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1.INTRODUCTIONCotton is considered an essential national product in Greece, and great attention has been given to all the stages of its production, from cultivation to the final product, i.e., cotton yarns and fabrics. Greece contributes approximately 79% of the total EU production, while cotton accounts for 9% of the country’s final agricultural output, with cultivated areas totaling 350,000 hectares, representing approximately 13% of the total cultivated land in Greece. However, in Greece, as water over-use has no direct impact on cultivation, farmers tend to ‘be on the safe side’ and irrigate beyond crop water needs, especially when the water tariffs are low. It is considered that typically only approximately 55% of the irrigation water is used by the crop, 12% is lost through its transfer, 8% is lost through its application, and 25% is considered as excessive water, lost through evapotranspiration and surface runoff. Unfortunately, such misuse of irrigation water is not restricted to this specific crop or location but is somewhat representative of the low efficiency of water use in agriculture in general [7]. This research study aims to address issues of sustainable water management and its resources for the specific cultivation of cotton in Karditsa Prefecture, Thessaly, Greece. Additionally, this research will take a brief view of cotton cultivation, which a very important for the specific area. 2.LITERATURE REVIEWCottonCotton Crop’s history.Pausanias describes the cultivation of cotton in Greece in the 2nd century B.C. Greece is the largest cotton producer in Europe and the top dozen countries worldwide. In Greece, cotton is regarded as a crop of national importance. It accounts for more than eight percent of total agricultural output. Although cotton is grown mainly for fiber, the cottonseed remains after processing and is used to produce oil and oilseed cake for animal feed [8]. Cotton is an arable crop used mainly for fiber. The cottonseed, which remains after cotton is ginned, is used to produce oil for human consumption or oilseed cake for animal feed. Cotton growing ConditionsCotton,”Gossypium”, is a shrub from the family Malvaceae, which includes hollyhocks, mallow, hibiscus, okra, and cocoa. The genus Gossypium includes 50 cotton species, four of which have been domesticated for the fiber their seeds produce. Two species originating in the Americas now account for most of the cotton produced worldwide: Gossypium hirsutum, from Mexico, which produces some 90%, and Gossypium barbadense, from Barbados, which produces the best fibre but only accounts for around 5% of the total. The other two species originated in the Old World: Gossypium herbaceum, from southern Africa, and Gossypium arboreum, from India, account for around 5% of global output. Their shorter, thicker fibres are generally used by local spinners and weavers. Cotton plants flower as they grow and are thus said to have a continuous growth cycle. This means that at any given time, a plant may bear buds, flowers and fruits, known as “bolls,” which contain the seeds. The bolls split to reveal a small white ball of fiber. [9]. Cotton is grown between 35°N and 41°N latitude, but only about 1000 ha (0,5%) are lower than 38°N parallel [10], [3]. Cotton is grown between 37 degrees North in Ukraine and 30 degrees south in Australia in a warm, frost-free, sunny climate. Cotton requires a lot of sunshine temperatures between 60 to 95 degrees Fahrenheit (16-35 degrees Celsius) [11]. Cotton is a crop with an uncertain or ambiguous growth habit and has a dynamic growth response towards the environment and management practices [12] Water, the significant component, constitutes about 70–90% of plant fresh mass. Plant development and physiological processes are highly dependent on availability and quality. The crucial role of water in plant physiology, viz. nutrient transportation, transpiration, and chemical and enzymatic reactions, suggests that water-stress can cause changes in the anatomy and morphology and alter the physio-biological processes. [12] The fate of irrigation water in agricultural fields includes soil evaporation, crop transpiration, and deep percolation below the root zone. Among these, the beneficial pathway for crop growth and yield is transpiration. Improved and deficit irrigation management strategies could increase the proportion of water crops use as transpiration and reduce soil water loss in evaporation and deep percolation [13]. Plant’s anatomyStem &Branches Cotton is grown between 37 degrees North in Ukraine and 30 degrees south in Australia in a warm, frost-free, sunny climate. Cotton requires