International Rainwater Catchment Systems Conference
Mannheim, Germany - September 2001
Rainwater Catchment in Agriculture
Effects of Rainwater Harvesting on Dry Farming
Zhu Qiang and Li Yuanhong
Gansu Research Institute for Water Conservancy
The middle and eastern part of Gansu, one of China's driest and poorest
provinces, is a typical dry farming region. Most of the area is mountainous,
crisscrossed by ravines and gullies and covered with deep loess soil.
The annual precipitation is only 330 mm with unfavourable distribution
within the year. Due to the climatic and geological conditions, the runoff
coefficient is as low as 0.05 and there's a lack of groundwater. Frequent
droughts made the agriculture production a very low level. Serious water
scarcity caused food insecurity and inadequate drinking supply for the
people. In the past decades, people have made many efforts within the
conventional measures of dry farming, including the cultivation measures
such as deep ploughing and harrowing, mulching, breeding of varieties
adapted to water stress, etc. The soil and water conservation measures
such as terracing, contour planting and constructing fish scale pits are
also adopted to retain rainfall-runoff. All these measures have proven
to be effective in raising crop yield, however, the effects are limited
especially in the dry years. They could not bridge the gap between the
time rainfall occurs and the time when crops demand water. Figure 1 shows
the water demand versus rainfall in the crop periods for winter wheat.
We can see that crop water deficit is mainly owing to the rainfall distribution
rather than the yearly water shortage. The soil porosity is far from enough
to store all the excessive water in summer and autumn for the next spring.
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