Soil fertility and crop yield can be increased by the combine addition of some organic amendments like humic substances and phosphatic fertilizers. This practice involves an increase in the solubility and availability of P in soils. An incubation experiment was conducted during 2017 to evaluate the impact of various P fertilizers applied with and without humic acid on P availability. Three different rates of humic acid as 0, 5 and 10 kg ha-1 with three different P sources as nitrophosphate (NP), single superphosphate (SSP), and di-ammonium phosphate (DAP) at a recommended rate of 90 kg P2O5 ha-1 were applied. Soils amended with different P fertilizers with and without HA showed mix trend in AB-DTPA extractable P at day zero of incubation and then a rapid mineralization and weekly turnover were increased up to 84 days of incubation period. Maximum mean available P of 14.32 mg kg-1 was recorded in soils which were amended with DAP and 10 kg HA ha-1, whereas the lowest available P concentration of 8.09 and 7.82 mg kg-1 was recorded in soils where SSP and NP were applied, respectively, without any amendment of HA. Weekly turnover and mineralization potential increased with incubation periods as well as with the application of different HA levels. Maximum weekly P turnover rate and mineralization potential were 1.35 mg kg-1 and 67.71 kg P ha-1 season-1, were recorded in the soils that were treated with DAP and 10 kg HA ha-1, whereas the lowest were noted in soils that were applied SSP and NP alone. Data regarding the water soluble phosphorus showed significant increased with increasing levels of HA and incubation days with maximum mean available water soluble P of 1.219 mg kg-1 in soils treated with DAP and 10 kg HA, while the lowest of 0.565 mg kg-1 was noted in soils that were applied with recommended level of NP alone. It was concluded that the application of recommended dose of DAP with HA can be the optimal source for the improvement of P availability and mineralization in given soil conditions.
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