Tillage effects on humus content in the soils of Ukraine: A meta-analysis of current scientific evidence

Abstract

Tillage is an agrotechnological factor with the strongest influence on soil properties, especially, agrophysical and agrochemical ones. Soil fertility depends on numerous soil traits, but mainly on the content of humus (soil organic matter). The current food crisis and the aggravation of negative climate impacts on environmental systems require a scientifically sound reaction of current agriculture to future challenges. Adoption of optimal tillage practices is crucial for the preservation of soil health and, consequently, for food security. The study is devoted to the meta-analysis of current scientific evidence on optimal tillage systems for Ukrainian soils in terms of humus content preservation. The meta-analysis was carried out through the standardized mean differences algorithm. The average effect size was calculated by the Cohen’s distance. Publication biases were estimated using fail-safe numbers. The heterogeneity of the studies was estimated by Higgins coefficient the Chi2 homogeneity test. Only robust domestic scientific studies were included in the meta-analysis. To search for scientific publications, the Google Scholar engine was applied. In general, 18 eligible studies out of more than 50 were enrolled and processed. It was established that there is not sufficient scientific evidence in favour of no-till systems in Ukraine. The meta-analysis provided inconclusive results because of lack of high-quality scientific research, high bias of publications and high intra-studies variability. As for the comparison between conventional ploughing and ploughless tillage systems, strong evidence was established in favour of ploughless tillage. Notwithstanding the subtle general effects size of 0.24, it was statistically significant at 95% confidence interval. Low heterogeneity and intra-studies variability strengthen the evidence in favour of ploughless tillage without soil layer inversion. More thorough scientific investigations should be performed to provide more evidence on the benefits of zero-tillage systems on Ukrainian soils.