Effect of Irrigation Interval and Nitrogen Amount on Water Requirement, and growth of Rice (Oryza sative L.) Hashemi Cultivar under Gilan Climate Conditions

Rice (Oryza sative L.) is an essential crop among cereals and shared a significant component in the global human diet, especially in developing countries. About 80% of water consumption in Asia is for the agriculture sector, and half of it would be used for rice production. Rice needs roughly 8000 to 1000 m3 of water per hectare and 1Kg of its dry matter needs to 700 liters of water. Rice farmers tend to keep their farms flooded continuously to make sure the product is more productive by too much water storage and, in this way, prevent against weeds. Up to the year 2050, rice production should increase by 50%, which requires improved cultivars and enhanced field management. For achieving high crop yield, applying fertilizers to maintain high soil fertility is quite necessary. Nitrogen is one of the main crop’s nutrient requirements and is a limiting factor for rice production. Nitrogen fertilizer affects the accumulation of dry matter and its allocation in different parts of the plants. The difference in the accumulation of dry matter in response to nitrogen arises from the difference in the amount of active radiation received by photosynthesis of vegetative canopy and plant efficiency in the use of solar radiation. Nitrogen deficiency reduces leaf growth, and leaves become less colorful since the amount of chlorophyll in the leaves decreases, accelerates aging leaves, therefore, reduce the amount of solar radiation, and it reduces the accumulation of dry matter in plants, finally. Nitrogen, plays an important and direct role in the development of grains by increasing the level of enzymes and enzyme activity, and this increases the transfer and processing of sucrose to seeds. Many studies have shown that increasing nitrogen up to a threshold has highly increased rice grain yield. Growth analysis indices are essential to realize how the crop yield may change in response to management and environmental factors. Therefore the application of appropriate management factors that have a positive effect on growth indices can enhance grain yield.

This study was conducted as split-plot based on a randomized complete block design in Rice Research Center of Rasht in 2014-2015 and 2015-2016. Irrigation with five levels (daily irrigation, rotational irrigation with 5, 8, 10, and 15 days interval) as main plot and nitrogen at six levels (0.0, 30, 45, 60, 75, and 90 kg.ha-1) as subplot were considered in this experiment. At flowering and harvest leaf and dry stem matter was measured. Then leaf area index (LAI), Crop Growth Rate (CGR), Net Assimilation Rate (NAR), Leaf Area Ratio (LAR), Relative Growth Rate (RGR) and Specific Leaf Area (SLA) were calculated.

Our results showed that the interaction of irrigation and nitrogen significantly (P≤0.01) affects stem and leaf dry matter, LAI, and NAR. Irrigation was significantly (P≤0.01) effective on CGR. Among irrigation levels, daily irrigation resulted in the highest LAI and NAR. Our results indicated that daily and every five days irrigation and considering almost no difference between 75 and 90 kg.ha-1 nitrogen, then 75 kg.ha-1 urea can be suggested as the optimum fertilization value. However, at higher irrigation intervals, 90 kg.ha-1 nitrogen would be recommended. Daily irrigation and 90 kg.ha-1nitrogen showed the highest water consumption (6663 m3.ha-1), but 15 days irrigation interval and 0.0 kg.ha-1nitrogen showed the lowest water consumption (4691 m3.ha-1). It seems that low rate release nitrogen fertilizers, along with suitable irrigation practice, would be the optimum management to achieve high yield and lowest possible irrigation water consumption.

The results of this study showed that applying nitrogen and irrigation increased LAI and crop productivity indices, which resulted in higher biomass yield production. Among irrigation levels, daily irrigation resulted in the highest LAI and CGR. Under daily irrigation and five days of interval irrigation, the application of 75 kg.ha-1 nitrogen can be recommended. Although there was not a significant difference between 70 and 95 kg.ha-1 nitroge, but due to environmental concerns, 75 kg.ha-1was recommended.