The Effect of Drought Stress on Yield and Yield Components of Maize Using Meta-Analysis Method

Meta-analysis is a method that summarizes and combines independent results from the number of different articles, which can be used to determine the results of a series of studies. Meta-analysis is a method for statistically comparing the results of independent studies on a subject. Meta-analysis is a type of research on other research. It can be used to re-examine the various studies that have been done on a particular topic and to compare them statistically. This approach is an independent study in itself.

For this purpose, this study was conducted as a meta-analysis of the effect of drought stress on corn yield. The sample of the study included collecting articles from the Sid site, which selected a total of 13 papers and theses from among 61 articles. The first step in performing the meta-analysis is to calculate the standard difference between the mean of the control and experimental treatments (the stress treatment), which is called effect size (d). Therefore, a value of d is calculated for each of the 13 independent experiments examined in this meta-analysis. At first, the remote and asymmetric part of the funnel diagram was removed after estimating the number of studies in this part. Were replaced with their missing symmetric part around the center. Finally, the estimate of the total mean as well as the corresponding variance was obtained based on the completed Funnel diagram. In meta-analysis, it should be considered which studies agree with the null hypothesis and which oppose it; for this purpose, the accumulation or Forrest diagram was used. All calculations and charts were performed in Excel.

In this study, four traits were studied. The standardized values for the effect of drought stress on biological yield were significant in all four treatments (P <0.001). It should be noted that the effect size for each trait is the difference between the mean drought modulus of the control treatment (without stress), so the positive values indicate the higher mean of drought stress treatment than the control treatment. Based on effect size chart, standardized size values were significant for drought stress on grain yield in all 4 treatments compared with control. From the collection of d collected studies, the accumulation diagram related to the study of the effectiveness of grain yield against drought stress was drawn. The research used in this trait shows the estimation of the effect of the treatments very close to zero and with a low confidence interval. Among the high-weight researches, we can refer to the articles of Khadem et al. (2011). Regarding the funnel diagram, the articles are in the range of 95% and the amount of bias is less and its bias is more, which is considered a positive thing as a result of research. In the above diagram, T is an exact experiment that has less standard deviation and has a smaller number on the x-axis and is located at the top of the diagram and close to the vertical zero-axis. Only 5 studies on the effect of drought stress on grain yield were not significant and were excluded from the funnel.

The results of this study showed that, despite numerous studies on the effect of drought stress on yield and yield components of maize in the country, the results are very diverse and have high dispersion. This issue has not yet determined the exact effect of drought stress, especially on yield and yield components of maize. As a robust statistical method, the meta-analysis provided a proper and accurate tool for combining the results of independent experiments and established specific ranges for the effects of drought stress, especially on the corn counts.