Nitrate Concentration Of Lettuce Research Articles

Nitrate accumulation and physicochemical characteristics of lettuce as affected by sodium selenite and synthesized selenium nanoparticles

ABSTRACT Exogenous selenium (SE) application during lettuce (Lactuca sativa L.) production may prevent Se deficiency. Low concentrations of Se have beneficial effects on plant cell metabolism and application of Se can increase growth, yield, and quality and reduce nitrate concentration in lettuce. In the present study, biosynthetic synthesis of selenium (Se) nanoparticles (NPs) was carried out via Se ions reduction during exposure to rosemary (Salvia rosmarinus Spenn.) extract. Using scanning electron microscopy (SEM), the shape and size of the Se NPs were determined. To investigate effects of concentrations of sodium selenite (1, 2, and 4 mg∙L−1) and Se NPs (1, 2, and 4 mg∙L−1) on morphological and physiochemical traits of lettuce. Most nutrient solutions, especially 2 mg∙L−1 Se NPs, increased plant height, leaf number, fresh weight, chlorophyll a, total chlorophyll, and nitrate reductase activity of plants. Application of 2 and 1 mg∙L−1 Se NPs, caused a decrease in the level of nitrate accumulation. Under nutrient treatments, concentrations of P, K, Fe, Zn, and Se, and concentration of N decreased. Foliar application of biosynthetic synthesized Se NPs, may have potential for improved quantity and reduced nitrate accumulation in lettuce.

Excess Nitrogen Exceeds the European Standards in Lettuce Grown under Greenhouse Conditions

Core Ideas Lettuce yield was decreased by excessive nitrogen fertilization. Deficit irrigation did not cause a decrease in yield. Temperatures, photoperiod, and sunshine duration decreased the nitrate accumulation. Nitrogen is one of the most important plant nutrients for lettuce (Lactuca sativa L. var. Kitare). However, excess use of N causes environmental and health problems. In this study, the response of lettuce plants to different amount of N and irrigation levels were studied. The experiment was conducted under glasshouse conditions for winter and spring growing seasons in Batı Akdeniz Agricultural Research Institute (BATEM), Antalya, Turkey. This study used a factorial design with three replications. Plant evapotranspiration varied from 14.4 to 28.8 and 16.3 to 32.6 L plant–1 in winter and spring, respectively. Nitrogen fertilizer levels affected lettuce yield in both growing seasons, whereas irrigation levels did not impact yield. The average yield varied from 354 to 472 g plant–1 in the winter growing season and from 333 to 611 g plant–1 in the spring growing season. The nitrate concentration in lettuce leaves increased with N rate and irrigation level, and was lower in spring than winter. The average nitrate accumulation varied from 4000 to 6000 and 2100 to 3600 mg kg–1, in the winter and spring growing season, respectively, exceeding the health standards of the European Union.

Effect of NO3 and NH4 concentrations in nutrient solution on yield and nitrate concentration in seasonally grown leaf lettuce

ABSTRACTThe effect of suboptimal supply of nitrogen (N) and of replacing nitrate in the nutrient solution with ammonia on growth, yield, and nitrate concentration in green and red leaf lettuce was evaluated over two seasons (autumn and spring) using multiple regression analysis. The plants were grown in a greenhouse on a Nutrient Film Technique (NFT) system. Nitrogen concentrations in the nutrient solution were either 3 mM or 12 mM, and the form of N was varied as follows: 100% NO3, 50% NO3 + 50% NH4, and 100% NH4. In both seasons, the biomass (fresh weight) of lettuce heads increased with increasing NO3 concentrations and in autumn, NO3 even at 1.5 mM was sufficient for high yield. However, head dry weight was affected neither by the season nor by changes in the composition of the nutrient solution. The concentration of NO3 had no effect on root dry weight, but it decreased at higher concentrations of NH4. The number of leaves increased as the ratio of NO3 to NH4 in the nutrient solution increased and was higher in autumn because of the longer growth period. Increasing the concentration of NO3 in nutrient solution increased both total N and nitrate concentration in lettuce heads (dry weight) but decreased the concentration of total C. Also, leaf nitrate concentration was lower in spring than in autumn and decreased with increasing NH4 concentration. Nitrogen utilization efficiency was maximum when NH4 levels in the nutrient solution were either 0% or 50% irrespective of the season. Our results thus show that suboptimal N supply in autumn will not affect lettuce yield, and that nitrate concentration in leaves is lower when NH4 concentrations in nutrient solution are higher and also much lower in red lettuce than in green lettuce.

