Sweet Orange Orchard Architecture Design, Fertilizer, and Irrigation Management Strategies under Huanglongbing-endemic Conditions in the Indian River Citrus District

The prevalence of Huanglongbing (HLB) in Florida has forced growers to search for new management strategies to optimize fruit yield in young orchards and enable earlier economic returns given the likelihood of HLB-induced yield reductions during later years. There has been considerable interest in modifying orchard architecture design and fertilizer and irrigation management practices as strategies for increasing profitability. Our objectives were to evaluate how different combinations of horticultural practices including tree density, fertilization methods, and irrigation systems affect growth, foliar nutrient content, fruit yield, and fruit quality of young ‘Valencia’ sweet orange [Citrus sinensis (L.) Osbeck] trees during the early years of production under HLB-endemic conditions. The study was conducted in Fort Pierce, FL, from 2014 to 2020 on a 1- to 7-year-old orchard and evaluated the following treatments: standard tree density (358 trees/ha) and controlled-release fertilizer with microsprinkler irrigation (STD_dry_MS), high tree density (955 trees/ha) with fertigation and microsprinkler irrigation (HDS_fert_MS), and high tree density with fertigation and double-line drip irrigation (HDS_fert_DD). Annual foliar nutrient concentrations were usually within or higher than the recommended ranges throughout the study, with a tendency for decreases in several nutrients over time regardless of treatment, suggesting all fertilization strategies adequately met the tree nutrient demand. During fruit-bearing years, canopy volume, on a per-tree basis, was higher under STD_dry_MS (6.2–7.2 m3) than HDS_fert_MS (4.3–5.3 m3) or HDS_fert_DD (4.9–5.9 m3); however, high tree density resulted in greater canopy volume on an area basis, which explained the 86% to 300% increase in fruit yield per ha that resulted in moving from standard to high tree density. Although fruit yields per ha were generally greatest under HDS_fert_MS and HDS_fert_DD, they were lower than the 10-year Florida state average (26.5 Mg·ha−1) for standard tree density orchards, possibly due to the HLB incidence and the rootstock chosen. Although tree growth parameters and foliar nutrient concentrations varied in response to treatments, management practices that included high tree density and fertigation irrespective of irrigation systems produced the highest fruit yields and highest yield of solids. Soluble solids content (SSC) and titratable acidity (TA) were lower, and the SSC-to-TA ratio was highest under STD_dry_MS in 2016–17, with no treatment effects on quality parameters detected in other years. Both drip and microsprinkler fertigation methods sufficiently met tree nutrient demand at high tree density, but additional research is needed to determine optimal fertilization rates and better rootstock cultivars in young high-density sweet orange orchards under HLB-endemic conditions in the Indian River Citrus District.

Biotic and abiotic drivers of soil microbial functions across tree diversity experiments

AimSoil microorganisms are essential for the functioning of terrestrial ecosystems. Although soil microbial communities and functions may be linked to the tree species composition and diversity of forests, there has been no comprehensive study of how general potential relationships are and if these are context-dependent. A global network of tree diversity experiments (TreeDivNet) allows for a first examination of tree diversity-soil microbial function relationships across environmental gradients.LocationGlobalMajor Taxa StudiedSoil microorganismsMethodsSoil samples collected from eleven tree diversity experiments in four biomes across four continents were used to measure soil basal respiration, microbial biomass, and carbon use efficiency using the substrate-induced respiration method. All samples were measured using the same analytical device in the same laboratory to prevent measurement bias. We used linear mixed-effects models to examine the effects of tree species diversity, environmental conditions, and their interactions on soil microbial functions.ResultsAcross biodiversity experiments, abiotic drivers, mainly soil water content, significantly increased soil microbial functions. Potential evapotranspiration (PET) increased, whereas soil C-to-N ratio (CN) decreased soil microbial functions under dry soil conditions, but high soil water content reduced the importance of other abiotic drivers. Tree species richness and phylogenetic diversity had overall similar, but weak and context-dependent (climate, soil abiotic variables) effects on soil microbial respiration. Positive tree diversity effects on soil microbial respiration were most pronounced at low PET, low soil CN, and high tree density. Soil microbial functions increased with the age of the experiment.Main conclusionsOur results point at the importance of soil water content for maintaining high levels of soil microbial functions and modulating effects of other environmental drivers. Moreover, overall tree diversity effects on soil microbial functions seem to be negligible in the short term (experiments were 1-18 years old). However, context-dependent tree diversity effects (climate, soil abiotic variables) have greater importance at high tree density, and significant effects of experimental age call for longer-term studies. Such systematic insights are key to better integrate soil carbon dynamics into the management of afforestation projects across environmental contexts, as today’s reforestation efforts remain focused largely on aboveground carbon storage and are still dominated by less diverse forests stands of commercial species.

