The value of on-farm rapid tests for measuring nitrate in leafy vegetables and in hydroponic solutions

Nitrate accumulates in leafy vegetables and is undesirable in terms of reducing product quality and nutritional value. In this study, the leafy vegetables pak choy [Brassica rapa L. ssp. chinensis (L.) 'Sumo'], Swiss chard [Beta vulgaris var. cicla 'Silverstar'] and cos lettuce [Lactuca sativa L. var. longifolia 'Vivian'], were grown at a lowrate (50 mg N L-1) and at a high rate of nitrate (300 mg N L-1), considered excessive in hydroponics but nonetheless used by some growers. The high nitrate supply was associated with high concentrations of shoot nitrate, and in some shoots with reduced fresh weight. This highlights that nitrate monitoring on farm could be used to prevent yield loss associated with excessive fertiliser application. To complement this study we reviewed the performance of two handheld tools in terms of their suitability for measuring nitrate on-farm: nitrate-selective electrodes and nitrate-sensitive test strips. Substances, including chloride, can interfere with measurements using nitrate-selective electrodes and the effects are potentially greater in xylem or shoot sap than in hydroponic solutions, i.e., test strips are the more likely to offer better quality on-farm measurements of sap nitrate.