Die Bodenkultur - Journal for Land Management, Food and Environment
S. Daba and E. Zewedie:
Evaluation of the residual value of phosphorus fertilizer for Sorghum (Sorghum bicolor L.) grown on a Vertisol
The residual value of P fertilizer for sorghum (Sorghum bicolor L.) grain yield was evaluated on a calcareous Vertisol at Alemaya University of Agriculture field experiment station, eastern Ethiopia, from 1993-1996. The study was conducted using 1993 crop season as a base year whereby the phosphate levels 0, 23,46,69,92 and 115 kg/ha P20S were applied. Results showed that the residual P fertilizer effects varied from year to year depending on rainfall amount and distribution. Generally it was observed that 23 and 46 kg/ha P205 levels were not of significant importance to have practical residual value for subsequent cropping as observed from the yield responses. On the other hand, when the phosphate level was greater than or equal to 69 kg/ha P20S' the residual P fertilizer value was of practical significance.
Beyond this level, the residual value of P fertilizer was observed to be of equal importance for at least 1-2 subsequent crop seasons compared to the annual application. Linear regression analysis of residual P yield of the subsequent crop season and the preceding crop season for the respective P levels showed strong significant correlation confirming the importance of residual P fertilizer for the subsequent cropping.
Key words: Direct P, Ethiopia, Residual P, Sorghum, Vertisol.