Effect of irrigation management under soil water potential on water productivity of Rosmarinus officinalis L.

In arid and semi-arid areas, water can be a limiting factor for plant growth and agricultural yields. It is an important input to agricultural production and also an essential requirement for domestic, industrial and municipal activities. Increasing population and standards of living are contributing to a steep rise in demand for fresh water. By using proper irrigation management in farm, we are able to utilize water, soil and fertilizer to produce high yield and quality products. Drip irrigation is considered one of the most efficient irrigation methods. One of the major advantages is its ability to apply water to the soil as often as desired and in smaller quantity than the other irrigation methods. Drip irrigation has been practiced for many years for its effectiveness in reducing soil surface evaporation and it has been widely used in horticultural crops in both greenhouse and open field. Also, deficit irrigation is one of the strategies for efficient use of water and increasing water use efficiency in agricultural district. Deficit irrigation is a suitable solution to gain acceptable and economic performance by using minimum amount of water.

In order to investigate of surface and subsurface drip irrigation systems under soil matric potential on Rosmarinus officinalis L., a field experiment was carried out during 2015 growing seasons at center of seed and plant production of Kerman municipality. The treatments were laid out in randomized complete block design with three replications. The treatments were comprised of three soil matric potentials of 40, 60, and 80 centi-bar for initiation of irrigation in the main plot and sub plot consisted of two drip irrigation systems (surface and subsurface). In this study, surface systems, drip lines were placed on the soil surface at a distance of 15 cm from the plant and subsurface systems, drip lines were placed at a depth of 30 cm. The irrigation time was determined based on the readings of metal Tensimeters. These tensiometers were installed in three depths of 15, 30 and 50 cm of soil and at a distance of 20 cm from the plant. In this regard, in both irrigation systems, a Tensiometer mounted at a depth of 15 cm of soil was used for early growth and growth development, and from Tensiometers mounted at depths of 30 and 50 cm soil, for reading in the middle and final stages of growth. In order to carry out irrigation at the potential point of view, the tensiometers were fully controlled and when the calibrated tensiometer screen showed the desired potential point, irrigation was carried out and the irrigation process continued until the soil moisture reached the crop capacity level. Dry weight, leaf area index (LAI), number of shoots, plant height, water productivity were measured. Data were analysed statistically using SAS Statistical software. Treatment means were compared using LSD test.

The results showed that in comparison to 40 and 60 c-bar tension, parsimony of water usage equal 44.6 mm (21.7 percent) achieved. Moreover dry weight, number of shoots per plant and height of plant decreased 12.5, 12.8 and 11 percent respectively but water use efficiency increased 10.5 percent. Moreover dry weight in subsurface drip irrigation was increased 48 gr.m2 compared with surface irrigation. Also parsimony of water usage equal 10 percent and water use efficiency increased 21.4 percent. Number of shoots per plant and height of plant increased 8.2 and 8.7 percent respectively in subsurface drip irrigation.

According to the results, for Rosmarinus officinalis L. cultivation in Kerman area, application of the 60 centi-bar of soil matric potentials in subsurface drip irrigation system is the best way to increase the water use efficiency for the drought years.