a lot of sunshine temperatures between 60 to 95 degrees Fahrenheit (16-35 degrees Celsius). A cotton plant starts from seeds. The seeds germinate in 5 to 10 days, and the cotton plant begins its growth with two cotyledons (the seed leaves that form nodes opposite each other at the base of the main stem) until the plant forms true leaves (leaves produced subsequent to the cotyledons). Cotton has a tap root system, and roots go deeper into the soil in search of nutrients. The development of a healthy root system for acquiring soil nutrients is vital to feed the growing plant. As a cotton plant grows, it develops a series of nodes up the main stem. Beginning with the fifth or sixth node, the plant forms fruiting branches that bear the cotton fruit. Typically, a cotton plant will continue to add nodes and fruiting branches for 16 to 22 nodes, with 12 to 16 fruiting branches. Leaves: Leaves provide a carbohydrate energy supply for adding nodes and branches and growing bolls. Photosynthesis converts light energy into chemical energy stored as sugars in the plant. All plant metabolic reactions are dependent on this energy source. Roots: Cotton has a tap root system, and the roots can be as deep as 10 inches in the first 3 weeks. Roots can grow up to 2 inches per day during the early stages of cotton, making them twice as long as the plant’s height. When plants begin to set bolls, root growth slows abruptly. Reproductive Stage-Squares, Bolls, and Fruits The flower bud that first appears on the plant when reproductive growth begins is called a ‘square’. Three bracts enclose the flower bud. Squares grow for about three weeks before a flower appears. Cream or yellow flowers open during early morning hours. During this time, the male and female flower parts expand rapidly. The flower petals turn pink on the second day, dry up, drop off, and then form a ball. The cotton plant is constantly adding squares to the plant and then aborting squares or young bolls to balance out the demand of the growing boll load. Boll retention should begin near the level of square retention and show a gradual decline throughout the bloom period as the plant reaches its capacity for supplying bolls with carbohydrates. [11] EvapotranspirationThe term evapotranspiration (ETo), refers to ETo is the rate of evapotranspiration from a large area covered by green grass, 8 to 15 cm tall, which grows actively, completely shades the ground, and is not short of water [14]. Evapotranspiration is a natural process by which water is transferred from the soil and plants to the atmosphere. Direct and indirect methods can perform the determination of evapotranspiration levels. The data obtained from these methods are highly relevant to optimizing water resources and energy savings, especially in areas where rainfall has an irregular distribution and where irrigation systems are used [15]. According to the literature, cotton has the most evapotranspiration during June, July, and August [16]. 50 to 90 days from the sowing are the most demanding for water. Remember that cotton is sowing from late April to May. These months are essential for irrigation. Using the IRMA_SYS application, it comes that using surface irrigation (technical rain), cotton water needs are in June: 127-154 m3/str, July: 146-173 m3/str, and in August: 135-162 m3/str Commonly used systems in cotton for irrigation.The irrigation method selected from each cotton farmer depends on irrigation measures in that area, the available irrigation water, soil type, terrain and shape of the field, and the organization (economic, social), but many times and from the tradition of the region. The main irrigation methods are:
3.STUDY AREA AND DATAThe study area in which the (crop) cultivation is located is Solonetz – like allusions sediments with a high level of groundwater [18]. Palamas soil is a deep, sandy loam to loam (sand 37-45%, silt 51-43%, clay 12%), moderately fertile (0.9% organic matter content at 40cm depth), characterized by a groundwater table fluctuating from some 2 m below the soil surface (receives artificial drainage) in May, to deeper layers later in summer, and is classified as Aquic Xerofluvent [19]. During April, May, June, September and October, you will most likely experience good weather with pleasant average temperatures. Some climate details for the area are:
The size of the field is 50 str. (5 ha.). The approximate yield of the cotton cultivation on this field is 300 kg/str and the selling price of the cotton is 0.48 euros/kgr on average (2019). As it was mentioned in previous paragraph, the importants months for cotton irrigastion are June, July and August. 4.MATERIALS AND METHODSFor the accurate calculation of the (crop’s) water needs and proper irrigation system, a compilation of tools was used: 1. Use of Blaney-Cridle method was made with the help of Excel sreadsheet. Use of smartphone applications:
