Agronomical factors analysis on grain maize yield decreasing in Iran with meta-analysis method

To identify the limiting factors in grain maize production in Iran, a study has been carried out to particulate effective and influential management factors of this crop’s production in the country. The data come from 95 final reports or extracted articles in Agricultural Research, Education, and Extension Organization (AREEO), undergoing meta-analysis. Based on this study, of all grain maize variation, 2.93% is justified by plant density, 6.81% by planting structure, 11.12% by planting rotation, 2.28% by conservation agriculture, 25.28% by drought stress, 4.99% by cultivar, 4.46% by planting date, and 25.84% by nitrogen fertilizer. Accordingly, 100 thousand plants per hectare, zigzag double rows planting structure, maize-leguminous crops planting pattern, cultivating in residue, optimum irrigation without drought stress (in case of water availability), 700 maturity group cultivar (in case of adequate growing season), planting in May and early August in temperate and tropical climate, and using maximum 100-300 kg urea fertilizer per hectare are recommended to decrease yield gap in grain maize production.