Ground cover management and farmyard manure effects on soil nitrogen dynamics, productivity and economics of organically grown lettuce (Lactuca sativa L. subsp. secalina)

Ground cover management and farmyard manure (FYM) management have important roles in organic lettuce production. However, there is not enough information about their combined effects. In order to assess the effects of individual and combined ground cover and FYM management on soil mineral N (NH4-N and NO3-N) dynamics, lettuce yield and economics in organic farming, a two-year field experiment was conducted on a certified organic farm in Kisač (Vojvodina, Serbia). The experiment had a two-factorial split-plot completely randomized block design. FYM was applied on the half of the experimental field as a whole-plot factor, while ground cover management included the following four treatments: (I) control, without ground cover management (Ø); (II) hoeing (H); (III) agrotextile cover; (IV) straw mulch (SM), which were applied on split plots. The applied SM and AT increased soil moisture by 12.83 and 3.73%, respectively, compared to the control treatment. FYM increased soil mineral N concentration, the lettuce fresh matter (FM) yield and nitrate concentration in lettuce. However, nitrate concentration in lettuce in all treatments was below the limit required by the European Commission (EC) (2001). The highest lettuce yield was obtained by AT (39 122 kg), followed by SM (33 925 kg), and it was higher with FYM application by 16.85%. Hoeing did not positively affect the yield, probably due to its negative effect on soil moisture. Additional profit was higher with FYM, showing the following decreasing order: AT>H>SM>Ø. However, value/cost ratio (VCR) was in the order Ø>H>SM>AT on FYM fertilized plots. FYM application led to higher lettuce yield and higher profit and VCR. In case a farm does not have FYM, SM is the best alternative due to its positive effect on the yield and low investment costs.

Effects of nitrogen fertilizers on the growth and nitrate content of lettuce (Lactuca sativa L.).

Nitrogen is an essential element for plant growth and development; however, due to environmental pollution, high nitrate concentrations accumulate in the edible parts of these leafy vegetables, particularly if excessive nitrogen fertilizer has been applied. Consuming these crops can harm human health; thus, developing a suitable strategy for the agricultural application of nitrogen fertilizer is important. Organic, inorganic, and liquid fertilizers were utilized in this study to investigate their effect on nitrate concentrations and lettuce growth. The results of this pot experiment show that the total nitrogen concentration in soil and the nitrate concentration in lettuce increased as the amount of nitrogen fertilizer increased. If the recommended amount of inorganic fertilizer (200 kg·N·ha−1) is used as a standard of comparison, lettuce augmented with organic fertilizers (200 kg·N·ha−1) have significantly longer and wider leaves, higher shoot, and lower concentrations of nitrate.

Effects of short-term treatment with various light intensities and hydroponic solutions on nitrate concentration of lettuce

A glasshouse experiment was conducted to investigate the effects of five days’ treatment before harvest with various light intensities and seven hydroponic solutions on nitrate reduction in lettuce. The results showed that SPAD of new and expanded leaves were elevated by most of the hydroponic solutions under shading compared with the full nutrient solution, while no effect was demonstrated under non-shading. Additionally, lettuces under non-shading presented slightly higher leaf SPAD than those under shading. Nitrate concentrations of lettuce new leaves, expanded leaves and petiole were lowered significantly by all hydroponic solutions under shading and non-shading conditions compared with the full nutrient solution. Under non-shading, the efficiencies of seven hydroponic solutions varied largely, but no efficiency differences were showed under shading. N-free solution, 0.75 mM potassium sulphate solution and 5×10−5 mM ammonium molybdate solution functioned more efficiently in reducing nitrate concentration both in expanded leaves and petiole of lettuce before harvest. In conclusion, proper light intensity is a key important factor that determines the efficiencies of nitrogen-free hydroponic solution treatments in lowering nitrate concentrations in leaf blades and petioles of lettuce before harvest.

