Evaluation of Agronomic Traits and Chlorophyll Fluorescence Parameters in Rice Genotypes under Flooding and Underneath Irrigation

Rice is the second most important cereal in the world, and it has the highest water requirement among grain crops. Applying different irrigation methods is necessary in order to determine the best method to achieve maximum yield. Therefore, in this research, the effects of flooding and underneath conditions on chlorophyll fluorescence and agronomic traits of rice have been investigated.

This experiment was conducted in 2017 at the research farm of Gonbad-e-Kavos University. Two experiments were designed for agronomic and photosynthetic traits in flooding and underneath irrigation conditions in order to investigate two genotypes 87.110 (line selected from mass populations) and AE121 (an aerobic line). The first experiment was combined in two separate experiments (flooding and underneath) and 18 replicates. Given the uniformity of the ground, the base design was considered as CRD. The second experiment was conducted to compare the performance of irrigation methods and cultivars with the first experiment in a land with a greater area (100 m2) in three replications. The germinated seeds were transplanted to nursery on 12 May. During the stage, care was taken in the nursery, such as irrigation, fertilizer, aeration and weeding. In this design, the distance between the plots was one meter and the distance between the blocks was two meters, so that the adjacent plots had no effect on the moisture content. Transplantation was carried out after 3-4 leaves with the selection of healthy and uniform seedlings on June 20th by 20 × 20 cm spacing and three seedlings. In the method of flood irrigation, the land was prepared as usual. To prepare underneath irrigation treatments, each plot was removed to a depth of 40 cm and porous clay capsules were used. The irrigation system consisted of three main pipelines (the number of irrigation treatments), one valve head and one volume meter installed on each main pipe. The main tubes were spread along the floor and the water needed for each treatment was taken using 16 mm tubes at the beginning of each plot. By placing the pressure gauge at the beginning of the pipelines, the system pressure was modulated in the underwater irrigation system. At the end, the agronomic traits and chlorophyll fluorescence parameters were measured.

The results showed that in the first experiment, the maximum water use efficiency was related to underneath conditions. This result was also repeated in the second experiment. In terms of flooding, the amount of water consumed was 6540 units higher than underneath conditions. The amount of water consumed in flooding irrigation was 864.71 and 1267.34 units more than underneath irrigation in the first and second experiment, respectively. Differences between irrigation treatments and cultivars were significant in most agronomic traits except length, width and area of flag leaf, yield, total weight, number of infertile panicle and main panicle length. Also, the effect of cultivar and irrigation methods were significant on chlorophyll fluorescence traits except F' and Y (II).

The results indicated that most of the studied traits in the floodwater irrigation conditions were better than the underneath irrigation. The yield was also higher in underneath conditions than in the case of flooding conditions. The results of analysis of variance of both experiment in the studied traits showed that there is a significant difference between flooding conditions and underneath irrigation and also between genotypes under irrigation conditions. The mean comparison in underneath conditions also showed that the AE121 genotype has a higher potential under both conditions and can be recommended for high yielding.