Determination of Applied Water and water productivity of lemon orchards in Iran

Most regions of Iran are considered as arid and semi-arid regions. Water management in the agricultural sector is very important as the largest consumer of water resources in the country. In order to better plan and manage water resources in the agricultural sector, it is necessary to have sufficient information about the amount of water used in different products. Given the importance of its lemon product in the country, and conducting little research on this issue, determining the applied water for lemon orchards in the country can be useful for planning and macro decisions in the country. A review of literature shows that a lot of information has been collected in the world about the required water and the effect of different irrigation methods on citrus fruit yield. However, little research has been done on irrigating lemon trees under the management of gardeners. In Iran, little research has been done on the management of lemon irrigation. Therefore, in this study, the volume of applied water and water productivity of lemon trees in the country have been measured and evaluated.

In this field study, irrigation water volume and lemon yield in over 210 selected orchards in Fars, Hormozgan, Kohgiluyeh, Boyer-Ahmad and South Kerman provinces were measured directly. Fruit yield was obtained in three consecutive years and their mean was used in the analysis. Analysis of variance was used to investigate the possible differences in yield, irrigation water volume and water productivity in lemon production. After determining the inflow of water to the garden by carefully monitoring the garden irrigation program and measuring the area under cultivation, the volume of irrigation water applied by lemon trees in each garden was measured. Multiplying the flow rate during the total irrigation period during the season, the amount of irrigation water volume was obtained. In each of the gardens, items such as soil texture of the gardens, electrical conductivity of soil and irrigation water, etc. were also measured. The amount of evapotranspiration of the lemon tree in each region was calculated using meteorological data of the station closest to the project implementation area in the last 10 years and the year of the research using the Penman-Montieth method. The results were compared with the calculated net required irrigation water and the values presented in the National Water Document (NETWAT).

The results showed that the differences in yield, applied water volume, and indicators related to water productivity were significant in the mentioned provinces. The weighted average yield of lemon was 21.7 tons per hectare. The weighted average volume of irrigation water and total applied water were 11938 and 12993 cubic meters per hectare, respectively. The weighted average irrigation water productivity was estimated to be 1.94 kg/m3. Weighted average water+long-term effective rainfall productivity was 1.59, kg/m3. Weighted average of water and current year effective rainfall productivity were 1.75 kg/m3, respectively. The proportion of irrigation water volume of lemon orchards with gross water requirement in selected provinces was similar. In general, the average difference between the depth of irrigation water and annual and long-term gross water requirement in the country was -17 and -1 percent, respectively. In the orchards under drip irrigation system compared to surface irrigation, fruit yield and water productivity increased 43 and 89 percent, while irrigation water volume decreased about 20 percent. Salinity of water and soil, age of trees, literacy level of gardeners, climate, soil texture were some of the factors that affected yield, water productivity and volume of irrigation water.

Accurate determination of plant required water and volumetric water delivery can be very effective in reducing irrigation water and increasing water productivity. In addition to these two factors, adhering to irrigation scheduling in lemon orchards can produce the maximum yield per allotted amount of water. In creating or renovating of lemon orchards, cultivars should be planted that are resistant to cold and salinity and have the ability to export, while increasing the area under cultivation in proportion to water resources.