2.2. Soil and water chemical properties
Soil detachment and the volume and chemical quality of runoff
water and leachate were assessed after each rainfall event (i.e., 11
times during the experiment). Monthly rainfall amounts are shown in
Fig. 1. The volume of eachwater samplewasmeasured and then filtered
through GF/Fmembrane filters (Whatman, 0.7 μmporosity) to measure
the concentration of suspended solids and nutrients. Following filtration
of runoff water and oven-drying of the sediment at 50 °C, sediment loss
was measured as the sediment weight. This sediment weight is assumed
to represent the quantity of soil lost during rainfall events on
1 m2 plots. The pH of each water sample was measured. Total N and
phosphorus (P) were evaluated in the filtrate solution according to
Standard Methods for the Examination of Water and Wastewater
(Clesceri et al., 1998). The concentrations of nutrients, NNH4
+, NNO3
−, K,
and P, were measured in the solutions.
The percentage of organic C was determined using the Walkley–
Black method (TCVN 4050-85) for soil samples and dry combustion
with a Carlo Erba NC2100 analyzer for water samples. Total N was determined
using the Kjeldahl method (ISO 11251-95) for soil samples