Phosphorus and Potassium Distribution and Adsorption on Two Florida Sandy Soils.

Phosphorus and K are critical nutrients in citrus production whose deficiency or excess can affect yield, fruit quality, and water quality. However, no study has been conducted to understand the nutrient distribution in the root zone using intensive fertigation practices in Florida's sandy soils. Thus, experiments were conducted to: (i) compare the performance of intensively managed drip and microsprinkler fertigation systems with conventional grower practices; and (ii) determine P and K adsorption based on recommended fertilizer application rates on Candler (hyperthermic, uncoated Lamellic Quartzipsamments) and Immokalee (sandy, siliceous, hyperthermic Arenic Alaquods) fine sands. Phosphorus and K were applied and tracked with time and distance from point of application. Soil P on Immokalee soil was 27 to 163% higher in the irrigated zone for drip and restricted microsprinkler fertigation than the unirrigated zone and up to 70% greater in the 0- to 15-cm depth of the irrigated zone than conventional microsprinkler practices. Soil K was 5 to 61% greater in the upper 0- to 15-cm of the irrigated zone with drip and microsprinkler fertigation than conventional microsprinkler practices on Immokalee fine sand. Soil P and K on Candler also differed by fertilization method, depth, and between irrigated and unirrigated zones. The linearized P sorption coefficients for Candler were threeto fourfold greater than the corresponding depths for Immokalee, while sorption coefficients for K were similar for the two soils. It is unlikely that P or K would present a water quality concern as strictly related to irrigation practice. The P application rate for Candler should be lowered for young trees (<3 yr old). [ABSTRACT FROM AUTHOR]