Depth Of Placement Impacts Efficiency Of Estimating Plant Nutrient Availability In Semi-Arid, Low Fertility Soils With Ion Exchange Resin Capsules.

Ion exchange resin capsules are a possible alternative method to conventional soil testing. Research on resin capsules outside the laboratory has focused on major nutrients in highly fertile soils, creating questions about the validity of their use in semi-arid, low fertility soils. Previous studies suggest that effectiveness of resin capsules (especially as related to non-mobile elements such as phosphorus) may be related to the placement depth. Field studies were established in Rush and Skull Valleys, UT on loam and sandy loam soils, respectively. Thirty 4m² plots were established at each field site. Fertilizer was applied with six N, P and S treatments (0, 5.6, 11.2, 22.4, 44.8 and 89.6 kg ha^-1 for N and P and 0, 6.7, 13.4, 26.9, 53.8 and 107.5 kg ha^-1 for S) applied as ammonium sulfate and treble super phosphate. Resin capsules were placed on June 15, 2010 at depths of 0–5 cm, 5–10 cm, and 10–15 cm in the soil. The capsules were removed and replaced after approximately 90 d (Sep 13, 2010). They were removed again on May 4, 2011. Soil samples were taken at the same depths. NaHCO₃-extracted P was significantly related to P application at all depths and times except the bottom two depths at the time of last sampling, and resin capsule P was only related in the spring at the 0–5 and 5–10 cm depths (r² = 0.82, r²=0.92). Resin capsule N was related to N application and gave a more cumulative measure of N availability over the spring while soil test N showed no relation to N application at the second sampling. For sulfur, both soil test S and resin capsule S were related to S application rates, even at the time of the second sampling (soil test r²=0.98, resin capsule r²=0.96).