Photograph by C. Newhall
A tractor equiped with blades mixes volcanic ash on the surface of this field with the underlying soil in San Marcelino, Philippines. This helps reduce the amount of ash that can be stirred up by wind and improves the mulching effect of the ash in soil. Mixing the ash with soil also prevents the development of a hardened crust of ash on the ground; such a crust can increase the surface runoff during rainfall, which can lead to increased erosion along furrows, gullies and stream channels.
A variety of factors determine the effects of ash on agricultural land, including the thickness of the ash deposit, the type of crop that is being grown, and the maturity of the crop at the time of the ashfall. Also, livestock can become ill and die from ingesting flourine-rich ash.
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