Quality changes in hydroponic lettuce grown under pre-harvest short-duration continuous light of different intensities

SummaryThe effect of pre-harvest light intensity on the quality of hydroponically-grown lettuce (Lactuca sativa var. capitata L.) was studied by growing lettuce under 48 h of continuous illumination delivered by red- or blue-light-emitting diodes (LEDs) with a red:blue ratio of 4.0. Four light intensity treatments (50, 100, 150, or 200 µmol m–2 s–1) were applied. The results showed that the nitrate concentrations in lettuce shoots decreased significantly after treatment with 48 h of continuous light, while the contents of soluble sugars and vitamin C increased substantially. It was observed that the effect of pre-harvest short-duration continuous light (PSCL) on improving lettuce quality was significantly influenced by the intensity of the light. The decrease in nitrate concentration and the increases in soluble sugars and vitamin C contents were relatively low at a light intensity of 50 µmol m–2 s–1, but increased gradually as the light intensity increased from 50 µmol m–2 s–1 to 200 µmol m–2 s–1. However, the marginal benefit of increased light intensity in lowering nitrate concentration and increaseing vitamin C content declined rapidly when the light intensity increased beyond 100 µmol m–2 s–1. In conclusion, PSCL offers an effective method by which to improve the quality of lettuce, and a light intensity of between 100 µmol m–2 s–1 – 150 µmol m–2 s–1 is the economic optimum.

Nitrate concentration in lettuce leaves depending on photosynthetic photon flux and nitrate concentration in the nutrient solution

The nitrate accumulation in plant tissues can occur due to low light availability. However, published studies have not linked nitrate accumulation to photosynthetic photon flux (PPF) measured during the growing period. This study aimed to evaluate the effect of the reduction of photosynthetic photon flux and the concentration of nitrate in the nutrient solution on agronomic characteristics and accumulation of nitrate in lettuce grown in hydroponics. The trial design was entirely randomized in a factorial scheme (4 x 2) with three repetitions, and four shading levels: 0, 30, 50, and 80% and two nitrate levels in nutrient solution: 5 and 10 mmol L-1. The dry matter production decreased directly and linearly with the reduction of light. The lowest level in nitrate solution also led to reduction in dry mass yield. The maximum accumulation of nitrate reached 966.3 mg kg-1 fresh mass, with PPF of 118 μmol/m²/s and 140 mg L-1 of N-NO3-1 (below the maximum levels recommended by the European Union), and the minimum of 200 mg kg-1 with PPF of 455 μmol/m²/s and 70 mg L-1 of N-NO3-1 in the nutrient solution. The reduction of nitrate in the nutrient solution from 140 to 70 mg L-1 led to the reduction of nitrate accumulation in shoots, but also caused a decrease in the production of phytomass of shoots, as well as reduced leaf area significantly.

Short-term treatment with hydroponic solutions containing osmotic ions and ammonium molybdate decreased nitrate concentration in lettuce

Two glasshouse experiments were conducted to investigate the efficiencies of various hydroponic solutions and their concentration effects in reducing nitrate concentration of lettuce after short-term treatment. The first experiment showed that hydroponic solutions of 0.1 mM KCI, 0.75 mM K2SO4, 0.1 mM KCI plus 0.75 mM K2SO4 and 5.0×10− 5 mM (NH4)6MO7O24 significantly decreased nitrate concentration in expanded leaves of lettuce, and tap water and distilled water did slightly. However, all treatment solutions did not significantly lower the nitrate concentration in petioles. The second experiment showed that all KCI, K2SO4 and (NH4)6MO7O24 solutions reduced nitrate concentration both in leaves and petioles, but increased concentration of treatment solutions did not enhance the efficiencies. In conclusion, 0.1 mM KCI, 0.75 mM K2SO4, 0.1 mM KCI plus 0.75 mM K2SO4 and 5.0×10− 5 mM (NH4)6MO7O24 were efficient treatment solutions to decrease nitrate concentration of hydroponic lettuce for short-term treatment, but their efficiencies were not improved with the increased solute concentration.

