ABSTRACT
Crop yield is generally related to the amount of water that is available to a crop from the soil. Greater capacity to hold water because of greater clay content can result in greater crop yields on eroded land in years when rainfall is less than normal.[21,22] Since the amount and time of precipitation have great effects on crop yield, the effects of erosion are more pronounced in some years than others.[23]
Because of the impact of soil water on yield, position in the landscape has an influence on productivity.[21-25] In general, linear slopes are more eroded than foot and head slopes. This relationship between landscape position and erosion adds to the difficulty of assessing the effects of erosion on crop productivity. On sloping terrain, landscape variations contribute to the many factors determining where water infiltrates and where it flows after a rainfall event. In general, water tends to run off steep sloping areas and infiltrate in lower landscape positions. Thus, lower landscape positions tend to be more productive than steeper slopes.[8,24]
In addition to landscape position, poor plant production can be attributed to changes in soil-water holding characteristics which can be altered by erosion.[26] Water is held in the soil under greater negative pressure, making it less available for crop use, with increasing level of erosion because of increases in clay content in the exposed lower horizons. Damage to soil physical properties caused by erosion has a significant negative impact on crop production.[6,13,27]
EROSION AND CROP PRODUCTION: SOIL CHEMICAL PROPERTIES
Organic matter not only plays an important role in shaping the soil physical characteristics, but also affects soil chemical properties. It serves as a source of plant nutrients and aids in the soil pH buffering capacity. Humus, or stable soil organic matter, is one of the most chemically active components in soil and serves as a major reservoir for charged molecules, reducing the loss of nutrients and pesticides by
leaching.[18-20] When organic matter is reduced by erosion, there is a greater potential for leaching of nutrients which leads to a decline in soil productivity.