Use of platforms
The process followed was as following: For the accurate calculation of the cotton’s water needs, the use of Blaney-Criddle method was made. The first step is to calculate the evapotranspiration (ETo) of the cotton field in the abovementioned area. Based on a smaller version of the evapotranspiration equation: Where: In order though to compute the beneficial rain, the following equation should be taken in consideration: Where: The terrain factor is connected to the slope of the field and based on how high or low it is, a value from 10 to 20 is inserted on the equation, based on empirical information. Since the cotton field that is examined in this paper has a slope of 0.1% (as someone can see from the photos) it is considered to have a low slope. Therefore, in this case the terrain factor will be equal to 10. When it comes to the Rm, according to the National Meteorological Service of Greece, the mean amount of rainfall in the area of Palamas were used based on meteorological data taken from Hellenic National Meteorological Service. (The nearest meteorological station is in Larissa, 40 km from the examined field. Therefore, these values should be considered accurate under prejudice.) Following, for the calculation of the beneficial rain with the Blanney-Criddle method, the equation below is used. Where: For cotton, K1 factor is equal to 16. For the computation of the climate factor the following equation was used. Where: The mean temperatures of each one of the three critical months were used, based on data from the Hellenic National Meteorological Service. It should be made clear though, that this information was once again based on the same time-period as the aforementioned and should be once again considered accurate under prejudice. For the identification of the p value, the following nomograph is used. Since according to the literature, the critical irrigation needs of soybean are June, July and August, while at the same time the field’s latitude is on 40o (39.48075 actually) and it is located on the North hemisphere, each month’s line was precisely followed to each percentage respectively. The next step is to determine the Crop irrigation Use. Brouwer and Heibloem, (1986) in FAO “IRRIGATION WATER MANAGEMENT, Training manual no. 3” describing the role and the calculation of Crop Irrigation needs [6]. In the case of Thessaly, part of the crop water need is supplied by rainfall and the remaining part by irrigation. In the irrigation water need (IN) is the difference between the crop water need (ET crop) and that part of the rainfall which is effectively used by the plants. Approximately, this can be determined from the following equation: Where: Pe: effective rainfall (mm/month) In order to calculate the Pe a simple formula will be used: [6]. This formula is used because in Palamas, the rainfall per month during the three months (June, July and August) is less than 75 mm/month. In excel Table someone can see that the real needs of the cotton plants are very close to the pure irrigation needs, partly because the rain is in low levels his period. 5.RESULTS AND DISCUSSIONAfter inserting the metadata on the excel calculator, it appeared to have been resulted that during the June, cotton needs 125m3 of water per str, while July 125.76 m3 –being the critical amount, and 117.87 m3 on August. The total irrigation needs amounted to be 355.05 m3/str or 3.550,50 m3/ha. Therefore, the total amount of irrigation needed for this three-month period concerning the study area in the farm for the total of 50 str., is equal to 17752.5 m3. Table 1.The analytical calculations of cotton’s irrigation need. While examining the irrigation needs of cotton cultivation, it can be noticed that there is an increase of 7.92% from the month of June to month July and a decrease from July to August which amounted to –8.18%. The percentage of every month’s irrigation is shown in the above table. July is the month with the highest need of irrigation. As can also be seen from the chart below, the irrigation needed during July is much higher than the other two months. Table 2.Mean Temperature of Larissa - chart. Table 3.The presentation of the cotton’s irrigation needs - chart. A possible reason of the increased needs of irrigation for July can be that during this month the growth and development of the cotton plants are in their peak and the temperature has the highest level during the year. 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