poster - International Conference of Agricultural Engineering

the effect of rice straw mulch and rice straw mat mulch on the reduction of runoff and NPS
pollution discharges from field scale runoff plots under natural rainfall conditions.
2. Methods
Six runoff plots of 5x22 m in size were prepared in an existing sandy loam field of about 3%
slope. A flume, water level meter and water sampler was installed at the lower bottom of
each plot to measure runoff and collect water samples during rainfall-runoff events. Three
treatments of control, rice straw mulch and rice straw mat mulch were applied right after
plowing and growth bed preparation. Each treatment was duplicated. The size of rice straw
and rice straw mat that was applied to the runoff plot was 3,409 kg/ha and 3,136 kg/ha,
respectively. And the resulting residue cover rate of the soil surface was 64.7% and 74.7%,
respectively. Spring radish and fall Chinese cabbage were cultivated and runoff and selected
NPS pollution was measured under sixteen natural rainfall-runoff condition in 2011 growing
season. Sixteen rainfall events were monitored with respect to runoff and concentration of
selected NPS pollutants. Collected water samples were analyzed with respect to SS, TN and
TP concentration by the relevant standards. And the effect of the sresidue mulch on the
reduction of runoff and NPS pollution load was analyzed.
3. Results and Discussion
3.1. Rainfall characteristics
Thirty year (1981~2010) average annual rainfall of the study area was 1,298.7 mm which
was a little smaller than the national average of 1,307.7 mm. Frequency of heavy rainfall of
100 mm/day or higher was 1.5 times per year. Total rainfall amount of the heavy rainfall took
about 17% of the total rainfall. Annual rainfall of the study area in 2010 and 2011 was
1,476.4 mm and 2,029.1 mm, respectively, which was greater than average. In 2011, rainfall
frequency of 50 mm/day and 100 mm/day or higher occurred 10 and 3 times, respectively.
Rainfall in 2011 was exceptionally higher than other years. It might mean that runoff and
NPS pollution discharge could be larger in 2011 than other years because of the large
annual rainfall.
3.2. Runoff rate
The size of rainfall events during the study ranged from 12.8 mm to 538.2 mm. Runoff during
the events was 0.02-39.6 m 3 from control, 0-37.4 m 3 from straw mulch, and 0-26.6 m 3 from
straw mat mulch plots. Runoff rate of the 16 runoff events ranged between 0.01-0.67
(control), 0-0.63 (straw mulch), and 0-0.45 (straw mat mulch). Annual average runoff rate
from control, straw mulch and straw mat mulch was 0.409, 0.299, and 0.184, respectively.
These results were smaller than the results of Shin et al. (2011) who performed similar
experiment with straw mat and wood shavings. It was thought that the large rainfall in 2011
increased the runoff rate in general. Reduction of runoff by straw and straw mat mulch
ranged 5.4-99.7% (annual average 26.9%) and 32.9-100% (annual average 55.1%),
respectively, compared to that of control plots. The annual average reduction of runoff was
somewhat less than expected because of large and heavy rainfall in 2011. However, it was
thought that the straw mulch effectively covered the soil surface, prevented the soil from
clogging, and helped keep infiltration high, compared to control plots. Residue cover rate of
straw mulch was lower than that of straw mat because the straws at the top of the ridge
moved down to furrow during the growing season. Because of this, runoff reduction was
larger in the straw mat mulch plots than in the straw mulch plots. The same trend also
observed in NPS pollution reduction.
3.3. NPS pollution
Average EMC (event mean concentration) of SS, TN and TP from control plots was 490.7
mg/L, 16.2 mg/L, and 1.4 mg/L, respectively. Average EMC from straw mulch was 289.9