Study the responses of some leaf physiologic characteristics to different water and nitrogen levels in maize (Zea mays L.)

Changes in water and nitrogen amounts cause different physiological reactions in plant. These changes are created for respond to stress in order to reduce or eliminate the stress effects. Improper management of water and nitrogen are main growth limiting factors of maize. The proper reaction of maize to nitrogen which leads to higher yield, is reason the use excessive amounts of nitrogen fertilizers. Nitrogen losses are the results of high nitrogen usage. The new irrigation methods, such as deficit irrigation, play important roles in preventing leaching and nutrients maintenance in root zone. Under water deficit conditions, nutrients absorption decreases, therefore fertilizer recommendation should be done according to existing water conditions. The study of physiological reactions of maize to different amounts of water and nitrogen helps to estimate accurately the crop need for water and nitrogen. Therefore, this research was conducted to evaluate the role of water and nitrogen in causing physiological changes in maize leaves.
This experiment was done at Razi University, Kermanshah, Iran, during 2014 and 2015. The experiment was conducted as split plot. Main-factor was four irrigation levels included supplying 60, 80, 100 and 120% water requirement (I60%, I80%, I100% and I120%, respectively), and sub-factor included four nitrogen levels 40, 70, 100 and 140% (N40%, N70%, N100% and N140%, respectively) recommended amount based on the soil test. To calculate water requirement, Penman-Monteith-FAO equation was used. For each treatment the amount of water was measured. Partitioning of nitrogen at times the two-leaf stage, the six-leaf stage and before tassel emergence was equal. Leaf physiologic traits included relative water content, stomatal conductance, temperature, photochemical efficiency of PSІІ, SPAD, photosynthesis rate, transpiration rate and photosynthetic water use efficiency measured. Statistical analysis and mean comparisons were performed using SAS software and LSD method.
Air temperature during the crop growth in 2014 was less than 2015. Therefor leaf area index (4.9 and 4.5 in 2014 and 2015, respectively), relative water content (82.5 and 70.4%) and stomatal conductance (47 and 23 mmol.m-².s-1) in 2015 were less than 2014, but leaf temperature was higher (38.6 and 43.1 ºC). In 2014, PS ІІactivity was not affected by irrigation treatment, but negative effect of deficit irrigation on PSІІ activity was observed in 2015. In 2014, there was no significant difference between stomatal conductance in I120% and I100% (60.8 and 57.3 mmol.m-².s, respectively), but mild and severe deficit irrigation caused to significant reductions in stomatal conductance (43.5 and 26.5 mmol.m-².s, respectively). In 2015, stomatal conductance in I100% was 26.3 mmol.m-².s-1 significantly less than from I120% (34.7 mmol.m-².s). The lowest stomatal conductivity was recorded with mild and severe deficit irrigation in 2015 (14.9 and 15.8 mmol.m-².s-1 respectively). In 2014, leaf temperature in I100%, I80% and I60% (0.78, 1.70, and 1.84ºC respectively) was higher than I120%. These values were obtained 2.66, 3.66 and 4.60ºC in 2015 respectively. In I120%, I100%, I80% and I60%, CO2 stabilization rate was 29, 26.1, 17.7 and 14.9 μmol.m-².s-1, respectively. Nitrogen consumption up to crop requirement had a positive effect on photosynthesis rate. The photosynthesis rate in N140%, N100%, N70% and N40% was 25.5, 23, 20.6, and 18.6μmol.s respectively. Mild and severe deficit irrigation reduced transpiration rate. However, in I100%, using 70% nitrogen demand, transpiration rate was significantly higher than other nitrogen levels. By reducing water amount and less nitrogen consumption, photosynthetic water use efficiency was decreased. Nitrogen deficiency in I120% and I100% reduced photosynthetic water use efficiency. In I80%, photosynthetic water use efficiency reaction to different nitrogen levels was varied. In I60%, effect of different nitrogen levels was not significant.
Leaf area, relative water content, stomatal conductance, photosynthesis and transpiration rate were reduced with increasing of water deficit. Increasing of nitrogen up to the crop requirement led to increased leaf area and photosynthesis rate. Under adequate water condition, nitrogen consumption up to recommended amount led to increased photosynthesis rate, decreased transpiration rate and finally improved photosynthetic water use efficiency. But under deficit irrigation, there were no significant differences in traits among nitrogen levels.