An agro-economic analysis of briquette production from fibre hemp and energy sunflower

The current study estimated (i) the effect of mineral N fertiliser (NH4NO3), municipal sewage sludge and cattle slurry on hemp cultivar (cv) USO-31 and sunflower cv Wielkopolski above ground biomass yield, (ii) the efficiency of nitrogen recovery of the applied amendments (nitrogen recovery, %), nitrogen use efficiency (NUE, kg kg−1) and the profitability (%) of briquette production from hemp and sunflower above ground biomass. A long-term field trial was established in 2008-2011 at Estonian University of Life Sciences (58̊23′N, 26̊44′E) on Stagnic Luvisol soil (sandy loam surface texture, C 1.12%, and N 0.12%, pHKCl 5.6). The plants were grown on different N treatments: N0 (without N), N100 (mineral N fertiliser NH4NO3), sewage sludge from the city of Tartu, and cattle slurry. The applied amount of N for all treatments (with the exception of the N0 treatment) was 100 kg N ha−1. The energy sunflower has high potential to produce vigorous above ground biomass in north European conditions. But, it is necessary to continue the field trials with this crop to clarify the biomass yield stability over many years. In point of profitability, the sewage sludge could be used as organic fertiliser for energy crops, because the biomass increase by 1 kg of sludge N was the highest and biomass yield over trial years more stable of the fertilisers tested. In most years 100 kg N ha−1 did not guarantee profitable above ground biomass production of hemp in low fertility soil. Cattle slurry for energy crops with slow initial development is not a promising organic fertiliser.