ABSTRACT

Mapping the location of K-fixing soils in the San Joaquin Valley continues. In 2001 and 2002, 33 soil profiles were sampled. They fall into three categories: Sierra Nevada coarse-textured alluvium, Coast Range coarse-textured alluvium, and fine-textured alluvium. So far, complete mineralogical assays have been made on 5 profiles. Sierra Nevada alluvium soils have high amounts of vermiculite and >60% K fixation, and fixation increases with depth; Coast Range alluvium has more chlorite and <60% K fixation. On the samples characterized so far, K measured by the sodium tetraphenyl boron method (hypothesized to extract exchangeable K and a portion of fixed K) was not consistently related to conventional soil test K, or to the source of parent material. On the other hand, K fixation measured by amount of K removed from an 18 mmol solution in a 7-day incubation was related to source of parent material.