Citrus Root Growth as Affected by Soil Aluminum Level under Field Conditions

Abstract

AbstractMost research on the effects of Al on citrus rootstocks has been limited to nutrient‐solution studies. This study employed an implanted soil‐mass technique to determine the effects of Al level in soils on growth and mineral content of fibrous citrus roots under field conditions. The implanted soil, E horizon material from an Immokalee fine sand (sandy, siliceous, hyperthermic Arenic Haplaquod), had a pH of 4.2 and a very low exchangeable‐Al content. It was either limed, unamended, or amended with three levels of Al using AlCl3. Each of the five treatments was replicated 15 times. Mesh bags containing the treated soil were placed in holes at the drip line of mature trees (Citrus aurantium L. sour orange rootstock) in a producing citrus grove. The bags were removed after 46 d. Results showed that, at a concentration of 9.14 mg Al L−1 of soil saturation extract, root density was twice that of the unamended treatment (0.13 mg Al L−1) and equaled that of the lime treatment (0.03 mg Al L−1). More roots grew into the bag, and they produced more lateral roots. Aluminum concentrations in roots were lower than those in the unamended treatment, however. Root‐length density decreased to about 60% of the value for the unamended treatment when Al concentration increased to 34.60 mg L−1. The optimum Al concentration for root growth appears to be 10 mg L−1 calculated by a curvilinear regression equation. In general, the concentrations of Zn, Fe, and Mn in roots decreased with increased Al application to the soil, while concentrations of Ca, Mg, K, P, and B were unchanged.