Effect of Selected Concentrations of Calcium Bicarbonate on Expression of HLB in greenhouse and grove.

Effect of Selected Concentrations of Calcium Bicarbonate on Expression of HLB in greenhouse and grove.

Report Date: 08/01/2017
Project: 838   Year: 2018
Category: ACP Vector
Author: Kelly Morgan
Sponsor: Citrus Research and Development Foundation

Typically, citrus trees in Florida groves under low volume microsprinkler irrigation concentrate fibrous roots in the wetted zone. In recent decades, soils under citrus tree canopies statewide have increased in pH and bicarbonate concentrations because of irrigation with alkaline water from deep wells extending into Florida�s limestone aquifers. As soils become more alkaline some nutrients become more available (e.g. N and Mg) for uptake by plants and others (e.g. Fe, Mn, Zn and B) become less available for uptake. Elevated soil pH is not known to cause decline in healthy trees. However, declines in tree vigor and productivity above that caused by Huanglongbing (HLB) alone have been documented in trees growing in soils impacted by alkaline irrigation water. To verify the relationship between soil alkalinity and growth of trees affected with HLB, a greenhouse experiment was initiated to maintain HLB positive or negative trees by exclusion of the vector. Water uptake by trees receiving water supplemented with calcium bicarbonate was significantly reduced (10-15%) compared with health trees but substantially greater reduction for HLB affected trees (>20%). Tree heights were similar for HLB affected and healthy trees irrigated with calcium carbonate but significantly smaller than healthy trees not receiving modified irrigation water. Mean leaf Ca, Mg, Mn, Zn and B concentrations were not significantly different during the study period (April 2014 to April 2017). However, all nutrients were significantly different among treatments with the exception of Ca during the last year of the study. The cause of reduced water and nutrient uptake appears to be correlated with reductions in root density and increases in soil pH in soil irrigated with higher concentrations of calcium carbonate resulting in reduced leaf area and tree height. Two field studies (one grove with trees >10 years old, and one grove with trees < 5 year old) were conducted to determine the effect of soil pH on tree health. Leaf Ca, Mg, Mn, Zn and B concentrations in leaves were greater at both sites with reduced water and/or soil pH than non-treated controls at both the young tree and mature tree groves. Leaf Ca, Mg, Mn, and Zn concentrations were significantly different among treatments in the mature tree grove but only significantly different for Ca, Mn, and Zn at the young tree grove when averaged over the entire study period. However, Ca, Mg, Mn, Zn and B were significantly different among treatments when only the last year of data was considered. Root density samples taken in February to June indicate a significantly greater root length density with lower soil pH. These results indicate a positive correlation between root density and reduction in soil pH from greater than 7.0 to less than 5.0. Leaf Ca, Mg, Mn, and Zn in November samples were greater for trees treated with both irrigation water acidification and sulfur application compared with irrigation water acidification only. These results verify previous finding that leaf nutrient status is negatively correlated with soil pH.


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