Effects of light level, time of harvest and position within field on variability of tissue nitrate concentration in commercial crops of lettuce (Lactuca sativa) and endive (Cichorium endiva)

Richard Mark Weightman (1) , Chris Dyer (2) , John Buxton (2) , Derek Farrington (3)

1 Centre for Sustainable Crop Management
2 Centre for Sustainable Crop Management
3 Direct Laboratories Ltd

Seven commercial crops of lettuce and one crop of endive were sampled in order to study the variability in plant tissue nitrate concentration (TNC). Assuming that an appropriate sampling pattern was employed, 10 plants was sufficient to give an acceptable estimate of the mean TNC. Short-term shading (24-48 h) had no significant effects on mean TNC, unlike the increase in TNC known to occur following dull periods 10-14 days prior to harvest. The effect on TNC of time of day harvested was significant, but there was no obvious pattern of diurnal variation. Averaged over all experiments, the coefficient of variation for TNC was of the order of 35%. Increasing the sample size from 10 to 40 plants would only be expected to decrease the standard error of measurement of TNC from 16 to 12% of the mean, because of the underlying analytical error which would remain constant.

Mots clés: Life Sciences

Richard Mark Weightman, Chris Dyer, John Buxton, Derek Farrington. Effects of light level, time of harvest and position within field on variability of tissue nitrate concentration in commercial crops of lettuce (Lactuca sativa) and endive (Cichorium endiva). Food Additives and Contaminants, 2006, 23 (05), pp.462-469. ⟨10.1080/02652030500522606⟩. ⟨hal-00577580⟩