Yield and nitrogen use efficiency of fodder and sugar beet (Beta vulgaris L.) in contrasting environments of northwestern Europe

• Yield and nitrogen utilization efficiency is higher for sugar beet than fodder beet.
• Increased yield is caused by a higher sucrose concentration in taproot dry matter.
• Improved harvest index is not the cause for increased sugar beet yield.
• Increasing fertilizer N dose increased yield in some environments only.
• Sugar beet perform better as bioenergy crop than fodder beet in various environments.

Yield and nitrogen (N) use efficiency (NUE) are important traits for the evaluation of crops used for renewable energy production. Contrary to other bio-energy crops, data on NUE are not available for beet crops from the Beta genus for high yielding conditions of northwestern Europe. Thus, our study aimed to provide such information for one current representative of the cultivar groups sugar and fodder beet. Field experiments were conducted with six mineral fertilizer N doses (0–200 kg N ha−1, 40 kg steps) at one site in Germany (DE), The Netherlands (NL) and Denmark (DK) in 2010 and 2011; each combination of site and year (DE10, DE11, NL10, NL11, DK10, DK11) was evaluated as distinct environment.The environments strongly differed in yield (dry matter, sugar), N uptake, harvest indices and N-utilization efficiency (NUtE) parameters. Increasing the fertilizer N dose increased dry matter yield and sugar yield in the environments NL10, NL11, DK10 and DK11, but not at DE10 and DE11. Harvest indices decreased with increasing fertilizer N dose in the environments NL10, NL11, DK10 and DK11 only, which were characterized by a 70–110 kg N ha−1 lower N uptake at zero fertilizer N than DE10 and DE11. The N uptake continuously increased while NUtE decreased with increasing fertilizer N dose at all environments. When regarding environmental and fertilizer N effects, yield was neither related to harvest indices nor NUtE.Despite several significant interactions between environment and cultivar, the data clearly reveal that yield, sucrose concentration in taproot dry matter, total plant N uptake, NUtE and apparent fertilizer N recovery were considerably higher for sugar beet (SB) than for fodder beet (FB). Contrastingly, harvest index on taproot dry matter basis and N harvest index were higher in FB than in SB, while harvest index for sugar was similar. An improved harvest index was obviously not the cause for the higher sugar yield of SB compared to FB, while sucrose concentration in taproot dry matter was clearly favourable for SB. Although SB crops incorporated more N into the leaves than FB, NUtE was considerably higher in SB, especially when focusing on sugar instead of dry matter production. In conclusion, SB offers a higher potential for producing bio-energy per unit of arable land with less N use related greenhouse gas emissions per unit of energy gain than FB.