Optimum water utilization through precise soil salinity control under steady state conditions

For conservation of soil and water resources and maintaining sustainability of agricultural productivity، water application under saline conditions should be conducted under precise application of crop leaching fraction. To evaluate leaching requirement and salt tolerance of alfalfa، a lysimeteric study (40 cm diameter and 180 cm height) was conducted through completely randomized design with three levels of salinity irrigation water (3، 7 and 13 dS/m) and three levels of leaching fractions (12، 25 and 50 %) as a factorial experiment with four replicates. After soil packing، the lysimeters were leached out until the salinity of their leaching water reduced to 3 dS/m and the columns were sown with alfalfa seeds (Yazd cultivar). To adjust the irrigation water salinity، natural saline water from Sadouq Salinity Research Station with 14 dS/m salinity was blended with tap water to obtain the required saline water treatments. Crop water requirement including leaching fraction was precisely calculated and supplied to the plants. The amount of collected drainage water was again recorded after 48 hr and its quality indexes were measured. Any deviation from the designed leaching fractions was compensated in the next irrigation event. This way، the precise water and solutes balance was determined. After some irrigation events، depending on salinity and leaching fraction level، drainage water salinity was fitted to the predicted steady state simulation models. The minimum required irrigation cycles to reach steady state conditions was obtained to be 12 cycles which was increased by increasing salinity and decreasing leaching fraction. The overall results showed that implementation of a defined leaching fraction can reduce soil salinity more than what was predicted by WatSuit model. Thus، soil salinity control at a desired level can be obtained by less leaching fraction level which is especially important for optimum water utilization under saline conditions when irrigation is linked to more salt application.