Effects of Rotation Irrigation and Planting Distance on Rice Growth Indexes under Gilan Province Climate Conditions

Rice is a global important food and in Asia alone is the source of food for 3.5 billion people. Such demand for rice imposes a plan to find new technology and approaches to replace old production methods. About 75% of global rice production is practiced on low lands. At field scale, rice compared to other plants receive two or three times more water and based on some calculations, about 34-43 percentage of global irrigation water or 24-30 percentage of drinking water consumed by rice plant. In this situation, the most important challenge with regard to rice production, water storage, increased water productivity and rice production is less than water. Recently, rice production systems such as rice alternate irrigation, where less water can be produced, has been considered as rice increasing demand for water in industry and cities have imposed the reduction of water consumption for agriculture. Rice is one of the most sensitive plants against water scarcity as a floodplain plant and has the most need for water in the cereals. Rice has the highest crop area than other irrigated plants.

This experiment was conducted as split-plot, using irrigation as main-plot at five levels (full irrigation, irrigation at ever 5, 8, 10, and 15 days), and planting distance as sub-plot at four levels (20x20, 25x25, 30x15, and 30x20 cm) within format of random complete block design with three replications. The study was performed in two years (2016-17, 2017-18) in national rice research center. Soil samples were taken to determine the soil tissue, soil water holding capacity, and some chemical characters including EC, PH, and amount of Ca, Na, and Mg. Within firs 15 days after transplanting, the rotation irrigation was not employed so the plant be able to establish in the field. The plowing was performed in two times. The first plow in the late autumn and early winter and the second plow were perpendicular to the first plowing in the spring. Fertilization was done based on long term local practice. Transplanting was done in may, 15 and at this time transplants were 20-25 cm height carrying 4-5 leaves. All traits including stem and leaf dry matter, leaf area index (LAI), crop growth rate (CGR), net assimilation rate (NAR), leaf area ration (LAR), relative growth rate (RGR) and specific leaf area (SLA) were measured and calculated. SAS and SPSS software’s were used for analysis of variance. Excel software was used for drawing slices.

ANOVA results showed that interaction of irrigation and planting distance were significantly (P <= 0.01) affected leaf and stem dry matter, LDW, TDW and CGR Individual effects of each treatment significantly affected the LAI and NAR but did not affect LAR, LWR, RGR, and SLA. As light absorption i a limiting factor in crops production, then where is no other environmental stress, increasing light absorb will increase crop production. In contrast to other crops light capture competitions a major issue for rice. Increasing panting density, vegetative growth and LAI would be lower and as planting density decreases, due to availability more spaces, both vegetative growth ad LAI increased.

 In general, this study results showed that rotation irrigation significantly affected the rice growth indexes, and reduction levels of study traits depends on irrigation timing at growth stage. Planting distances showed that planting at 20x20 cm, provided the most optimum conditions for rice plants under different stress, the worst conditions resulted in 25x25 cm planting distance. At lower planting density, due to lower competition between plants till flowering time but after this stage, competition for photosynthetic materials increased among the seeds which can result in small dead seeds.