Effects of Water Content and Amendments on Citrus Production in Weak Soils Using Sorghum as a Bioassay Indicator.

Spatial soil-limited yield reduction and soil amelioration were studied in a citrus grove (10 ha) located near Wauchula, in Hardee County, Florida, to evaluate the effect of water addition and amendments on growth parameters of sorghum, used as a bioassay indicator. The grove was divided into five productivity zones based on tree canopy volume measured with an ultrasonic array and a DGPS. Soil samples were collected from very poor and very good productivity zones up to the root zone depth of citrus trees (60 cm) and used for a greenhouse experiment. The experiment was a completely randomized block design with factorial treatment structure. The treatments included two soil types, water contents (100 and 50% of FC), amendments (Phosphatic Clay and Fe-humate) and amendment rates (1 and 2.5%). Soil moisture was monitored and maintained using capacitance probes attached to data loggers. Height and chlorophyll meter readings of the plants were measured weekly. Shoot weight, shoot height, root weight and root lengths were recorded as growth parameters at harvest. The results showed that soils from very good zones performed better than very poor zones when compared at the same water content. Higher water content showed 40 and 25 % increase in shoot height in soils of very poor and very good zones, respectively. Shoot growth was the same in both the soil types at lower water content. Root weight and root length increased with addition of the amendments and higher rates of the amendments increased root weight by about 31%. The results indicated that the productivity of citrus groves can be evaluated using indicator bioassays. Application of frequent irrigation to maintain high water content in the root zone of citrus trees could be a successful tool to increase the productivity of citrus groves on weak soils.