yield of wheat by 11, 17 and 26% over control respectively whereas 33.33, 66.67 and 100% NPK fertilizers increased the grain yield by 10, 24 and 30%, respectively over the control. Vermicompost applied at 6 tha-1 resulted in the highest nutrient uptake and it increased grain uptake of N, P and K by 51, 110 and 89% over control respectively whereas among fertilizer rates, the highest uptake was produced by 100% NPK treatment and it increased the N, P and K uptake in the grain by were 79, 100 and 96% over control respectively. Combined application of vermicompost and NPK fertilizers has also significantly increased nutrient uptake, yield and yield components of wheat. It is concluded that wheat responds significantly to application of vermicompost and NPK fertilizers suggesting that nutrient contents of experimental soil is low for optimum production of wheat. Field verification and demonstration of results are recommended.

An experiment was conducted to determine the effects of vermicompost, inorganic fertilizers and their combinations on release of soil nutrients at different growth stages of wheat. A factorial combination of four levels of inorganic fertilizers (0, 33.33, 66.66, and 100% of the recommended NPK fertilizers) and vermicompost (0, 2, 4 and 6 t ha-1) were laid out in complete randomized design with three replications. Soil was collected before planting and after planting (at tillering, flowering and maturity stages of wheat) from each pot in order to determine dynamics of selected nutrients (NPK). The interaction between vermicompost and chemical fertilizers were not significant for NPK contents of the soil at all growth stages except phosphorus at heading stage. In all cases, highly significant increases in total N, available P and K in the soil were observed due to the increasing rates of main effect vermicompost or inorganic fertilizers during all growing periods. The highest available as well as total contents of NPK in the soil were found at tillering stage. This initial increment at tillering stage for both factors showed a declining trend later at heading and maturity stages. However, the observed decline was in exception for vermicompost applied at 6 t ha-, 1 which maintained highest level of available P and K and 4 t ha-1 which continued mineralization of K up to heading stage. In general, application of 6 ton vermicompost per hectare was found proportional with the full dose of the recommended fertilizers in supplying NPK for wheat crop. Therefore, building up the total as well as available NPK to higher levels up to heading stage can bring maximum nutrient uptake and yields of wheat.