Derivation of sufficiency values of a chlorophyll meter to estimate cucumber nitrogen status and yield

• Published in: Computers and electronics in agriculture 2017-09, Vol.141, p.54-64
• Main Authors: Padilla, Francisco M., Peña-Fleitas, M. Teresa, Gallardo, Marisa, Giménez, Carmen, Thompson, Rodney B.
• Format: Article
• Language: English
• Subjects: Autumn; Chlorophyll; Crop growth; Crops; Cucumis sativus; Fertilization; Greenhouses; Measuring instruments; Monitoring; N management; Nitrogen; NNI; Nutrition; Phases; Proximal optical sensor; SPAD; Spring (season); Studies; Vegetable crop; Vegetables
• ISSN: 0168-1699; 1872-7107
• DOI: 10.1016/j.compag.2017.07.005

•SPAD measurements strongly related with crop NNI and yield in two different seasons.•Stronger relationship in the reproductive and harvest phases than in the vegetative.•Sufficiency values for maximum growth and yield from regressions with NNI and yield.•Small differences in sufficiency values for growth, yield and phenological phase.•Sufficiency value for growth, yield and all phenological phases of 45.2 SPAD units. Chlorophyll meters are a promising approach for monitoring crop N status of intensively-produced vegetable crops. To do so effectively, it is fundamental that the nature and strength of the relationships between chlorophyll measurement and actual crop N status and yield, throughout the whole crop cycle, be evaluated. Another fundamental requirement for the practical use of chlorophyll meters for crop N monitoring is the availability of sufficiency values or ranges, for a given crop, that indicate N deficiency (below the value) or sufficiency (above the value). The SPAD-502 meter was evaluated as an estimator of crop N status and yield in cucumber, and sufficiency values of SPAD measurements were derived for maximum crop growth and for yield. Two crops were grown in soil in a greenhouse in Almeria (SE Spain), in different cropping cycles, in Autumn 2013 (from early September to late November) and in Spring 2014 (from early March to late May). Chlorophyll measurements were made on a weekly basis throughout the crop cycle and relationships were established between measurements and the Nitrogen Nutrition Index (NNI), i.e. the ratio between actual and critical crop N contents, and yield. Sufficiency values for maximum growth were based on the relationships with NNI and sufficiency values for maximum yield were based on linear-plateau relationships with yield. Relationships of SPAD measurements with crop NNI and yield had average coefficients of determination (R2) of 0.59 and 0.55, respectively, for most of the Autumn crop, and R2 values of 0.84 and 0.83, respectively, for most of the Spring crop. In both crops, relationships were weak in the initial vegetative phase and were stronger in the subsequent reproductive and harvest phases. Generally, there were small differences between the sufficiency values for maximum growth and those for yield, and between the three phenological phases. The average sufficiency value for all phenological phases for both maximum growth and maximum yield was 45.2±0.7 SPAD units. This study showed that measurements of t