Root samples were collected with cylinders (110 mm in
diameter and 250 mm high) fromfive sites in each plot after the
harvest of second rice in 2011, resulting in 15 cylinders in eachfield
treatment. The roots were separated from the soil by soaking the
cylinders with 0.6 mol L
1
sodium hexametaphosphate and
washing in water on a 0.053-mm sieve. The root morphological
parameters such as total root length and numbers of root tips were
measured with WinRHIZO (a commercial package to scan image of
roots). Finally, all the root samples were oven dried to calculate
root weight