Water is the physical mechanism by which plants take up nutrients. Water is the mechanism through which nutrients are extracted from the soil and relocated to where the plant needs it most – roots, stalk, leaf, flower, and seed. Once present, water becomes the way in which roots can extend to access more moisture and additional nutrients found deeper in the soil. It is a balancing act of right moisture conditions resulting in optimum growth, deeper roots, more moisture – and the cycle continues. But how do we know if there’s enough moisture in the soil for plants to do this?
At a basic level, soil moisture can be thought of as the mix between soil and moisture (water) in soil. The following diagram describes a continuum from the most (left) moisture to the least (right).
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When talking about water levels soil moisture in a field, we’ll commonly use the concept of a “bucket” and how much water is in the bucket. When growing crops, it’s important to keep your fields above the wilting point - where the bucket is effectively empty from the perspective of a crop - and within the “Available water” zone. Above field capacity, you can think of the bucket as having a small hole - where any additional water added to the bucket drips out (is pushed deeper into the soil via gravity). There are many ways to measure the water in the bucket (see https://www.swatmaps.com/post/understanding-terms-used-to-discuss-soil-moisture-variability) that we won’t get into in this introductory article.
While at first this may seem like a fairly basic, there are actually many factors that impact:
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