Percent increase in AB-DTPA extractable phosphorus concentration as affected by different P sources applied with different levels of humic acid. NP: Nitrophosphate; SSP: Single superphosphate; DAP: Di-ammonium phosphate; HA1: HA@5 kg ha-1; HA2: humic acid @10 kg ha-1; Bars having different letters are statistically different from each other.