Eco. Env. & Cons. 20 (3) : 2014; pp. (1247-1251) Copyright@ EM International ISSN 0971 765X Simulation of rice water demand under conventional and modified water management practices using DNDC model in Bhavanisagar basin J*. Kavitha Mary, K. Senthilraja, R. Anbhazhagan and A.P. Ramaraj Agro Climate Research Centre, Tamil Nadu Agricultural University, Coimbatore 641 003, India (Received 20 Deecember, 2013; accepted 25 January, 2014) ABSTRACT Rice-DNDC (DeNitrification Decomposition) model is mainly used to calculate methane emission from rice ecosystem. It also calculates the water requirement and uptake by plants. The present study was carried out to simulate rice water demand for the year 2013 and 2014 under different management practices (conventional and 10 days Mid Season drainage in the 45 th DAT and 65 th DAT). For this study simulated weather parameters for the year 2013 and 2014, soil properties and farming practices for Bhavanisagar basin is given as input for Rice-DNDC model. The results show that precipitation will be calculated as 891.4 mm for 2013 and 724.2 mm for 2014. Irrigation water requirement for conventional cultivation is 2245 mm water and 1945 mm for mid-season drainage for three consecutive paddy crops. Mid-season drainage will reduce the water requirement and methane emission from rice ecosystem because decomposable organic matter was decomposed under aerobic conditions. In the present investigation water demand is similar for both conventional and modified irrigation method (768.66 mm for 2013 and 888.6 mm for 2014). Water uptake is reduced in mid-season drainage (656.05 mm, 715.88 mm) than conventional (707.51 mm, 826.55 mm) in 2013 and 2014 respectively. Water stress is negligible in both conventional and mid-season drainage (2.95 and 2.96 mm respectively). Hence mid-season drainage is a water saving method which also reduces the methane emission from paddy ecosystem. Key words : DNDC, Rice-water demand, Simulation Introduction It is well known that the yield of paddy rice varieties largely depends on soil water. Hasegawa and Nakayama (1959) reported that the yield of a paddy rice variety decreased by 22% when it was grown under soil water potential greater than -50kPa because of a poor growth at the panicle initiation stage. Bouman and Tuong (2001) also reported that rice yields were reduced by 10-40% when soil water potential in the root zone reached -10 to -30kPa. However, fresh water for irrigation is becoming scarce because of increasing competition from urban, industrial, and environmental factors. The traditional irrigation practices for paddy keep standing water/saturated soil moisture throughout the rice growth season. Traditional water consumption for rice cultivation in paddy fields was 9,795.2 m 3 /ha, with 8,279.85 m 3 /ha of this being irrigation water. The average evaporation rate was calculated as 2.07 mm/d, and the leakage rate was 1.89 mm/d. Resulting water productivity was 0.82 kg/m 3, and the irrigation water use efficiency was 0.97 kg/m 3 (Zheng Jia-guo, 2004). Water resource limitations threaten the sustainability of irrigated rice systems in many countries. Rice offers great *Corresponding author s email: kavitha_jackson@yahoo.co.in
1248 Eco. Env. & Cons. 20 (3) : 2014 potential for saving irrigation water because it s physiological water requirement (4500 m 3 water/ha) is much less than what is currently considered to be needed and what is currently applied. Many studies proved that the mid-season drainage, entailing purposeful drainage and subsequent field drying for around ten days at the later tillering stage could increase the productive tillering volume and rice yields (Mao, 1996; Peng et al., 1998; Li et al., 1997) and the soil drying after the milk ripening stage will prevent the delayed ripening. Therefore, it is very important to understand the change regulation of eco-environment of paddy field with the different soil moisture conditions. DNDC is a comprehensive biogeochemistry model that simulates crop growth and soil C and N dynamics based on input data on soil properties, climate, and farming practices (Li et al., 1994). The DNDC model was originally developed for predicting C-sequestration and trace gas emissions for nonflooded agricultural lands (Li et al., 1992). It also assesses the water requirement for each crop. With this information in background current study was taken to simulate water requirement for the future 2013 and 2014 for Bhavanisagar basin with the modified water saving practices. Materials and Methods The present investigation was carried out for Bhavanisagar basin using simulated weather parameters for the year 2013-2014. Comprehensive biogeochemistry model, DNDC, developed by Li et al. (1992) was used to seek the best water management practices for paddy cultivation. In this study the DNDC model (version 9.3; http:// www.dndc.sr.unh.edu/) was applied. Future weather projections for the year 2013 and 2014 were extracted from the website http:// gismap.ciat.cgiar.org/marksimgcm/ using ECHam5 model with A1B scenario. The reliability of the projected climate data is cross checked with past ten years data. Cropping sequence was taken for two consecutive years. Input parameters such as Climate (Daily air temperature and precipitation), Atmospheric N deposition, Soil Bulk density, Texture (clay fraction), Total organic C content, ph and crop Management practices (Tillage, Irrigation, Fertilization, Manure amendment Grazing) were given. Two water management practices, continuous flooding and continuous flooding with midterm drainage on 45 th to 55 th DAT and 65 th to 75 th DAT were examined for its water use efficiency. Results and Discussion Weather analysis Observed weather data was analyzed from 2002 to 2012 along with simulated data of 2013 and 2014. There is no considerable change in the maximum temperature. For the past ten years the maximum temperature ranged between 33-35 0 C. Projected temperature also falls within this limit (35 0 C). Minimum temperature was ranging from 19-22 0 C in the past and increment of 2 0 C in the projected data (24.18 0 C). Precipitation was higher in the starting (921 mm) and decreased from 2008 onwards. Projected precipitation also fallows the same trend (739 mm and 724 mm) (Fig. 1). Fig. 1. Temperature and precipitation trend in the study area
