Smart Control of Water Flow and Depth Within Rice Field for Improving Irrigation Management and Mitigating Methane Emission

Refaie K.M 1 ., H.M. El Sharkawi 1 , A. A. Khalil 1 , T. F. Metwally 2 , S. M. Abolmaty 1 , B.A.A. Ali 1 and M. K. Hassanein 2 . 1. Central Laboratory for Agricultural Climate, Agricultural Research Center, P.O. Box 296 Imbaba 12411 Dokki, Giza, Egypt. 2. Rice Research and Training Center, Field Crop Research Institute, Agricultural Research Center,Giza, Egypt. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History

A two-year field experiments were carried out at the Experimental Farm of the Central Laboratory for Agricultural Climate, Agriculture Research Center, Egypt during 2015 and 2016 successive rice seasons. such investigation aimed to study the productivity and CH 4 emission capacity of two Egyptian rice varieties (Sakha101 and Sakha106) under different irrigation water depths (4, 8 and 12 cm) from the soil surface. Innovated siphon container were connected to a water valve to maintain the continually of the water head at the desired depths. The water depth treatments were laid out in a randomized complete block design with four replications for each variety in both seasons. A combined analysis was used between the two varieties in each season to interpret the data. Plant height cm, root length cm and chlorophyll SPAD at 30 and 55 days after transplanting, panicle length cm, number of tillers m -2 , number of grains panicle -1 , number of unfilled grains panicle -1 , 1000grain weight, grain yield t ha -1 , straw yield t ha -1 and harvest index were recorded. Methane fluxes were measured by using closed chamber method. Water depth affected significantly all studied characteristics. The maximum values of most of the studied characteristics were recorded at 8 cm water depth. On the other hand, the lowest values were observed at 12 cm water depth. CH 4 emission was dramatically reduced by decrease the water depth. There was significant correlation coefficient between methane emission and all studied agronomic characteristics except 1000-grain weight and harvest index. The methane emission from rice fields decreased significantly with the increase of plant growth and yield. Irrigation water depth at 8 cm seem to be the recommendable treatment to achieve the promising rice yield and methane mitigation value.

ISSN: 2320-5407
Int. J. Adv. Res. 5(1), 2904-2910 2905 irrigated rice. These rice areas require a large amount of irrigation water. Most of the rice farmers think that increasing water depth in their rice fields up to maximum level will reflect directly on rice grain yield irrespective to these hazardous side effect on environmental system. Talpur et al. (2013) reported that the maximum plant survival and tallest average plant height were recorded in 5 cm water depth compared to 10, 15 and 20 cm from cultivation till to mid stage of growth. The maximum water depth of 20 cm produced the shortest root, while 5 cm produced the longest root. The weight of 1000 grains has more affected by a deeper water depth as compared to shallower water depth but the total yield was opposite of these. It was observed that the number of grains loss due to excessive water depth has an adverse impact as compared to deficient water depths. Kima et al. (2014) indicated that water reductions at the vegetative stage delayed plant growth and affected grain filling rate and 1000-grain weight, but the recovery process induced by effective rainfall contribution was such that grain yield was not affected. In water scarcity context, applying 180% of soil saturation water seems suitable for increasing both rice production and irrigation water productivity in tropical climate conditions. They argue that, rather than the daily application of the small amount of water, saturated soil culture practice can be adopted in the specific agro-climatic zone by adjusting the irrigation water depth according to the irrigation intervals. Weekly application of a 3 cm water depth above soil surface can be recommended to farmers as an alternative to save irrigation water, time, energy, and increase outputs.
Methane is the second most important culprit of GHGs. Its emissions rose by about 40% from 1970, with an 85% increase from the combustion and use of fossil fuels. Agriculture, however, is the largest source of CH 4 emissions (Aulakh et al., 2001). Agricultural lands (used for agricultural production, managed grassland and permanent crops including agro-forestry and bio-energy crops) occupy about 40-50% of the Earth's land surface and release a significant amount of CO 2 , CH 4 , and N 2 O in atmosphere (Cole et al., 1997;IPCC, 2001and Paustian et al., 2004. Agriculture accounts for 10-12% of total global anthropogenic emissions of GHGs. This sector contributes about 47% and 58% of total anthropogenic emissions of CH 4 and N 2 O, respectively, with a wide range of uncertainty in the estimates of both the agricultural contribution and the anthropogenic total. Globally, agricultural CH 4 emission increased by 17% from 1990 to 2005, an average annual emission increase of 58 Mt CO 2 -eq yr -1 . Methane is produced when organic materials are decomposed anarobically. Water management practices have a strong influence on the processes involved in CH 4 emission from rice paddy fields. The presence of surface standing water is essential for the development of the anaerobic conditions in paddy soil by limiting the transport of atmospheric oxygen into the soil. In the Japanese rice cultivation; short-term floodwater drainage is commonly performed to aerate the paddy soil during the flooding period to prevent some negative effects of soil reduction on the growth of rice plant. Yagi and Minami (1990) detected a decrease in CH 4 emission rates during the period of midsummer drainage in Japanese rice paddy fields. Sass et al. (1992) demonstrated that CH 4 emission rates varied markedly with water regime, showing the lowest emission with multiple intermittent draining practices.
Zheng Bing-song, et al. (2006) reported that water deficiency is one of the primary yield-limiting factors in rice. Different rice genotypes showed different relative root parameters and relative nutrition content and water use efficiency under different water supply conditions (0 cm (submerged), 40 cm and 80 cm groundwater levels below the soil surface). The length and number of adventitious root are more important than seminal root length in water and nutrition uptake, and maintaining the grain yield and increasing dry matter, but the adventitious root number could not be served as an index for screening drought-resistant genotypes.
the main target of this work was to throw light on the role of irrigation water depth in rice field in mitigating methane emission in relation to growth, yield and yield components of rice crop.

