Which factor is most directly used to determine irrigation zoning in a site with varying microclimates?

• A. Seasonal precipitation.
• B. Plant water needs and evapotranspiration differences due to microclimates.
• C. Soil texture alone.
• D. Color of leaves.

Answer: (B)

Irrigation zoning is determined by how much water plants actually need in different parts of a site, which changes with microclimates. The best factor to use is plant water needs and evapotranspiration differences caused by those microclimates. ET encompasses temperature, humidity, solar radiation, and wind, all of which can vary across a site, so areas with higher ET require more irrigation than cooler, shaded areas. Seasonal precipitation affects the overall water budget but doesn’t define where to place zones, and soil texture influences how water moves and is stored but doesn’t directly set zoning by itself. Leaf color isn’t a reliable basis for zoning since it can reflect many issues beyond sustained irrigation needs.