APPLICATIONS OF AN OPERATIONAL COMPUTER PROGRAM FOR IRRIGATION PLANNING AND MANAGEMENT IN ROMANIA

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1 APPLICATIONS OF AN OPERATIONAL COMPUTER PROGRAM FOR IRRIGATION PLANNING AND MANAGEMENT IN ROMANIA AdrianaCornelia Marica, Petruta Tuinea, Jozsef Urban National Institute of Meteorology and Hydrology, Sos. BucurestiPloiesti 97, Bucharest 71552, Romania Phone: , Fax: amarica@meteo.inmh.ro Abstract: Over the last decade, different regions of Romania were facing severe and prolonged droughts, where soil moisture deficits during the vegetation season frequently affected the crop growth, development and yields formation. The aim of this paper is to evaluate the soil moisture dynamics and soil water deficits at the rooting depth of the maize crop by using CropWat model, in order to provide information necessary in taking decisions on irrigation management. The model, that calculates evapotranspiration and crop water requirements, allows the development of recommendations for improved irrigation practices, the planning of irrigation schedules under varying water supply conditions, and the assessment of production under rainfed conditions or deficit irrigation. For the purpose of this paper, the model was run for the specific weather conditions of the year 2, at two sites located in the south part of Romania, one of the most sensitive zone to drought. Simulation results analysis suggests that in these areas, where the maize water requirements exceeds the water supply, by application of adequate irrigation scheduling the yield losses are significantly reduced. 1. Introduction The drought phenomenon on Romanian territory is a specific characteristic related to the continental influences of the temperate climate, with rather very large deviations from year to year as compared to the normal values of the climatic, agroclimatic and hydrological parameters. Generally, the agricultural crops are well adjusted to the mean climatic conditions of our country and shows little sensitivity to moderate variations around the means. As conditions become more extreme, the capacity of plants to adapt declines with corresponding consequences upon production.

2 This paper seeks to demonstrate the use of CropWat model in planing and management of irrigation for maize crop in the specific weather conditions of the year 2, at two sites located in the south Romania. The main objectives of the study were to compare the simulation results of various options for water supply and irrigation management conditions and finally, to estimate the yield reduction due to crop stresses under rainfed conditions or deficit irrigation. Low precipitation during vegetation season (less than 1 mm) associated with high temperature have represented the major restrictive factors to growth for maize crop. The year 2 has considered as a severe drought year and as a consequence in the areas without irrigation the yield loss was considerable, up to 8 9%, the maize crop was practically compromised. 2. Methodology 2.1. Model description and input data CropWat for Windows is a decision support system developed by the Land and Water Development Division of FAO, Italy with the assistance of the Institute of Irrigation and Development Studies of Southampton, UK and National Water Research Center, Egypt. The model carries out calculations for reference evapotranspiration, crop water requirements and irrigation requirements in order to develop irrigation schedules under various management conditions and scheme water supply. It allows the development of recommendations for improved irrigation practices, the planning of irrigation schedules and the assessment of production under rainfed conditions or deficit irrigation. CropWat for Windows uses the FAO (1992) PenmanMonteith method for calculation reference crop evapotranspiration. The development of irrigation schedules and evaluation of rainfed and irrigation practices are based on a daily soilmoisture balance using various options for water supply and irrigation management conditions. Scheme water supply is calculated according to the cropping pattern provided in the program. Selected sites For the purpose of this study, there were selected 2 areas situated in the main agriculture production zone of Romania: Craiova and Alexandria. These areas are located in the southern part of Romania and cover the diversity of the agropedoclimatic conditions in this region. Climatic data The following monthly climatic data of the year 2 for the both sites were used: minimum and maximum air temperature, relative humidity, wind speed, sunshine duration and rainfall. The National Institute of Meteorology and Hydrology provided these data. Crop and soil data For this study, sets of standard maize crop data that are included in the program were used. The crop coefficient (Kc) and crop yield data (Ky) have been updated by FAO. Maize crop is planted on 2 and 25 April for Alexandria and Craiova, respectively. The crop is assumed to be planted all at the same time and cover 1% of the projected area. The model requires information on soil type, such as: total available moisture, readily available moisture and initial available moisture.

