ABSTRACT
Fertilizer recommendation based on choosing an effective soil nutrient extractants and calibrating soil tests against yield responses to applied nutrient has been little used in Ethiopia. An experiment was conducted during 2009, 2010 and 2011 cropping seasons in 35 different farmer fields from five Districts of Metekel zone. Six levels of phosphorus (0, 10, 20, 30, 40 and 50 kg ha-1) arranged in Randomized Complete Block Design (RCBD) with three replicates were used to determine the critical level of phosphorus (P) for maize and to compare Bray II, Olsen and Mehlich III P extraction methods. Grain yield of maize responded positively and significantly to P fertilizer application of the study area. Compared with the control, grain yield increased 19.8 to 35.3% by applications of P fertilizers. Extractable P concentration extracted after three weeks of planting by using three extraction methods were significantly differed among P fertilizer rates. Using the Cate and Nelson graphical method, the critical levels of soil extractable P were 12, 8 and 10 mg P kg-1 soil for Bray II, Olsen and Mehilich III extraction methods, respectively. Results shows that at values less than these critical levels of extractable P, P fertilizers should be applied to increase maize yield. The Bray II P was more correlated (r = 0.38) with relative maize grain yield than and Olsen and Mehlich III extraction methods. In addition, the quantities of P extracted by the three extractants were in the following order: Bray II > Mehlich III > Olsen P extraction method. The result indicated that Bray II was found to be the most suitable as soil testing method for estimating extractable P in the study area.
References
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