Effect of Selected concentrations of calcium bicarbonate on expression of HLB in the greenhouse and grove

Effect of Selected concentrations of calcium bicarbonate on expression of HLB in the greenhouse and grove

Report Date: 01/17/2016
Project: 838   Year: 2015
Category: ACP Vector
Author: Kelly Morgan
Sponsor: Citrus Research and Development Foundation

Two citrus groves, one – 20 year-old Hamlin sweet orange trees predominately on Swingle rootstock and a second consisting of three year old Hamlin sweet orange trees on Swingle rootstock have received acid injection to selected blocks with and without sulfur applications for fifteen months. Irrigation water was acidified at one of four target water pH (7.5, 6.0, 5.0, and 4.0). A controlled release form of elemental sulfur was applied to half of the trees in each pH treatment (main effect) including the non-acidified control (pH~7.5). A controlled released form of elemental sulfur (Tiger 90) was allied at a rate of 500 pounds per treated acre to plots receiving either acidified irrigation water or control plots receiving irrigation water that was not acidified in June. Soil samples collected in August indicate that soil pH in the plots recieving sulfur applications remained near target pH level at both sites. However, plots not receiving sulfur applications increased in soil pH levels by an average of 0.75 pH units with plots to have pH between 6.0 and 7.0 returning near the pH of the irrigation water . This result is similar to data collected in 2014. The cause of soil pH is the low amount of irrigation required during the summer months. At both the mature and young tree site, no significant difference in root density was found in samples collected in August 2015. Significant increases in nutrient concentrations of leaves collected in June 2015 were been found in plots at both sites with reduced water and/or soil pH. The greatest increase in leaf nutrient concentrations were found for Mg, Mn, Zn, and B. These results may indicate increased nutrient uptake from soils with soil solutions below 6.5. Nutrient deficient symptoms consistent with HLB positive trees have lower nutrient concentration in their woody tissues and thus can not provide nutrients to leaves until these reserves are replenished by higher nutrient availability presumed at lower soil pH levels (5.5 to 6.5). Average Hamlin and Valencia tree water uptake under greenhouse conditions were not significantly different from one another. However, water uptake by trees affected with HLB were 20%-25% lower than healthy trees. These data have been consistent for the past year. There is increasing evidence of reduced water uptake for trees receiving water supplemented with calcium bicarbonate. The cause of reduced water uptake appears to be lower but non-significant reductions in root density and soil pH increases in soil irrigated with higher concentrations of calcium carbonate. Reduced water uptake by trees receiving calcium carbonate in irrigation water would account for reduced leaf area and trunk diameter.


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