# Nutrient composition, plant chemistry and stock design Canonical HTML: https://flavorotor.com/research/nutrient-composition Machine-readable index: https://flavorotor.com/research/data/chapters/index.json Elemental mass balance, real hydroponic N–P–K dose responses, cultivar-by-solution effects on lettuce chemistry and the measurements required to estimate plant nutrient state. In brief How complete elemental recipes, coupled ions, stock compatibility and tissue measurements replace simplistic nutrient-to-taste rules. ## Explanation Adding one fertilizer changes every ion carried by that salt. A KNO₃ dose changes both potassium and nitrate; it is not a pure “sweetness” command. ## Mass balance NUT-1 n i , n e w = n i , o l d + ∑ j ν i j C j V j − U i − L i n_{i,\mathrm{new}}=n_{i,\mathrm{old}}+\sum_j\nu_{ij}C_jV_j-U_i-L_i n i , new ​ = n i , old ​ + j ∑ ​ ν ij ​ C j ​ V j ​ − U i ​ − L i ​ Ion i changes through stock additions j, stoichiometric coefficients ν, plant uptake U and losses L. **Explanation**The new amount of one ion equals the previous amount plus stock additions, minus plant uptake and losses. NUT-2 C i , n e w = n i , n e w V r e s e r v o i r , n e w C_{i,\mathrm{new}}=\frac{n_{i,\mathrm{new}}}{V_{\mathrm{reservoir,new}}} C i , new ​ = V reservoir , new ​ n i , new ​ ​ Concentration follows ion amount and the final mixed reservoir volume. **Explanation**Final concentration is the final ion amount divided by the final mixed solution volume. ## Separate N, P and K limitation The USDA Bibb lettuce dataset changes one target nutrient concentration at a time and reports fresh mass through day 32 after transplant. The day-32 response is not monotonic for every nutrient. Nitrogen rises from 1.16 g at 5 mg·L⁻¹ to 250.73 g at 132 mg·L⁻¹, then falls to 74.11 g at 264 mg·L⁻¹. Phosphorus rises from 9.14 g at 1 mg·L⁻¹ to 250.73 g at 31 mg·L⁻¹. The potassium series contains a wide interval at 42 mg·L⁻¹, so that treatment mean should not be read without its uncertainty. [R58] Note. Values reproduced from Sharkey, Chen, and Altman (2025), author-formatted NPK.CrossT.All.xlsx, day 32 after transplant. No curve was fitted and no point was interpolated. [R58] The graph preserves each nutrient's actual concentration scale and the authors' 95% confidence intervals. It demonstrates two practical points: nutrient response can be curved rather than linear, and equal EC values do not imply equal elemental availability. ## Nutrient solution and tissue chemistry El-Nakhel and colleagues tested green and red lettuce with calcium-, magnesium- or potassium-dominant macrocation ratios. The complete design contains three biological replicates in each of six cultivar-by-solution cells. The published measurements include total nitrogen, sulphate, six organic acids and total chlorophyll. [R59] Note. Means calculated from the complete 2 × 3 × 3 design published by El-Nakhel et al. (2020). The downloadable table includes each replicate, standard deviation, standard error and two-way ANOVA output. [R59] A balanced two-way fixed-effects ANOVA was recomputed from all 18 published observations. For malate, the nutrient-solution effect was F(2, 12) = 106.39 with Holm-adjusted p = 3.94 × 10⁻⁷, and the cultivar-by-solution interaction was F(2, 12) = 21.40 with adjusted p = 9.93 × 10⁻⁴. For total chlorophyll, the interaction was F(2, 12) = 25.38 with adjusted p = 4.89 × 10⁻⁴. The interaction means the solution effect changes with cultivar; one universal nutrient-to-chemistry coefficient would discard that structure. ### Estimating plant nutrient state Visible colour is useful but not chemically specific. Nitrogen limitation, water stress, senescence, exposure error and disease can all alter RGB appearance. FlavoRotor therefore joins four records at the same plant and time: the delivered elemental formulation, pH and EC history, the repeated image, and a reference measurement such as tissue mineral composition or chlorophyll. A supervised model predicts a declared laboratory endpoint, not an undefined label such as “nutrient health”. NUT-STATE x ^ t = f  ⁣ ( I t − k : t , u t − k : t , s t − k : t , g , d ) \hat{\mathbf{x}}_t=f\!