3 2.2. Simulations The key steps in the simulation were: running the CropWat model for maize crop with the monthly climatic data for the two sites and different scheduling criteria: rainfed conditions, irrigate when 1 and 7% of readily soil moisture depletion occurs, irrigate at fixed intervals and depths, irrigate at variable interval and depths (userdefined); analyzes the model results and selection the most suitable irrigation schedule option. 3. Results The effects of the different irrigation scheduling criteria simulated with CropWat model on estimated total maize yield reduction in the weather conditions of the year 2 are presented in Table 1. The simulated values of reference crop evapotranspiration (Eto), crop water requirements (CWR) and irrigation water requirement (IWR) during the maize growing season at Craiova site are shown in Figure 1a. Reference evapotranspiration (mm/day) is smoothed between the months with a polynomial curve. Crop water requirement follows the slope of a typical Kc curve and it rises above the Eto curve when the crop coefficient is greater than 1.. The effective rainfall makes the difference between CWR and IWR. In the rainfed conditions, the calculated soil moisture deficit shows the effect of rainfall only. Due to the low precipitation during maize vegetation season (92 mm at Craiova and 65 mm at Alexandria), the soil moisture deficit reaches the limit of the easily available moisture (RAM) in the first decade of May at Craiova and the end of May at Alexandria. Beginning from June the soil moisture deficit increases up to the limit of total available moisture (TAM). In this case, the maize crop has a low yield, the yield reduction is estimated to be 9% for Craiova and 82% for Alexandria (Table 1 and Figure 1b). In case of irrigation scheduling for maize crop at both sites, the daily soil moisture balance option was selected to show the status of the soil every day thought the cropping pattern, how the soil moisture changes in the growing season and estimated total yield reduction. By using the following scheduling criteria: irrigate when 1% of readily soil moisture depletion occurs (irrigation timing) and refill to 1% of readily available moisture (application depth), the soil moisture deficit not fall below readily available moisture. These two options defines optimal irrigation where the irrigation intervals are at a maximum whilst avoiding any crop stress. Figure 1c shows soil moisture changes during maize growing season at Craiova site, using these options. Figure 1d shows soil moisture changes during the maize growing season at Craiova site, using the scheduling criteria: irrigate at fixed intervals of 14 days and fixed depths of 6 mm net irrigation, beginning from the first day of the vegetation season (25 April). In this case the simulated soil moisture deficits indicate over irrigation at the start of the season and some crop stress in mid season, beginning from midjune to the end August. The vertical bars showing the negative soil moisture deficit mean lost irrigation (143 mm), which is assumed to runoff. The predicted crop stress is small and the estimated total yield reduction is not high (15%) as compared with the rainfed conditions. By selecting this fixed irrigation schedule, in which the irrigation is applied

4 from the first day (at sowing date) a significant amount of water will be lost, 143 mm at Craiova and 187 mm at Alexandria (Table 1). Scheduling option with 7 irrigation of 6 mm applied from the first day when the ratio of actual crop evapotranspiration to the maximum crop evapotranspiration (Etc/Etm) decreases bellow 1% (31 May for Craiova site and 1 June for Alexandria site) seems to be the most suitable option. The amount of irrigation applied in the growing season at both sites is lowest, without lost irrigation as compared with the other irrigation options. Also, the estimated total yield reduction is about the same as in the case that the irrigation is applied from the first day of the season, but lowest as compared with the rainfed conditions (Table 1). Table 1. The effect of the rainfed and different irrigation options simulated with CropWat model on estimated total maize yield reduction in the weather conditions of the year 2. (Eff. Rain: effective rainfall the amount of rainfall that enters the soil; ETc: actual crop evapotranspiration; Net Irr.: the irrigation depth applied; Lost Irr.: irrigation water that is not stored in the soil; Yield red.: the estimated yield reduction due to crop stress; RAM: readily available moisture). Site Options Eff. Rain (mm) ETc (mm) Net Irr. (mm) Rainfed Irr. 1% of RAM Craiova Irr. 7% of RAM Irr. fixed int.&depth(25apr/6mm) Irr. fixed int.&depth(31may/6mm) Lost Irr. (mm) 143 Yield red. (%) 9% 15.1% 17.6% Alexandria Rainfed Irr. 1% of RAM Irr. 7% of RAM Irr. fixed int.&depth.(2apr/6mm) Irr. fixed int.&depth.(1jun/6mm) % 1.3% 1.7% 4. Conclusions CropWat for Windows provides information necessary to make decisions on irrigation management and allows the assessment of production under rainfed conditions or deficit irrigation. Low precipitation during the maize growing season (less than 1 mm) at the both sites analyzed and in a severe drought year (2) makes irrigation a necessity. Simulation results analysis suggests that in these areas, where the maize water requirements exceeds the water supply, by application of adequate irrigation scheduling the yield losses are significantly reduced, from 89% to 117%. The most suitable option from economic point of view is to irrigate from the first day when the ratio of actual crop evapotranspiration to the maximum crop evapotranspiration decreases bellow 1%.

