**2.4 EH1 fertilizer-planting density-coppicing study**

EH1, planted in June 2015 on a sandy former pasture in five 3-row (26 trees/row) plots receiving one of five fertilizers (control, GE 6-4-0 + micronutrients at 112, 224, and 336 kg of N/ha rates, and diammonium phosphate equivalent to 336 kg of N/ha) and two replications of 5-tree row plots of three planting densities (1196, 1794, and 3588 trees/ha), was coppiced in June 2019. The interior row of each plot was periodically measured for tree size, and number of coppice stems/stool at least half the DBH of the largest stem, through November 2021.

Given eucalypt's high productivity and their use for traditional forest products and because economic feasibility is one of several conditions for a sustainable BC system [20], our financial analysis goal using Land Expectation Value (LEV) and IRR in Sections 2.1–2.4 was to estimate the cost of potential carbon sequestration by *Eucalyptus* genotypes with and without BC as a soil amendment.

*Carbon Sequestration by Eucalypts in Florida, USA: Management Options Including Biochar… DOI: http://dx.doi.org/10.5772/intechopen.104923*

#### **2.5** *E. grandis* **WBs**

Two-row WB 5A, consisting of four *E. grandis* cultivars in 20-tree plots (two staggered rows 2.4 m apart with 10 trees at 1.5 m spacing within rows) systematically positioned in 14 replications, was established in June 2009 at Water Conserv II. All replications were irrigated with reclaimed water. The cultivars were measured periodically through 52 months for height and DBH. Assumed sequestration in roots was ≈10.3% of total aboveground sequestration [16].

In June 2012, two-row WBs (5B and 5C) composed of four *E. grandis* cultivars (G1, G2, G3, and G4) in one row and up to eight *Corymbia torelliana* progenies in an adjacent staggered row 2.4 m away were established around two Water Conserv II Rapid Infiltration Basins (RIB 2-3 and RIB 3-2). The trees were subsequently irrigated with reclaimed water. From the 290 clones of the cultivars replicated up to five times in row plots around RIB 2-3 and from the 308 clones replicated up to five times in row plots around RIB 3-2, typically 10-tree subsets in the row plots were measured periodically.

On March 30, 2014, two-row WB 5D was established at a citrus grove following Roundup application in mid-March. At 2.4 m spacing, 68 G3s were planted in the interior (north) row and 68 *C. torelliana* in the staggered (1.2 m offset) exterior (south) row. The trees were subsequently irrigated for 4 years and measured in May 2020.

Two-row WB 5E, consisting of three *E. grandis* cultivars in one row and four *C. torelliana* progenies in an adjacent row offset 1.2 m away, was established in July 2017 to assess BC and GE as silvicultural management options. Initially a randomized complete block design with four complete and one incomplete replications of the cultivars at 1.8 m within row spacing, in February 2018, all four complete replications received GE (6-4-0 + micronutrients equivalent to 336 kg of N/ha) and two interior replications also received 11.2 Mg/ha of GCS' Polchar BC by rotovating the two treatments into the soil to a 20 cm depth between and within 1.2 m of the two rows. The incomplete replication served as a control. The cultivars were measured periodically through June 2020.

#### **2.6** *E. grandis* **dendroremediation studies**

Two dendroremediation studies (**Table 1**) represent the potential use of *Eucalyptus* for managing wastewater. Study 6A had 44-month-old *E. grandis* cultivars G2 and G3 at 2.4 × 1.5 m in sandy soil in a stormwater retention pond in Tampa, FL, at the Tampa Port Authority (TPA). Study 6B on muck soil at the Everglades Research and Education Center (EREC) at Belle Glade, FL, included two *E. grandis* cultivars (G3 and G4) planted at a 1.5 × 1.5 m inside an agricultural runoff collection pond and measured for tree size and survival at 12 months. Above- and below-ground carbon sequestration was estimated as described in Section 2.2.

### **2.7 Other BC field studies**

Seven recent BC studies, all on sandy soil, are described in **Table 3**. GCS' Polchar BC was used for studies 7A, 7B, 7C, 7D, and 7E. Four studies (7A, 7C, 7D, 7F) involved levels of BC only, two (7B, 7E) also had GE alone and in combination with BC, and one (7G) included BC/compost mixes. The crops and soils were monitored periodically for up to two years.