Nickel supplementation effect on the growth, urease activity and urea and nitrate concentrations in lettuce supplied with different nitrogen sources

Effect of nickel (Ni) in the nutrient solution on yield, N metabolism, and nitrate content of leafy vegetables is poorly understood. The aim of this nutrient solution culture experiment was to investigate the effects of Ni supplementation on the nitrogen (N) metabolism and growth of lettuce ( Lactuca sativa L. cv. Baker) with either urea or nitrate as the N source. Nickel supplement at 0.04 μM reduced urea toxicity to the urea-fed plants. Addition of Ni to the nutrient solution significantly increased the leaves and root growth of the urea-fed lettuce plants while it increased the growth of lettuce plants fed with nitrate only at N level of 20 mM. At N level of 20 mM, the leaves fresh weight of the urea-fed plants promoted by Ni supplement was comparable with the nitrate-fed plants untreated with Ni. Nickel supplementation increased the leaf total N concentrations in the urea-fed plants, although the nitrate-fed plants accumulated greater N in their leaves compared with urea treated plants at without Ni treatment. Nickel addition decreased the concentrations of leaf urea-N in the urea-fed plants and NO 3-N in the nitrate-fed plants. Nickel addition enhanced urease activity in the leaves of urea-fed plants. The results indicated Ni supplementation enhances the growth of the urea-fed lettuce plants while it has role in decreasing leaf nitrate concentration and thus, improving the health quality of the nitrate-fed plants.

Nitrate in leafy vegetables, culinary herbs, and cucumber grown under cover in Estonia: content and intake

The content of nitrate in leafy vegetables, culinary herbs, and cucumber was determined during the years 2006–2008. All samples of Estonian origin, except white cabbage, were grown under cover. Seasonal differences in nitrate concentrations were observed in lettuce and spinach. Nitrate concentrations in lettuce were 22% and those in spinach were 24% higher in winter crops compared with samples collected in summer. The mean nitrate level was 3023 mg kg–1 for fresh lettuce and 2337 mg kg–1 for spinach. On average, 11.6% of fresh lettuce and spinach samples nitrate concentration exceeded the maximum level specified in European Commission Regulation No. 1881/2006. The mean levels were 999 mg kg–1 for imported iceberg lettuce and 1287 mg kg–1 for frozen spinach, which are below the maximum European Commission limits. Parsley, dill, basil, thyme, and rucola contained high concentrations of nitrate from mean levels of 2134 mg kg–1 for parsley up to 8150 mg kg–1 for rucola. Mean nitrate concentrations ranged from 382 to 1115 mg kg–1 for white cabbage and Chinese cabbage, respectively. The per capita mean daily intake of nitrates related to the consumption of leafy vegetables, culinary herbs, and cucumber for the whole Estonian population was 31.3 mg day–1, which comprised 14.2% of the acceptable daily intake (ADI).

Nitrogen Nutrition Effects on Nitrate Accumulation of Soil‐Grown Greenhouse Butterhead Lettuce

Leafy vegetables are the major source of dietary nitrate intake of humans. Nitrates can have many detrimental effects on human health besides some beneficial effects. A further reduction in nitrate concentration thus can represent added value for vegetable products rich in carotenoids, vitamins C and E, selenium, dietary fiber, plant sterols, and so on. Though nitrate accumulation is governed by a plenitude of factors (i.e., genetic setup, environmental conditions and nutrients), the factor most readily controllable is nitrogen nutrition. This study examined the dependence of butterhead lettuce crops' nitrate concentration on soil mineral nitrogen (N) content. It was shown that the effect of the soil's mineral N content at harvest was strongly associated with the nitrate concentration of lettuce at a low to intermediate mineral N content (<100 kg N ha−1). This demonstrates the importance of N‐fertilization practices. Results of 24 comparative experiments, based on two different N‐fertilization recommendation procedures, did show that an N application difference at the start of the growing period has an effect on the nitrate concentration at harvest. A lower N application at either recommendation resulted in 71% of the experiments (17/24) having a lower leaf nitrate concentration. The head weight was negatively affected in only 2 of these 17 experiments. Minimizing the N input and hence lowering the soil N content at harvest points to the possibility of further reducing the nitrate concentration level in greenhouse lettuce, while having no significant negative effect on economic yield.

