Necessity of using meta-analysis in field crops researches

Each year, many studies carried out on various aspects of crops. Results of these studies were not similar and sometimes were inconsistent, due to different effects of environment. For example, results of studies on the effect of seed size on seedling emergence rate were varied: some of them were reported a positive impact, some negative impacts and some no impact. In such cases, the final conclusion is difficult. Meta-analysis is created for such cases. Using this method, various studies on a specific topic can be analyzed statistically and reliable conclusions can be obtained from several studies that were fragmented and even contradictory. This method is recently gained attention by the field crops researchers and most published articles are new on meta-analysis in agronomy sciences. There is no published study in field crops researches and agronomy in Iran and it is necessary to use this methods. Whit this method, it could be possible to summaries many studies on a specific topic (i.e. density, planting date, application of water and fertilizers, and application of various treatments) and to find a final conclusion about the topic. The statistical basis of meta-analysis method is described in this article, the advantages and limitations of its application are discussed with some examples (from national and international studies).