Nitrogen (N) is an essential nutrient for plant growth and development and is especially important in the production of high quality leafy green vegetables. In this experiment, leaf N concentration, chlorophyll concentration (Chl) and weight above fresh matter (AFM) of romaine lettuce (Lactuca sativa L. var. longifolia) were estimated by correlations between in situ SPAD and atLEAF readings. Lettuce was grown in high tunnels during 42 days and was irrigated at five nitrogen levels: 0, 4, 8, 12 and 16 mEq·L-1 of NO3-, based on the Steiner nutrient solution. The N concentration, Chl concentration and AFM were determined in the laboratory, while SPAD and atLEAF readings were measured in situ weekly. SPAD readings had high, positive and significant linear correlations with N (R2 = 0.90), Chl (R2 = 0.97) and AFM (R2 = 0.98); atLEAF readings had a similar linear correlation with N (R2 = 0.91), Chl (R2 = 0.92) and AFM (R2 = 0.97). Besides, SPAD and atLEAF readings had high, positive, and significant linear correlation (R2 = 0.96). Thus, SPAD and atLEAF meters can be used to non-destructively and accurately estimate the N status of lettuce, in a reliable and quick manner during the crop production cycle. In addition, atLEAF is currently more affordable than SPAD. ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********
Determinations of nitrogen (N) and chlorophyll (Chl) by destructive methods are precise but time-consuming and frequently expensive. The objective of this study was to determine the relationship between SPAD, atLEAF, and MC-100 readings with the concentrations of Chl, N, and fresh matter (FM) in basil 'Nufar'. In addition, we determined the relationship of the N concentration with fresh matter (FM). The plants were irrigated with five levels of N (0, 4, 8, 12, and 16 mEq·L-1 of NO3) based on a modified Steiner solution for 42 days after transplant. Plants were evaluated weekly with SPAD, atLEAF and MC-100 portable chlorophyll meters in the greenhouse, while fresh matter and the concentration of chlorophyll and N were determined in the laboratory using conventional techniques. The relationship between SPAD readings, Chl, N, and FM was strong, positive, linear, and significant, with correlation coefficients (R2) between 0.94 and 0.98. For atLEAF and MC-100 readings, R2 values were 0.96 to 0.99 and 0.96 to 0.99, respectively. The relationships between SPAD, atLEAF and MC-100 readings were strong, positive, and significant, with R2 values of 0.98. Similar behavior was shown by the relationship of N concentration and FM with R2 of 0.88. With these results, we conclude that SPAD, atLEAF, and MC-100 can be used to estimate the nutrient status of N in a non-destructive, rapid and reliable manner during basil production.
Destructive methods for crop nutrition estimation are accurate and standardized but costly and limited by spatial scale. Non-destructive techniques such as the use of digital imaging provide fast and reliable results in situ; however, there is limited information on these non-destructive techniques in leafy vegetable crops. During the study it was estimated the concentration of nitrogen (N) and chlorophyll (Chl) in romaine lettuce using spectral indices derived from the RGB (red, green and blue) digital images. The lettuce crop was grown in plastic tunnels and irrigated with five N levels: 0, 4, 8, 12, and 16 mEq L -1 NO 3 -N (corresponding to 0, 248, 496 and 744 mg L -1 , respectively) based on a modified Steiner solution. The treatment of 16 mEq L -1 NO 3 -N showed the highest growth at 42 days after transplanting (DAT). Digital images of the plants were acquired weekly with a RGB camera and processed to obtain scale mosaics and twelve spectral vegetation indices. Correlation analysis of the spectral indices indicated that normalized green-red difference index (NGRDI), excess green (ExG) and green channel (g) indices showed a positive linear correlation with the concentration of N (r > 0.93) and Chl (r > 0.93). Besides, an exponential correlation with leaf area (r > 0.86) was founded, which was stronger in the last 21 DAT due to the acceleration in leaf growth during the vegetative stage of the crop. These results show that RGB digital images are a low cost, non-destructive, reliable and accurate method to estimate N and Chl concentration and leaf area in romaine lettuce during production. Therefore, this technique could be an affordable alternative that combined with portable meters (i.e. SPAD) provides real-time monitoring of the nutritional status of the lettuce crop, especially in crop factories.
El nitrógeno es un nutrimento esencial para las plantas y el elemento más requerido en hortalizas de hoja, por lo que es importante conocer sus niveles en relación con la formación de clorofila y producción de biomasa. El objetivo de esta investigación fueestimar, mediante medidores portátiles no destructivos, la concentración de clorofila y relacionarla con los niveles de nitrógeno y de biomasa fresca en arúgula (Eruca sativaL.). La investigación se realizó en un invernadero donde las plantas fueron sometidas a diferentes dosis de fertilización nitrogenada empleando cinco tratamientos de N-NO3(0, 4, 8, 12 y 16 meq·L-1), con base en la solución nutritiva de Steiner. Se realizaron evaluaciones semanales en las plantas hasta 42días después del trasplante utilizando los medidores SPAD, atLEAF y MC-100, junto a determinaciones en el laboratorio de los niveles de clorofila, nitrógeno y biomasa fresca por planta. Los resultados mostraron que la relación entre lecturas SPAD, nitrógeno, clorofilay materia fresca fue positiva y significativa, con coeficientes de correlación de 0,93-0,97; para lecturas atLEAF, se observaron relaciones similares, con coeficientes de correlación de 0,96-0,99. Las relaciones entre lecturas SPAD, atLEAF y MC-100 fueronpositivasy significativas, con coeficientes de correlación de 0,97-0,98. Esto indica que estos medidores son instrumentos válidos para estimar in-situel estado de clorofila y nitrógeno en el cultivo de arúgula de manera no destructiva, rápida y precisa.
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