Estimation of lettuce shoot nitrogen via a portable spectrophotometer

Abstract Lettuce are vegetables with a high commercial value and a short cycle production, which requires precise managements to guarantee a profitable production. For this, the nutritional providing is an important factor, highlining the nitrogen, a macronutrient considered essential for the proper development of plants due to its participation in the composition of the main plant molecules, such as chlorophyll. In this sense, non-destructive strategies to monitor the balance nutrition is fundamental to avoid deficiency or excess of nutrients during the lettuce cycling, and the agriculture 4.0, brings to light new technological means to achieve this goal. This work aimed to verify the potential to use a portable spectrophotometer to estimate N shoot in lettuce, as a non-destructive, precise, quickly, cheap, waste free option to be operated by the lettuce farmers, on farm, for the N monitoring, based on the destructive laboratory analysis for N shoot and chlorophyll, and the widely used sensor chlorophyll meter (SPAD). For this, a greenhouse experiment was conducted with lettuce cropped under N levels input, corresponding to 0, 25, 50, 75, 100 and 125% of the lettuce recommendation. The estimation for N in the lettuce shoot was performed by destructive analysis: i) shoot N; ii) chlorophyll and non-destructive analysis: iii) chlorophyll meter SPAD and iv) a portable spectrophotometer. Non-destructive measurements were performed 3 times at: 20, 23 and 26 days after transplanting (DAT). The lettuce harvest occurred 28 DAT, to determine N shoot uptake and chlorophyll, using a destructive way, and lettuce production. The estimation of N shoot in lettuce using the portable spectrophotometer showed a high correlation to the standard destructive laboratory analysis and the chlorophyll meter (SPAD), showing high explanation of the data and so a high potential to estimate N shoot in lettuce using the proposed portable spectrophotometer as an optimum non-destructive, precise, quickly, cheap, waste free option to be operated by the lettuce farmers, on farm, for the N monitoring.