Solid biomass fuels are useful and cost effective renewable energy source. The energy content of biomass is determined by its calorific value. The objective of this study was to determine experimentally the gross calorific value (GCV) of different agroforestry species and bio-based industry residues that could be used by: a) companies specialized in processing raw biomass solid biofuel production, b) small-scale consumers (households, medium-sized residential buildings, etc.). The fuel samples used were from agricultural residues and wastes (rice husks, apricot kernels, olive pits, sunflower husks, cotton stems, etc.), energy crops and wetland herbs (cardoon, switchgrass, common reed, narrow-leaf cattail), and forest residues (populus, fagus, pinus). The GCV of the biomass samples was experimentally determined based on CEN/TS 14918:2005, and an oxygen bomb calorimeter was used (Model C5000 Adiabatic Calorimeter, IKA ®-Werke, Staufen, Germany). The GCV of different agroforestry species and residues ranges from 14.3-25.4 MJ•kg −1. The highest GCV was obtained by seeds and kernels due to higher unit mass and higher lipid content. Pinus sylvestris with moisture content 24.59% obtained the lowest GCV (13.973 MJ•kg −1).

The effect of green manure on the growth of irrigated corn (Zea mays L. cv Cisko) was investigated under different drip irrigation rates on a clay soil in Greece. A feed pea (Pisum sativum L. cv Olympus) crop was established in autumn and incorporated into the soil in spring, about 3 weeks before the sowing of the subsequent corn.During the growing period, the growth stages and yield of corn were assessed under three drip irrigation levels I1 (33% low), I2 (66% moderate) and I3 (100% full of actual evapotranspiration, ETm) and two cultivation practices a) application of green manure and b) experiment without previous green manuring. The positive effects of green manuring were greater in the moderately and fully irrigated plots. Drip irrigation was applied to minimize nitrate leaching which requires low volume of water. In plots receiving moderate or full irrigation, biomass, leaf area index (LAI) and seed yield were much higher in comparison to stressed plants (33% ETm). Increased yield and dry biomass obtained in the plots after incorporation of feed pea residues, may be attributed mainly to the elevated amount of soil organic matter (SOM). The increased yield exceeds the overall cost for green manure application, and this economic incentive is expected to be even more significant taking into account the continuous improvement of soil conditions.

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Panicum virgatum could produce cattle feed with lower costs due to the low input requirements and its perennial nature. Dry biomass yield vs. N-P-K nutrient uptake relations as well as the N-mineralization and the N-fertilization recovery fraction for Panicum virgatum (cv. Alamo) were determined under field conditions for four N-fertilization (0, 80, 160 and 240 kg ha -1 ) and two irrigation levels (0 and 250 mm), οn two soils in central Greece with rather different moisture status. It was found that the dry fodder yield on the aquic soil may reach 14 t ha -1 using supplemental irrigation; while on the xeric soil a lower yield of 9-10 t ha -1 may be produced only under supplemental irrigation. Moreover, the average N, P and K concentration was 1.3%, 0.14% and 1.3% in leaves, and 0.5%, 0.85%, and 1.5% in stems, respectively, showing the very low crop requirements. Furthermore, linear biomass yield-nutrient uptake relationships were found with high R 2 , pointing to nutrient use efficiency of 132 and 75 kg kg -1 , for N and K respectively. The base N-uptake ranged from 71-74 kg ha -1 on the aquic to 60 kg ha -1 or less on the xeric soil. Finally, it was found that N-recovery fraction was 20% on the aquic soil and lower on the xeric. Therefore, it could be conclude that Panicum virgatum seems to be a very promising crop for fodder production and its introduction in land use systems (especially οn aquic soils of similar environments) should be taken into consideration.