The Effect of Irrigation and Nitrogen on Growth Attributes and Chlorophyll¬ Content of Garlic in Line Source Sprinkler Irrigation System

With 12 million tons production per year, garlic is the fourth important crop in world. In addition to its medical value, it has been used in food industry. The Hamedan province with 1900 ha cultivation area and 38 percent of production is one of the most important garlic area productions in Iran. Few studies on water use and management of garlic exist in the world. Garlic is very sensitive to water deficit especially in tubers initiation and ripening periods. The current research was done because of scarce research on garlic production under water deficit condition in Iran and importance of plant nutrition and nutrients especially nitrogen on garlic production under stressful conditions. Nitrogen is necessary and important element for increasing the yield and quality of garlic. Application of nitrogen increases the growth trend of garlic such as number of leaves, leaf length and plant body. Reports have shown that garlic has high nitrogen requirement, particularly in the early stages of growth.
This study was conducted for evaluating the combined effects of nitrogen and irrigation on the yield and quality of garlic (Allium sativumL.). The study was performed as a split-block based on randomized complete blocks design with factors of irrigation at four levels (0-3(normal irrigation), 3-6 (slight water deficit), 6-9 (moderate water deficit) and 9-12 (sever water deficit) meters distance from main line source sprinkler system), nitrogen at four levels (0, 50,100 and 150 kg nitrogen per ha) using three replications and line source sprinkler irrigation system. The total water of irrigation levels was measured by boxes that were fixed in meddle of each plot. The statistical analysis of results were performed using themethod described by Hanks (1980). The chlorophyll index was measured using the chlorophyll meter 502 (Minolta, Spain). The chlorophyll a and bwas measured by the method described by Arnon (1946) and Gross (1991) in fresh leaf samples using spectrophotometer at 645 and 663 nm. Data were subjected to analysis of variance using MSTATC and SPSS softwares. Duncan’s multiple range test at p≤0.05 probability level was applied to compare the mean values of measured attributes. The Excel software (Excel software 2007, Microsoft Inc., WA, USA) was used to draw Figures.
The results showed that, the application of nitrogen significantly affected most of measured attributes. The application of 150 kg N per ha showed highest stem height (40.5 cm), dry weight of stem (5.34 g),wet weight of stem (69.5 g), chlorophyll index (49.7),chlorophyll a (9.8 mg.g-1dw) and chlorophyll b (4.04 mg.g-1dw) and increased stem height, dry and wet weight of stem, chlorophyll index and chlorophyll a and b around 7, 6, 7, 12, 22 and 36 percent, respectively. The irrigation levels significantly affected most of measured attributes similar to the nitrogen levels. The application of 409 mm irrigation water per growing season resulted to maximum stem height (41.9 cm), leaf number (7.5), dry weight of stem (5.39 g) and wet weight of stem (70.1 g), chlorophyll index (50.5) and chlorophyll a (10.2 mg.g-1dw) and chlorophyll b (4.04 mg.g-1dw). The severe water deficit (application of 138 mm irrigation water per growing season) decreased stem height, leaf numbers, dry and wet weight of stem, chlorophyll index and chlorophyll a and b about 13, 36, 12, 12, 19, 42 and 44 percent, respectively. The two way interaction of nitrogen and irrigation was significant and mostly synergistic on wet and dry weight of stem. The highest amounts of stem wet weight (73.2 g) and stem dry weight (5.63 g) were resulted from application of 150 kg nitrogen per ha under full irrigated condition that increased dry and wet weight of stem 17 and 25 percent respectively comparing with without nitrogen application under sever water deficit condition. Application of 409 mm irrigation and 100 kg N per ha is suitable for condition that enough irrigation waterexists. However in water deficit condition, the application of 150 kg nitrogen per ha could be recommended.
In general, to achieve the optimum growth of garlic in similar soils and climatic conditions, application of 100 kg nitrogen per ha would be recommended under normal irrigation conditions while at water deficit conditions the application150 kg nitrogen per ha could be recommended that had only two percent difference with the mentioned treatment and this difference was not significant.