Effect of different planting methods on soil salinity, root yield and water use efficiency of madder (Rubia tinctorum L.) under saline conditions of Yazd province

Introduction Madder (Rubia tinctorum L.) is one of the crop plants that has been utilized as a salt tolerant crop and it has been cultivated by farmers for many years in different parts of the country. With regard to salt tolerance, madder is a salt tolerant crop which has a threshold salt tolerance of 4 dS/m a 2.3% of the slope of yield reduction for each unit of salinity. Although madder cultivation was used to extract useful compounds from its roots in many saline areas, especially in pistachio orchards, little research has been done on the agronomic aspects, including proper planting method. The aim of this research was determination of the best planting method for maximum madder yield and high water use efficiency in comparison to traditional method under saline conditions.   Materials and methods This research was conducted in Sadooq Salinity Research Farm to investigate different planting methods for madder production and compare them to the traditional method in the form of complete randomized block design with three replications, during 2011-2015. Treatments were traditional method (planting as a clump covering with sandstorm), planting as a clump covering with soil, planting over the ridge, planting at beside slopes of a ridge, planting at bottom of  a furrow and planting as a row in a flat bed. For all treatments, the amount of seeds was 300 Kg/ha and all plots irrigated with saline water of 10 S/m with 10 Cm in depth, and continued at this level during the growing season. To control soil salinity, soil sample was taken during the growing season and average soil salinity of saturated extract of the root zone was determined. At the late time of growing season, in September, madder roots were removed from the soil and dry weighed.   Results and discussion Results of this experiment showed that in the method of planting over the ridge, the average soil salinity of saturated extract of root zone increased gradually with depths. Results of the average soil salinity of saturated extract of root zone during three years showed that the value of salinity was minimum for planting at bottom of a furrow and also planting as a row in a flatbed methods (10.99 dS/m), While it was significantly high, in the method of planting over the ridge (15.91 dS/m). Results showed that the maximum fresh and dry yield was related to rowing planting method (185.23 and 49.77 ton/ha, respectively) and the least was for planting over the ridge (13.10 and 3.41 ton/ha, respectively). As a whole, madder cultivation with rowing planting method, made an increase of 2.5 fold in root dry yield compared to traditional method. The highest water use efficiency (0.79 kg/m3) was obtained from rowing planting method, as well. It seems madder cultivation by rowing planting method as lines of 20 centimeters of each other, could improve root yield and water use efficiency and also better control of soil salinity under saline conditions. Therefore, based on the results of this research, rowing madder planting as 20 centimeters lines is recommended for higher yield, high water use efficiency, lower soil salinity and so on, under saline conditions.