Effect of irrigation, plant density and nitrogen levels on yield and yield components of Eruca sativa

Introduction  Iran with mean annual precipitation of 240 mm is categorized in arid zones of the world. High evapotranspiration, limited water resources and other parameters invokes the interests for studying the effect of water stress in field crops. Also, N fertilization and plant density were important factors for growth and production of field crops. Management of balanced and efficient use of fertilizers is certainly necessary to obtain maximum yield. Plant deficit per unit area prevents maximum usage of production parameters and on the other hand, excessive density can increase the competition and decrease the yield. The objective of the present study was to examine the influence of the plant density and N application levels on yield and yield components of Eruca sativa under late-season water deficit stress in Birjand, Iran.   Materials and Methods  This research was carried out in the research farm of Islamic Azad University of Birjand, Iran in 2013-2014 in a factorial split-plot experiment on the basis of a Randomized Complete Block Design with three replications. The main plot was devoted to irrigation at two levels of no stress (optimum irrigation) and stop irrigation in reproductive stage, the sub-plot was devoted to plant density at two levels of 50 and 150 plants m-2 and  N fertilization at three rates of 0, 100 and 200 kg N ha-1 as factorial. In optimum irrigation treatment, the farm was irrigation with the intervals of 9 days during whole growing season. The N demand of the plots in terms of N fertilization levels was supplied at the first   irrigation after final thinning of the plants in late-March from urea source. The texture of the soil in research farm was loam with the pH of 7.79, electrical conductivity of 7.23 mmos/cm whose organic carbon, total N, P, and K content was 0.17%, 0.04%, 15.4 ppm and 266 ppm at the depth of 0-30 cm, respectively. In the end, all data were analyzed by MSTAT-C statistical software and means were compared by Duncan Multiple Range Test at 5% level.   Results and Discussion Analysis of variance revealed that seed yield was significantly influenced by irrigation, plant density, N fertilization and the interaction between irrigation and N and between irrigation, plant density and N. The interaction between irrigation and plant density was significant for seed number per pod, pod number per m2 and pod number per plant. The interaction between irrigation and nitrogen was significant for pod number per m2, pod number per plant, seed yield and biological yield. The interaction between plant density and nitrogen was significant for pod number per plant and biological yield. Also, the interaction between irrigation, plant density and nitrogen was significant for seed yield and biological yield. The results showed that stop irrigation in reproductive stage increased pod number per m2, pod number per plant, 1000-seed weight, seed yield and biological yield, 60.1, 51.3, 23.6, 68.5 and 62.7%, respectively. Also, the increase in plant density from 50 to 150 plants. m-2 increased pod number per m2, seed yield and biological yield 41.5, 29.5 and 41.9%, respectively and decreased pod number per plant 36.49%. Moreover, the increase in nitrogen application from 0 to 200 kg N ha-1 increased pod number per m2, pod number per plant, seed yield and biological yield 91.8, 68.3, 70.2 and 55 %, respectively. Means comparison for the interaction between irrigation and N revealed that the highest seed yield (174.27 g m-2) was produced under the treatment of optimum irrigation fertilized with 200 kg N ha-1 and the lowest one (41.78 g m-2) under the treatment of water deficit stress at reproductive stage with no application of N fertilization. In other words, at under optimum irrigation, E. sativa was able to use N more effectively for increasing seed yield. It implies that the necessary condition for appropriate efficiency of N use is the availability of enough moisture in root zone so that soil N content can readily be available to plant and is used for inducing vegetative growth, photosynthesis and seed yield enhancement. Furthermore, means comparison for the interaction between irrigation, plant density and N showed that the highest seed yield (193.30 g m-2) was produced under the treatment of optimum irrigation at the density of 150 plants m-2 fertilized with 100 kg N ha-1 and the lowest one (33.67 g m-2) under the treatment of water deficit stress at reproductive stage at the density of 50 plants m-2 and no application N fertilization. Seed yield variation under optimum irrigation is tangibly affected by the variations of plant density and N, while the treatment of water deficit stress at reproductive stage did not result in significant changes in seed yield between various levels of density and N rate, so that all density levels and N rates were ranked in the same statistical group.   Conclusions Generally based on means comparison of interaction effects, it is recommended to use the density of 150 plants m-2 optimally irrigated and fertilized with 100 kg N ha-1 for cultivation Eruca sativa because of its optimum seed yield and which takes environmental issues under consideration too.