Effects of Short-term Drought Stress and Mechanical Harvesting on Sweet Orange Tree Health, Water Uptake, and Yield

Abstract

<jats:p>One of the primary reasons for the slow adoption of mechanical harvesting by Florida citrus growers is the physical injuries associated with it, including loss of leaves, twigs, flowers, and young fruits, limb breakage, and injuries to the bark and root. However, it has been shown that well-managed trees are capable of tolerating defoliation, limb loss, and root and bark injury caused by mechanical harvesting. Irrigation management is one of the most crucial factors that influence citrus tree health. A multiple-year field study was conducted on ‘Valencia’ sweet orange trees in a commercial citrus grove near Immokalee, FL, to determine the effect of initial tree canopy density and short-term drought stress on tree health, water uptake, and productivity of mechanically harvested trees. Three blocks were based on canopy density and overall appearance and indicated as low, moderate, and high canopy density. The experiment was laid in a split-plot design with four replications of six-tree plots of hand-harvested or mechanically harvested trees, taking drought stress or full irrigation as main treatments. The experimental design was repeated with trees in each plot of one of the three canopy density categories. After harvest, each six-tree plot was split into two three-tree subplots, where one subplot was drought-stressed and the other was fully irrigated. Harvesting was conducted in the Spring of 2010, 2011, and 2012 with the same experimental design and data collection procedures. The effects of short-term drought on water use and stem water potential were masked by heavy rains in Spring 2010 and thus no differences in the irrigation treatments were observed. In 2011 and 2012, stem water potential was unaffected by harvesting method. Water use was unaffected by harvesting method across the 3 years. Drought stress significantly increased pull force required to remove fruit and stem water potential after harvest. Although mechanically harvested trees lost leaf mass, with no rain before harvest, results from Spring 2011 and 2012 indicated that short-term drought stress had no effect on citrus leaf area irrespective of harvest method. Drought stress significantly increased fruit detachment force in low and moderate density but not in high-density trees resulting in increased force required to remove fruit from trees with moderate- to low-density canopies. Yield increased from 2010 to 2011 for mechanically harvested trees compared with hand-harvested for low-canopy density trees by 17% and moderate-canopy density trees by 8%, whereas high-density plots indicated similar yield after mechanical harvesting. Comparatively, yield in 2012 decreased in the low and moderate densities compared with yield in 2011 but increased in the high density by 14% and 53% in hand- and machine-harvested trees, respectively. Despite finding 2- to 3-fold more debris in the mechanically harvested trees than the hand-harvested trees, yields and other measured parameters were unaffected suggesting that mechanical harvesting of citrus trees did not have an adverse effect on growth and production of well-watered citrus trees.</jats:p>

Harvesting Method Affects Water Dynamics and Yield of Sweet Orange with Huanglongbing

“…Indicating higher stress and slower recovery for mechanically harvested trees. Regardless of harvesting methods, among all experiments, average sap flow declined after harvesting in both treatments which is similar to [21] observations. Sap flow decreased under mechanically harvested trees by greater percentages than hand-harvested treatments, indicating higher water stress symptoms under the mechanical treatment.…”

Improved Irrigation Management of Sweet Orange with Huanglongbing

“…Stem water potential was measured during dry and wet seasons of 2014 and 2015 (Table 1) using a Portable Plant Water Status Console (Model 3115; Soilmoisture Equipment Corp, Santa Barbara, CA). Stem water potential was measured as recommended by the manufacturer and other researchers (Morgan et al, 2014). Four representative leaves per tree (two trees per treatment) were randomly selected 24 h before measurements and covered with a thin film of plastic and aluminum foil to allow the water potential of the leaves to equilibrate with the water potential of the stem.…”

Smartphone Apps for Irrigation Scheduling

“…It has been determined that the water status of the trees leads to much of the reduced health and production of affected trees (Kadyampakeni et al, 2014a(Kadyampakeni et al, , 2014b. Likewise, tree health following mechanical harvesting of citrus has been found to be affected by irrigation before and after harvest (Morgan et al, 2014).…”