Abstract
A detailed knowledge of how poplar leaf litter decomposes under Mediterranean marginal conditions can help to minimize fertilization inputs and determine the profitability and sustainability of energy crops established in these particularly sensitive areas for bioenergy. Leaf litter decomposition was monitored for 32 months using the litterbag technique in a poplar crop under short rotation conditions in a marginal Mediterranean area. In addition, nutrient dynamics, together with the production and composition of the woody and foliar biomass produced, were studied for a period of four years. Leaf litter decomposition was relatively slow, particularly during the winter months, and accelerated in early spring, coinciding with the rainy season. At the end of the decomposition study 50% of the initial litterfall was decomposed, releasing roughly 60% of the N, 40% of the K, and 70% of the P initially present in fresh leaves. Annual yields of 6.0 dry Mg ha−1 were obtained. The aerial biomass produced the first year of the second rotation cycle extracted 83, 8.7, and 29 kg ha−1 of N, P, and K, respectively, whereas the amount of nutrients that were estimated to be naturally supplied to the system through leaf litter decomposition were 180 kg ha−1 of N, 19 kg ha−1 of P, and 30 kg ha−1 of K. Therefore, four years after establishing the energy crop, leaf litter was able to release higher amounts of primary macronutrients into the environment than the nutrient uptake by the produced aboveground biomass (woody and foliar biomass).
Highlights
The ambitious targets set by the recent EU Renewable Energy Directive (RED II)2018/2001/EC [1], which stipulates that 32% of member states’ total energy consumption should come from renewable sources by 2030, has drawn the attention of the scientific community towards the use of marginal land that is not suitable for food production to produce bioenergy feedstock
Similar yields were obtained on long-term studies of poplar crops in short rotation systems on marginal Mediterranean conditions, reporting annual production between 2 and 10 Mg ha−1 year−1 across clones, fertilization treatments, and different harvest alternatives [6,8]
Experiment, it it was was found found that that leaf leaf litter litter decomposition decomposition was was very very slow slow during during
Summary
2018/2001/EC [1], which stipulates that 32% of member states’ total energy consumption should come from renewable sources by 2030, has drawn the attention of the scientific community towards the use of marginal land that is not suitable for food production to produce bioenergy feedstock. The planting of energy crops in arable marginal lands with low agricultural profitability can supply biomass which can contribute to meeting the EU energy targets, while avoiding, at the same time, the energy–food dilemma. It can be seen as a way to contribute to the restoration of degraded soils, controlling erosion, and slowing down the depopulation of rural areas [2]. Most of them are low productivity areas where winter cereal grain production is below 1.5 Mg ha−1 due to poor soils that have organic matter contents below 2% [4]
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