Nitrate content of lettuce (Lactuca sativa L.) after fertilization with sewage sludge and irrigation with treated wastewater

A romaine-type lettuce (Lactuca sativa L.) was cultivated over three crop seasons (spring 2005, spring 2006 and autumn–winter 2006) in six 36 m2 plots in Alcázar de San Juan, Spain. A drip irrigation system was used to water all plots: five plots with drinking water and one plot with wastewater from the activated sludge system of a wastewater treatment plant (WWTP). One drinking water-irrigated plot was not fertilized (control). Five different treatments were applied to the soil: three organic mixtures (sewage sludge, sewage sludge mixed with pine bark and municipal solid waste with composted sludge) and a conventional fertilizer were applied to the four plots irrigated with drinking water. The last plot was irrigated with treated wastewater. The treatments were tested for their effect on plant growth and nitrate concentration in vegetable tissue. An increase in fresh weight in the lettuce was linked to the dosage of sewage sludge. The highest nitrate level was observed in the sewage sludge treatment in all crops and seasons, although, in general, all values were below the maximum limits established by the European Commission for nitrate content in fresh romaine lettuce. In the third crop season, a significant increase in nitrate content was observed in lettuce from organic treatments. Nitrate concentration in lettuce from irrigated treated wastewater was higher than control, although significant differences were not found.

A questão do nitrato em alface hidropônica e a saúde humana

A alface (Lactuca sativa L.) destaca-se como a espécie mais produzida em sistema hidropônico. Nesse tipo de cultivo, a maior parte do nitrogênio é fornecida na forma de nitrato, o que pode acarretar acúmulo deste íon nos vacúolos celulares. O teor de nitrato nas plantas depende de fatores genéticos, da disponibilidade desse nutriente no sistema radicular e de fatores ambientais. Diversos estudos indicam que o consumo de nitrato pode ser nocivo à saúde humana, causando metahemoglobinemia e câncer gástrico. Porém, pesquisas recentes discorrem que não há ligação entre nitrato e as doenças citadas, destacando ainda o papel benéfico do nitrato à saúde humana, como protetor contra gastrenterites. Existem indícios de que a presença de certas vitaminas em vegetais inibe uma possível ação negativa do nitrato. Altas concentrações de nitrato em alface cultivada sob hidroponia em países do norte europeu causaram apreensão da comunidade científica e de consumidores brasileiros. Porém, as pesquisas realizadas no Brasil demonstram que, por haver maior disponibilidade de radiação solar, devido às menores latitudes, os teores de nitrato encontrados em alface produzida em hidroponia são bastante inferiores aos limites máximos preconizados pela união européia, indicando não haver risco à saúde humana.

Influence of Plant Part on Nitrate Concentration in Lettuce and Spinach

ABSTRACT The concentration of nitrate-nitrogen (NO3-N) varies between lettuce (Lactuca sativa L.) and spinach (Spinacia oleracea L.). Nitrate is potentially harmful if consumed in large amounts by humans; therefore, understanding which cultivars and plant parts concentrate NO3-N can be useful in developing approaches to reduce dietary NO3-N intake. We determined NO3-N concentration and distribution in cultivars of field-grown lettuce and spinach. In 2006, NO3-N concentration was highest in the outer leaf whorl and lowest in the center of spinach; no difference was found in lettuce. In 2007, overall soil and tissue NO3-N concentrations were lower and there was no interaction between plant part and species or cultivar and no difference among leaf whorls; all cultivars had higher NO3-N concentrations in the midrib and petiole than in the leaf. Differences in NO3-N concentration and distribution suggest that practices such as cultivar selection and selective removal of high NO3-N parts can lower NO3-N consumption by humans.

Effect of organic and inorganic fertilizers applied during successive crop seasons on growth and nitrate accumulation in lettuce

Abstract A romaine-type lettuce ( Lactuca sativa L.) cv. Corsica was cultivated during three successive crop seasons (late-spring, late-autumn and late-winter) in the same soil of an experimental greenhouse in S.W. Peloponnese, Greece. Seven long-term fertilization treatments were tested for their effect on plant growth and nitrate concentration in the external lettuce leaves. Treatments included: three different doses of organic fertilization (composted sheep manure) applied at the start of each crop season, three different doses of inorganic N fertilization applied via fertigation during each crop season, and a control treatment in which no fertilizer was applied. A drip irrigation system was used to water all plants. The highest nitrate levels were observed in the medium and maximum inorganic fertilization treatments (572–664 mg kg −1 ) in all crop seasons. They were significantly higher compared to the respective organic fertilization treatments (253–435 mg kg −1 ) and all other fertilization treatments (148–435 mg kg −1 ). Crop season affected lettuce growth more than nitrate accumulation in the lettuce leaves: lettuce biomass production was the smallest and most uniform in the late-autumn season and did not respond to the fertilization treatments tested (ranging from 409 to 439 g plant −1 ), while in the late-spring season biomass production was the highest and most variable (561–841 g plant −1 ), it correlated with nitrate concentration in the leaves and in the medium and maximum inorganic fertilizer doses it significantly exceeded production from all other fertilization treatments (827–841 g plant −1 ). Following the three crop seasons the residual availability of N, P and K was clearly enhanced in the soil receiving the organic compared to the inorganic fertilization. Nitrate concentration in lettuce leaves was far below the upper limits set by the European Commission in all fertilization treatments throughout the three crop seasons, a result attributed mainly to the sufficient level of light intensity and duration throughout the year in Southern Greece.

