Meta-analysis of the Effect of Planting date on Yield and Water use Efficiency in Potato

Introduction
Potato (Solanum tuberosum L) is a relatively cold-tolerant plant and is a cool-season vegetable. One of the important factors in the growth, development, and yield of potatoes is the planting date (Struik, 2023). When determining the planting date for potatoes, care must be taken to ensure that the plant is planted at a time when it has achieved maximum vegetative growth before being exposed to hot temperatures and long day lengths, which leads to optimal tuber production and quantity (Dehdar et al., 2014). Various experiments have been conducted to investigate the effect of different potato planting dates in Hamedan and different potato-growing regions of the country with relatively similar and comparable climatic conditions to Hamedan province. Despite the fact that potato planting date experiments have a long history in different potato growing regions of the country, the results have been accompanied by many differences. With the aim of reaching a single guideline and examining the degree of convergence and consistency of the desirable effects of planting date on yield and water use efficiency in potatoes, research conducted in different regions of the country over a 20-year period was subjected to meta-analysis.
 
Materials and Methods
 In this research, firstly, researches were conducted in different regions of Iran, in a period of 20 years from the beginning of 2000 to 2019 from WOS foreign data bank and internal data bank and official websites of Iran DOC. , Fipak, Magiran.Com and SID were searched. In the following, screening was done among the searched researches. Then, the final sources were extracted which had a lot to do with the issue of planting date and its effects on yield and water efficiency. In the investigation of the planting date in the conducted studies, it was found that the set of studies could be separated into two evaluation groups of autumn and summer planting date in potato. For this purpose, the full text of the extracted sources was fully examined and the required statistical data from each of the studies including mean, standard deviation and sample size were extracted from the control planting date and other experimental planting date in each independent studies. Finally, the resulting data were combined and subjected to meta-analysis using Stata/SE version 11.1, StataCrop, Lp, Station, TX software. To evaluate the homogeneity of the study results, the I² index and the Q test (Hedges et al, 1999; Higgins and Thompson, 2002) were used.
 
Results and Discussion
 Analysis of variance of the initial studies on the effect of planting date in potatoes and meta-analysis revealed that there was a significant difference (P≤0.05) in total yield in both groups of planting dates: fall or winter and spring or summer. By examining the forest plot obtained from the meta-analysis, it was found that in autumn and winter crops, there is a significant homogeneity of the average of the studies within the range of deviation from the average yield. In four of the six studies conducted, the weighted yield values ​​were very close. The average yield of the experimental treatments in these four cases intersected or was tangent to the standard deviation ratio balance line, which is an indicator of homogeneity in the meta-analysis. The average of the experimental treatments in two cases of the autumn planting group is much higher than the average of the whole group, and this is due to the planting in autumn and winter and the harvesting in spring. The result of the homogeneity assessment using the Q test in summer planting date was 54.71%, which indicates moderate homogeneity with a tendency towards weakness in the standard deviation results of the data of the studies compared to autumn planting date. In two of the four studies conducted in this group, the yield of the planting date treatments increased significantly compared to the control. However, in only one study, the planting date treatments showed a decrease in yield compared to the control. By examining the results of the planting date meta-analysis, it was found that generally in autumn planting date, the production capability and capacity of potatoes decreases, and the specific reason for this is that the length of the potato growing season coincides with the warm climate in these regions compared to summer planting date. In the final study of summer cultivation, the plausible reason for the reduced yield of the planting date treatments compared to June 15 (control) was the implementation of 2 delayed planting dates in these 5 treatments. In delayed planting date, as has been shown in the result of Meta-analysis, there is a relative decrease in yield. However, the results of other experiments (Hassan Panah and Hassan Abadi, 2017; Parvizi and Ghadami Firouzabadi, 2014) have shown that delayed cultivation saves about 15 to 20 percent of water consumption in early-maturing varieties and about 20 to 25 percent in late-maturing varieties.
 
Conclusion
Totally, based on the results of the meta-analysis conducted in this study, it was determined that although the average yield of autumn potato planting date is significantly lower compared to summer planting date, they have relatively higher homogeneity. It is also necessary that in order to achieve the desired state of yield and higher water productivity in the country, a large part of the summer potato planting date be carried out with a delay of 20 to 25 days compared to the current planting date. Therefore, it is better to move from late June to early July to July 20 to 25.