Abstract
Optical sensors can be used to assess crop N status to assist with N fertilizer management. Differences between cultivars may affect optical sensor measurement. Cultivar effects on measurements made with the SPAD-502 (Soil Plant Analysis Development) meter and the MC-100 (Chlorophyll Concentration Meter), and of several vegetation indices measured with the Crop Circle ACS470 canopy reflectance sensor, were assessed. A cucumber (Cucumis sativus L.) crop was grown in a greenhouse, with three cultivars. Each cultivar received three N treatments, of increasing N concentration, being deficient (N1), sufficient (N2) and excessive (N3). There were significant differences between cultivars in the measurements made with both chlorophyll meters, particularly when N supply was sufficient and excessive (N2 and N3 treatments, respectively). There were no consistent differences between cultivars in vegetation indices. Optical sensor measurements were strongly linearly related to leaf N content in each of the three cultivars. The lack of a consistent effect of cultivar on the relationship with leaf N content suggests that a unique equation to estimate leaf N content from vegetation indices can be applied to all three cultivars. Results of chlorophyll meter measurements suggest that care should be taken when using sufficiency values, determined for a particular cultivar
Highlights
In intensive vegetable production, large applications of nitrogen (N) fertilizer are used to ensure high yields [1,2]
Cultivar had an effect on SPAD-502 and MC-100 chlorophyll meter measurements when the
Measured with the Crop Circle ACS470 sensor, there was no effect of cultivar, regardless of N applied
Summary
Large applications of nitrogen (N) fertilizer are used to ensure high yields [1,2]. N is susceptible to nitrate (NO3 − ) leaching [2,3], and to subsequent N contamination of aquifers and surface water bodies [4,5]. Nitrate contamination of aquifers and surface water bodies, from intensive vegetable production, has been reported for diverse regions, such as southeast Spain [6], southeast. For optimal management of N in intensive crop and vegetable production, with minimal N loss to the environment, it is necessary to match N supply to crop N demand [8]. Assessment of crop N status informs of the immediate balance between N supply and demand [8,9]. Chlorophyll meters have been extensively researched and are used commercially to assess crop N status because their
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