تأثیر تناوب‌های زراعی مختلف بر عملکرد دانه و برخی خصوصیات زراعی گندم (Triticum aestivum L.) در شرایط دیم کرمانشاه

Introduction
Crop sequencing with a particular arrangement in a 2-3 or more yearly period is known as crop rotation. Considering crop diversity and soil fertility crop rotation is essential because it prevents soil degradation which is a result of sequential cultivation of one crop causing nutrients imbalance, exudation of different compounds and antibiotics from crop roots. Determining crops sequencing, affects crops yield and its quality. It was reported by many researchers that including the forage crops and legumes as a winter crop in rotation either for forage production or green manuring, i.e. growing two or three crops annually was a necessary practice for improving the soil fertility as well as increasing the annual revenue. So, this study was conducted to investigate effects of different crop rotations on grain yield and some agronomic traits of wheat in dryland conditions.
Materials and methods
The experiment was carried out based on randomized complete block design (RCBD) with four replications in two neighbor sites in dryland agricultural research sub-institute Sararood - Kermanshah during six years from autumn 2006 fall to 2012 summer. Treatments were concluded five crop rotations as wheat (Triticum aestivum L.) - wheat, fallow - wheat, chickpea (Cicer arientinum L.) - wheat, vetch (Vicia dasycarpa Ten.) - wheat and safflower (Carthamus tinctorius L.) - wheat. All crop rotations were included wheat so in one site the first year wheat was cultivated in all plots and in other site the other components of crop rotations were cultivated. Plot area was 10×20 m2. Plant height (10 randomized plants), number of spikes per meter square, number of seeds per spike, thousand seeds weight, biologic yield and grain yield were analyzed.
Results and discussion
Main effect of year on wheat plant height and yield components were significant and showed different climatically conditions in experiment years. Interaction effect of rotation × year was significant on wheat plant height and number of spikes per m2, and in the end of rotation period (2011-12) effect of continuous wheat appeared on number of spikes per m2 as in this year the lowest number of spikes per m2 in continuous wheat observed compare to other rotations. Ghaffari (2002) considered the rotation of chickpea, sunflower (Helianthus annuus L.) and fallow with wheat and reported no significant effect on plant height of wheat in three period of rotation. The results of thousand kernel weight showed non significance difference among rotations and year × rotation interaction that were similar to results of Dogan et al. (2008) in two rotation period of wheat and sunflower, canola (Brassica napus L.), chickpea and forage pulses. Results of composite ANOVA for biologic and grain yield of wheat showed significant effect of year and treatment × year on these traits; and continuous wheat had the lowest yield and other rotations were located in higher classes. Continuous wheat treatment at the last year had the lowest spikes per meter square among rotations. Stevenson and Kessel (1996) stated an increasing trend in wheat grain yield in pea (Pisum sativum L.) – wheat rotation compared to continuous wheat due to breaking of diseases cycles and availability of potas, phosphorous and sulfur. Correlation between wheat grain yield in different rotations with total precipitation showed that in all rotations except continuous wheat, there was a positive significant correlation between precipitation and wheat grain yield. So, it can be concluded that continuous wheat has reduced the potential usage of optimum growing conditions.
Conclusion
Rotation of wheat with each of these crops (chickpea, vetch and safflower) can be proposed, considering the importance of crop diversity and additional yield of these crops.