Introduction: Hedge parsley (Torilis arvensis) is one of the important weeds of cereal and plants of the Apiaceae family, which produces two types of mericarps, spiny and hairy. Nitrogen is essential for all vital plant processes and plays an important role in the growth, yield and quality of crops. Salinity stress is one of the most important environmental stresses in arid and semi-arid regions of the world. Salinity is one of most prevalent abiotic stresses that limit crop productivity in arid and semi-arid regions. Salinity tolerance of plants is a complex phenomenon that involves morphological and developmental changes as well as physiological and biochemical processes. Response by plants to salt stress is a complex network affecting almost all processes, including nutrient uptake and metabolism, ion accumulation and photosynthesis. One of the most important nutrients whose absorption is affected by salinity is nitrogen and the reduction of its uptake by salinity is one of the important factors in reducing plant growth. It has been shown that increasing the concentration of nitrogen in saline soil solution has a positive effect on the adsorption of other elements. Due to the severe inhibition of dinitrogenase activity under salinity stress, the addition of mineral nitrogen partially compensated for the salinity effect.  Application of nitrogen fertilizers in saline conditions reduces the uptake of sodium and chlorine and increases the uptake of potassium in the plant.
Materials and Methods: In order to study the effect of salinity and nitrogen on the competition between coriander and Torilis arvensis, a factorial experiment with three factors of competition (The absence and the presence of Torilis arvensis), nitrogen fertilizer (0, 30, 60 and 90 kg ha^-1) salinity stress (0, 50, 75 and 100 mM NaCl) was carried out in a completely randomized design with three replications in the research greenhouse of Faculty of Agriculture, Razi University in 2018.
Results and Discussion: Nitrogen and salinity affected on coriander growth characteristics. With the increasing salinity level, plant height, leaf number, fresh and dry weight of plant and leaf, yield and leaf area decreased. But nitrogen had a positive effect on morphological characteristics studied. The interaction between salinity and nitrogen showed that in all three levels of salinity with increasing nitrogen concentration increased coriander growth characteristics. So that the highest plant height, fresh and dry weight of the plant and leaf dry weight were observed in treatment 0 mM NaCl with 60 and 90 kg ha^-1 nitrogen levels. The highest number of leaf (13.99) was in treatment 0 mM NaCl with 60 kg ha^-1 nitrogen. Using nitrogen fertilizer could reduce the negative effect of salinity stress. Nitrogen is the first nutrient element that has a shortage in saline areas. Therefore, the correct management of nitrogen fertilizers is a suitable strategy to increase plant tolerance to salinity stress. Due to the important role of nitrogen in the structure of amino acids, proteins, nucleic acids, chlorophylls and alkaloids, its supply will increase plant metabolism and ultimately increase plant photosynthesis, which will lead to an increase in biomass. It seems that increasing nitrogen fertilizer by providing the nutrients needed by the plant, will affect the division and elongation of plant cells and will lead to an increase in plant height.  Salinity as a inhibitory factor slows down the process of seedling establishment and also reduces various plant characteristics. One of the most important damages due to salinity stress is ion imbalance due to reduced ion absorption and accumulation of harmful ions and dehydration due to decreased water absorption which is accompanied by decreased protein synthesis, transpiration, ion transport which ultimately reduces yield. It can also be stated that with the addition of nitrogen fertilizer under conditions of high salinity stress, the plant is forced to absorb it, while assimilation does not have enough to fix nitrogen. Therefore has a negative effect on yield. When the reason for the decrease in leaf dry weight per plant is related to the decrease in leaf area as well as the number of leaves. 
Conclusions: Based on the obtained results, application of 90 kg ha^-1 nitrogen reduced the negative effects of salinity on the growth of coriander and ultimately improved the morphological characteristics of coriander. Nitrogen and salinity influenced the growth characteristics of coriander. With increasing salinity level, plant height, number of leaves, fresh and dry weight of plants and leaves, yield and leaf area decreased. But nitrogen had a positive effect on the morphological characteristics of the study. The interaction between salinity and nitrogen showed that in all four levels of nitrogen, with increasing salinity concentration, the growth characteristics of coriander decrease. Under salinity stress, Torilis arvensis competition reduced the number of coriander leaves.