Root Shoot Partitioning and Nitrate Concentration in Lettuce

A two-compartment model previously developed for lettuce is extended by splitting the structural compartment into shoot and root. The partitioning of structural material between the root and the shoot is based on the imbalance between the root nitrate supply capacity and the shoot demand. The model is used to study the response of lettuce to a reduced nitrate supply toward the end of the growing season, as a possible mean of reducing the leaf nitrate concentration. Simulation results show that reducing nitrate supply leads to a larger root, a smaller shoot, and a lower nitrate concentration.

Expression of a chimeric nitrate reductase gene in transgenic lettuce reduces nitrate in leaves

Transgenic plants of four glasshouse-grown lettuce cultivars ('Cortina', 'Evola', 'Flora' and 'Luxor') were obtained by co-cultivating excised cotyledons with Agrobacterium tumefaciens. The Agrobacterium strain LBA4404 contained the binary vector pBCSL16, which carried a nitrate reductase (nia) cDNA linked to CaMV promoter and terminator sequences, and the neomycin phosphotransferase II (nptII) gene. Transformed shoots were selected by their ability to root on medium containing kanamycin sulphate, by a positive NPTII assay and by PCR analysis. The presence of the nia cDNA in transgenic lettuce was confirmed by nitrate reductase (NR) enzymatic assay, a reduction in the nitrate content of leaves and by Southern hybridisation. PCR analysis of cDNA fragments from transgenic plants confirmed that both nia and nptII genes were expressed in first seed-generation (T1) lettuce plants. The commercial importance of reduced nitrate concentrations in lettuce is discussed.

Monitoring for nitrate in UK-grown lettuce and spinach

To comply with European Commission requirements, the UK is carrying out a monitoring programme on nitrate concentrations in lettuce and spinach. This paper reports the results obtained between June 1996 and April 1998. A total of 182 samples of protected lettuce, 131 samples of outdoor-grown lettuce and 34 samples of fresh spinach were taken from the main growing areas of the UK. Nitrate concentrations in protected lettuce were influenced by the season with summer-grown crops (mean of 2382mg/kg) having lower levels than those grown in the winter (mean of 3124mg/kg). Weather conditions also affected concentrations in protected lettuces with long hours of sunshine and low rainfall associated with low nitrate levels. Nitrate concentrations in outdoor-grown lettuces were lower (mean of 1085mg/kg) than those in protected lettuces but there were insufficient data to determine if they were affected by the weather conditions or season. Similarly there were insufficient data to determine if weather conditions or season influenced nitrate concentrations in spinach (mean of 1900mg/kg) but regional differences were observed.

NITRATE CONCENTRATION IN GREENHOUSE LETTUCE: A MODELING STUDY

A simple two-state-variable model was developed to describe the nitrate concentration in lettuce when nitrate supply is unlimited. A central element of the model is a negative correlation between the concentrations of soluble carbohydrates and nitrate in the cell sap, a correlation which reflects the equivalent roles of nitrate and organic solutes in the maintenance of cell turgor. A conventional carbon balance model was used to predict the fluctuations of soluble carbohydrates as a function of time. The carbohydrate-to-nitrate correlation was then used to compensate for these fluctuations by adjusting the nitrate concentration. The concentration of carbohydrates in the non-structural buffer (vacuoles) is determined by the balance between source activity (supply of carbohydrates by photosynthesis, controlled by light and CO2) and sink activity (demand for carbohydrates by growth and maintenance, controlled by temperature). As a result, winter conditions, characterized by source-limited growth, result in a depletion of carbon from the cell sap and, via the negative correlation, in a high nitrate concentration. Conversely, summer conditions result in low nitrate levels. A fair agreement was obtained when the model was tested with an available experimental data set for all-year-round production of greenhouse lettuce in Northern Germany.