کمبود نیتروژن

Nitrogen is one of the important nutrient elements necessary for the production of agricultural products, but the excessive application of nitrogenous chemical fertilizers and their leaching cause environmental pollution. Crops’ cultivars with high nitrogen use efficiency is one of the environmental friendly aproaches to mitigate this problem.

To evaluate grain yield and nitrogen use efficiency in barley genotypes under low input conditions (without fertilizer application), a field experiment was conducted in research field of the agricultural faculty of Shahed University, Tehran, Iran in 2016-2017 cropping season. Thirty six barley genotypes, purified for three cropping seasons, were planted using simple alpha lattice design with two replications.

The results showed that genotypes; 106, 107, and 68 had the highest grain yield (7963, 7920 and 7900 kg ha-1, respectively), the highest nitrogen use efficiency (58.6, 58.5 and 56.9 kg.kg-1, respectively) and the highest nitrogen uptake efficiency (2, 2 and 2.25 kg.kg-1, respectively). The results of multiple regression analysis showed that the three variables of nitrogen use efficiency, nitrogen uptake efficiency, and biomass yield explained 98.2% of variation in grain yield. Principle component analysis revealed that barely genotypes divided into four groups. The first group included genotypes; 88, 119, 54, 107, and 68 for nitrogen uptake efficiency and nitrogen use efficiency, grain yield and quality. These genotypes are suitable for low input cropping systems to increase nitrogen use efficiency.

The results of this experiment indicated that further investigations are required for recommendation of barley genotypes with higher nitrogen efficiency and grain yield for low input cropping systems.

There are mathematical equations to distinguish nitrogen (N) status based on the concept of critical nitrogen (Nc), the lowest N concentration required to achieve maximum growth. The Nc demonstrates the ideal N status in crops. Whenever crop N concentration is greater than the Nc, at that time N is in surplus, but if it is less, then N is inadequate. The contribution of the stem dry matter (SDM) toward total crop dry matter is significantly higher than that of other tissues, therefore, it is the most determinant factor for N dilution of the whole plant. The objectives of this research were to construct a Nc dilution curve based on SDM and to evaluate the plausibility of this curve for assessment of the N nutrition status of spring rapeseed.

A field experiment was conducted with seven levels of N fertilizer application (0, 50, 100, 150, 200, 250 and 300 kg N ha-1) in which the amount of the SDM and stem N concentration (SNC) of two spring rapeseed cultivars (Hyola 401 and Dalgan) were measured during the growing season. The approach proposed by Justes et al. (1994) was used to construct the SDM basis Nc dilution curve. The N nutrition index (NNI) on each sampling date was calculated by dividing actual SNC by stem Nc concentration. The accumulated N deficit (Nand) in rapeseed stems for each sampling date was determined by subtracting the N accumulation in stems under the Nc condition from actual N accumulation in stems under different N fertilizer application rates.

Overall, both SDM and SNC showed an increasing and decreasing trend with increasing crop age, respectively, regardless of fertilizer treatment. The Nc dilution curve of both cultivars during the growing season was described by the equation Nc = 5.71SDM-0.29. Both NNI and Nand criteria were able to diagnosis the N deficiency or excess in the spring rapeseed cultivars studied. At all of the crop growth stages, there was a significant positive correlation between the difference value of the N application rate (∆N) and the difference value of NNI (∆NNI). For both cultivars studied, however, the positive correlation between ΔN and differences in Nand among N fertilizer treatments (ΔNand) was not significant at early growth stages. In any case, for accurate management of N fertilizer during the growing season, it is sufficient to determine only one of the two NNI or Nand criteria per day from planting to silique formation, and then the N fertilizer required for maximum growth is calculated based on the equations presented to describe the relationships between ΔN and ΔNNI or between ΔN and ΔNand.

The N concentration in the stems decreased with advancing maturity, while a higher N application rate generally exhibited a higher stem N concentration. The present Nc dilution curve based on SDM provides an insight into N nutrition status in spring rapeseed crop and can serve as a novel tool to improve N fertilization management in spring rapeseed.

In order to detect the QTL associated with nitrogen-deficiency tolerance at seedling stage, a population of 96 lines derived from Ahlami Tarom and Neda cross were studied at 2014. For genetic linkage map construction, 30 SSR and 15 ISSR makers were used. The resulted linkage map covered 1411.3 cM of rice genome with an average of 15.34 cM distance between two markers. A total of 37 QTLs were identified for the traits under study. qRV-10 under conditions of nitrogen deficiency explained 11.4% of the phenotypic variations of root volume. QTLs controlling root number (qRN-3 and qRN-6b) and root weight (qRW-5b and qRW-5c) under normal conditions were detected in the major stress that this is justified QTL accounted for over 20 percent of phenotypic changes. Markers linked to the QTL as markers linked to traits are likely to be used for marker-assisted selection in breeding programs.

Water deficit is one of the main factors limiting production in arid and semiarid regions. This study was carried out to investigate the effect of the interaction of water deficit and N fertilizer rate on relative water content, proline content, leaf chlorophyll content, pollen number and pollen viability, photosynthesis rate and stomata conductance parameters in two hybrid sweet corn (968 and 926) in greenhouse condition. The experimental layout was split plot factorial design arranged in a randomized complete block design with three replications in 2010 in the Agriculture Crop Science, Putra University Malaysia (UPM). Treatments consisted of four levels of irrigation (including irrigating all the growing season (control), vegetative drought, reproductive drought and vegetative and reproductive drought), three levels of Nitrogen as urea (40, 120 and 200 kg ha-1) and two varieties of sweet corn varieties (including hybrids 968 and 926), respectively. Results showed that the interaction effects of water deficit and Nitrogen fertilizer were significant and reduced leaf chlorophyll content, photosynthetic rate and stomata conductivity under water and Nitrogen rate deficit. Also the results showed that water deficit at vegetative and productive growth stages reduced photosynthesis rate compared to normal irrigation by 54% and 84%, respectively. But Nitrogen treatments at 200 and 120 kg ha-1 did not show any significant decrease in stomata conductivity. Whereas. Proline content increased under water deficit. Pollen number reduced with water and nitrogen deficit. Pollen viability reduced only under water deficit by 39%.