Nitrogen (N) supply needs to be closely matched to crop demand to achieve optimum N use efficiency (NUE). Sub-optimal N supply can lead to poor yields, whereas excess N application may cause nitrate leaching and environmental pollution. An experiment with five rates of N: 0, 25, 50, 100 and 200 kg ha −1 , was carried out at Lincoln, Canterbury, in New Zealand to define the effects of N supply on growth, N uptake and define how derived NUE may influence nutritive value of fodder beet production. Both dry matter (DM) yield and N uptake increased with N supply, by 39% and 129%, respectively, when 200 kg N ha −1 was applied, compared with the control plots. Leaf area index (LAI) also increased with N supply. However, the control crop did not attain critical LAI (LAI crit ) and those receiving 25 and 50 kg N ha −1 attained LAI crit for only a short period of time compared with crops supplied with ≥100 kg N ha −1 . This meant that they intercepted less radiation and subsequently had lower DM yield than the high N treatments. The specific leaf nitrogen increased 13% to 2.34 g N m −2 leaf when ≥50 kg N ha −1 was applied, compared with the control plots. The NUE decreased by 64% from 93 kg DM kg −1 N for the 25 kg N ha −1 plots compared with the 200 kg N ha −1 plots. Nitrogen rate had no effect on the nutritive value of fodder beet. The results suggest 100 kg N ha −1 was adequate for optimum DM production and N was important for canopy development and subsequent DM accumulation.Keywords: Beta vulgaris L.; critical leaf area index (LAI crit ); nitrogen use efficiency (NUE); uptake efficiency (NupE); utilisation efficiency (NutE); nutritive values and specific leaf nitrogen (SLN)

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Nitrate-N (NO 3 − -N) leaching losses from dairy cow urine and nonurine areas of simulated winter grazing of fodder beet (Beta vulgaris L.) were quantified using large intact soil monolith lysimeters (50 cm diameter × 70 cm depth), containing Balmoral/ Lismore stony silt loam soil. Fresh cow urine was applied to half of the lysimeters in mid-to late-June at 300 kg N ha −1 in 2012 and 250 kg N ha −1 in 2013, following simulated fodder beet grazing. The remaining half did not receive urine to represent non-urine areas of a grazed paddock. Most of the N leached was from the urine-treated lysimeters and 92%-98% was in the form of NO 3 − -N. Total NO 3 − -N leached from the urine-treated lysimeters represented an equivalent of 21% (64 kg NO 3 − -N ha −1 ) and 32% (84 kg NO 3 − -N ha −1 ) of the total urine-N applied in 2012 and 2013, respectively. Nitrate-N leaching losses from lysimeters receiving no urine were between 10 and 11 kg NO 3 − -N ha −1 . ARTICLE HISTORY