عنوان مقاله [English]
Introduction: Successful greenhouse and nursery production of plants is largely dependent on the chemical and physical properties of the growing substrate. An ideal potting substrate should be free of weeds and diseases, heavy enough to avoid frequent tipping over and yet light enough to facilitate handling and shipping. The substrate should also be well drained and yet retain sufficient water to reduce the frequency of watering. Other parameters to consider include cost, availability, consistency between batches and stability in the media over time. Greenhouse crops in general, have higher nutrient demands than field grown crops. Therefore, in order to optimize production it is essential to focus on the growing substrate and fertilization. The physical properties of the growing medium are important parameters for successful plant growth, as these are related to the ability to adequately store and supply air and water to plants. Humic acid is a principal component of humic substances, which are the major organic constituents of soil (humus), peat and coal. It is also a major organic constituent of many upland streams, dystrophic lakes, and ocean water. It is produced by biodegradation of dead organic matter. It is not a single acid, but it is a complex mixture of many different acids containing carboxyl and phenolate groups so that the mixture behaves functionally as a dibasic acid or occasionally as a tribasic acid. Humic acids can form complexes with ions that are commonly found in the environment creating humic colloids. Humic and fulvic acids (fulvic acids are humic acids with lower molecular weight and higher oxygen content than other humic acids) are commonly used as a soil supplement in agriculture. Humic Plus contains humic acid, fulvic acid, macro micro nutrients and proprietary constituents essential for plant growth. Organic matter soil amendments have been known by farmers to be beneficial to plant growth for longer than recorded history. However, the chemistry and function of the organic matter have been a subject of controversy since humans began their postulating about it in the 18th century. Selection of the proper media components is critical to the successful production of plants. So, the objective of this study was to assess the effect of humic acid foliar application and various substrate on quantitative and qualitative characteristics of tomato seedling.
Material and Methods: The experiment was conducted in a greenhouse at Bardsir Faculty of Agriculture , Shahid Bahonar University of Kerman in 2015, as a factorial arrangement based on completely randomized design with five replications. The experimental treatments were substrate in 7 levels (peat, coco-peat, leaf-soil, compost, vermi-compost, manure and clay soil), humic acid in two levels (foliar application and non- foliar application). After preparation of substrates, plastic boxes with 12 cm diameter and 10 cm height were chosen. After extracting gravity water, tomato (cv. Canyon) seeds were sown in pots. Rain irrigation was done daily. Foliar application of humic acid with concentration of 0.001 liter was performed from seedling emergence to transplanting every two days. The germinated seeds was daily counted and number and rate of seed emergence was estimated. Plant height, stem diameter, number of internodes, leaf area, shoot and root dry matter and chlorophyll contents were calculated at transplanting time of seedling.
Results and Discussion: The substrate treatment had a significant effect on rate and percent of germination, plant height, shoot dry matter, leaf area, number of internodes and, chlorophyll a and carotenoid contents. According to the results, the greatest and smallest rate and percent of germination was found in peat and manure treatments, respectively. Also the greatest shoot dry matter (1.17 g), leaf area (125.9 cm plant-1), number of internodes (6.19), plant height (13.51 cm) and chlorophyll a concentration (2.55 µg/ml) were observed for peat substrate. Manure and clay soil substrates showed the smallest of these measurements and carotenoid contents. It seems that physical characteristics of peat was better than other substrates. Plant height, shoot dry matter, leaf area, number of internodes, chlorophyll a and carotenoid contents showed a significant effect by humic acid application. Foliar application of humic acid significantly increased the mentioned traits.
Conclusion: The results illustrated that between substrates in this study, peat was the best for seedling production of tomato. Foliar application of humic acid had a positive effect in improving growth characteristics of tomato seedling.