Abstract
The variable performance of trees on Swingle citrumelo [Citrus paradisi Macf. × Poncirus trifoliata (L.) Raf] rootstock in southern flatwoods soils appeared to be related to differences in root growth and soil characteristics. We examined the root systems of trees at several locations in the Indian River and Southwest Florida production areas by trenching between adjacent trees using a small backhoe with a 16 inch wide bucket. The exposed roots were observed and the abundance and relative proportions of fibrous and secondary roots noted. The soil morphology of each profile was described and samples were collected for organic matter, pH, Ca, Mg, P, and K analyses. All trees were over 10 years old, growing in double-row beds, and were either apparently healthy or in decline. Healthy tree root systems had a shallow, flat distribution with fibrous and secondary roots present, but located mostly in the A horizon. Of the total root biomass, about two-thirds was on the crown side and one-third on the furrow side of the bed. Declining trees commonly had fewer fibrous roots than healthy trees, few or no secondary roots, and root decay was evident. Adequate soil drainage and the presence of a thick, dark surface horizon appeared to be the most important characteristics contributing to healthy root system development. There was little correlation between tree vigor and any measured soil chemical property.
