Poplar short rotation coppice is not a first choice crop for cattle slurry fertilization: Biomass yield and nitrogen-use efficiency

Abstract

Little is known about the effect of cattle slurry fertilization on poplar short rotation coppice (SRC). This study addresses the following research questions: (i) is the biomass productivity of poplar SRC responsive to slurry application? (ii) what is the efficiency with which poplar SRC utilizes the N applied in the form of cattle slurry? (iii) does the ratio of carbon (C) to N (C/N) in harvested dry matter vary with rates of N fertilization? Fertilization treatments were: (i) no fertilization (control); (ii) cattle slurry 10mm, i.e. 10Lm−2 (CS10); (iii) cattle slurry 20mm, i.e. 20Lm−2 (CS20); and (iv) industrial fertilizers, consisting in 120kgNha−1 in the form of urea and 120kg P2O5 in the form of superphosphate (IF). The agronomic efficiency of applied N (AEN) varied from 5 to 14kg yield dry matter per kg N applied. The recovery efficiency of applied N (REN, kg N uptake per kg N applied) was merely 7.3–10.6%. The physiological efficiency of N uptake (PEN) was 79–123kg yield dry matter per kg N uptake. The threshold of 0.6% N, which is considered the guide value for high-quality biomass feedstock for combustion, was exceeded with the treatment CS20 in the first harvest cycle. Overall, our findings suggest that poplar SRC is not a first choice crop for cattle slurry application. In fact, N supply determined poor agronomic efficiency, a modest fraction of the N applied was recovered by the crop, and the rise of N concentration in the harvested biomass was detrimental for the quality of the feedstock product for combustion.