EXTRACTABLE PHOSPHORUS AS AFFECTED BY HUMIC ACID APPLICATION IN SALT AFFECTED SOILS

To use of organic fertilizer sources for increasing crops production on sustainable basis has become imperative because the cost of chemical fertilizers is high. An experiment was conducted during 2006 on two saltaffected soils of District Charsadda to evaluate the effect of different levels of single super phosphate (SSP) alone and in combination with humic acid (HA) on phosphorus availability in an incubation study. Humic acid was applied at the rate of 0, 0.5 and 1.0 kg ha^-1, while SSP was applied at the rate of 0, 60, 90 and 120 kg ha^-1. Soil treated with different levels of SSP alone or reinforced with HA showed an initial decline in NaHCO3 extractable P in the first 7 or 14 days and then rapid mineralization up to 84 days of incubation. The highest mean available P was recorded as 21.1 mg kg^-1 in Majokay and 16.5 mg kg^-1 in Meerabad soils. Weekly turnover increased at 0, 60, 90 and 120 kg P2O5 ha^-1 alone or reinforced with HA. The highest weekly P turnover rate in Majokay soil was 0.31 mg P kg^-1 soil and in Meerabad 0.51 mg P kg-1 soil treated with 120 kg P2O5 and 1.0 kg HA ha^-1. Humic acid increased mineralization potential of 0, 60, 90 and 120 kg P2O5 ha-1. The highest mineralization potential of Najokay soil was 14.9 kg P ha^-1 season^ -1 and that of Meer abad soil was 24.8 kg P ha^-1 season^-1 treated with 120 kg P2O5 ha^-1 reinforced with 1.0 kg HA ha^-1. Therefore, the results show that application of 120 kg SSP ha^-1 reinforced with HA may be considered as an optimum dosage for the improvement of P mineralization in prevailing soil conditions.