Determination of Soil P for Optimum Durum Wheat Production in Ada'a, Akaki and Chefe Donsa of The East Shewa, Oromiya Regional State In Central Ethiopia

Abstract

To respond to the ever escalating prices of chemical fertilizers and getting optimum crop production per unit usage of fertilizers for the continually increasing population, an on-farm soil test based phosphorous determination research experiment was carried out at three locations of East Showa during 2005-07 cropping seasons. Thirty six farmers field were selected for this study. Six levels of phosphorous including the blanket recommendation (0, 11.50, 22.99, 34.49, 45.98 and 57.50 kg P₂O₅) were applied as a treatment, replicated four times and each treatment were laid out in RCBD experimental design. All experimental plots received recommended level of nitrogen (60 kg N) uniformly from urea. The analytical results of both agronomic as well as soil data have showed that application of 34.49 kg P₂O₅ ha^-1 and 22.99 kg P₂O₅ ha^-1at Ude and Akaki provided the maximum mean grain yields of 3.75 and 2.44 t ha^-1, respectively in 2005. In the 2006 cropping seasons, however, the absence of any application of external phosphorous gave the highest (3.38 t ha^-1) at Chefe Donsa and the least mean grain yield (1.74 t ha^-1) was recorded in Ude by 34.49 kg P₂O₅ . In the final year of this study, the results revealed that the two treatments from Chefe Donsa and Akaki gave the maximum comparable mean grain yields 4.89 and 4.49 t ha^-1 by the application of 57.50 and 22.99 kg P₂O₅ but and the least yield was obtained through the application of soil P only (1.88t) in Ude. This study showed that all the thirty six farms do vary in terms of phosphorous contents and hence blanket recommendation by no means governs wheat yields. Therefore, a total of thirty six regression equations, one for each farmers field, were developed and out of which eighteen were selected in order to map the soil P that remained after phosphorous application in each plot, farm and mineralization of soil reserve (ppm) versus different levels of phosphorous addition resulted in biomass yield of wheat. Accordingly, an average of 97.0, 96.5 and 96.5 (2005), 86.0, 93.0, and 89.5 (2006) and 92.0, 91.5, and 92.5% (2007)remained in the soil for every application of external phosphorous at Akaki, Chefe Donsa and Ude, respectively. In most years, an average of over 85% of the applied phosphorous remained in the soil. In some locations, non-significant differences among the mean grain as well as straw yields of wheat were obtained due to this. It seems that these soils are being saturated by the application of phosphorous all years around with blanket recommendation and probably the crop might get its demand from other means or forms in the soil system rather than from the applied source. Therefore, any phosphorus recommendation for optimum durum wheat production should be on the basis of its soil P value. This experiment also proved that even if the soil phosphorous continuously increases through the application of external phosphorous, it didn't reflect in the increment rather forced to decline mean grain yield. Further research work has to be conducted to find out the mechanisms of how plant use phosphorous from the soil and even the extraction methods along with soil types, environment and in its interaction.

Keywords: Equation, extractions, on-farm, P-values, soil test, regression