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Erosion control in the tropics - Part 4

4 How erosion effects agriculture In Chapter 2 a few examples have been given as to how erosion can be observed in the field. Sooner or later, all the changes observed have consequences for agriculture. To mention one example: small rills, unlike gullies, can still be ploughed by the farmer. | 4 How erosion effects agriculture In Chapter 2 a few examples have been given as to how erosion can be observed in the field. Sooner or later all the changes observed have consequences for agriculture. To mention one example small rills unlike gullies can still be ploughed by the farmer. If the gully system is very close then the land may become completely inaccessible badlands . By a few examples we will try to show how the farmer in his daily routine on the farm may be confronted with erosion. 4.1 Consequences for the soil When thinking of the effect of erosion on the soil we often have ideas of spectacular gullies in our minds. However there are less obvious but just as serious consequences for crops in the field. We will discuss the two most important of these Limitation of the water retention capacity Because the pores in the soil are disturbed erosion reduces the infiltration and the water retention capacity of the soil. Less water can then be retained in the soil and after the rains stop there is less water available for the plants. This results in a shortening of the growing season. Crops with a longer growing period suffer more readily from dry spells. Some drought resistant varieties may give lower yields others are unable to survive. The farmer has fewer crops to choose from. Leaching of nutrients In areas with much rainfall a decline in moisture retention by the soil may have other consequences too. Since the water cannot be retained in the soil part of the water percolates to a deeper level or to the ground water. Through this process nutrients that are dissolved in the soil-moisture will leach to a deeper level and are out of reach for the 26 Erosion control in the tropics plant roots. Obviously this will be at the expense of the crop yields. Deep rooting plants are sometimes able to retrieve some of these nutrients. Especially trees fulfil this requirement and by doing so keep a lot of nutrients in circulation see figure 12 . Crop rotation too can .