Interactive effect of nitrogen and salinity on yield, oil content and nitrogen use efficiency in canola

Abstract
Background and objectives: In most saline and non-saline soils, nitrogen is the most restrictive nutrient for plant growth. In saline soils, interactive effects of salinity and soil fertility is very important from optimum production. Nutrient imbalance is one of the problems with saline soils. In these circumstances, the fertilizer application may to increase osmotic effect of salt, the question is whether fertilizer is necessary or not, in saline soils? In order to answer these questions, an experiment with factors of salinity and nitrogen were carried out on canola.
Materials and methods: In order to evaluate the interaction of salinity and nitrogen, a factorial experiment in a randomized complete block design with factors of salinity and nitrogen were carried out on canola. Salinity treatments were included a non-saline water (0.3 dS m-1), and natural saline waters with salinity of 3, 6, 9 and 12 dS m-1. Nutrient nitrogen levels were four value: zero (N1), 75 (N2), 150 (N3) and 300 (N4) mg N per kg of soil as the ammonium nitrate. The soil texture used in this research was sandy loam containing low amounts of salinity and nitrogen.
Results: The results showed that with increasing salinity, seed canola yield reduced and increased by adding nitrogen to the soil. In this experiment, nitrogen application even to the amount of 300 mg N kg, increased percentage of seed canola oil. The increase was little in the salinity of less than 12 dS m-1. Generally, with increasing water salinity and nitrogen application, nitrogen agronomy efficiency (NAE) decreased for oil production. NAE threshold for oil production in saline conditions depended on the amount of nitrogen application. NAE threshold for oil production in the first level of nitrogen equal to 0.3 dS m-1 and at higher levels of nitrogen increased to 6 dS m-1. By increasing nitrogen levels decreased sharply the percentage of nitrogen apparent recovery (NAR).
Conclusion: With increasing salinity, canola yield reduced and increased by adding nitrogen to the soil. In general, by increasing salinity (especially in high salinity), at all levels of nitrogen, nitrogen physiological efficiency (NPE) of canola increased. In the highest salinity value, N application, increased canola seed oil content so significantly. Nitrogen agronomic efficiency threshold for producing of canola oil in saline conditions depended on the amount of nitrogen application. According to the results, it is recommended to act more cautiously using large amounts of nitrogen in salt condition.