4. CONCLUSIONS
A strategy to evaluate soil erosion hazard degree and soil conservation
planning for agriculture regions of the BSR of China has been proposed.
The innovative aspect of this strategy is the combination of the known
relationship between A horizon thickness and crop yield for the BSR with
a soil erosion model that bases predictions upon the spatial
distribution of the current A horizon thickness and soil properties by
soil types. Erosion hazard degree and relative crop yield under
different soil conservation scenarios including current tillage
(conventional tillage), contour tillage, straw incorporated tillage,
no-till farming and two combinations of terracing and “green for
grain” practices were evaluated. Knowing that an A horizon thickness of
20 cm is the critical threshold for crop productivity, a soil life
expectancy was calculated. Croplands with soil life expectancies of
<0 a, 0 a~20 a, 20 a~100 a,
100 a~1000 a and ≥1000 a, were classified as
“Damaged”, “High hazard”, “Moderate hazard”, “Low hazard” and
“No hazard”, respectively.
The soil erosion model was validated from 137Cs
erosion rate measurements for three watersheds of the BSR. The spatial
distribution in soil erosion rates for the BSR was linearly and
positively correlated with slope gradient and dependent upon the
conservation practice scenario. The current tillage practice exhibited
the highest soil erosion rates while no-tillage had the lowest soil
losses. On average, about 13 cm of A horizon has been eroded away since
the establishment of cultivation. Across the BSR, 8% of the sloping
croplands are already classified as Damaged which will increase to 27%
within 100 years under current practices. The corn yield decreased very
fast (0.8% per decade) under the current tillage practice. Despite the
effectiveness of no-till to control erosion, this was the third highest
practice tested for loss in crop yield due to issues in applying no-till
farming in cold regions. The best practice for High hazard, Moderate
hazard and Low hazard was Combo 2, applying no-till, contour farming
terraces and “green for grain” practices according to the slope
gradient and regional temperature (cool or warm). For “High hazard”
croplands, conservation practices should be applied immediately as these
areas will convert to “Damaged” in just 20 years under current
practices. Future research should include other management strategies,
such as winter cover crops, strip tillage for flat and ridge system,
furrow dikes made from soil or possibly cornstalks, or flat tillage.
Such management options could be incorporated into the model predictions
of erosion hazard and crop yield once the relationships are
experimentally established.
A scheme for optimum spatially and temporally distributed scheduling of
soil conservation practices is presented.
The plan is designed to maintain
all soils to have an A horizon above 20 cm by selecting and scheduling
the implementation of conservation practices according to their degree
of hazard. Scheduling the implementation of conservation practices
according to the township’s maximum erosion hazard will optimize the
distribution of labor and serve as a training tool for later-acting
townships. Soil erosion estimates are conservative, and as such the soil
life expectancy estimates are under-predicted due to not considering
gully and wind erosion processes. This study quantifies the urgency in
taking action to apply conservation methods in the BSR in order to
sustain agriculture while maintaining soil health.