\left(\mathbf{I}_{t-k:t},\mathbf{u}_{t-k:t},\mathbf{s}_{t-k:t},g,d\right) x ^ t ​ = f ( I t − k : t ​ , u t − k : t ​ , s t − k : t ​ , g , d ) Estimated plant state uses an image sequence I, delivered nutrient and light inputs u, measured environmental state s, cultivar g and day after transplant d over a defined history window. **Explanation**Estimated plant state combines a recent image sequence, delivered treatments, measured environmental conditions, cultivar and day after transplant. Evaluation keeps all observations from one plant or cultivation cycle in the same fold. The report includes MAE for continuous chemistry, balanced accuracy for declared deficiency classes, calibration of uncertainty and performance for each cultivar and growth stage. ## Why EC is insufficient EC is an indirect bulk response to all dissolved ions. Closed systems can maintain a target EC while individual nutrients become deficient or excessive. [R17] [R34] [R35] [R36] ## Four-channel implication The four FlavoRotor channels must be assigned to chemically defined and compatible fluids. Channel labels describe the liquid, not an expected flavour. The formulation must account for coupled ions, precipitation risk, source-water composition and the limited degrees of freedom available with four reservoirs. [I03] [R34] [R35] ## Validation Recipe trials report the full elemental formulation, source water, pH, EC, solution replacement, delivered stock volumes and tissue composition. Sensory conclusions are made only after chemical and blinded sensory measurements. ## References - [I03] FlavoRotor project team (2026). FlavoRotor peristaltic pump technical record. *Internal engineering record*. - [R17] Vought, Kelsey; Bayabil, Haimanote K.; Pompeo, Jean; Crawford, Daniel; Zhang, Ying; Correll, Melanie; Martin-Ryals, Ana (2024). Dynamics of micro and macronutrients in a hydroponic nutrient film technique system under lettuce cultivation. *Heliyon*. https://doi.org/10.1016/j.heliyon.2024.e32316 - [R34] Cho, Woo-Jae; Gang, Min-Seok; Kim, Dong-Wook; Kim, JooShin; Jung, Dae-Hyun; Kim, Hak-Jin (2023). Decision-tree-based ion-specific dosing algorithm for enhancing closed hydroponic efficiency and reducing carbon emissions. *Frontiers in Plant Science, 14, 1301490*. https://doi.org/10.3389/fpls.2023.1301490 - [R35] Bamsey, Matthew; Graham, Thomas; Thompson, Cody; Berinstain, Alain; Scott, Alan; Dixon, Michael (2012). Ion-Specific Nutrient Management in Closed Systems: The Necessity for Ion-Selective Sensors in Terrestrial and Space-Based Agriculture and Water Management Systems. *Sensors, 12, 13349–13392*. https://doi.org/10.3390/s121013349 - [R36] Miller, Alexander; Adhikari, Ranjeeta; Nemali, Krishna (2020). Recycling Nutrient Solution Can Reduce Growth Due to Nutrient Deficiencies in Hydroponic Production. *Frontiers in Plant Science, 11, 607643*. https://doi.org/10.3389/fpls.2020.607643 - [R58] Sharkey, Andrew; Chen, Yongsheng; Altman, Asher (2025). Hydroponic Cultivation of Bibb Lettuce in Nitrogen Phosphorus Potassium (NPK)-Limited Conditions. *USDA Ag Data Commons, Version 2*. https://doi.org/10.15482/USDA.ADC/28801286.v2 - [R59] El-Nakhel, Christophe; Pannico, Antonio; Kyriacou, Marios C.; Petropoulos, Spyridon A.; Giordano, Maria; Colla, Giuseppe; Troise, Antonio Dario; Vitaglione, Paola; De Pascale, Stefania; Rouphael, Youssef (2020). Dataset on the organic acids, sulphate, total nitrogen and total chlorophyll contents of two lettuce cultivars grown hydroponically using nutrient solutions of variable macrocation ratios. *Data in Brief, 29, 105135*. https://doi.org/10.1016/j.dib.2020.105135