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Poplars (Populus spp.) managed in short rotation woody crop (SRWC) systems are considered very promising in terms of biomass production for energy purposes in a temperate zone. In this study, several gaps in knowledge regarding the selection of the plant material, cultivar‐specific responses to coppicing and rotation length are addressed. Five‐ and 10‐year rotation lengths were considered, with a focus on the sustainability of the plantation and the quantification of the biomass production of 10 commercially available hybrid poplar cultivars during two consecutive 5‐year rotation cycles versus one 10‐year rotation in northern Poland. The biomass production varied considerably among cultivars, ranging from 1.6 ('AF8') to 7.5 ('NE42') Mg ha−1 year−1 at the end of the first 5‐year rotation, and 0.0 ('AF8')–5.4 ('Degrosso') Mg ha−1 year−1 in the second 5‐year rotation, while in a single 10‐year rotation, the mean annual increment (MAI) ranged from 1.0 ('AF8') to 15.1 ('NE42') Mg ha−1 yr−1. The 5‐year rotation cycles negatively influenced the sustainability of the plantation due to the high mortality of stems and sprouts in the second 5‐year coppice rotation. In the case of 5‐year and longer rotations, replanting (not resprouting) after harvest may be a more advantageous practice for maximizing the regeneration. The 10‐year rotation cycle allowed for enough development of the crown and root systems to produce sufficient basal area and height to achieve maximal MAI in the trees. The study revealed that an age ≥10 is a biologically optimal rotation age as the slope of MAI was equal/close to zero. This study further showed the crucial importance of testing cultivars before introducing them on a commercial scale and provided valuable information on poplar cultivars available to stakeholders in the biomass market. [ABSTRACT FROM AUTHOR]

We calibrated and evaluated the agricultural model AquaCrop for the simulation of water use and yield of a short-rotation coppice (SRC) plantation with poplar ( Populus) in East Flanders (Belgium) during the second and the third rotation (first 2 years only). Differences in crop development and growth during the course of the rotations were taken into account during the model calibration. Overall, the AquaCrop model showed good performance for the daily simulation of soil water content ( R2 of 0.57-0.85), of green canopy cover ( R2 > 0.87), of evapotranspiration (ET; R2 > 0.76), and of potential yield. The simulated, total yearly water use of the SRC ranged between 55% and 85% of the water use of a reference grass ecosystem calculated under the same environmental conditions. Crop transpiration was between 67% and 93% of total ET, with lower percentages in the first than in the second year of each rotation. The observed (dry mass) yield ranged from 6.61 to 14.76 Mg ha−1 yr−1. A yield gap of around 30% was observed between the second and the third rotation, as well as between simulated and observed yield during the third rotation. This could possibly be explained by the expansion of the understory (weed) layer; the relative cover of understory weeds was 22% in the third year of the third rotation. The agricultural AquaCrop model simulated total water use and potential yield of the operational SRC in a reliable way. As the plantation was extensively managed, potential effects of irrigation and/or fertilization on ET and on yield were not considered in this study. [ABSTRACT FROM AUTHOR]

Nitrous oxide emissions are of critical importance for the assumed climate neutrality of bio-energy. In this study we report on the N2 O fluxes from a bio-energy poplar plantation measured with eddy covariance for 2 years, after conversion of agricultural fields to few months after harvesting of the plantation. A pulse peak of N2 O was detected after the land use change and in the wake of the first heavy rainfall. The N2 O- N emission during just a single week was 2.7 kg N2 O- N ha−1 which represented approximately 42% of the total N2 O- N emitted during the 2 years of measurements. After this peak emission, N2 O fluxes were constantly rather low, not increasing after rainfall events any longer. Lowest emissions (and even N2 O sink) occurred mostly during the end of the second growing season with maximum canopy development, and water table deeper than 80 cm. Gross primary production ( GPP) explained 68% of the monthly averaged variability in N2 O emission from August to December 2011. Probably N uptake by vegetation during the peak of the second growing season limited N2 O emission, which in fact increased again after the plantation was coppiced. For the majority of the measuring period, N2 O fluxes did not present a well-defined diurnal pattern, with the exception of two periods: (1) from 19-22 August 2010 and (2) from September-November 2011. In both cases wind speed played a major role in controlling the diurnal pattern in these fluxes (explaining up to 80% of the diurnal variability in N2 O fluxes on 19-22 August 2010), whereas at the end of the second growing season (September-November 2011), GPP explained 73% of the diurnal pattern in N2 O fluxes. [ABSTRACT FROM AUTHOR]