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GIS-based comparative analysis of potential soil erosion in two agricultural systems: Dry farming and center-pivot irrigation. A case study in Southern Portugal


Results
In Figure 1, the rain-fed system, is possible to see that in an average year this field could be classified in general as a low risk area for soil erosion (<1.0 103 kg ha-1), with the exception of same small areas where the risk could be classified as small to moderate (1.0 - 2.0 103 kg ha-1) or moderate to high (2.0 - 6.0 103 kg ha-1).


Figure 1 - Potential erosion values for the rain-fed system.

For the same field considering the irrigated production system (Figure 2) the erosion risk is higher. The area classified as low risk area is less and there are even some areas with high to severe erosion risks (> 6.0 103 kg ha-1).

Figure 2 - Potential erosion values for center-pivot irrigation.

The difference from these two situations is mainly due to the different water application, which in the second case is made with higher application rates, leading to higher erosivity factors. The EI30, which increases along the center-pivot lateral (Table 1), can achieve, after the third span (150 m length) values higher than those from natural rainfall, even in severe years.

With application rates so high and soils with low infiltrability, and sloppy areas, it's easy to accept that the impact of using low-pressure center-pivots could be high. Taking soil conservation as a priority, a preliminary study could determine that the study area was not adequate for an irrigation system with the characteristics of the one studied. The alternative would be the use of a system with lower application rates, like center-pivots with high pressure rotating sprinklers, solid-set sprinkler systems or even trickle irrigation, which could irrigate the field applying lower water application rates and thus having less erosive power.

Conclusions
The use of GIS tools can play an important role in the evaluation of irrigation systems impact, allowing to estimate their erosion risks.

For the same area a center-pivot irrigation system could be much more erosive than the natural rain, especially if it's a low-pressure system working in sloppy fields with low infiltrability soils.

References
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