determined by suspending them in distilled water at the soil to water ratio of 1:2.5 (w/v). Soil organic matter was oxidized with K
2
Cr
2
O
. Available N was extracted with 1 mol/L NaOH and titrated with 0.01 mol/L H
7
, and total N was determined by the Kjeldahl method. Available P (Olsen-P) was extracted using 0.5 mol/L
2
SO
4