The impact of various soil fertilizers on yield and growth criteria of saffron: A meta-analysis of field studies

The goal of meta-analysis is to provide knowledge and better understanding of the phenomena under study. The statistical technique of a large collection of analysis results from individual studies for the purpose of integrating the findings. We conducted a global meta-analysis to evaluate the effect of various fertilizers on saffron yield using data obtained from peer-reviewed publication (71 studies representing 14 studies on biofertilizers, 16 studies on compost, 14 studies on humic acid, 26 studies on chemical fertilizers (NPK) and 16 studies integrated application of fertilizers). Based on the results, the highest effect size was related to the impact of humic acid on dried weight of stigma (g=3.434). After humic acid, biofertilizer, chemical fertilizer and compost were computed in the next ranks. The standard error for compost (E = 0.101) was calculated less and with higher accuracy, so it is recommended with 95% confidence interval. Based on the results of Begg and Mazumdar correlation, all studies except humic acid on dried weight of stigma, humic acid on fresh weight of stigma, manure on flower number, chemical fertilizers on dried weight of stigma and chemical fertilizers on fresh weight of flower were homogeneous. Among the application of manure rate, 60 t cow manure per ha and 5 t poultry manure per ha had the highest and lowest effects, respectively. The results of meta-analysis for compost rates on dried weight of stigma indicated that 60 t per ha had the maximum impact. The highest effect of humic acid on dried weight of stigma was computed for 30 kg/ha. Based on the results it seems that there is no good long-term plan to resolve existing problems of soil fertilizers on saffron production systems and most of the experiments are based on researcher’s opinion, ease of implementation or following published articles in credible journals. Generally, the meta-analysis results provide a basis for conducting trade-off analyses to support the fertilizer management and development strategies based on available scientific findings.