Study 7E (**Table 3**) had two replications of four treatments: 0, GE equivalent to 336 kg of N/ha, 11.2 Mg/ha of GCS' Polchar BC, and GE + BC. The BC was banded


#### **Table 3.**

*Description of field studies receiving BC, GE, and/or compost—location in FL, amendments, crop, soil type, and culture.*

and incorporated into beds twice, and the GE was banded on top of fully formed beds. Soil samples were taken in January 2021 after all treatments has been applied.

The five experiments in Study 7F (**Table 3**) were conducted in two major commercial tomato production areas during the fall and winter of 2018–2019. Plastic beds (20 and 18 cm high in the middle and on the edges, respectively, and 81 cm wide) were formed at 1.8 m centers. Following formation, they were fertilized with a fertilizer/BC mixture (BC from coconut shells blended with the fertilizer at the blending facility at 268 lbs/ha), fumigated with 1,3-Dichloropropene and Chloropicrin (40:60) at a rate of 123 and 134 kg ha−1, and covered with virtually impermeable film. In all trials, preplant dry fertilizer (ammonium nitrate, triple superphosphate, and potassium sulfate plus micronutrients) was broadcast as "bottom mix" and two fertilizer bands were applied on the bed shoulders as "top mix" for a total nitrogen-phosphorus-potassium (N-P-K) of 207-49-344 kg ha−1. Fertigation supplemented the pre-plant fertilizer with 112-0-167 kg ha−1 N-P-K from tomato flowering to the first harvest. Roma-type tomatoes were harvested two to three times at the mature-green stage and graded into marketable sizes and weighed separately according to USDA specifications: extralarge (>7.00 cm), large (6.35–7.06 cm), and medium (5.72–6.43 cm).

Study 7G's three BC levels and two compost/BC mixes (**Table 3**) were applied annually to "Valencia" bud-grafted to "US812" planted in spring 2016. Tree growth measurements consisted of trunk diameter and fruit yield. Fruit mass per plot was assessed annually by weighing harvested fruit from entire plots using a Gator Deck scale (Scale Systems, Novi, MI).

## **3. Results**

### **3.1** *E. grandis* **mulch wood plantations**

The MAImax and biological rotation age for OP seedlings and G2 clones were 10.5 green Mg/ha/year at age 8.0 years and 16.5 green Mg/ha/year at age 7.0 years, *Carbon Sequestration by Eucalypts in Florida, USA: Management Options Including Biochar… DOI: http://dx.doi.org/10.5772/intechopen.104923*

respectively, and their associated total carbon sequestrations at MAImax were 27.0 and 37.0 Mg C/ha (**Figure 1**). The observed yields corresponded to site index (base age 8 years) values of 15.2 and 21.3 m for the seedlings and clones, respectively. LEVs at an 8% real discount rate, with and without carbon, ranged between −\$731/ha and −\$517/ha with IRRs between 4.3 and 5.9% (**Table 4**).

These yields for improved *E. grandis* OP seedlings were similar to earlier *E. grandis* spacing trial results in south Florida [21]. Under operational culture and without carbon credits, stumpage prices ≥ \$15/green Mg would favor clonal deployment over family forestry with IRRs exceeding 6.1%. Clonal deployment could generate higher LEVs at stumpage prices as low as \$13/green Mg with carbon credits included. Family forestry under operational culture and without carbon credits is favorable when stumpage prices are <\$15/green Mg and can exceed a 6% IRR when stumpage prices are ≥\$16.30/green Mg.

#### **3.2** *E. grandis* **cultivar planting density studies**

On former citrus lands and phosphate mined clay settling areas in central and south Florida, *E. grandis* cultivars had MAImaxs as high as 78.2 green Mg/ha/year with

#### **Figure 1.**

*Estimated total (stem + crown + roots) carbon sequestration (C, Mg/ha) for mulch wood plantations of E. grandis OP families and G2 clones established at 1,495 trees/ha on poorly drained, sandy Flatwoods sites in South Florida.*


#### **Table 4.**

*Estimated total carbon sequestration at MAImax, MAImax, and associated rotation age, and LEVs at 8% real discount rate and associated IRRs with and without carbon credits, for mulch wood plantations of E. grandis genotypes OP families and G2 cultivar established at 1495 trees/ha on bedded flatwoods soils.*

associated IRRs greater than 10% [8]. Total carbon sequestration estimates ranged from 38 to 95 Mg/ha at the time of MAImax, with longer-term totals over 100 Mg/ha in 6 years, depending on cultivar, site, planting density, and harvest age.