MARY ET AL 1249 Simulation of crop water requirement For simulating crop water requirement for the year 2013-2014 cropping sequence is taken for two consecutive years. Irrigation schedule is modified for mid-season drainage. Mid-season drainage is given for ten days from 45 th to 55 th DAT and 65 th to 75 th DAT. Precipitation will be calculated as 739.6 mm for 2013 and 724.2 mm for 2014. For conventional method 2200 mm water will be irrigated and for mid-season drainage1850 mm water will be irrigated. Number of irrigation is reduced in mid-season drainage compared to conventional. 38 irrigations will be scheduled for mid-seasonal drainage with precipitation and 45 irrigations will be scheduled for conventional. This method may reduce the amount of irrigated water and also) decreases CH 4 emission, especially in lowland rice cultivation, because more decomposable organic matter was decomposed under aerobic conditions. Water demand for the year 2013 will be estimated. 786.66 mm of water will be required for conventional method and 769.11 mm for mid-season DNDC run for Bhavanisagar (mid-season drainage) drainage. Water uptake is higher in conventional (707.51 mm) than mid-season drainage (656.05mm). Hence nearly 50 mm of water will be saved through modified irrigation method (Table 1). Similarly for 2014 water demand and water uptake is calculated. Water demand is similar for conventional and midseason drainage (888.6 mm) and water uptake is higher in conventional (826.55 mm) than mid-season drainage (715.88 mm). Nearly 100 mm of water will be saved for the year 2014 (Table 2). Water stress is negligible amount in both the years irrespective of the irrigation method. Water use efficiency Water use efficiency of the two irrigation method conventional and mid-season drainage (45 th to 55 th DAT and 65 th to 75 th DAT) is assessed for Bhavanisagar basin using the DNDC model. Conventional method requires 2200 mm water for irrigation but mid-season drainage requires only 1850 mm for three consecutive paddy crops. Potential evopotranspiration will be 1706.97 mm for the year DNDC run for Bhavanisagar ( conventional) Fig. 2. Water budgeting under conventional and mid-season drainage
1250 Eco. Env. & Cons. 20 (3) : 2014 Table 1.Water budget for the year 2013 under conventional and modified water management practices Crop Water demand (mm) Water uptake (mm) Water stress (mm) Conventional Mid-Season Conventional Mid-Season Conventional Mid-Season drainage drainage drainage Paddy 1 309.37 309.82 272.78 307.82 0.96 0.97 Paddy 2 210.72 210.72 204.08 163.75 0.99 0.99 Paddy 3 248.57 248.57 230.65 184.48 1.00 1.00 Total 768.66 769.11 707.51 656.05 2.95 2.96 Table 2. Water budget for the year 2014 under conventional and modified water management practices Crop Water demand (mm) Water uptake (mm) Water stress(mm) Conventional Mid-Season Conventional Mid-Season Conventional Mid-Season drainage drainage drainage Paddy 1 319.65 319.65 292.14 295.91 0.99 0.99 Paddy 2 292.35 292.35 270.18 186.78 0.99 0.99 Paddy 3 276.60 276.60 264.23 233.19 1.00 1.00 Total 888.6 888.6 826.55 715.88 2.98 2.98 Table 3. Water use efficiency in conventional and Mid-Season drainage Factors mm water/year 2013 2014 Conventional Mid-Season drainage Conventional Mid-Season drainage Precipitation 739.60 739.60 724.20 724.20 Irrigation 2200.00 1850.00 2200.00 1850.00 PET 1706.97 1706.96 1710.73 1710.73 Transpiration 876.90 877.09 879.86 880.01 Soil evaporation 468.83 432.29 468.97 435.33 Run off 722.25 722.25 707.29 707.29 Leaching 673.88 413.32 720.21 463.96 2013 and 1710.73 mm for the year 2014. Transpiration, respiration and water conveyance losses such as runoff and leaching are similar for both conventional and mid-season drainage. But leaching is reduced in mid-season drainage (413.32) than conventional (673.88 mm) in 2013. Similarly in 2014 leaching lose is 463.96 mm for mid-season drainage and 720.21 mm for conventional method (Table 3). Conclusion Water-saving rice cultivation methods that can offer greater water productivity are urgently needed to keep up with future food demands, while they are at the same time important for ensuring the future viability of rice production systems. The DNDC model simulated that the continuous flooding irrigation uptake more irrigation water than the intermittent irrigations (mid-season drainage). Longer the drainage period for 4-day and 3-day flooding treatments seemed to produce more rice yield by the DNDC model. Hence mid-season drainage is an alternate method for the reduction of irrigated water. References Bouman, B.A.M and Tuong, T.P. 2001. Field water management to save water and increase its productivity in irrigated lowland rice. Agric. Water Manag., 49: 11-30. Hasegawa, S. and Nakayama, K. 1959. Comparison of the growth and yield of paddy- and upland-rice grown under paddy- and upland-field conditions. Jpn. J. Crop Sci., 27: 354-356 (in Japanese with English summary). Li, C., Frolking, S. and Harriss, R.C. 1994. Modeling car-
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