Document Type : Original Article

Authors

• Babak Mirshekarnezhad ¹
• Farzad Paknejad ²
• Ebrahim Amiri ³
• Mohammad Reza Ardakani ²
• Mohammad Nabi Ilkaee ⁴

¹ PhD graduates in Agronomy, Department of Agronomy, Karaj Branch, Islamic Azad University, Karaj, Iran

² Professor, Department of Agronomy, Karaj Branch, Islamic Azad University, Karaj, Iran

³ Associate Professor, Department of Agriculture, Lahijan Branch, Islamic Azad University, Lahijan, Iran

⁴ Associate Professor, Department of Agronomy, Karaj Branch, Islamic Azad University, Karaj, Iran

Abstract

Introduction
In many parts of the world where agriculture is important, crops usually encounter a large variation in water supply during their growing seasons. Thus, water deficit is a major constraint to crop production, even in humid environments (Soltani and Sinclair, 2012). In the context of improving water use efficiency (WUE), there is growing interest in deficit irrigation which involves applying stress levels to plants that have minimal effects on yields in order to optimize yields per unit of water used as well as crop returns increment (Rodrigues and Pereira 2009). One of the planting date goals is to detect the time after which crops could be able to keep immune even versus adverse climatic conditions Berzsenyi & Lap (2005). Arid and Semi-arid climate in the most parts of Iran with limited water resources highlights applying adaptive methods as well as new approaches to support crop producers in selecting proper varieties, accurate planting date and using water in an optimum way to maximize productivity and‌ returns.‌

Material and methods
In order to probe those of agronomic traits contributing to final yield and detecting susceptible growth stages of corn to water stress a field study took place in research farm of College of Agriculture and Natural Resources, University of Tehran. Considering irrigation management and planting date as adaptive techniques and due to the rating of relative maturity (RM) of maize hybrids, (S.C. 704) selected as late-maturing hybrid in this experiment. The experiment implemented in split-plot template based on randomized complete block design with three replicates in 2015 and 2016 cropping seasons. The experimental treatments consist of three planting dates, (PD1: 21^st April, PD2: 11^th May and PD3: 31^st May) assigned to main plots and four irrigation treatments, (100%ETc, 80%ETc, 60%ETc and 40%ETc) of the estimated evapotranspiration (ET) placed in sub plots.

Results and discussion
The lower of grain yield (4150.30 and 3589.60 kg ha^-1) and less total biomass (14354.60 and 13563.90 kg ha^-1) resulted in stress treatment of 40%ETc respectively in 2015 and 2016. The highest values of irrigation water use efficiency based either on grain yield (1.39 and 1.20) or total biomass (4.79 and 4.53) were culminated in 40%ETc treatment for the period of two years respectively. It seems that in the presence of deficit irrigation plant capability in converting per unit of water to biomass will be improved through transpiration. Our results corroborated by those of Chaichi et al. (2015) who issued stepwise reduction for ear yield, total dry matter and grain yield in stress treatment as ETc decreased. Also lower rates of harvest index (28.76 and 26.34%) also recorded at 40%ETc treatment in both years respectively. Similar results revealed by Farré and Faci (2006) who found that HI decreased markedly with increasing water stress. The lower values of grain yield and total biomass obtained at the later-planted corns due to coincidence of pollination phase with the higher levels of temperature and evapotranspiration in mid and late planting dates (PD2 and PD3).

Conclusion
In fact crops planted earlier in the season tend to develop more gradually, under cooler temperatures with enough accessibility to more abundant soil water supplies and nitrogen availability. In this experiment, water stress during pollination time affected corns under common planting date (PD2). However, as the tail-end maturation of later-planted corns (PD3) approach cooler temperatures of early autumn, due to rapid loss of leaves there is less time for them to compensate yield losses and generally results in lower overall productivity. To help farmers for applying water more efficiently, they must pay attention to align planting date and applied hybrid with local agro-ecological endowments to avoid of irrigations that are surplus to requirements.

Keywords

• Biomass
• Evapotranspiration
• Maize Pollination stage
• Water deficit stress