Without effective fertility management, citrus yields will be reduced on alkaline soil types.
Most calcareous soil situations are created during the bedding process on flatwoods soils. A typical flatwoods soil has an alkaline, loamy horizon (layer) about 40 inches down from the soil surface. If this layer is closer to the soil surface than 40 inches, then much of this material is brought to the soil surface from the furrow when the beds are formed with the grader.
Calcareous situations also can be manufactured when drainage ditches are dug and the subsoil is spread out by rows along the ditch bank. “Flatwoods groves wind up with scattered areas that are alkaline rather than large areas with high pH issues,” says Tim Gaver, citrus Extension agent based in Ft. Pierce, FL. “These areas are problematic because they are scattered throughout the grove and are difficult to manage.
Calcareous soils generally require increased nutritional management for successful production. Growers should carefully consider their options before planting these sites. The management headaches and associated costs may outweigh the economic returns.
Planning Fertility in Calcareous Soils
Because tree health, vigor, and yields are reduced in calcareous soils, growers need to account for this in their fertility management programs. The CaCO3 (calcium carbonate) in the soil affects the uptake or availability of nitrogen, magnesium, potassium, manganese, zinc, iron and copper. Soil acidification of high pH areas can be accomplished by applying elemental sulfur, potassium, or ammonium thiosulfate. These treatments will have to be repeated as the effects are only temporary. The length of efficacy is dependent upon the pH and CaCO3 content of the soil.
In those areas that have a high pH, the efficiency of ammoniacal nitrogen (ammonium nitrate, ammonium sulfate) fertilizers can be reduced as a portion of the nitrogen is lost through volatilization. Irrigation soon after the application may reduce volatilization in the portion of the rooting zone that is irrigated.
“The uptake of soil applied potassium fertilizers also may be reduced and require either supplemental potassium above the standard recommendation or foliar potassium sprays,” says Gaver. “Foliar magnesium concentrations also will be affected and can most efficiently be remedied by the application of foliar magnesium nitrate sprays.”
According to Gaver, most citrus rootstocks are naturally poor foragers for manganese, zinc, iron and boron, and this issue is magnified on calcareous soils. Iron chlorosis is a major production concern for trees grown on calcareous soils. “Foliar application of the micronutrients will be necessary to grow a healthy tree on these soil types,” he says. “However, iron is not taken in well on citrus foliage and needs to be applied to the soil as a chelated material (FE EDTA or FE EDDHA).”
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