Meta-analysis of biochar application effects on soil fertility and yields of fruit and vegetables in greenhouse

Objectives Greenhouse cropping is one of the most important practices for vegetable production. Qualification and assessment of biochar application effect in greenhouse are of significance to enhance their popularization.

Methods By selecting independent research literatures with certain criteria, we collected 214 paired data set and conducted a meta-analysis to quantify application effects of biochar with various characteristics (e.g. raw material, pyrolysis temperature, C/N, pH etc.) and artificial application practices (e.g., application amount and duration) on yields of fruit and vegetables and soil chemical and physical properties.

Results Biochar application under greenhouse condition increased soil pH, and content of soil organic carbon, nitrogen, and phosphorus significantly. Compared to the Control, biochar application increased the yield of fruit and vegetables significantly. The increment in yield was 23.9% for leafy vegetables, 43.3% for tubers, 60.6% for fruit and vegetables, and 79.5% for beans, respectively. The averaged increment in yield was 30.8% when the application rate was less than 10.0 t/hm², and 14.0%–27.4% at the rate of 10.0–80.0 t/hm². The improvement of yield was remarkable within 6 months after biochar application, and it reached a maximum of 30.4%. However, the yield improvement was not significant 6 month later after biochar application. Feedstock sources showed significant effect on the yield improvement of biochar application. The yield improvement followed the order of livestock and poultry manure (66.4%) > straw (31.2%) > wood (19.0%) > shell residue (5.9%). Pyrolysis temperature also showed impact on yield improvement with biochar application significantly as well. The increment was 20.4%–36.5% when the pyrolysis temperature was lower than 600℃. However, it showed no effect on yield improvement when temperature was over 600℃. The increment in yield was 19.3%–49.1% when the biochar C/N value was less than 100, showing a rapid decreasing trend with the increase of biochar C/N ratio. Alkaline biochar (pH 9–10) showed better improvement effect than that of the acid ones.

Conclusions The feedstock sources and application rates of biochar are the two key factors that regulating the yield improvement of fruit and vegetables and soil fertility. Application of biochar derived from pyrolysis temperature of 400–500℃ with C/N value less than 100 and pH 9–10 are recommended for better yield improvement. The application rate of not over 10 t/hm² and application with intervals less than 6 months are recommended to save the cost and improve economic benefits.