Agriculture Reference
In-Depth Information
Anions
Along with the base saturation test, you may have some anions tested, such as phosphor-
us and the nitrate form of nitrogen. Organic matter isn't generally tested for minerals on a
soil test. The nitrogen test, therefore, is not especially reliable because about 98% of soil
nitrogen is tied up in the organic matter. There are other factors that make it difficult to get
an accurate result. Some labs ask you to bring in a sample at just a couple of degrees above
freezing to improve the results, but it's just not feasible for most of us.
That being said, labs do give you a number for nitrogen. In theory, nitrate nitrogen levels
that are too high may contribute to increased blossom drop, decreased fruit set, and in-
creased frost damage and winter kill. If the cation form of nitrogen — ammonia nitrogen
— is low, which is very common, it indicates a lacking soil food web. That needs to be ad-
dressed in order to bring the level of this form of nitrogen up, which is necessary for optim-
al fruiting and flowering. More important to us is how much organic matter we have in the
soil and whether we have the microbes to convert some of it into usable nitrogen.
Phosphorus is another tricky one. There are a few different tests used to determine how
much phosphorus is in the soil, but it's difficult to get an accurate picture. The interpreta-
tion of a phosphorus test is again very challenging because phosphorus uptake by plants is
many times higher from organic matter than from mineral soil. There is a better nitrogen
and phosphorus test coming up in the next section.
