Factors Affecting Relative Growth Rate of Lettuce and Spinach in Hydroponics in a Greenhouse

Abstract

<jats:p>Relative growth rate (RGR), the relative increase in weight per day, can analyze the effect of environment and nutrition on growth. I examined which of the parameters responding to plant growth scaled according to RGR for lettuce and spinach grown in heated greenhouses in hydroponics with control of the nutrient solution. The experiments for lettuce in 2006–08 included all times of year, high vs. low temperature, and effect of withdrawal of nitrogen. There were four parameters that were significant in multiple linear regression vs. RGR; irradiance divided by leaf area index if it was greater than one, or normalized daily light integral (NDLI), solution temperature, electrical conductivity (EC), and logarithm solution nitrate when it was between 3 and 55 mg·L<jats:sup>−1</jats:sup> N. NDLI had the most significant coefficient, but the other parameters had regression coefficients more than three times <jats:sc>se</jats:sc>. For experiments on spinach in 2009–10, all the parameters mentioned previously were significant in multiple linear regression vs. RGR, except EC. The coefficient for NDLI in spinach was about half the value in lettuce. The coefficients for solution temperature and low nitrate were two and three times that in lettuce. In a third set of experiments on lettuce in 1996–98, solution temperature was the only significant parameter among those mentioned previously. The coefficient for solution temperature was similar to that for regression of lettuce in 2006–08.</jats:p>

Foliar Spray Application of Chlorella vulgaris Extract: Effect on the Growth of Lettuce Seedlings

“…Finally, as reported in Table 2, the relative growth rate (RGR) calculated for treated seedlings resulted to be significantly higher than that estimated in control lettuce. Gent [26] showed that in lettuce the RGR, representing the relative increase in weight per day, slowly changes when plants grow in a constant environment, whereas environmental and nutritional alterations have effects on their growth. Therefore, being fixed in the experimental conditions, as it is in the present trial, the increase of RGR in treated lettuce was certainly linked to the biostimulant effect of CV extract.…”

“…Relative growth rate (RGR) was determined, as reported in Gent [26], from the shoot weights harvested just before the treatment and at the end of the experimental period (21 days after the first treatment) using the following equation:…”

Growth, Physiology and Yield Responses of Four Rock Melon (Cucumis Melo Var. Cantaloupensis) Cultivars in Elevated Temperature

“…The differences of atmospheric [CO 2 ] and temperature between AT and ET were recorded as 5-8 ppm and 5°C during 9 am to 5.59pm hours and 9-11ppm and 1°C during 6pm to next day 8.59 am. Relative growth rate is the mathematical interpretation of relative increase of plant dry weight per day and RGR reveals the relative impact of environment on plant growth (Gent, 2017 andSonsteby, et al, 2016). Plant RGR analysis data in vegetative phase, had no significant difference between varieties but had a significance difference between two temperature regimes.…”

Seasonal Changes in Growth, Nitrogen Nutrition, and Yield of Hydroponic Lettuce

“…They found that planting dates in September or April (warmer cropping season) resulted in a shorter growth cycle than those in December or January (cooler cropping season). Environmental factors such as temperature and light are well known to positively influence growth traits (De Pinheiro Henriques and Marcelis, 2000;Gent, 2017;Hatfield and Prueger, 2015). In that sense, higher daytime temperatures during the spring season resulted in more heat unit accumulation, likely leading to greater growth rates due to enhanced photosynthetic functions.…”