Simulating the irrigation plan in colza cultivation to improve growing pattern and increasing the productivity indexes

Differences in climatic conditions, rainfall, transpiration of plant and evaporation from soil surface cause changes in yield production and crop water requirement. Due to the limitations of field assessment of plant growth, use of growth models can be a suitable tool for the study of plant behavior under different management conditions. Depending on different purposes over time, different models, including AquaCrop have implemented. Growth simulation methods are used to develop a sustainable strategy of water distribution, during the growing season, for achieving the best performance in reducing water consumption. Colza as a strategic product with high economic value is one of the main priorities in the cultivation pattern of the plains with different weather conditions. Therefore, this study was conducted to simulate a colza growth model and find the sustainable irrigation plans and groundwater allocation strategy, using crop growth simulation in four different climatic regions of Iran. This study aims to collect farm information and develop the colza crop growth pattern in four climatic regions of Iran. The experimental farms were located in Birjand, Bushehr, Shahrekord and Gorgan with arid, semi-arid, semi-wet and wet conditions, respectively. Simulation was performed to measure the level of canopy cover with the aim of achieving the final yield of the crop by AquaCrop software in the 2018-19 crop season. The information required to calibrate the AquaCrop model (including cultivation parameters, plant characteristics, growth schedule and soil texture) was entered into the model and calibrated to achieve actual crop yield. One of the main components of modeling is the daily estimation of soil moisture, which affects the water requirement, root growth rate and canopy cover of the plant, and thus the final yield production. Understanding the relationship between water, soil and plants has expanded widely since the presentation of the relationship between Doorenbos and Kassam (1979). The need to increase water productivity as a tool for water scarcity has led the Food and Agriculture Organization of the United Nations (FAO) to develop the AquaCrop model to simulate the response of crops to the amount of water consumed. Water productivity (kg/m3) is expressed as the ratio of final crop yield (kg/ha) and irrigation water (m 3/ha). Moreover, different scenarios of groundwater allocation were considered to supply crop water requirement, using soil water balance model in the root zone. The results showed that the highest amount of plant transpiration was obtained in Bushehr, Birjand, Shahrekord and Gorgan farms with a total of 900, 790, 717 and 407 mm, respectively. The highest yield was estimated in Shahrekord with more than 1800 kg/ha and the highest irrigation water productivity in Gorgan with 0.26 kg/m3. The results also showed that cultivation of colza at the beginning of the autumn planting period in each region increases the use of precipitation for canopy growth and thus reduces irrigation water consumption at the end of the season and increases productivity. Among the studied areas, the best range was related to Shahrekord colza cultivation with long growth period, acceptable yield, adaptive climatic conditions and suitable rainfall distribution for rainfed cultivation. The planting date is one of the effective management parameters in increasing water use productivity and effective use of rainfall. Therefore, the modeling results estimated an average decrease of about 10% in plant water requirements and a 1% increase in water productivity due to a ten-day reduction in planting date compared with the experiments performed. Notably, this crop is planted alternately with crops such as rice and cereals and the spring crop which generally has a higher economic value; also there is a limitation after harvest to prepare the field regarding the planting date. Therefore, attention to crop rotation and the possibility of changing and managing the time of planting and harvesting the first crop should also be studied. Effective use of rainwater, especially in areas such as Birjand and Bushehr, where water constraints are the main cause of reduced performance can be considered by relying on planning based on daily information. Differences in plant transpiration rate in daily, weekly and monthly scales indicate that irrigation intervals in Bushehr should be done with irrigation intervals of less than seven days at the end of the growing season to complete the flowers and fill the seeds with increased yield. In addition to rainfed cultivation for Golestan area, rainfed cultivation with supplementary irrigation at the end of the growing season is recommended for climatic conditions near Shahrekord and sprinkler irrigation for arid areas.