Sampling methods
Topsoil samples were collected from 5 sampling points per
plot and were mixed into a composite sample that was air-dried and
sieved through a 2 mm sieve. Soil organicmatter (SOM)was analyzed
by dichromate oxidation and titration using ferrous ammonium
sulfate (Liu, 1996). Soil total nitrogen (TN) was measured using the
Kjeldahl method. Soil total phosphorus (TP) was determined using
H2SO4/H2O2 digestion followed by colorimetric analysis. Soil total
potassium (TK) was analyzed, after H2SO4/H2O2 digestion, using
atomic absorption spectrophotometry (Baruah and Barthakur,1999).