اثر همزیستی میکوریزا و آبیاری تکمیلی بر عملکرد و عناصر دانه و بقایای گیاهی نخود (Cicer arietinum)

Introduction
As water supplies decline and/or the cost of water increases, it is clear that producers are being driven toward deficit irrigation management, and some level of plant water stress is inevitable. The challenge is to define management systems that minimize the negative impact of the expected stress. Chickpea (Cicer arietinum L., Fabaceae family), a resistant pulse plant to drought and heat, producesan acceptable yield in poor soils. Chickpea is also used as a low-cost product in semi-arid tropical regions of cropping systems. Since the chickpea production in most regions is limited caused by lack of moistureparticularly during the generative growth stage, irrigation can be effective for improving the performance and its stability. Supplemental irrigation has a key role to reduce tensions in the critical stages of plant growth, and also compensate the serious yield lost. The occurrence of drought stress in some stages of plant growth could be irreparable damages. The recognition of the critical stages of plant growth and water stress when they need to meet in order to obtain maximum yield. West Azerbaijan has a large portion of the area under cultivation and production of chickpea (66500 ha), especially in rainfed condition. Plant rhizosphere is known to be preferred ecological niche for soil microorganisms due to rich nutrient availability. Rhizosphere microorganisms (particularly fungi) can improve plant performance under stress environments and, consequently, enhance yield. There is considerable evidence to suggest that arbuscular mycorrhizal fungi have the potential to increase the tolerance of their host plants to water-deficit stress. The mycorrhizal fungi improve profitability nutritional status of host plant due to water and nutrient (especially P) uptake in irrigated and rainfed conditions.
 
Materials & Methods
A two-year (2014-2015) factorial experiment was conducted based on randomized complete block design with three replications at West Azarbaijan Agricultural and Natural Resources Research Center. Treatments were rain interrupted (10 May, 24May and 7 June), mycorrhizal symbiosis (non-mycorrhizal plants and inoculation with Glomus intraradices) and irrigation (rainfed and one supplemental irrigation). Plant residues (ash, protein, calcium, potassium and phosphorus) and grain (protein, potassium and phosphorus) quality were respectively determined at podding and seed maturity (Association of Official Analytical Chemists, 2005; AACC, 2000). Chickpea plant residuesand grain yields were measured by harvesting of 1 m2 of each plot. Data were analyzed using SAS9.1 and means were compared by Duncan's new multiple range test (MRT) at 5% level of probability.
 
Results & Discussion
The combined analysis of 2-year data showed a significant effects of year, rain interruption, mycorrhiza and supplemental irrigation on the forage (plant residues) yield and quality (ash, calcium, phosphorus and protein), and also significant effect on the grain yield and quality (potassium, phosphorus and protein). Significant interaction effects of year, rain interruption, mycorrhiza and supplemental irrigation on quality of plant residuesand grain exhibited varied response of chickpea to these above studied treatments. Means comparison indicated that in the studied area one irrigation improved the yield of chickpea grain and plant residues. In the current study, it was found that the inoculation of chickpea with G. intraradices regardless of irrigation regimes enhanced theplant residues (phosphorus, calcium, ash and protein) and grain (phosphorus and protein) quality. Delay in rain (from 10 May to 7 June) increased the performance of chickpea, so the highest grain and forage (plant residues) yield were obtained from irrigated mycorrizal plants in continuing rainfall until the 7 June. Chickpea grain yield was more under supplemental irrigation than dryland farming. The early rain interruption showed a bigger yield loss because of longer stress, but the supplemental irrigation compensated a part of this negative effect. The yield compensation in mycorrhizal chickpea plants was better than non-mycorrhizal one. Rainfall continued up to 7 June, increased the plant residues (1451 kg/ha) and grain (602 kg/ha) in irrigated mycorrhizal plants more than earlier rain interruption (10 and 24 May).
 
Conclusion
Generally, quality of rainfed chickpea plant residues and grain were improved by supplemental irrigation. Mycorrhizal symbiosis, regardless to rainfall interruption, enhanced the quality of chickpea plant residues and grain yield (up to 20 % for supplementary irrigation and 24% for rainfed). Results showed that the supplemental irrigation and mycorrhizal symbiosis are reliable techniques to achieve optimal performance of rainfed chickpea.