The Effect of Concentration and Time of Application of Humic Acid on Morpho-physiological Characteristics of Spinacia oleracea

Spinacia olerace is the most important leaf vegetable of the Chenopodiacea family, which has a special place in human nutrition because of its variety of minerals and vitamins. Cultivation of this plant in Iran is several thousand years old and accordingly Iran is considered as the main place and a source of spinach in the world. Growth of plants is affected by genetics, environmental conditions, growing season, nutrients, and soil, harvesting method, temperature, intensity and quality of light. Among these factors, soil nutrients have a significant influence on plant growth and yield. Nowadays, the consumption of organic matter as fertilizer due to its high cost and limited availability is not sufficient and the major nutritional needs of plants are met by chemical fertilizers, which can lead to environmental problems and, over time, reduced yields. In this connection humic acid is a naturally occurring organic compound and contains 2% to 5% organic matter. Humic acid can be used to seedling nutrition and improve its quality and quantity. Given the recent use of organic acids such as humic acid to improve crops and horticulture, but little research has been done on transplant birth, this experiment was conducted to investigate the application of different levels of humic acid in irrigation water at the time of irrigation. Different effects and their effects on growth indices and spinach production were investigated.
The present experiment was conducted to investigate the application of different concentrations of humic acid at different times and its effects on quantitative and qualitative indices of spinach in a factorial completely randomized design with three replications in research greenhouse at Torbat Heydariyeh University. Treatments consisted of three concentrations of humic acid (0, 3 and 6 ml/L) at two application times (one-week and two-week). The mean daily greenhouse temperature at the time of plant growth was 25°C and the mean nighttime temperature was 18°C, the average relative humidity was 60%. After seedlings were planted in the main pots at four-leaf stage, they were irrigated with humic acid (0, 3 and 6 ml/L) at different intervals once a week, twice weekly. The humic fertilizer used belonged to Green Seed Company, containing 24% humic acid and 3% folic acid and 2% potassium. Five weeks after treatment, the traits were measured. Transplant growth indices including number of leaves (by counting the number of shoots per plant), leaf length and width, leaf area, canopy, height, chlorophyll index, chlorophyll a, b, carotenoid and dry weight of each plant were determined.
Based on the results of this experiment, the effect of humic acid concentration on morphological and physiological traits of spinach transplant was significant. The highest leaf number (4.6) at 3 ml concentration and the lowest number (3.5) were at zero concentration. These traits were subjected to humic acid titer, but the increase in concentration had no significant effect on these traits. The increased number of leaves and traits mentioned in the early stages of transplant growth is probably due to the rapid expansion of the root system of the plant at high concentrations of humic acid, which in turn leads to increased nutrient uptake, better plant growth and subsequent growth. Leaf number and other traits become leaf dependent. The results showed that the highest chlorophyll a (1.8 ml/g fresh leaf), chlorophyll b (2.5 ml/ml fresh leaf), carotenoids (7.1 ml/ml). Fresh leaf g) and biomass (150 mg) at 3 ml concentration and the lowest at zero concentration. The highest chlorophyll index (74.1 ml/ml fresh leaf g) was also found in the concentration of 6 ml and the lowest was obtained from zero concentration. Humic acid increased spinach transplant biomass by increasing the amount of photosynthetic pigments and leaf area or the same photosynthetic capacity. In most of the traits, the two-week application time was higher than the one-week, so that spinach transplant biomass increased by 110% over the two-week application period. So that spinach transplant biomass was 156 at the two-week application and 74 mg at the one-week application. Based on the results of this experiment, humic acid application can improve the quantitative and qualitative traits of spinach transplant and its production.
Production of vegetable seedlings have an important role in the production and olericulture economy. Specializing in different activities in the vegetable production process will simplify the production process and increase efficiency. This means that the best conditions for seedling growth should be provided during transplanting. Application of humic acid organic fertilizer instead of chemical fertilizer can reduce environmental pollution in line with sustainable agriculture and healthy eating with vegetables to prevent the accumulation of chemicals in the human body to be effective. In this regard, the results of this study showed that using low humic acid as organic fertilizer can improve morphophysiological traits of spinach transplant.