Effect of Nitrogen and Water Deficit Stress on Corn (Zea mays L.) Root Characters and Grain Yield

In recent years regulated deficit irrigation as a part of conservation and saving practices in water consumption has received attention. Vegetative growth stage of corn has a relative tolerance to water deficit stress. Therefore, yield loss is negligible. Nitrogen shortage stress leads to decrease in leaf area, leaf senescence and reduction of photosynthesis as a result of decrease in chlorophyll content. Roots play an important role in soil searching for water and nutrients. Root ability to change soil biochemical and physiological processes consider as a remarkable mechanism to tolerate environmental stress. Considering the role of nitrogen in corn production and irrigation in summer crops, understanding the response of corn to water stress and nitrogen consumption level are important. Furthermore, corn growth recovery after water deficit stress is critical for better understanding of water saving techniques. This study designed to determine morphological change in root of corn and their effect on corn yield under different irrigation and nitrogen levels.

In order to evaluate the impact of different levels of nitrogen consumption and water deficit stress on corn (SC 704) in field condition, an experiment conducted during 2015 in the experimental field of Ferdowsi University of Mashhad. Nitrogen levels were, including 100 and 200 kg ha-1and irrigation applied in 6 levels, including W1: complete irrigation, W2: moderate water stress (55% of field capacity) at V4-V6 growth stage, W3: severe water stress (45% of field capacity) at V4-V6 growth stage, W4: moderate water stress (55% of field capacity) at V4-V6 growth stage followed by deficit irrigation (65% of field capacity), W5: severe water stress (45% of field capacity) in V4-V6 growth stage followed by deficit irrigation (65% of field capacity), W6: deficit irrigation (65% of field capacity) after V6 growth stage. Effect of water deficit stress and re-watering concurrently with two levels of nitrogen consumption attested by crop growth rate index between stress time and 10 days after rewatering. Furthermore at silking stage, SPAD, leaf area index, the number and angle of crown and brace roots, grain yield, agronomic nitrogen use efficiency, nitrogen uptake efficiency and nitrogen harvest index measured and calculated.

Result showed that under severe water stress re-watering at the same time with applying nitrogen led to faster growth. Effects of nitrogen and irrigation were significant on SPAD, leaf area index, the number of brace roots, grain yield, agronomic use efficiency and nitrogen uptake efficiency in 5% probability level, while effect of nitrogen on number of crown root, angle of crown root and number of lateral root in crown root were significant at 5% probability level (p-value < 0.05). Grain yield had a significant and positive correlation with leaf area index, the number of brace roots and SPAD, whereas yield had a negative correlation with brace root angle. Despite highest yield obtained under the consumption of 200 kg ha-1 nitrogen with complete irrigation, yield reduction due to water deficit at V4-V6 growth stage was 6% which shows the relative tolerance of corn to water deficit stress during aforementioned growth stage and effective tolerance of root and shoot of corn for minimizing the consequences of water stress on our experiment condition.

Although highest grain yield obtained with consumption of 200 kg ha-1 nitrogen with complete irrigation, flexible management with considering availability of water and nitrogen during vegetative growth stage lead to maximum profitability. Relative tolerance of corn seedling to water deficit stress and growth recovery of crop makes it possible to save water. Flexibility of corn root number and angle can be used in breeding program to obtain hybrids with more effective nitrogen use efficiency.