Overgrazing is caused by all of the following except which?

The focus of the question is on identifying a factor that does not contribute to overgrazing. Overgrazing occurs primarily when livestock consume too much vegetation before it has a chance to regenerate, and this can be further exacerbated by factors like muddy water holes and damaged root systems from animal hooves.

The correct choice points out that poor irrigation techniques, while they may cause a range of other agricultural issues, do not directly cause overgrazing. Poor irrigation can lead to water scarcity or inefficient use of water resources, potentially affecting the overall health of plants. However, it does not directly relate to the issue of animals consuming vegetation beyond sustainable levels.

In contrast, the other options directly highlight how livestock impact the land. When animals eat grass before seeds can be produced, it prevents regrowth. Additionally, when water holes become large mud holes, it can lead to further degradation of the land, making it harder for vegetation to thrive. Also, animal hooves can compact the soil and damage root systems, contributing to the deterioration of the grasslands necessary for sustaining healthy livestock grazing.