The Effect of Reduced application of Water and Nitrogen on Growth Management of mixed Turf-Grass

Introduction: Regular watering and application of nitrogenous fertilizers in turf-grasses is a conventional operation, especially in warm and dry or semi-dry climates, which arecommon in many parts of Iran. Nitrogen is a mobile nutrient in soil or substrates, especially in the form of nitrate. Nitrate leaching due to the regular watering has been reported in many sources. The managing nitrogen application can help to minimize the loss of this element regarding the ability of soil-plant system. Attempts have been made to control the growth of turf-grass using various types of chemicals, but similar to the concerns associated with the consumption of nitrogenous fertilizers, this is also concerned with environmental pollutions. Therefore, the growth of turf grasses can be controlled without using chemicals and by limiting the use of nitrogen and managing the irrigation.The purposes of this study were to limit the application of nitrogen in order to control vegetative growth of the turf grass and maintain its visual quality, and to manage irrigation in order to preserve this mobile element (nitrogen) near the root system and prevent its leaching. Materials and Methods:The effects of reduced water and nitrogen supply on the control of vegetative growth of turf grasses, commonly named as sport turf,were evaluated.Therefore, an experiment was designed in a factorial based on randomized complete block design with three replications. Mixed seeds of sport turf grass were planted with the density of 40 g m-2in boxes, which placed atthe depth of30 cm and leveled with sandy loam soil in mid-spring. Nitrogen was applied as ammonium nitrate via fertigation in five levels of 0, 0.5, 1, 1.5 and 2 mg m-2 month-1, andirrigation treatments performed at four levels of 100%, 80%, 60 % and 40% of field capacity. Watering was done every two days for 5 months during the warm season of the year after the first mowing on June 2013. Some traits such as plant height, fresh and dry weight, density, color and quality, and chlorophyll and proline contents were evaluated during growth period or at the end of the experiment.The data were subjected toananalysis of variance (SAS, 1996),and differences among the treatments were compared using Duncan’s multiple range test at 95% probability level. Results and Discussion: The results showed that decreasein nitrogen level up to 0.5 gdid not significantly change density index,,whilethe index showed a significant reduction in treatment containing zero nitrogen application and the lowest irrigation regime (40% of the field capacity).Quality and color of the turf grass had no significant correlation with nitrogen treatment, while the factor was significantly decreased when irrigation regime of 40% of the field capacity was applied. It was determined that although color of the turf grass was greener with lower levels of water,a good color was found with high level of non-organic fertilizer at the time that the amount of nitrogen leaching was also limited. Therefore, regardless of the different nitrogen levels applied, quality and color indiceswerethe lowest when irrigation at 40% of field capacity was applied. Limiting the level of nitrogen up to 0.5 gramand irrigation up to 60% of field capacity was desirable to control and reduce the height of turf grass. Reduction in water level up to 80% of field capacity caused no significant changes in fresh weight, but a significant decreasewas resulted with the reduction of water consumption up to 60% of field capacity. The maximum fresh weight was found with 1.5 grams nitrogen. However, reducing nitrogen level upto 0.5 gramdid not bring about significant changes in this trait. Dry weight also followed the same pattern as fresh weight. Although reduction in the level of applied nitrogen did not reduce the height, it caused a significant reduction in fresh and dry weight of the turf grass. The highest chlorophyll content was found when 2 grams of nitrogen and irrigation regime of 40% of field capacity were used. Regardless of the nitrogen level, the highest chlorophyll content was found in irrigation of 40% of field capacity,while the lowest amount was observed in the treatment containing irrigation at100 and 80% of field capacity. Plants were dark green in 40% of field capacity. Proline content showedincreasealong with the decrease inirrigation as well as nitrogen levels. Conclusion:Plant height, fresh and dry weight, chlorophyll and proline contents were significantly affected by limiting the use of nitrogen and water, but density and quality indices were not significantly influenced. Regardless of the nitrogen levels applied, quality and color traits were the lowest only in irrigation regime of 40% of field capacity. Therefore, it was concluded that reduction of nitrogen supply to 1 mg m-2 month-1and irrigation regime up to 60% of field capacity could result in thereduction ofvegetative growth of turf grass, while quality traits were not affected negatively.