Tanka P. Kandel

Chemical composition and methane yield of reed canary grass as influenced by harvesting time and harvest frequency

This study examined the influence of harvest time on biomass yield, dry matter partitioning, biochemical composition and biological methane potential of reed canary grass harvested twice a month in one-cut (OC) management. The regrowth of biomass harvested in summer was also harvested in autumn as a two-cut management with (TC-F) or without (TC-U) fertilization after summer harvest. The specific methane yields decreased significantly with crop maturity that ranged from 384 to 315 and from 412 to 283 NL (normal litre) (kgVS)(-1) for leaf and stem, respectively. Approximately 45% more methane was produced by the TC-F management (5430Nm(3)ha(-1)) as by the OC management (3735Nm(3)ha(-1)). Specific methane yield was moderately correlated with the concentrations of fibre components in the biomass. Larger quantity of biogas produced at the beginning of the biogas assay from early harvested biomass was to some extent off-set by lower concentration of methane.

Measurement and modelling of CO2 flux from a drained fen peatland cultivated with reed canary grass and spring barley

Cultivation of bioenergy crops has been suggested as a promising option for reduction of greenhouse gas (GHG) emissions from arable organic soils (Histosols). Here, we report the annual net ecosystem exchange (NEE) fluxes of CO2 as measured with a dynamic closed chamber method at a drained fen peatland grown with reed canary grass (RCG) and spring barley (SB) in a plot experiment (n = 3 for each cropping system). The CO2 flux was partitioned into gross photosynthesis (GP) and ecosystem respiration (RE). For the data analysis, simple yet useful GP and RE models were developed which introduce plot‐scale ratio vegetation index as an active vegetation proxy. The GP model captures the effect of temperature and vegetation status, and the RE model estimates the proportion of foliar biomass dependent respiration (Rfb) in the total RE. Annual RE was 1887 ± 7 (mean ± standard error, n = 3) and 1288 ± 19 g CO2‐C m−2 in RCG and SB plots, respectively, with Rfb accounting for 32 and 22% respectively. Total estimated annual GP was −1818 ± 42 and −1329 ± 66 g CO2‐C m−2 in RCG and SB plots leading to a NEE of 69 ± 36 g CO2‐C m−2 yr−1 in RCG plots (i.e., a weak net source) and −41 ± 47 g CO2‐C m−2 yr−1 in SB plots (i.e., a weak net sink). Standard errors related to spatial variation were small (as shown above), but more significant uncertainties were related to the modelling approach for establishment of annual budgets. In conclusion, the bioenergy cropping system was not more favourable than the food cropping system when looking at the atmospheric CO2 emissions during cultivation. However, in a broader GHG life‐cycle perspective, the lower fertilizer N input and the higher biomass yield in bioenergy cropping systems could be beneficial.

Prediction of biogas yield and its kinetics in reed canary grass using near infrared reflectance spectroscopy and chemometrics.

A rapid method is needed to assess biogas and methane yield potential of various kinds of substrate prior to anaerobic digestion. This study reports near infrared reflectance spectroscopy (NIRS) as a rapid alternative method to the conventional batch methods for prediction of specific biogas yield (SBY), specific methane yield (SMY) and kinetics of biogas yield (k-SBY) of reed canary grass (RCG) biomass. Dried and powdered RCG biomass with different level of maturity was used for biochemical composition analysis, batch assays and NIRS analysis. Calibration models were developed using partial least square (PLS) regression from NIRS spectra. The calibration models for SBY (R(2)=0.68, RPD=1.83) and k-SBY (R(2)=0.71, RPD=1.75) were better than the model for SMY (R(2)=0.53, RPD=1.49). Although the PLS model for SMY was less successful, the model performance was better compared to the models based on chemical composition.

Carbon balance of rewetted and drained peat soils used for biomass production: A mesocosm study

Rewetting of drained peatlands has been recommended to reduce CO2 emissions and to restore the carbon sink function of peatlands. Recently, the combination of rewetting and biomass production (paludiculture) has gained interest as a possible land use option in peatlands for obtaining such benefits of lower CO2 emissions without losing agricultural land. This study quantified the carbon balance (CO2, CH4 and harvested biomass C) of rewetted and drained peat soils under intensively managed reed canary grass (RCG) cultivation. Mesocosms were maintained at five different groundwater levels (GWLs), that is 0, 10, 20 cm below the soil surface, representing rewetted peat soils, and 30 and 40 cm below the soil surface, representing drained peat soils. Net ecosystem exchange (NEE) of CO2 and CH4 emissions was measured during the growing period of RCG (May to September) using transparent and opaque closed chamber methods. The average dry biomass yield was significantly lower from rewetted peat soils (12 Mg ha−1) than drained peat soils (15 Mg ha−1). Also, CO2 fluxes of gross primary production (GPP) and ecosystem respiration (ER) from rewetted peat soils were significantly lower than from drained peat soils, but net uptake of CO2 was higher from rewetted peat soils. Cumulative CH4 emissions were negligible (0.01 g CH4 m−2) from drained peat soils but were significantly higher (4.9 g CH4 m−2) from rewetted peat soils during measurement period (01 May–15 September 2013). The extrapolated annual C balance was 0.03 and 0.68 kg C m−2 from rewetted and drained peat soils, respectively, indicating that rewetting and paludiculture can reduce the loss of carbon from peatlands.

