Nitrogen, Calcium, and Magnesium Inconsistently Affect Tree Growth, Fruit Yield, and Juice Quality of Huanglongbing-affected Orange Trees

Abstract

The bacterial disease Huanglongbing (HLB) has drastically reduced citrus production in Florida. Nutrients play an important role in plant defense mechanisms and new approaches to manage the disease with balanced nutrition are emerging. Nutrients like nitrogen (N), calcium (Ca), and magnesium (Mg) could extend the productive life of affected trees, although interactions among these nutrients in HLB-affected citrus trees are still unclear. A 2-year study was established in Florida to determine the response of HLB-affected trees to applications of N, Ca, and Mg. The study was conducted with ‘Valencia’ trees (Citrus sinensis L. Osbeck) on Swingle citrumelo (Citrus paradisi Macf. × Poncirus trifoliata L. Raf.) rootstock on a Candler sand. Applications of N at 168, 224 (recommended rate), and 280 kg⋅ha−1 N were used as the main plots. Split-plots consisted of a grower standard treatment receiving only basal Ca (51 kg⋅ha−1) and Mg (56 kg⋅ha−1); supplemental Ca (total Ca inputs: 96 kg⋅ha−1) only; supplemental Mg (total Mg inputs: 101 kg⋅ha−1) only; and supplemental Ca (total Ca inputs: 73.5 kg⋅ha−1) and Mg (total Mg inputs: 78.5 kg⋅ha−1). The following variables were measured: tree size, fruit yield, and juice quality. Although some differences in tree growth among treatments were statistically significant (e.g., greater canopy volume with Mg fertilization at 168 kg⋅ha−1 N), there was no clear and consistent effect of plant nutrition on these variables. Fruit yield was higher with Ca and Mg relative to the grower standard at the lowest N rate in 2020, and there were no other statistically significant differences among treatments. Juice acidity was significantly higher with Mg fertilization relative to other treatments in 2019. As N rates had no significant effect in this study, unlike secondary macronutrients, N rates could potentially be reduced to 168 kg N⋅ha−1 in HLB-affected citrus without affecting vegetative growth, fruit yield, and juice quality. However, this will require optimizing the supply of secondary macronutrients and all other nutrients to develop a balanced nutritional program. Ultimately, the effects of N, Ca, and Mg obtained in this 2-year study should be confirmed with longer-term studies conducted at multiple sites.

Foliar micronutrient applications enhance growth and yield of huanglongbing (HLB)‐affected sweet orange

“…Percent change in yield was calculated using the method described by Esteves et al. (2021) in Equation (). Canopy efficiency that measures the ratio of yield per canopy volume was calculated by dividing fruit yield per plot by canopy volume for the plot as described in the following equation.…”

“…Fruits were then used for juice quality (including soluble solids-Brix, titratable acid, and Brix/acid ratio). Percent change in yield was calculated using the method described by Esteves et al (2021) in Equation ( 5). Canopy efficiency that…”

Micronutrients Improve Growth and Development of HLB-Affected Citrus Trees in Florida

“…There has been multiple research that supports the use of ENPs to mitigate the damaging effects of HLB [ 18 , 22 , 24 , 39 , 40 , 41 , 42 ]. When citrus trees are infected by HLB disease, they show signs of micronutrient deficiencies (for example zinc, manganese, and iron) and this may be because the severity of HLB causes phloem plugging, thus limiting nutrient translocation within the plant [ 14 , 25 ] and as a result damages more than 40% of the fibrous roots [ 7 , 32 ], which may, in turn, inhibit nutrient absorption.…”

“…From the information gathered, it appears that the HLB-affected trees require more micronutrients than what is traditionally recommended for citrus production in Florida to achieve optimum nutrition. It has also been observed that foliar application of micronutrients to supplement soil-applied nutrients is able to correct deficiencies for HLB-affected trees [ 22 , 24 , 39 , 42 ]. HLB can impact yield due to poor growth and development, because of reduced root biomass and nutritional deficiencies [ 6 , 7 , 8 , 19 ], it is important that growers supply optimum nutrition while the tree is still young (between 1–4 years old).…”

A Comparison of the Effects of Several Foliar Forms of Magnesium Fertilization on ‘Superior Seedless’ (Vitis vinifera L.) in Saline Soils

“…Many researchers have begun to investigate magnesium nutrition and the determination of magnesium requirements for economically important crops [23] such as 'Washington navel' orange trees [24] and banana plants, and they have reported on the influence of magnesium on yield and fruit quality, stating that magnesium fertilization increased the yield and fruit quality of the aforementioned fruit species [25]. In addition, using the magnesium application can induce a state of magnesium deficiency during growing [26].…”