5 Eto, CWR & IWR Soil Moisture Change When Scheduling Maize (in rainfed conditions) mm/day Apr 9May 23May 6Jun 2Jun 4Jul 18Jul 1Aug 15Aug CWR CIR Eto 29Aug mm Apr 9May 23May 6Jun 2Jun 4Jul 18Jul 1Aug 15Aug 29Aug TAM RAM Daily SMDCropWat a) b) Soil Moisture Changes When Scheduling Maize (optimal irrigation) Soil Moisture Change When Scheduling Maize (Irrigate at fixed int. & depth) mm Apr 2May 9May 16May 23May 3May 6Jun 13Jun 2Jun 27Jun 4Jul 11Jul 18Jul 25Jul 1Aug 8Aug 15Aug 22Aug 29Aug 5Sep Net Irr TAM RAM SMD mm Apr 9May 23May 6Jun 2Jun 4Jul 18Jul 1Aug 15Aug Net Irr Lost Irr TAM RAM SMD 29Aug c) d) Figure 1.CropWat model simulation results for maize crop at Craiova site in the weather conditions of the year 2: a) reference crop evapotranspiration (Eto), crop water requirements (CWR) and irrigation requirements (IWR) in the maize growing season; b) soil moisture deficit in the rainfed conditions; c) soil moisture change in the case of application optimal irrigation; d) soil moisture change when irrigation is applied at fixed intervals and fixed depths.

6 References Clarke D., M.Smith, K.ElAskari, CropWat for Windows: User Guide, University of Southampton; Craciun I. & Craciun M., Irrigated maize response under water supply, Romanian Agricultural Researches I; Doorembos J. & Kassem A.H. Yield response to water, Irrigation and Drainage Paper 33, FAO, Rome; Itier B., Y. Brunet, Recent developments and present trends in evaporation research: A partial survey, p. 12. (In: Evapotranspiration and Irrigation Schedulling, Proc. Inter. Conference Nov. 36, Eds. C.R. Camp, E.J. Sadler & R.E. Yoder), Am. Soc. Agric. Engng. 1996; Marica Adriana, V. Cuculeanu, 2. Use of a decision support system for drought impact assessment and agricultural mitigation options in Romania, Proceedings of the Central and Eastern European Workshop on Drought Mitigation, 1215 April, BudapestFelsogod, Hungary, pp ; Marica Adriana, V. Cuculeanu, Uses of a decision support system for agricultural management under different climate conditions, Abstracts Volume of the 4 th European Conference on Applications of Meteorology (ECAM99), Norrköping, Sweden, 1317 September, pp. 135; Smith M., CROPWAT, A computer program for irrigation planing and management, FAO Irrigation and Drainage paper 46; Tuinea Petruta, V. Turcu, V. Adamiade, A. Palade, 2. Drought phenomenon risk zonality on Romanian agricultural territory and its impact upon agricultural yields, Proceedings of the Central and Eastern European Workshop on Drought Mitigation, 1215 April, BudapestFelsogod, Hungary, pp