Comparing the amount of sugar beet irrigation water using the NIAZAB system and field measurement

Introduction
Most of the regions of Iran are located in arid and semi-arid climates, the characteristic of this climate is dry and long seasons without rain. In these areas, the lack of water is one of the most important factors limiting the production of agricultural products, in such a situation, the competition for water is increasing with the increase in population, urbanization and industrialization, and on the other hand, the lack of water is aggravated by improper irrigation management in agriculture. Accurate estimation of irrigation water quantity, water productivity of cultivated sugar beet in Iran are important and key indicators in agricultural sector planning. The purpose of this study was to investigate the results of field and farm measurements of irrigation water and sugar beet yield under farmers' management and compare it with estimating the NIAZAB system in 16 Township during a crop season (2016-2017) as well as determining sugar beet water productivity. The results showed that the average amount of sugar beet irrigation water in the method measured in farms and systems was 13088 and 13856 cubic meters per hectare, respectively, and the average grain yield of sugar beet in the method measured in farms and systems was 71846 and 64206 kg, respectively. The average water productivity of sugar beet in the field measurement method and NIAZAB system was 5/8 and 4/9 kg / m3. The results showed that the NIAZAB system with a normal root mean error of 0.21% and agreement coefficient of 0.89 estimates the amount of sugar beet irrigation water in the township scale and sugar beet grain yield with a normal a root mean error of 0.27% and agreement coefficient of 0.81 and estimates the productivity of sugar beet water with a root mean a normal error of 0.34%,. The values of the efficiency coefficient of the model show that the model provides acceptable results in determining the amount of irrigation water and sugar beet water productivity in the country farms. Therefore, the NIAZAB system can be used to estimate the volume required for the irrigation of plants in the Iran and also in farm water management.
 
Materials and Methods
This study was conducte based on field and field measurement and system-oriented approach (NIAZAB system) on a national scale to estimate the amount of sugar beet irrigation water. The main variables and implementation steps of this study are as follows: Theoretical foundations:. First step: estimation of the reference evaporationtranspiration, second step: determining the phenology stages of sugar beet plants, third step: estimating the amount of effective precipitation using, fourth step: estimation of the net irrigation water requirement of the sugar beet, fifth step: Estimating the gross irrigation water requirement of the sugar beet plant, ,sixth step: Accessible performance in the water demand system, seventh step: estimating the actual amount of irrigation water.
Practical foundations: first step: statistical population and sampling method: for an accurate estimation of the amount of sugar beet irrigation water in the country, targeted sampling was needed, based on this, a statistical population was used that included sugar beet farmers of the country, based on the statistical method, first of all 31 provinces of the country, the provinces that had a greater share in sugar beet production were selected. The selected provinces include 8 provinces (Ardebil, West Azerbaijan, Razavi Khorasan, Fars, Khuzestan, Semnan, Kermanshah, Hamedan) with an area equivalent to 105,875 hectares and a share equal to 75 The percentage of the cultivated area of the country was taken into account in selected provinces of 16 cities with an area equal to 71671 hectares.. Figure 1 presents the coordinates of the measurement points. second step: the method of measuring the selected field, third step: measurement of sugar beet yield, fourth step  Converting the measuring points to the city average and then compared with the estimated results of the amount of irrigation water of the NIAZAB system, it was compared, compared and validated.
 
Results and Discussion
In order to compare the results of the water requirement estimation system with the field and farm measurement values of the amount of irrigation water from farmers' sugar beet fields, the following was done. According to table 1, it can be seen that the amount of irrigation water for sugar beet based on the field measurement method in 16 cities of the country is equal to 13088 cubic meters per hectare and based on The estimation of the NIAZAB system at the level of 16 cities of the country was equal to 13856 cubic meters per hectare. Considering that there is a difference between normal averaging and weighted averaging, therefore according to table (3), the weighted average amount of sugar beet irrigation water according to the cultivated area in 16 cities in the field measurement method is equal to 12805 cubic meters and based on the system estimate The NIAZAB system was equal to 13817 cubic meters per hectare. Comparison of the average results of irrigation water measured in the field and estimated by the NIAZAB system shows that on average, the difference in the amount of irrigation water for sugar beet plants in the two methods was about 768.7 cubic meters per hectare and shows an equivalent error of 5.5%. According to table 1, it can be seen that the amount of sugar beet irrigation water varies between 7336 and 17950 mm in the entire growth period in 16 regions. The reason for the difference comes from the basics of estimating the amount of irrigation water. Considering the irrigation methods and calculating the efficiency of irrigation water use in the areas, but in the direct method, it was based on the actual measurement in the field, and however, the error value of 7.7% is reasonable and acceptable. Comparing the results of irrigation water quantity measurement and estimation of the NIAZAB system has a normal error of 21% and an agreement index of 0.89, and this shows the acceptable efficiency of the system. Therefore, NIAZAB system has the ability to estimate the amount of irrigation water for sugar beet plants at the level of the fields in the country scale.
 
Conclusion
The results showed that the average irrigation water of sugar beet plant from the measurement method in the fields and the estimated NIAZAB system is equal to 13088 and it was 13856 cubic meters per hectare. The results of the weighted average of sugar beet irrigation water which was estimated by the  NIAZAB system equal to 13817.9 cubic meters per hectare and directly measured from the fields equaled 12805 cubic meters per hectare, and it can be concluded for the surface of 140 thousand hectares of sugar beet irrigated lands the volume of irrigation water estimated by the NIAZAB system was 1.94 billion cubic meters and the volume of irrigation water measured in the field was equal to 1.79 billion cubic meters. The comparison of the results of the two methods showed that there is a difference of about 7.7% in the country.