عنوان مقاله [English]
Water and nitrogen fertilizer are the most important agricultural inputs in the production of tea leaves and shoots as yield. In some months (mid-June to early September), the amount of rainfall is less than the water requirement of tea plants and the amount and quality of the product due to water shortage stress is greatly reduced, which threatens the livelihood of farmers and the region's economy. Therefore, supplying the required water of the tea plant by using supplementary irrigation and correct principles of operation is the most important issue in increasing the quantity, quality and marketability of the tea produced and its economic efficiency. The use of conventional fertilizer application in the region, ie fertilizing mixed with soil in rainfed (without irrigation) and irrigated (sprinkler irrigation) fields had high losses and low efficiency. Reports show that more than 60% of tea plantations in Guilan and Mazandaran provinces are located in highlands and sloplands regions. Currently, sprinkler irrigation methods are used to irrigate less than 5% of the total tea growing regions (about 20,000 ha), while production in other regions is entirely dependent on precipitation. Technical limitations and restrictions related to the design and implementation of sprinkler irrigation methods in these regions are the main reasons for the underdevelopment of irrigated lands in tea growing regions. This issue and the lack of access to reliable water resources in these regions, highlights the importance of using drip irrigation in tea plantations. Therefore, the main challenge in this situation is the implementation and development of effective and low-cost irrigation methods that have high water productivity and are cost-effective for farmers.
In order to optimize water and fertilizer use in drip irrigation system in tea fields, a field experiment was conducted in 2017-2018 in tea plantation in Bazkiagoorab region, Lahijan (Guilan province). The experiment was conducted as split plots in a randomized complete block design with two factors of irrigation water and nitrogen fertilizer in three replications. Fertilizer was considered as main factor in four levels of 0, 100, 150, 200 kg N ha-1 (N0 to N3) and irrigation as a sub-factor in five levels of 0, 25, 50, 75 and 100 water requirement percentage (I0 to I4). In the irrigation system of this research, on-line drippers (surface drip irrigation) of Netafim company with design flow rate of 4 L hr-1 were used. Sub-pipes (laterals) approximately 5 m long were placed in the middle of every two rows of tea plants throughout the experimental plot (except plots without irrigation). Seven drippers with a distance of 0.7 m (one dripper per plant) were installed on 16 mm laterals. Drip irrigation scheduling in water stress period was conducted twice a week based on soil moisture monitoring and fertilization (nitrogen) program once a week during growth period by fertigation at plant root depth.
The maximum yield average (2581 kg ha-1 of made tea) and WP(I+P) (0.685 kg ha-1 m-3) with average water use of 3845 m3 and 150 kg N ha-1 was obtained during the growth period. The average water consumption of deficit irrigation levels I3, I2 and I1 was estimated to be 3380, 2917 and 2454 m-3, respectively. The biennial average of the highest yield of made tea for irrigation treatments I3 to I1 was 2640, 1449 and 1225 kg ha-1, respectively. At all levels of deficit irrigation of the experimental years, increasing the amount of nitrogen fertilizer increased water productivity, so that the productivity values related to deficit irrigation levels of 75% of water requirement (I3) were higher than the other two irrigation levels (50% and 25%). The highest water productivity for deficit irrigation levels I3, I2 and I1 was related to the use of 150 kg of nitrogen fertilizer equal to 0.625, 0.615 and 0.555 kg m-3, respectively.
Top dressing of 100 kg N ha-1 in rain-fed/no-irrigation conditions (192.7 mm of effective rainfall) resulted in 803 kg of made tea with rain water productivity of 0.42 kg ha-1 m-3. Due to the increase in yield (300%) and water productivity (60%) resulting from the application of drip irrigation fertilizer system compared to rainfed conditions, the application of this irrigation method to produce tea economically with less water and fertilizer consumption in tea growing regions, especially sloplands and highlands are recommended. In general, for more than 8000 kg of green tea leaves per hectare, application of 150 kg of nitrogen fertilizer and lower yield, application of 100 to 120 kg of nitrogen fertilizer as a solution in drip irrigation system (fertigation) is recommended