Growth, nitrogen partitioning and nutritive value of fodder beet crops grown under different application rates of nitrogen fertiliser
2014
Chakwizira, E | de Ruiter, JM | Maley, S
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.
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