Phosphorus availability in low phosphorous acidic soils as affected by liming and phosphorous addition

An incubation study was conducted to determine the effect of lime (L) as CaCO₃, and phosphorus (P) as triple super phosphate (TSP) on soil pH, available P, organic matter decomposition, inorganic nitrogen content, and calcium (Ca) content of soil. Three rates of lime equivalent to 0, 1 000, 2 000 kg (CaCO₃) ha^-1 and three rates of TSP equivalent to 0, 50 and 100 mg (P) kg^-1 were applied in combination as treatments with three replicates. With the increasing rate of lime, soil pH was significantly (p < 0.001) increased. Both lime and TSP had significant effects (p < 0.001) on P availability at three different soil test P extraction methods. Two thousand kg (CaCO₃) ha^-1 with 100 mg (P) kg^-1gave the highest available P irrespective of extractant used. Bray and Kurtz-1 method extracted the largest amount of P (5.63- 66.69 mg kg^-1) while Borax method extracted the smallest amount (3.42 – 42.42 mg kg^-1). Despite the varied ammonium nitrogen (NH4⁺-N) and nitrate nitrogen (NO3 ^--N) contents, the NH₄⁺-N content decreased and NO₃^- - N content increased in the all treatments when incubation progressed. With the increasing rate of liming, the decomposition of organic matter and the Ca content also increased.