The effects of adding BC as a soil amendment on sandy soils and of applying carbon credits were assessed (**Table 5**, **Figure 2**). Because BC increased growth and decreased time of MAImax, estimated cumulative carbon sequestration with BC decreased as rotation length decreased; for example, at 2148 trees/ha, sequestration was 69.4 Mg/ha C in 4.9 years without BC and 61.9 Mg/ha C in 3.5 years with BC. Under current market conditions in central and southern Florida, intensive management with BC will be more profitable than operational culture if BC application costs are ≤\$450/Mg. If BC costs \$450/Mg, for example, then the LEV for 4305 trees/ha with BC will exceed the LEV of 2148 trees/ha under operational culture. Increased stumpage prices and carbon credits and/or lower silvicultural management costs favor an intensive BC regime under current application costs.

Increased stumpage price and low BC cost (\$750/Mg) favor a higher planting density under intensive management over the current mulch wood/moderate planting densities under operational culture. For example, a planting density of 4305 trees/


#### **Table 5.**

*Estimated total (stem + crown + roots) carbon sequestration at MAImax, MAImax, and associated rotation age, and LEV and associated IRR for E. grandis cultivars at two cultural intensities (fertilization and fertilization + BC), with and without carbon credits (\$5/Mg C), two BC prices (\$750 and 1000/Mg), and four planting densities on sandy soils in central and southern Florida.*

*Carbon Sequestration by Eucalypts in Florida, USA: Management Options Including Biochar… DOI: http://dx.doi.org/10.5772/intechopen.104923*

#### **Figure 2.**

*Estimated total (stem + crown + roots) carbon sequestration (C, Mg/ha) for G Series E. grandis cultivars for 4 years under four planting densities and two cultural regimes (fertilization only vs. fertilizer + BC) on sandy bedded former citrus lands in central and southern Florida.*

ha under an intensively managed BC regime can be more profitable (LEV = \$3357/ ha) than the moderate 2148 trees/ha planting density under operational culture (LEV = \$2459/ha), assuming the \$18/green Mg stumpage price observed in central and southern FL mulch wood markets (no carbon credits), BC application cost of \$750/ Mg, and 8% real discount rate (and the same management costs outlined in **Table 2**).

#### **3.3 EH1 planting density study**

Through 81 months, the higher 2471 tree/ha density increased the yield of intensively managed EH1 [7]. Maximum annual biomass yields and time to those maxima were directly and inversely, respectively, related to planting density: >58 green Mg/ha/year in 3.7 years at 2471 trees/ha vs. 44 at 5.0 years for 1181 trees/ha. Associated total carbon sequestration estimates followed somewhat similar trends: 77.2 Mg/ha C at 4.7 years for 2471 trees/ha vs. 75.8 Mg/ha at 5.5 years for 1181 trees/ ha (**Table 6**, **Figure 3**). Assessing the economic feasibility of EH1 SRWCs at a stumpage price of \$13/Mg and without BC, LEVs, and IRRs increased with carbon credit and were highest at an intermediate planting density.

#### **3.4 EH1 fertilizer-planting density-coppicing study**

Planting density consistently influenced tree size, and the highest planting density had the smallest tree DBH at the 47-month harvest of the original rotation ([7], **Table 7**). However, carbon sequestration at 47 months was greatest at the 3588 density.

While planting density usually did not influence coppice stem DBH and number, at 23 months, the DBHs of the largest coppice stem/stool (**Table 7**) were similar to tree DBH at the same age in the original rotation. Should that trend continue and the number of coppice stems/stool with DBH at least half that of the largest stem exceeds one, coppice carbon sequestration at each planting density would surpass that of the original rotation.


#### **Table 6.**

*Estimated total carbon sequestration at MAImax, MAImax and associated rotation age, and LEV at 8% real discount rate and associated IRR with and without carbon credits (\$5/Mg C) for EH1 under operational culture without BC and three planting densities on sandy bedded former citrus lands in southern Florida.*

#### **Figure 3.**

*Estimated total (stem + crown + roots) carbon sequestration (C, Mg/ha) for EH1 at three planting densities (trees/ha, THA) through 4 years in study 4 without BC.*


#### **Table 7.**

*DBH and estimated total carbon sequestration of 47-month-old original and DBH and number of coppice stems of E. urophylla x E. grandis cultivar EH1 in Study 4.*