Materials and Methods:-
Two years field experiment were carried out at the Experimental Farm of the Central Laboratory for Agricultural Climate, Agriculture Research Center, Egypt during 2015 and 2016 successive rice seasons. such experments were conducted to study the performance of two rice varieties (Sakha101 and Sakha106) under different irrigation water depths (4, 8 and 12 cm) from the soil surface. Irrigation water depths were kept using a smart control flow system (Fig. 1). Innovated siphon container were connected to a water valve and flow meter to maintain the continually of the water head at the desired depths under low pressure. The depths of water were controlled in each replicate through a perpendicular wires installed over the container of the siphon that poise by water balance. The water depth treatments were laid out in a randomized complete block design with four replications for each variety in both 2906 seasons. A combined analysis was used between the two varieties in each season to interpret the data. Correlation analysis was done by Pearson correlation coefficient method using the PC software SPSS Ver. 14. Seeds of the two varieties were soaked in water for 24 hours before sowing the nursery, then drained and incubated for 48 hours to hasten the germination. Pre-germinated seeds were uniformly broadcasted in the nurseries on 1 st and 3 rd of May in the two seasons, respectively. The permanent field was well prepared. Seedlings were carefully pulled form nursery after 25 days from sowing and transferred to the permanent field. Seedlings were handly transplanted in hills at the rate of 2-3 seedlings hill -1 and at the spacing of 20x20 cm between hills and rows. The plot size was 12 m 2 (2×6m). The all recommended cultural practices were applied for each variety. The studied growth characteristics were plant height (cm), root length (cm) and chlorophyll SPAD at 30 and 55 days after transplanting. Chlorophyll meter (model SPAD-502, MINOLTA, Japan) was used to determine the leaves chlorophyll content. The studied yield attributes traits were panicle length (cm), number of tillers m -2 , number of grains panicle -1 , number of unfilled grain panicle -1 , 1000-grain (g) weight, grain yield (t ha -1 ), straw yield (t ha -1 )and harvest index. Methane fluxes were measured by using closed chamber method. This measurement system was a modified version of the system originally described by Schutz et al.,1990. For the measurements, an air-tight acrylic glass chamber (15 cm in diameter and 1 m high) was carefully placed on the wood frame. One day before the recording of CH 4 , this wooden frame was placed at a randomly selected measuring site inside each plot. In each replicate, two chambers were inserted into the soil after flooding. The closure period was 1 h, during which two gas samples from inside the chambers were taken at 30 min intervals. Methane emission was measured at 8.00-10.00 am and at 15.00-17.00 pm, and the average value was used as the flux value for the day. Methane emission rates were recorded after 65 days of transplanting. Average air temperature (32°C) was recorded just before measuring the CH 4 emissions. Methane concentration in the sampled air was measured using a FID-GC (Shimadzu GC-14APF). Statistical analysis: The analysis of variance by means of "MSTATC" computer software package was carried out as combined analysis for the two varieties in each season according to Gomez and Gomez (1984).   In both seasons the length of rice roots showed significant differences with the water depths for both varieties (Tables 1 and 2 Datta (1981) emphasized that extremely deep water resulted in poor growth and yield. Roots were deeper in Sakha106 compared to Sakha101. Ascha et al. (2005) reported that plant becomes adapted to water deficiency through the possession of pronounced root system, which maximizes water capture and allows access to water at depth.
Application of various water depths in rice varieties showed a significant impact on leave chlorophyll content at 30 and 55 DAT as shown in Tables 1 and 2. Chlorophyll content at 30 DAT decreased gradually by increasing water depth from 5 up to 12 cm while, at 55 DAT the highest values were recorded at 8 cm water depth for both varieties. Chlorophyll content in Sakha 106 was slightly higher than those in Sakha101. Kima et al. (2014) found a similar trend and reported that under shallow water depth, plants reduced evapotranspiration that led photosynthesis decrease which in turn induced chlorophyll decrease.
In both seasons panicle length was affected significantly by different treatments ( Table 3). The longest panicles were observed when 4 cm water depth was applied either to Sakha101 or to Sakha106. Number of tillers per meter square was affected significantly by different water depth. Application of 8 cm irrigation water depth to Sakha101 recorded the highest number of tillers followed by the same water depth to Sakha106. Data in Table 3 showed also that water depth treatments affected significantly number of grain per panicle. Sakha101 at 8 cm water depth produced the highest number of grains per panicle followed by Sakha106 at the same depth. All above mention results were fact in either 2015 or 2016 experimental seasons. Similar trend was found by Talpur et al. (2013) and Kima et al. (2014).

