Original scientific paper
BIOPRODUCTIVITY OF INDIGOBUSH (Amorpha fruticosa L.) IN ONE-YEAR, TWO-YEAR AND FOUR-YEAR ROTATION
Ante P. B. Krpan
; Akademija šumarskih znanosti, Zagreb
Željko Tomašić
orcid.org/0000-0003-1864-6371
; Hrvatske šume, Direkcija Zagreb
Željko Zečić
orcid.org/0000-0002-8471-9690
; Šumarski fakultet Sveučilišta u Zagrebu
Dijana Vuletić
orcid.org/0000-0003-4631-7604
; Hrvatski šumarski institut, Jastrebarsko
Abstract
At the beginning of 2008, within the scope of the project Forest products and harvesting technology agreed with Croatian Forests Ltd, Zagreb, we have set up a research of biopotential, energetic characteristics and harvesting technology and use of indigobush biomass. From the above mentioned project, in 2012, a separate project Biopotential and energy characteristics of indigobush was transferred to the Academy of forestry sciences. The research ground was established in the pure indigobush stand in the forest management unit of the Posavina Forests, department 126a, Forest Office Sunja, Forest Administration Sisak. Within the block system, four test fields have been established; each with six 5 x 5 m large sub-test plots. (Figure 1)
This paper shows the results of the fourth year of research of indigobush considering its bioproductivity potential with a reference to the prescribed standards, harvesting characteristics and market demands, all which determines its position within the family of renewable resources of wood biomass for energy purposes. The research has encompassed plots 1, 2 and 4, i.e. bioproductivity of indigobush in one-year, two-year and four-year rotations. Within the scope of forest biomass issues, a higher number of HRN EN standards was considered, and a critical review of the terminology related to forest biomass, i.e., hard fuels, a term unscrupulous authors use in their publications.
Data of plots 1 are shown in Figures 3 and 4. In a one-year rotation per hectare, there were 87 200 to 140 400 one-year-old sprouts of indigobush. Mean height of sprouts on plots vary in a narrow range of 16 cm, taking a value of 2.07 m on the test field IV and up to 2.23 m on the test field II. The smallest mean diameter is recorded on the test field II and it amounts to 7.11 mm, while the largest was found on the test field III and it was 7.56 mm. Green indigobush mass on plots 1 ranges between 18.50 kg to 33.00 kg or in the calculation per hectare of the surface, it ranges between 7.40 t/ha and 13.20 t/ha. The difference between the smallest and the biggest value of green mass production on plots 1 is significant and it amounts to 5.80 t/ha. Average bioproduction of the green mass of indigobush on plots 1 in the fourth year of research amounts to 10.15 t/ha. Mean mass of one sprout of indigobush for all four plots is 0.0897 kg.
Data of plots 2 are shown in Figures 5 and 6. Number of sprouts on plots 2 ranges from 225 on fields II and IV up to 303 on field I, respectively, from 90 000 pcs/ha to 121 000 pcs/ha. Minimal mean height of 2.67 m is recorded in field I, and the maximal in field II, namely, 2.81 m. Mean diameter was the lowest on plot 2 in field I and it amounts to 9.82 mm, while the largest of 11.77 mm was recorded on test field IV. After long vegetation the established production of green mass of indigobush on plots amounts from 55.50 kg to a maximum of 70.50 kg or from 22.20 t/ha to 28.20 t/ha.
Average biannual production of green biomass amounts to 24.52 t/ha, respectively, average annual value amounts to 12.26 t/ha. Mean mass of one sprout of indigobush on plots assumes the value from 0.199 kg to 0.264 kg, i.e. 0.240 kg on average for all plots.
The parameters of bioproduction of indigobush for plots 4 are shown in Figures 7 and 8. Mean sprout height on plots 4 varies from 2.82 m to 3.04 m, and the diameter from 11.49 mm to 13.96 mm. The accumulated green biomass of indigobush during four vegetative periods varies between 83.10 kg/plot to a maximum of 128.50 kg/plot. After four-year rotations, per hectare, we acquired from 90 800 to 131 600 or an average of 109 000 sprouts and green biomass between 33.24 t/ha and 51.40 t/ha or an average of 42.06 t/ha. Average annual production of green biomass on plots 4 ranges from 8.31 t/ha to 12.85 t/ha and the mean value for all plots is 10.52 t/ha. Mean mass of one sprout of indigobush on all plots is 0.386 kg.
Table 1 and Figures 9, 10 and 11 show data of the variation analysis of diameter at breast height, and Table 2 and Figures 12, 13 and 14 show data of the variation analysis of mean sprout height of indigobush, including a discussion.
Table 3 shows the production of green biomass, laboratory determined percentages of moisture ratio of green indigobush and dry biomass matter. On plots 1, the percentage of moisture of indigobush wood ranges from 35.27 % to 37.02 % with a mean value of 35.92 %, on plots 2 the range of moisture is between 35.26 % and 36.03 % with mean value of 35.71 %, while on plots 4 it ranges between 30.91 % and 35.59 % with a mean value of 33.19 %. The proportion of dry matter in the samples of indigobush wood, relevant for all tested plots, ranges from 62.98 % to 69.09 %. In average, it is lowest on plots 1 with 64.08 %; on plots 2 the average value is 64.29 %, and on plots 4 it is the highest and it amounts to 66.81 %. Absolute values of the produced dry indigobush biomass in 2011 on plots 1 ranges from 11.88 kg/plot to 21.36 kg/plot or in average 16.26 kg/plot, i.e., or 6.5 t/ha of dry biomass.
On plots 1, which are harvested on a yearly basis at the end of every vegetative period, the annual level of bioproductivity of dry biomass after the first vegetation in 2008, it amounted to 12 t/ha (Krpan and Tomasic, 2009), after the second (2009) it was 7.87 t/ha (Krpan et al. 2011 –2), after the third (2010) it was 9.79 t/ha, and in 2011 it was 6.5 t/ha, and thus it could be concluded that bioproductivity of indigobush in one year rotation varies and has a decreasing trend in comparison with the first vegetation.
In a two-year rotation on plots 2, it was produced between 35.64 kg and 52.30 kg, with an average of 40.99 kg/plot (Krpan et al. 2011 –2). Therefore, the mean biannual bioproductivity of dry indigobush matter amounted 16.40 t/ha or on an annual average basis it was 8.20 t/ha which increases the value of bioproductivity for 0.31 t/ha in comparison with the second biannual yield in 2011.
In the four-year rotation of indigobush on plots 4, the established bioproductivity of dry biomass of indigobush has a value from 55.05 kg/plot to a maximum of 86.62 kg/plot or an average of 70.25 kg/plot, respectively, 28.10 t/ha. Mean annual bioproductivity of dry biomass in the four year rotation was 7.03 t/ha.
Bioproductivity of indigobush in this paper, based on the measurements of growth and increment parameters, density of the sprouts, parameters of laboratory research, its green mass, moisture and dry matter per plot unit in one-year, two-year and four-year rotation, despite the understandable variations, shows the potential benefit of indigobush within the family of solid fuels derived from forest biomass for energy. This paper showed previous research results based on which, due to the variations in the annual biomass production, it is not possible to choose and recommend an optimal rotation.
Keywords
indigobush bioproductivity; biomass standards; lowland forest ecosystems; Croatia
Hrčak ID:
141813
URI
Publication date:
30.4.2015.
Visits: 2.044 *