Effect of Different Tillage Systems and Deficit Irrigation on Yield and Water Use Efficiency of Sugar Beet

Conventional tillage is widely used in sugar beet growing areas. However, conventional farming uses more labour and machines that has a negative effect on soil and the environment. Due to limited water resources and recent droughts, proper use of modern tillage and irrigation methods can increase water efficiency and prevent soil degradation as a result of sustainable agriculture.

An experiment was conducted to investigate different methods of tillage and water requirements on quantitative and qualitative yield and sugar beet water productivity in the drip irrigation system in Ekbatan Research Station of Hamedan Province from 2018 to 2019. A strip plot experiment with sixteen treatments and three replications was used. Tillage methods in four levels, consisting of T1- plowing with moldboard plow to a depth of 25-30 cm in autumn + power harrow to a depth of 15-20 cm in spring, T2- subsoiling to a depth of 35-40 cm + plowing with moldboard plow to a depth of 25-30 cm in autumn + power harrow to a depth of 15-20 cm in spring, T3- plowing with chisel plow equipped with roller packer to a depth of 25-30 cm in autumn + power harrow to a depth of 15-20 cm in spring and T4- plowing with sweep plow equipped with roller packer to a depth of 25-30 cm in autumn + power harrow to a depth of 15-20 cm in spring and Irrigation factor consisting of I1-100%, I2- 90%,  I3- 80% and I4- 70% sugar beet water requirement were considered. Soil penetration resistance (PR), the volume of water consumption, root yield, sugar yield, white sugar yield and molasses were measured. Water efficiency in tillage and irrigation treatments was also calculated. MSTAT-C software was used for statistical analysis of data. The Duncan's multiple range test at a 1% probability level was used to compare the means.

At a depth of 0-30 cm, no significant difference was observed between tillage methods on soil penetration resistance. At greater depths (35-40 cm) T2 treatment (subsoil + moldboard plow) had the greatest effect in reducing soil resistance. The results showed that the effect of different tillage methods, water requirement and their interactions at the 1% probability level on root yield; sugar yield and white sugar yield were significant. There was no significant difference between sugar beet yield in the T4 tillage treatment and the conventional method (T1). Treatments T4 (with an average yield of 50686 kg ha-1) and T1 (with an average yield of 50507 kg ha-1) had the highest sugar beet root yield. Also, the tillage method (T4) compared to the conventional tillage method (T1) reduced fuel consumption by 14.7% and increased field capacity by 52.4% respectively. In the T4 tillage method, irrigation treatments I100, I90 and I80 with mean water productivity of 6.113, 6.087 and 5.523 kg m-3 of water consumption, respectively, had the greatest effect on increasing water productivity, while no significant difference was observed between them.

The tillage method (T4) compared to the conventional tillage method (T1) reduced fuel consumption by 14.7% and increased field capacity by 52.4%, respectively. There was no significant difference between sugar beet yield and water productivity in the T4 tillage treatment and the conventional method (T1). Although full irrigation treatment (100% water requirement) has the highest water efficiency, there is no significant difference between 90 and 80% water requirement treatment. Therefore, in order to save water consumption, 80% water requirement is recommended. The result is that in the T4 tillage method with a supply of 80% water requirement of sugar beet after plant establishment (approximately from the middle of the growing season) about 12% (1207 m-3) in water consumption without significant reduction in water productivity.