Comparing Nutrient Availability in Low Fertility Soils Using Ion Exchange Resin Capsules & Plant Bioavailability Under Greenhouse Conditions.

Commonly used soil analysis procedures have generally been developed to determine nutrient levels in fertile agriculture soils.  The purpose of these tests is to determine the amount of nutrient that correlates to that which is plant available.  Desert soils contain fewer levels of nutrients.  Thus the validity of the commonly used soil analysis procedures is uncertain.  In a previous study it was determined that ion exchange resin capsules can be used as an accurate measure of nitrogen and phosphorous levels in desert soils.  A second follow up study was conducted to determine if the amount of nutrient absorbed by resin capsules can be correlated to actual plant available nutrient.  Two native, desert soils were collected from different locations in Utah.  The soils were treated with five rates of nitrogen ammonium nitrate (34-0-0), and four rates of phosphorous as phosphoric acid (0-46-0).  Water was added to bring each soil to one-half field capacity, and placed in 8” diameter pots.  Two resin capsules were placed in each pot, seeded with Squirrel-tail Grass (Hordeum jubatum L.), and placed in a greenhouse.  The treatments were consistently watered over the duration of the experiment.  One resin capsule from each treatment was removed at two months, the other at four months, and each resin capsule was extracted with 2 N HCl.  Nitrate, ammonium and phosphorus levels were determined on this extract.  At four months, the grass was harvested and analyzed for yield as well as nutrient assimilation.  The grass and resin results were analyzed for statistical significance.