Radiation‐use efficiency for forage kale crops grown under different nitrogen application rates

• Published in: Grass and forage science 2015-12, Vol.70 (4), p.620-630
• Main Authors: Chakwizira, E, Brown, H. E, Ruiter, J. M
• Format: Article
• Language: English
• Subjects: accumulated solar radiation; Brassica; Brassica oleracea var. acephala L; canopy; critical N concentration; crop yield; crops; Efficiency; Experiments; fertilizer rates; forage; forage production; intercepted photosynthetic active radiation; Kale; leaves; N nutrition index; Nitrogen; nitrogen content; nutrition; Plant growth; radiation-use efficiency; specific leaf nitrogen; Vegetables
• ISSN: 0142-5242; 1365-2494
• DOI: 10.1111/gfs.12150

Crop growth is related to radiation‐use efficiency (RUE), which is influenced by the nitrogen (N) status of the crop, expressed at canopy level as specific leaf N (SLN) or at plant level as N nutrition index (NNI). To determine the mechanisms through which N affects dry‐matter (DM) production of forage kale, results from two experiments (N treatment range 0–500 kg ha⁻¹) were analysed for fractional radiation interception (RI), accumulated radiation (Rₐcc), RUE, N uptake, critical N concentration (Nc), NNI and SLN. The measured variables (DM, RI and SLN) and the calculated variables (NNI, Rₐcc and RUE) increased with N supply. RUE increased from 0·74 and 0·89 g MJ⁻¹ IPAR for the control treatments to 1·50 and 1·95 g MJ⁻¹ IPAR under adequate N and water in both experiments. This represented an increase in RUE of 52–146% for the range of N treatments used in both experiments, whilst Rₐcc increased by 9–17%, compared with the control treatments. Subsequently, the total DM yield of kale increased from 6·7 and 8 t DM ha⁻¹ for the control treatments to ≥ 19 t DM ha⁻¹ when ≥150 kg N ha⁻¹ was applied. The DM yields for the 500 kg N ha⁻¹ treatments were 25·5 and 27·6 t DM ha⁻¹ for the two experiments. RUE increased linearly with SLN, at an average rate of 0·38 g DM MJ⁻¹ IPAR per each additional 1 g N m⁻² leaf until a maximum RUE of 1·90 g MJ⁻¹ IPAR was reached in both experiments. There were no changes in RUE with SLN of > 2·6 g m⁻² and NNI >1, implying luxury N uptake. RUE was the most dominant driver of forage kale DM yield increases in response to SLN and NNI.