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.

Orig­i­nal article (German): Feld- und Gefäßver­suche mit Pflanzenkohle in Böden: Ergeb­nisse der ersten Dekade und Aus­blicke (Field and vessel exper­i­ments with biochar in soils: Results of the first decades and outlooks)
Author: Claudia Kammann, Hans-Peter Schmidt
Pub­lished in: Peter Quicker, Kathrin Weber (Hrsg): Biokohle. Her­stel­lung, Eigen­schaften und Ver­wen­dung von Bio­massekar­bon­isat­en. Springer Verlag 2016, p. 293–299