poster - International Conference of Agricultural Engineering

of 1 m × 1 m × 0.65 m (L×W×H) in size were filled with a soil that has the same texture to the
highland fields. The simulator was developed in the USDA Soil Erosion Laboratory in Purdue
University, USA. Three soil surface mulch treatmemts were the combination of (1) rice straw
mat + PAM + phosphogypsum, (2) rice straw mat + sawdust + PAM + phosphogypsum, and
(3) rice straw mat + rice chaff + PAM + phosphogypsum. The weight of straw mat, PAM, and
gypsum per ha was 3,300 kg, 10 kg, and 1,000 kg, respectively. The weight of sawdust and
chaff per ha was about 700 kg, respectively. Slope of the boxes were 10% and 20%, and
rainfall intensity was 30 mm/h. Three simulations were performed and each simulation lasted
60 minutes. Runoff and sediment samples were measured and analyzed. The treatments
were summarized in Table 1. Each treatment was duplicated. The results of these treatments
were compared with the results of control.
Surface mulch materials were prepared by gluing straw mat, PAM powder, chaff or sawdust
together. And gypsum powder was spread evenly over the soil surface. The use of PAM and
gypsum was much less than the common dose of 20 to 40 kg/ha and 5,000 kg/ha (Choi et al.,
2010; Jian et al., 2003; Lee et al., 2010), respectively, because of environmental concerns.
PAM (Soilfix G1, Ciba Chemical Co., Germany) and gypsum (Namhae Chemical Co., Korea)
were purchased at a market.
Table 1. Summary of the experimental treatments
Soil box
No.
Rain
(mm/hr)
Slope
(%) Code
Cover materials
Treatments
Ⅰ 30 10 Control Bare
Ⅱ 30 10 SPG Rice straw mat+PAM+Gypsum
Ⅲ 30 10 SSPG Rice straw mat+sawdust+PAM+Gypsum
Ⅳ 30 10 SCPG Rice straw mat+chaff+PAM+Gypsum
Ⅴ 30 20 Control Bare
Ⅵ 30 20 SPG Rice straw mat+PAM+Gypsum
Ⅶ 30 20 SSPG Rice straw mat+sawdust+PAM+Gypsum
Ⅷ 30 20 SCPG Rice straw mat+chaff+PAM+Gypsum
3. Results and Discussion
1.1. Time of initial runoff
Time of initial runoff from mulched plots was slower than that from control plots. The order of
initial runoff was Control > SPG > SSPG > SCPG. Under 10% slopes, time of initial runoff
from SPG, SSPG, and SCPG boxes retarded 81%, 105%, and 193%, respectively,
compared to that from control boxes. Time of initial runoff from the boxes under 20%
simulation was faster than that from 10% boxes but the differences among the mulched
boxes were not significant. It was thought that the chaff and sawdust helped increase the
surface cover rate, increase infiltration, and retard time of initial runoff.
1.2. Runoff rate
Runoff rate varied depending on mulch material, slope, and time of rainfall simulation. The
compaction condition of soil in the soil box and solubility of PAM seemed to affect the runoff
rate. It was thought because the runoff rate varied a little wider than expected during
simulation to simulation (Figure 1). However, runoff rates from mulched boxes were