Annual balances and extended seasonal modelling of carbon fluxes from a temperate fen cropped to festulolium and tall fescue under two-cut and three-cut harvesting regimes

This study reports the annual carbon balance of a drained riparian fen under two‐cut or three‐cut managements of festulolium and tall fescue. CO2 fluxes measured with closed chambers were partitioned into gross primary production (GPP) and ecosystem respiration (ER) for modelling according to environmental factors (light and temperature) and canopy reflectance (ratio vegetation index, RVI). Methodological assessments were made of (i) GPP models with or without temperature functions (Ft) to adjust GPP constraints imposed by low temperature (<10 °C) and (ii) ER models with RVI or GPP parameters as biomass proxies. The sensitivity of the models was also tested on partial datasets including only alternate measurement campaigns and on datasets only from the crop growing period. Use of Ft in GPP models effectively corrected GPP overestimation in cold periods, and this approach was used throughout. Annual fluxes obtained with ER models including RVI or GPP parameters were similar, and also annual GPP and ER fluxes obtained with full and partial datasets were similar. Annual CO2 fluxes and biomass yield were not significantly different in the crop/management combinations although the individual collars (n = 12) showed some variations in GPP (−1818 to −2409 g CO2‐C m−2), ER (1071 to 1738 g CO2‐C m−2), net ecosystem exchange (NEE, −669 to −949 g CO2‐C m−2) and biomass yield (556 to 1044 g CO2‐C m−2). Net ecosystem carbon balance (NECB), as the sum of NEE and biomass carbon export, was only slightly negative to positive in all crop/management combinations. NECBs, interpreted as emission factors, tended to favour the least biomass producing systems as the best management options in relation to climate saving carbon balances. Yet, considering the down‐stream advantages of biomass for fossil fuel replacement, yield‐scaled carbon fluxes are suggested to be given additional considerations for comparison of management options in terms of atmospheric impact.

Methane yield from anaerobic digestion of festulolium and tall fescue cultivated on a fen peatland under different harvest managements

ABSTRACT This study evaluated the effects of harvesting managements with two-cuts (2C) and three-cuts (3C) per year for subsequent specific methane yield (SMY) and methane yield per hectare (MYPH) of festulolium and tall fescue cultivated on a riparian fen peatland in a block-designed field experiment (n = 3). For the 2C managements, three timings of the first cut were implemented corresponding to growth stages of pre-heading (2C-early), inflorescence emergence (2C-mid), and flowering (2C-late). Anaerobic digestion batch assays with biomass samples were run for 68 days, showing that 90% of total methane (CH4) was produced within 38 days. Specific methane yield ranged from 315 to 464 NL CH4 kg−1 volatile solids (mean, 393 NL). On average, SMY of the final cut biomass was 13% lower than the first cut biomass. Methane yield per hectare ranged from 5277 to 6963 Nm3 CH4 ha−1 (mean, 6265 Nm3) and was predominantly influenced by biomass yield since SMY only deviated modestly in relation to harvest management (crop maturity). Methane yield per hectare of festulolium under 3C and 2C-late management were significantly higher than 2C-early and 2C-mid managements, whereas the harvesting managements did not influence MYPH of tall fescue. The levels of SMY and MYPH in the present study represented high-end of reported values due to a combination of high activity of the biogas inoculum and a high productivity of festulolium and tall fescue at the riparian fen peatland.

Effect of Time and Level of Pruning on Vegetative Growth, Flowering, Yield, and Quality of Guava

Poor quality fruit production in the rainy season and failure to manipulate production periods are common problems for guava production in India and Nepal. As a possible management to overcome these problems, a field experiment was conducted to understand the effect of time and level of pruning on growth, flowering, yield, and quality of guava. An experiment was laid out with split-pot design allocating three pruning times (mid-April, early May, and mid-May) and four pruning levels (0-, 10-, 20-, and 30-cm tip removal) with three replications in each treatment. Increased level of pruning in early May increased the leaf number and area both in rainy and winter seasons. Similarly, an increased level of pruning and delayed pruning increased the fruit size and fruit weight in both seasons. In the winter season, fruit yield per tree was increased by plants pruned in early May. Total soluble sugar (%) of fruits increased with the increased level of pruning in both seasons irrespective of timing of pruning, but fruit acidity was not affected by both treatments. In conclusion, pruning plants at a 20 cm pruning level in early May was the most effective management to reduce yield in the rainy season and to enhance yield and quality in the winter season.