Growth, Development, and Nitrogen Uptake of Fodder Beet ( Beta vulgaris L .) Crops Grown Under Differing Rates and Timing of Nitrogen Fertiliser in New Zealand

Fodder beet ( Beta vulgaris L.) is an important forage crop used for cattle wintering in New Zealand. Regional nitrogen (N) fertiliser experiments over two seasons (2016–2018) consisting of different N application rates (0–300 kg N/ha) and times of N application (sowing, canopy closure, and mid‐bulb development stage) were used to validate yield responses. Within site, there was a maximum of 3 t DM/ha difference in total biomass yield between control (no N) and high N treatments at maturity. Near maximum fodder beet yield was achieved in all sites with a rate of 100 kg N/ha applied as urea (split applications). Near optimum yields were achieved on higher fertility sites with preseason soil nitrate‐N + ammonium‐N (0–15 cm depth) of 75 kg N/ha or greater. Little additional fertiliser N was required for maximising crop yield. However, enhanced plant N concentration and crop N uptake were achieved with rates up to 300 kg N/ha. Fertiliser N management that stimulated full canopy expansion with optimum green leaf area (GLA) and GLA duration was required to maximise yield. Important management practices for maximising yield include the use of N fertiliser for earlier crop canopy closure and enhanced canopy duration during bulb development.