Organic Nitrogen Nutrition Does Not Increase Glucosinolate Concentrations in Broccoli (<i>Brassica oleracea</i> L. var. <i>italica</i>)

Abstract

Concentrations of specific secondary metabolites can be higher in organically grown crops. This may be linked to organic nitrogen (N) nutrition that provides a gradual supply of N to crops over the growing season. This study examined whether organic N nutrition influenced the concentration of glucosinolates in broccoli crops. Nitrogen release patterns were determined from three synthetic (Rustica, 12% N; calcium nitrate, 15.5% N; urea, 46% N) and two organic fertilizers in an incubation experiment. Broccoli seedlings were then grown in two N dose response pot trials with different N source or application timing treatments to investigate growth and glucosinolate responses. Synthetic fertilizers released 84 to 89% of total N after 28 days, while chicken manure pellets and composted cow manure had only released 52% and 13% of total N, respectively, after 91 days. Broccoli yield and N content were generally higher in synthetic fertilizer treatments. Glucosinolate concentrations were generally higher in the synthetic fertilizer treatments, and only sinigrin and glucoiberin concentrations in the 800 kg ha−1 N application rate of organic fertilizer matched those in the corresponding synthetic fertilizer treatment. Broccoli head weight was reduced when N was applied fortnightly compared to basal and weekly N applications, but glucosinolate concentrations were not significantly different. Overall, there was no evidence that organic (chicken manure) N nutrition, or the rate of N supply to broccoli plants, affect glucosinolate concentrations.

Keywords

• brassicas
• manure
• slow-release N