Grass legume intercrop to produce biomass for bioenergy

Transcription

1 Grass legume intercrop to produce biomass for bioenergy August 201 Among lignocellulosic crops i.e. energy crops for which the whole biomass is harvested and valorized for energy production perennial crops such as Miscanthus x giganteus or switchgrass are highyielding crops (Laurent et al., 201) whereas annual and multi-annual energy crops both allow high yields and a combination of energy, food and feed production in the crop sequence. However, annual crops have high needs for nitrogen fertilizer, leading to some negative environmental impacts such as high nitrogen losses and energy consumptions (e.g. Boehmel et al., 2008). Legumes, able to fix nitrogen could play a major role to reduce nitrogen fertilization of annual and multi-annual lignocellulosic crops (Jensen et al. 2012). Intercrop is defined as the cultivation of two or more species in the same space and for a significant time (Willey, 1979). In fact, Grass-legume intercrops are already used nowadays for various purposes, such as grain production and forage production and could present interesting benefits for bioenergy production (Pellicano et al., 201). This hypothesis was subject to experiment within the framework of LogistEC project. Figure 1. Triticale-vetch intercrop, INRA, Versailles, 2011 Original hypothesis: Grass legume intercrops are good candidates as annual or multi-annual energy crops. Study aimed at assessing the performances of various grass-legume intercrops for bioenergy production. MATERIAL AND METHODS Two experiments were set in Versailles in 2010, for 3 years, including annual winter crops and multiannual crops. In our experiment, both grass and legume species in the intercrops are sown at the same time, mixed within the row, and harvested together.

2 Vetch 0N Pea 0N Clover 0N Tri cale 0N Tri cale N Tri cale-vetch 0N Tri cale-vetch N/2 Tri cale-clover 0N Tri cale-clover N/2 Tri cale-pea 0N Tri cale-pea N/2 Alfalfa 0N Tall fescue 0N Tall fescue N Orchard grass 0N Orchard grass N Fescue-alfalfa 0N Fescue-alfalfa N/2 Orchard g.-alfalfa 0N Orchard g.-alfalfa N/2 v Intercrops sown at half density v N = kg N / ha (annual) / 3* kg N / ha (multi-annual) v N/2 = half compared to sole crops v 3 blocks, 11 or 9 treatments randomized within each block v Each plot 100 m2 Figure 1. Species and treatments tested in the two experiments (annual winter crops and multi-annual crops) Indicators measured or calculated Commercial biomass yield (harvested with a silage mower) Plot biomass yield (collected by hand), including the proportion of each species in the mixture Quality of the biomass (ash, lignin, cellulose, hemicellulose, C, N, H, S contents, monosaccharide composition and linkage analysis of polysaccharides), Residual soil mineral nitrogen (after harvest for annual crops, and 2 times per year, end of winter and after the second or third cut, for multi-annual crops), Greenhouse gas emissions (in kg CO 2 eq., accounting for direct and indirect emissions from machinery, direct emissions of N 2 O from N fertilization and from crop stubbles, and indirect emissions from N fertilizer and pesticide manufacturing) Energy cost (accounting for the machinery, the mineral nitrogen fertilizer and the pesticide manufacturing) and energetic efficiency (ratio energetic cost/commercial biomass yield) Cost of production (accounting for seeds, N fertilization and pesticide costs) and economic efficiency (ratio cost of production/commercial biomass yield) YIELDS

3 Yield (t DM / ha) CI 9% N 0N N 0N N/2 0 0N 0N N 0N N/2 Sample plot Pea Tri cale Tri cale_pea Commercial yield Pea Tri cale Tri cale_pea Plot yield Figure 2. Commercial yield and plot yield (ton dry matter per hectare) in 2013, for some annual winter crop treatments Intercrops, even without N fertilization, show the highest yields. Fertilized triticale also shows high yield, but twice more N fertilizer is applied compared to fertilized intercrops N fertilization of intercrops increases the proportion of cereal Similar results were obtained other years and for other species QUALITY OF THE BIOMASS Globally, the biomass quality of sole grasses is often more favorable to transformation processes than sole legumes, intercrop treatments presenting intermediate values. RESIDUAL SOIL MINERAL NITROGEN Residual soil mineral N after harvest of intercrops is lower than sole legumes, and similar to sole triticale No effect of N fertilization was observed There was in general no difference between treatments of multi-annual crops GREENHOUSE GAS EMISSION In general, there was no significant difference between treatments for the measured emission of N 2 O: unfertilized sole legumes or intercrops do not emit more N 2 O than unfertilized grass. Fertilized treatments (sole grass and intercrops) presented the highest values of estimated greenhouse gas emissions whereas unfertilized treatments (sole grass, sole legume and intercrops) presented similar values. ENERGY CONSUMPTION TO PRODUCE ONE TON OF BIOMASS

