Biochar effects on crop yield variability

Context or Problem: Numerous studies have demonstrated that biochar application can increase crop yield by improving soil properties and health. Yet, these studies, however, neglected how biochar alters yield variability across years - reflecting the yield stability. Objective or Research question: This study aimed to investigate the effects of biochar application on crop yield variability. Methods: Published data from 38 experimental sites were collected from the Web-of-Science. Two-thirds of the data were originated from three main staple crops: maize, wheat, and rice. The remaining were from rapeseed, soybean, sweet potato, and peppermint. Biochar effects on crop yield and its variability as well as their driving factors were analyzed by linear mixed models depending on soil conditions, field management practices, and climate types. Results: Biochar increased the crop yield globally by 14 %, especially in soils with low pH (< 5.5), low nitrogen (N) and phosphorus (P) inputs (< 120 kg N ha(-1), <35 kg P ha(-1)), with high biochar inputs (>= 20 Mg ha- 1), and under crop rotation. Biochar increased crop yields by 12% in short-term (< 5 years) and 21 % in long-term (> 5 years) experiments. Biochar increased yield variability by 42 % in acidic soils (pH < 5.5) and by 24 % with low N inputs (< 120 kg N ha(-1)), mainly because its liming and fertilization effects were short-lasting within the first few years. The yield variability after biochar application decreased with the increase in mean annual temperature, inter-annual variabilities of temperature and precipitation, but with the decrease in mean annual precipitation in the growing season. Yield variability under biochar increased in short-term experiments by 27 %, but there was no change (0 %) in long-term experiments because of the higher yield gains and resistance to fluctuating weather conditions. Therefore, crop yield variability decreased with increasing yield in long-term experiments. Conclusions: Biochar application increased short-term variability of crop yields, but its long-term variability remained unaffected. Implications or Significance: This study highlights that biochar can support steadily future crop production in the long run.