Table 3. Panicle length (cm), number of tillers m -2 , number of grains/panicle and number of unfilled grains of the two rice varieties as affected by water depth treatments.
Treatments  (Table 3). Unfilled grains per panicle increased significantly with the increase in water depth for both varieties. The highest number of unfilled grains per panicle was measured at 12 cm water depth by Sakha101 rice variety followed by 8 and 4 cm by Sakha101. Meanwhile 1000-grain weight was affected significantly by water depth treatments (Table 4). Shallow water depth recorded highest values of 1000-grain weight. these results are fairly true in both the two seasons. Water depth affected significantly grain yield as presented in Table 4. The maximum values of grain yield were recorded by Sakha106 at 8 cm water depth. On the other hand, the lowest values of grain yield were observed by Sakha101 at 12 cm water depth. This is agreed with results obtained by Talpur et al. (2013) and Kima et al. (2014). Reduction in rice grain yield under 12cm depth treatment in both cultivars and in both seasons could be attributed to the reduction in number of tiller/m2, number of grains/ panicle and the increase in number of unfilled grains/panicle (Table 3) as well as the decrease in 1000-grain weight (Table 4). It can be assumed that the increase in water depth up to 12cm caused a bad aeration conditions around root and shoots of rice plant. Adequate oxygen supplies are necessary to respiration and other essential physiological processes of plant and consequently rice yield and its components of deep water level plots was decreased. Sahka106 produced higher grain yield than Sakha101. This might be due to the substantial yield losses by the large percentage of unfilled grains in Sakha101. Table 4. Thousand-grain weight (g), grain yield( t ha -1 ), straw yield ( t ha -1 ) and harvest index of the two rice varieties as affected by water depth treatments. Straw yield was affected significantly by water depth treatments (Table 4). Sakah106 at 8 cm water depth produced the highest value of straw yield. Harvest index showed significant difference with the water depths used in this study. The maximum values of harvest index were measured at 8 cm water depth whatever the variety.
Methane emission values obtained under the three water depths in the two experimental seasons are presented in table 5. Methane flux ranged from 0.288-0.597 and 0.278-0.566 mg m -2 hr -1 in both seasons respectively. There was a significant differences in CH 4 emission values among water depths. Available results in Table 5 clear that methane emission values were increased as irrigation water depth increased. increasing water depth from 4cm to 8cm and 12cm level increase CH 4 emission from Sakha 101 plots by 28.6 and 107.1 % respectively in 1st season and by 9.4 and 89.6% in the second one. Analogous values for Sakha 106 cultivars plots were 17.9 and 89.37 % in 2015 and 14,9 and 92.6 % in 2016 season, respectively. There for, management of irrigation water level in rice fields can be used as a smart tool for mitigating CH 4 emission in irrigated paddy field. Variation in CH 4 emission rate was also 2909 detected between the two investigated cultivars. Sakha 101 plots emitted more CH 4 ( 2.448 mg/m 2 /ha) as a total of the two seasons comparing with 2.307 mg/m 2 /ha for Sakha 106. Our data showed, CH 4 emission was dramatically reduced by decrease the water depth wherein, suitable water management practice can be established by assessing appropriate controlling the irrigation and flow rate to reduce CH 4 emission with any adverse effects on yield and soil fertility. These results confirm the phenomena that the aeration under 3 cm water depthin paddy soil led to decrease methane emission. However, under 12 cm of water depth, reduction condition was prevailing which provide a good condition to emit more methane than under oxidized zone. Genotypic differences in the emission of methane from rice paddies are reported also by Nirmali Gogoi et al. (2008). Regarding the correlation coefficient between methane emission and the studied agronomic characteristics, data in Table 6 revealed that there was significant correlation coefficient between methane emission and all studied agronomic characteristics except 1000-grain weight and harvest index. The correlation coefficient was highly significant and positive between methane emission and number of unfilled grain per panicle. On other hand, it was highly significant and negative between methane emission and each of chlorophyll content SPAD at 30 DAT, root length at 55 DAT, chlorophyll content SPAD at 55 DAT, panicle length, number of tillers per m 2 and straw yield. The correlation coefficient was significant and negative between methane emission and each of plant height at 30 and 55 DAT, root length at 30 DAT, number of grains per panicle and grain yield. These results demonstrated that methane emission from rice fields decreased significantly with the increase in the rice plant growth and yield.

Conclusion:-
Rice yield and CH 4 emission were positively affected significantly by irrigation water depth. Methane emission was dramatically reduced by decrease the water depth. Irrigation water depth at 8cm seem to be recommendable treatment to obtain the promising rice yield and CH 4 mitigation value. There was significant correlation coefficient