*Carbon Sequestration by Eucalypts in Florida, USA: Management Options Including Biochar… DOI: http://dx.doi.org/10.5772/intechopen.104923*

#### **3.5** *E. grandis* **in WBs**

WBs 5A, 5B, 5C, and 5D were measured from as young as 4 months to as old as 74 months (**Table 8**). Because the four *E. grandis* cultivars in WB 5A had similar sizes at each measurement age, their carbon sequestration estimates were averaged for each age. Sequestrations increased with age, reaching 12 Mg/ha C at 52 months. In WB 5B, because the cultivars were bigger in RIB 2–3, at 16 months, the cultivars had higher sequestration in RIB 2–3; both 16-month sequestration levels approximated the 18-month level in WB 5A. In WB 5C at age 74 months, cultivar G3 grew well and sequestered 33 Mg/ha C in just over 6 years.

Sequestration estimates in these three WBs were influenced by the planting density presumed for the three WBs. While the within-row spacing and distance between rows were known for each WB, the area occupied by each WB tree was speculative and was set to 652 trees/ha for each WB. Had a higher planting density been used, the sequestration estimates would be higher.

Soil amendments in WB 5E caused large early soil nutrient, tree nutrient, and tree growth responses by three *E. grandis* cultivars [7], with sequestration of up to 34 Mg/ ha of C in 37 months with GE + BC (**Table 9**). GE and especially BC + GE greatly enhanced the nutrient properties of this inherently poor sandy soil.

GE greatly increased tree DBH and total carbon sequestration compared to the control, and GE + BC further increased DBH by 3.3 cm and C by 14 Mg/ha, respectively. Carbon sequestration from GE is primarily above ground while carbon sequestration by GE + BC is both above ground and in the soil. Assuming that all the BC applied remained in the soil, GE + BC increased total carbon sequestration by nearly 33% to some 45 Mg/ha of C.


#### **Table 8.**

*Tree height and DBH and estimated carbon sequestration at various ages of E. grandis cultivars in four WB studies.*


**Table 9.**

*Tree DBH, estimated total carbon sequestration at 37 months, and MAImax and associated rotation age of E. grandis cultivars receiving Control, GE, GE + BC treatments in WB Study 5E.*

#### **3.6** *E. grandis* **dendroremediation studies**

Studies 6A and 6B provided 12- and 44-month sequestration estimates, respectively (**Table 10**), for very different soil types and planting densities. Sequestration in 6A was 12 Mg/ha C at 44 months, or 12 Mg/ha C annually, on a sandy retention pond at 2778 trees/ha, while in 6B it was 12 Mg/ha C at 12 months on muck soil at 4444 trees/ha.

#### **3.7 Other BC field studies**

Five recent amendment studies involving BC, GE, and/or compost are summarized in **Table 11**. As suggested by Study 7A, notable soil and plant responses to BC may take up to 2 years, although BC immediately increased soil organic matter in Studies 7B, D, and E. Studies 7C and 7B had varied responses to BC rates.

In Study 7F, BC at 286 kg/ha only impacted the marketable yields in one out of five tomato trials (**Table 12**). Blending the BC with the broadcasting fertilizer application reduced the expense of an extra passing applying the BC; however, the rates were too low to produce an increase in marketable tomato yields. Similar studies indicate the use of BC was an effective and productive soil amendment as compared to compost [23–27]. Future trials with higher BC rates may impact tomato yields positively as may continue with yearly BC application at a lower rate.

Study 7G's first-year data indicated no differences in plant growth, but 892 kg/ha BC produced the highest fruit yields (**Table 13**), as application rates in this trial were too low to have a significant yield impact in the first year. Compost application in sandy


#### **Table 10.**

*Tree height, DBH, survival, and estimated above- and below-ground and total carbon sequestration of E. grandis cultivars in two dendroremediation studies.*


*Carbon Sequestration by Eucalypts in Florida, USA: Management Options Including Biochar… DOI: http://dx.doi.org/10.5772/intechopen.104923*

#### **Table 11.**

*Soil and plant responses in five BC and/or GE studies in Florida.*


#### **Table 12.**

*Effect of BC on the marketable yields of Roma and round-type tomatoes.*


#### **Table 13.**

*First-year trunk diameter and fruit yield of Valencia/US812 in response to five BC/compost soil amendments.*

soils had a positive impact on soil and crops elsewhere in Florida [28–32]. Long-term compost application at higher rates will promote soil health and increase yield [33, 34].