Trends in Soil Carbon Stockpile of Three Major Forests Along an Altitudinal Gradient in Indian Central Himalaya

Current investigation reveals the stock of soil organic carbon (SOC) along with altitudinal gradients in Oak (Quercus leuchotrichophora), Pine (Pinus roxburghii) and Sal (Shorea robusta) dominant forests in Shiwalik region of Kumaun Himalayas in India. The estimated soil organic carbon was found 16.0 ± 4.3 to 19.4 ± 6.4 g kg-1 for Oak, 17.8 ± 2.0 to 25.6 ± 1.6 g kg-1 for Pine and 15.8 ± 2.2 to 21.4 ± 1.9 g kg-1 for Sal forests, respectively in 0-10, 10-20 and 20-30 cm soil depths. SOC stock was found to be in decreasing pattern with increasing altitude from 193.6 to 166.4, 146.4 to 137.6 and 159.2 to 141.6 t C ha-1 in Oak, Pine and Sal forests, respectively. It is an indicator of higher biological activity or anthropogenic disturbance associated with top layers of these forest areas. Higher SOC was recorded in Sal forest compared to Oak. In Sal forest, high tree density leads to higher accumulation of SOC compared to conifers while it was low in wide spread Pine forest, resulting in less storage of carbon stock in turn. ECOPRINT 21: 7-13, 2014DOI: http://dx.doi.org/10.3126/eco.v21i0.11898

Diversité floristique spontanée des plantations de café et de cacao dans la forêt classée de Monogaga, Côte d'Ivoire | Spontaneous floristic diversity of cocoa and coffee plantations in the classified forest of Monogaga, Côte d'Ivoire (reviewed paper)

The inventory and the analysis of the woody species preserved in the different categories of cocoa and coffee plantations showed that they are relatively diversified (presence of endemic, rare and threatened species). They also preserved high tree density and high basal areas. The young plantations are especially diversified. Their number of species,density and basal areas and diversity index are similar to those of the neighbouring old growth and secondary forests. Older plantations display a sharp decline of diversity over time. Agricultural practices in the region represent a threat in the medium term to the preservation of biodiversity.

Performance of Citrus Scion Cultivars and Rootstock in a High-density Planting

`Hamlin' and `Valencia' oranges [Citrus sinensis (L.) Osb.], `Murcott' tangor (C. reticulata Blanco × C. sinensis), and `Redblush' grapefruit (C. paradisi Macf.) on 15 rootstock and own-rooted cuttings were planted at a 1.5 × 3.3-m spacing providing a density of 2020 trees/ha. Growth rate, productivity, and fruit quality varied among the scion and stock combinations. Combinations of moderate vigor and precocious fruiting performed better than very vigorous or dwarfing materials. Several freezes slowed canopy development and delayed production. Most trees had filled their allocated canopy space 7 years after planting. At that age, the orange trees yielded 23 to 75 t·ha-1. Scion and stock combinations with desirable vigor and fruiting characteristics were satisfactory in this high-density planting. However, there appears to be little advantage of high tree density under Florida conditions, and moderate densities of fewer than 1000 trees/ha may be preferable.