ABSTRACT
OIL TESTING is A GENERIC TERM that includes measurements made on soils for various purposes. In this chapter, which emphasizes the testing of soils for soil fertility evaluation and control, the usage of the term will
be restricted to measurements made for that purpose. Supplies of plant nutrients differ greatly among soils and among locations
within soils. The supplies of nutrients in soils have a direct bearing upon the most suitable addition of fertilizers, and they influence other soil management practices; consequently, they receive much attention from scientists specializing in soil fertility. This chapter deals with the nutrient availability concept, biological indexes of availability, the adaptation of chemical methods to evaluate different aspects of availability, and the combined use of chemical and biological methods to estimate fertilizer requirements of crops.
