2019 ASHS Annual Conference

Precise irrigation and fertigation management provides a better root environment while minimizing excessive irrigation and leaching of nutrients. This concept can improve citrus tree growth in the presence of Huanglongbing (HLB) and help optimize water and nutrient use. Higher tree density can also increase fruit yield per area under high HLB pressure. This study evaluated the efficiency of open hydroponics on ‘Ray Ruby’ grapefruit production under different irrigation systems and tree density. We tested a combination of rootstocks (Sour orange [SO] and US-897), tree spacing (standard [STD] and high density staggered [HDS]), fertilization (controlled-release fertilizer [CRF] and fertigation [fert]), and irrigation systems (drip and microjet), arranged on five treatments: 1) SO_STD_CRF_MS: SO + standard spacing + controlled-release fertilizer + microjet, 2) SO_HDS_fert_DD: SO + HDS + fertigation + drip, 3) 897_HDS_fert_MS: US897 + HDS + fertigation + microjet, 4) 897_HDS_fert_DD: US-897 + HDS + fertigation + drip, and 5) SO_HDS_fert_MS: SO + HDS + fertigation + microjet. Foliar nutrients, insecticides and fungicides were applied using standard practices and insect pests scouted monthly. HLB incidence reached 100% by five years after planting. The total number of fruit and fruit yield were 226% and 183% higher in 2016 compared to 2015. Trunk diameter and canopy volume increased through time and were higher on SO_STD_dry_MS compared to other treatments due to the higher space available for plant growth. However, SO_STD_dry_MS yielded 7,309 kg/ha in 2017 compared to an average of 22,153 kg/ha for other treatments. High-density plantings tend to increase the yield per area in comparison to yield per tree. Soluble solid content, acidity, and ratio were not significantly different between treatments (p>0.05). Total solids per hectare was always lowest in SO_STD_dry_MS. High density staggered planting resulted in higher fruit yield, irrespective of rootstock and irrigation system, representing an important advance to the grapefruit production system. However, labor cost and effects on plant growth over time still need to be determined.