If biochar is also composted, it is heavily loaded with nitrogen (nitrate) and promotes plant growth more strongly than uncomposted biochar. This was shown, among other things, in studies in which the effects of biochar were tested in the vineyard. The authors Schmidt and Kammann compiled the results in their book contribution on field and vascular experiments with biochar in soils in the standard work Biokohle (published by Quicker & Weber, Springer Verlag 2016).
No loss of quality
For example, 20 and 40 Mg/ha of biochar were ploughed into the soil of an Italian vineyard as part of a study. The findings showed significant effects on the yield, without loss of quality in sugar and acidity content for two consecutive years, without new addition biochar. According to the authors, this could also be due to an improvement in the water supply. In other studies, on the other hand, no increase in yield, but also
no reduction in yield could be determined. One example is the superficial application of biochar in geologically very young soil of a vineyard in Switzerland.
Lower erosion & higher yields
Another experiment of newly planted Riesling vines in a sandy soil in large containers at the University of Geisenheim showed no yield-boosting effects from the incorporation of pure biochar. However, nitrogen leaching was almost 60 percent less than in the control plantations (where it was almost 100% of the amount of nitrogen fertilizer used). However, if the biochar was incorporated into the soil together with compost, the mixture had a strong yield-increasing effect. Nitrogen losses also remained low for biochar compost mixtures (even in large quantities).
No negative environmental effects
In the already mentioned experiment of newly planted Riesling vines in a sandy soil, the positive effect of biochar also lay in the fact that larger amounts of compost could be added to improve this very nutrient-poor soil without fearing negative environmental effects if biochar was contained in the compost. To reduce nitrogen leaching, it did not matter whether the biochar was composted or subsequently mixed into the finished compost. However, the grape yield was higher during co-composting. According to Kammann and Schmidt, this can be explained very well by the enrichment of nutrients in the plant coal during co-composting. Co-composted biochar is already heavily loaded with nitrogen and gradually releases the nutrients back into its environment. Uncomposted biochar absorbs nitrogen from the soil (absorbs it like a sponge). This protects the nitrogen from leaching, but at the same time it reduces growth because the nitrogen is no longer available to the plant for the time being.