Factors influencing tissue nitrate concentration in field-grown wild rocket (Diplotaxis tenuifolia) in southern England

• Published in: Food additives & contaminants. Part A, Chemistry, analysis, control, exposure & risk assessment Vol. 29; no. 9; pp. 1425 - 1435
• Main Authors: Weightman, R.M, Huckle, A.J, Roques, S.E, Ginsburg, D, Dyer, C.J
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 01.09.2012; Taylor & Francis; Taylor & Francis Ltd
• Subjects: Biological and medical sciences; Brassicaceae - chemistry; Crops; Crops, Agricultural - chemistry; Diplotaxis; Diplotaxis tenuifolia; drilling; England; fertilizer rates; Fertilizers; Food industries; Fundamental and applied biological sciences. Psychology; green leafy vegetables; growers; guidelines; human health; laws and regulations; nitrate; nitrates; Nitrates - analysis; Nitrogen; nitrogen fertiliser; nitrogen fertilizers; nutrition; Public health; radiation; rocket; rucola; Soil - analysis; soil mineral nitrogen; soil minerals; soil types; summer; variability; Vegetables; yield; England; United Kingdom; Great Britain; Europe; British Isles, England; nitrogen fertiliser; rucola; Variability; Radiation; rocket; Nitrates; Concentration; nitrate; Nitrogen; Inorganic element; Soils; Tissue; Diplotaxis tenuifolia; Yield; soil mineral nitrogen
• DOI: 10.1080/19440049.2012.696215
• ISSN: 1944-0057; 1944-0049

Wild rocket (Diplotaxis tenuifolia) is a leafy vegetable known for its high tissue nitrate concentration (TNC) which can exceed the limits set in the relevant European legislation designed to protect human health. The aim of this work was to understand the factors influencing TNC and to develop best practice guidelines to growers. Commercial crops of field-grown wild rocket were studied over two seasons. In 2010, ten separate crops were sampled representing a range of soil types and time periods during the summer. Two fields sampled using a ‘W’- or ‘X’-shaped sampling pattern demonstrated that 10 incremental samples bulked to make 1 kg of fresh material could be used to provide an adequate sample for determination of TNC in the wild rocket crop, as is the case for other leafy vegetables. Of eight commercial crops sampled in 2010 with an average nitrogen (N) fertiliser application of 104 kg N ha⁻¹, two exceeded the limit of 6000 mg kg⁻¹ set in the legislation. In 2011, six N response experiments were carried out, and only two sites showed a significant yield response to N fertiliser. The reason for the lack of response at the other sites was principally due to high levels of soil mineral N prior to drilling, meaning the crops’ requirement for N was satisfied without additional fertiliser N. In the experimental situation at an N fertiliser application rate of 120 kg N ha⁻¹, 50% of crops would have exceeded the 6000 mg kg⁻¹ limit. In both seasons, low radiation levels in the 5 days prior to harvest were shown to increase TNC, although the relationship was also influenced by N supply. Strategies for optimising N nutrition of field-grown wild rocket are discussed.