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Collard green yield and nutritional quality with mineral and organic fertilization

A study was conducted to investigate the effect of organic and mineral fertilization on collard green yield, and to assess the macro and micronutrient and heavy metal concentrations of its leaves to assess the potential hazards of manure use. Collard plants (Brassica oleracea var. acephala, cv. couve-manteiga) were grown in 4-L pots filled with a clay soil under greenhouse conditions. The experimental design used was completely randomized design and the treatments in a 3 × 4 factorial arrangement: three N sources (pig slurry, poultry manure, and urea) and four N rates (0, 100, 200 and 300 mg kg-1), with four replicates. Collard greens leaves were harvested 70 days after seedling plantings. The manure application (pig slurry or poultry manure) resulted in collard yield equivalent to the application of mineral fertilizer. However, the pig slurry application resulted in an increase of leaf Fe, Mn, Zn, Cd, Cr, and Pb concentrations. Nitrogen application rates up to 300 mg N kg-1 result in the higher yield and nutritional quality of collard leaves. The application of high rates of manure, especially pig slurry, results in the increase of heavy metal (Cd, Cr, and Pb) concentrations. However, the maximum concentrations of 0.042 mg kg-1 Cd, 0.034 mg kg-1 Cr and 0.030 mg kg-1 Pb are well lower than maximum daily intake limit established by the Brazilian legislation, indicating that the consumption of collards from organic production systems with the manure application can be considered safe and without risk to human health.