4 Cost to produce 1 ton of biomass (MJ / t DM) Energetic Cost (MJ/ha) Com. Yield (t DM/ha) N 0N N 0N N/2 Pea Tri cale Tri cale_pea CI 9% INDIGO Bockstaller et al., 2009 Figure 4. Energetic cost to produce one ton of biomass (MJ / tdm) for some annual winter crop treatments Intercrops show the lowest energetic cost to produce 1 ton of biomass Fertilized cereal show the highest cost due to high N fertilization Sole legume and unfertilized sole cereal sometimes present high costs due to low yields Similar results were obtained for other species COST TO PRODUCE ONE TON OF BIOMASS Intercrops show similar or lower cost to produce 1 ton of biomass than sole cereal Depending on the year, sole legume shows higher cost due to lower yield Similar results were obtained for other species, even if a higher cost was obtained for clover (and triticale-clover) due to seed cost OVERALL PERFORMANCES OF INTERCROPS COMPARED TO SOLE CROPS Compared to sole crops, intercrops are more interesting accounting for all criteria together. In fact they presents: (1) high yield (specially fertilized intercrop) (2) intermediate or high dry matter content (3) lower residual soil mineral nitrogen after harvest compared to sole legume (4) good economic and higher energy efficiency compared to sole crops () lower greenhouse gas emissions (especially for unfertilized intercrops) compared to fertilized sole triticale. Accounting for multi-annual crops (Figure ), sole grasses are interesting for residual soil N after harvest, dry matter content (sole fescue) and greenhouse gas emission (unfertilized sole grass). Sole alfalfa is better for energy and economic efficiency, greenhouse gas emissions and commercial yield. Because the

5 proportion of alfalfa was high in intercrop treatments, they are close to sole alfalfa, even if fertilized intercrops are less good in term of economic and energy efficiency and greenhouse gas emissions. Orchard grass 0N Commercial Yield 11 Orchard grass N 9 Orchard grass-alfalfa 0N GHG 7 DM content Orchard grass-alfalfa N/2 3 Alfalfa 0N 1-1 Economic efficiency Residual soil N NRJ efficiency Fescue 0N Commercial Yield 11 Fescue N 9 Fescue-Alfalfa 0N GHG 7 DM content Fescue-Alfalfa N/2 3 Alfalfa 0N 1-1 Economic efficiency Residual soil N NRJ efficiency Figure. Overall performances of multi-annual crop treatments. Commercial yields, dry matter content, residual soil mineral nitrogen, energy efficiency, economic efficiency and greenhouse gas emissions have been transformed to 0 10 score using minimum and maximum average values, the score 0 representing the worst performance and the score 10 the best performance.

6 Key Outcomes: Results show that intercrops, even without nitrogen fertilizer applications, present higher yields and lower environmental impacts compared to sole crops. They generally show higher economic and energetic efficiency compared to sole crops. Indirect and direct CO 2 emissions are also in favor of intercrops. The biomass quality of intercrops may be more suitable to transformation processes than sole legumes. Hence, this study confirms the interest of grass-legumes intercrops as feedstock for bioenergy production. REFERENCES Boehmel, C., Lewandowski, I., Claupein, W., Comparing annual and perennial energy cropping systems with different management intensities. Agric. Syst. 96, Jensen, E., Peoples, M., Boddey, R., Gresshoff, P., Hauggaard-Nielsen, H., J.R. Alves, B., Morrison, M., Legumes for mitigation of climate change and the provision of feedstock for biofuels and biorefineries. A review. Agron. Sustain. Dev. 32, Laurent, A., Pelzer, E., Loyce, C., Makowski, D., 201. Ranking yields of energy crops: A meta-analysis using direct and indirect comparisons. Renew. Sustain. Energy Rev. 46, doi: /j.rser Pellicano, A., Romeo, M., Pristeri, A., Preiti, G., Monti, M., 201. Cereal-pea intercrops to improve sustainability in bioethanol production. Agron. Sustain. Dev. 3, doi: /s Willey, R.W., Intercropping - its importance and research needs. 1. Competition and yield advantages. Field Crop Abstr. 32, 1 10.