عنوان مقاله [English]
In Khuzestan province, waste water release from various sources, especially from agricultural farms, is a serious problem. The volume of drainage water resulting from irrigation and drainage networks of the Karun river basin is about two billion cubic meters per year, considering sugarcane agro-industries and fish farming as the main sources of drainage water. Time-Averaged salinity of this drainage water, with source of sugarcane agro-industries, is about 6 dS/m which is valuable to irrigate salt-tolerant crops or aquaculture with saline water as part of the solutions for drainage water management and providing sustainable environment. This can also affect the amount of water allocated to irrigation networks and sugar cane industries. In this regard, reusing of agricultural drainage water to produce rice salinity resistant varieties and lines as a high-yielding strategy in Khuzestan, especially in the central and southern areas with high water demand, can be very useful.
This study was conducted at farm code L08-20, in Mirza Koochak-Khan Agro-Industry Company, using split plot in a randomized complete block design with two factors and three replications. Irrigation interval with saline water daily, one-day and two-day alternations were main factors and three salinity-tolerant rice lines were sub factors. Subsequent selections from the International Treasury of rice cultivars, four salinity-tolerant breeding lines, one international control line and local cultivar were subplots. The amount of water applied to the plots was measured throughout the growing season and samples for determination of physical and chemical properties of soil and drainage water before planting until harvesting time for soil monitoring and soil salt balance analysis were collected. In this study, grain yield, biomass and harvest index were determined. Finally, water productivity was estimated as yield per cubic meter of water.
Results and Discussion
Due to the average salinity of irrigation water, 6 dS/m, the volume of water consumed during the growing season was estimated to be 30,000 m3/ha, based on water requirement calculations. Based on irrigation management, applied volume of water was estimated about 37500 m3/ha for treatment I0, 19500 m3/ha for treatment I1 and 13200 m3/ha for treatment I3. The average salinity of soil saturated extract was measured about 4 dS/m before cultivation. Except for the first 15 days, when irrigation was carried out with full irrigation for transplanting stage, the trend of soil salinity changes was decreasing, during the rest of the growing season until harvesting. Salinity of soil increased in all three irrigation managements. The rate of salinity changes varied from 50% in the daily irrigation round to 100% in the two-day irrigation round, compared to pre-cultivation soil salinity. During the crop growth from the transplanting, daily, one-day and two-day rounds irrigation managements caused enterance of 190, 99 and 66 tonnes of salt in the top 100 cm of soil profile. Increased salinity over growing time for daily, one-day and two-day round irrigation treatments, were 6, 6.5 and 7.2 dS/m respectively, according to soil salinity, 4 dS/m, before planting. Assuming the porosity of soil equal to 51%, it could be concluded that 7.6, 9 and 11 tonnes of salts stored in the upper 60 cm of soil profile for daily, one-day and two- day round irrigation management and the rest of the solutes extracted from soil profiles through underground drainage system. This behavior illustrated the importance of drainage, especially underground drainage system, in agricultural drainage reclamation and saline operations for soil conservation. The results showed significant decrease of farm applied water in daily irrigation water management relative to two-day and three-day intervals. Farm yield increased 6% from I0 with an average of 2139.3 to 2248 kg, I1 and then decreased by 30% in the three-day irrigation period.
The results showed that the highest and lowest water productivity were found in I2 and I0 irrigation treatments, respectively, with values of 0.128 and 0.057kg/m3. ESP monitoring showed that at the end of growing season, soil profile was not sodic and remained in saline condition for two irrigation regimes I0 and I1. However, in I2 irrigation regime, the soil profile status approached to the sodic state, with 17% increasing in ESP and 100% increasing in salinity relative to planting time. The reason for this behavoir was driness of land between two irrigation events which caused salinity moving upward to soil surface layers, so it could be addressed by considering the percentage of leaching at the end of the growing season.
The authors gratitude Mirza Koochak-Khan Agro-Industry Company, Khuzestan Water and Power Authority (KWPA), Agricultural Engineering Research Institute (AERI), Rice Research Institute of Iran )RRII), Khuzestan Agricultural and Natural Resources Research and Education Center for their overall supports to accomplish the study.