Soil phosphorus dynamics and maize response to different rates of phosphorus fertilizer applied to an Acrisol in western Kenya

In phosphorus deficient soils and under smallscale farming systems, the development of efficient management strategies for P fertilizers is crucial to sustain food production. A field experiment was conducted on a P-fixing Acrisol in western Kenya to study possibilities of replenishing soil P with seasonal additions of small rates of P fertilizers. Triple superphosphate was applied at 0, 10, 25, 50 and 150 kg P ha(-1) for 5 consecutive maize growing seasons followed by 4 seasons of residual crops. Maize yields and soil P fractions were determined. Although maize responded to additions of 10 kg P ha(-1) with a cumulative grain yield of 16.8 Mg ha(-1), at the end of the experiment, compared to 8.8 Mg ha(-1) in the non-P fertilized plots, soil labile P did not increase correspondingly. Seasonal additions of 150 kg P ha(-1) increased maize yields to a cumulative value of 39 Mg ha(-1) at the end of the experiment, and increased all soil inorganic P fractions. At the third season of residual phase, treatment with a cumulative addition of 750 kg P ha(-1) gave the highest yields compared to treatments in the same residual stage, but these yields were considered less than the maximum yield of the season. This indicates that the large build up of soil P was not available for crop uptake. The inorganic P fraction extracted by NaHCO3 was the most affected by changes in management, increasing during the input phase and decreasing after interruption of P addition, for all P rates. The decrease in this pool during the residual phase could be explained by the maize uptake. This study showed that seasonal additions of 25 kg P ha(-1) can increase maize yield with gradual replenishment of soil P.