Biochar Effects on Soil and on Crop Yields
Remark: The references mentioned in square brackets [ ] relate to the references used in the scientific report of dr. Arnold on the Biochar Calculator. You will find these references under References. The text is an excerpt of the scientific report.
EASY READING SUMMARY
Biochar acts as a soil amendment whether as a component of farm manure from stable bedding, as a manure additive or as a component of organic fertilizer substrates. Positive effects could be observed in scientific studies on the following points:
- Biochar increased soil organic matter after application and with that the fertility and quality of the soil.
- The porous surface of biochar allows for increased water retention in the soil.
- Biochar is also responsible for medium- and long-term storage of nutrients and microorganisms in the soil.
- Biochar creates resilience against stress from climate change.
- Biochar increases the yield of farm- and grassland in scientific studies between 10% to about 20% and up to 40%, with a relatively realistic average of 15%.
- Biochar also reduces also heavy metals in soil and also in the edible parts of the plants.
Biochar acts as a soil amendment whether as a component of farm manure from stable bedding, as a manure additive or as a component of organic fertilizer substrates.
Numerous studies (see, e.g., reviews in [ 73 ][ 74 ][ 78 ][ 84 ][ 86 ][ 89 ][ 117 ], and single study publications e.g. [ 121 ] to [ 140 ]) dealt with potential benefits and particular aspects of biochar application as soil amendment. Most of the studies investigated the change of the soil composition, e.g., regarding the increase of soil organic matter SOM and soil organic carbon SOC, after biochar application (e.g., [ 139 ]). Moreover, the porous surface of biochar allows for increased water retention in the soil, in addition to medium- and long-term storage of nutrients and microorganisms. This is becoming more important as the frequency and severity of droughts continues to increase due to climate change (see chapter 2.2.2).
From an agronomic point of view, the decisive factor for the use of biochar as a soil amendment, besides the sustainable increase in soil quality (humus content, soil organic matter SOM, microbial diversity…) and improved resilience against climate change-induced stress situations, is the expected yield increase in arable farming and grassland use.
Crop Yield Increase
The yield-increasing effect of biochar in agricultural soils depends on numerous factors and can therefore hardly be quantified across the board. Biochar in itself is not a fertilizer, but a vehicle for nutrients and microorganisms. The positive effect of biochar on plant growth therefore depends, among other things, on the loading of biochar with nutrients, the promoting influence of biochar on soil fauna, the organic biomass already present in the soil, moisture, soil pH, biochar composition, possible synergistic effects with fertilizers and soil substrates used at the same time, the type of crop grown on the area of interest, and much more. In general, it can be stated that “poor”, “stressed”, sandy and coarse-grained soils are more likely to benefit from biochar from a yield point of view than “rich” soils (“black soil”, chernozem) with an already existing high fertility. This is understandable, since the effect of biochar is more pronounced in less productive soils than in already productive soils (rough summary from [ 73 ]). “… the highest yield increases with biochar [can be achieved] in acidic, low-SOM soils.” (sited in [ 73 ]). Orientation and reference values are provided by some broad meta-studies from 2020, where annually recurring application rates of 0.5 to 2 Mt biochar/ha (0.22 to 0.89 US ton/acre) were used (cited in [ 73 ]).
The most comprehensive meta-study to date by Dai et al. [ 125 ] (1,254 data sets) provided a mean yield increase of 16%, although no distinction was made between biochar applications with and without fertilizer addition. Yeh et al [ 126 ] demonstrated that even in temperate climates, a biochar fertilizer application resulted in increased yields of 15% on average compared to fertilization with the same amount of nutrients but without biochar. Zhang et al [ 127 ] (444 data sets) found an average yield increase of 21%, averaged over several climates, but did not distinguish between biochar applications with and without fertilizer addition (discussed in [ 73 ]). Glaser reports an average additional yield of 10% in his 2018 review of 21 meta-studies [ 74 ]. In individual cases, higher additional yields were determined due to the effect of biochar in the soil, e.g., an old charcoal burner site in Belgium with an additional yield of 23% (maize). The highest additional yields were observed in studies on the effects of co-composted biochar as a soil additive. Wang et al. [ 128 ] determined an average yield increase of 40% for cereals in a similar case.
Against this background, an initial rough estimate of the yield increase to be expected from the use of biochar, charged with nutrients on agricultural land, in temperate climate zones and cropland soils of mid quality appears to be relatively realistic at 15%.
In addition, there is the effect of biochar on the improvement of soil and crop qualities. This includes, for example, the reduction of heavy metal contents in the entire biomass and also in the edible parts of the plants (e.g., chromium -64%, lead-49%, cadmium -32%) due to the adsorptive effect of biochar. Biochar produced at high pyrolysis temperatures achieved particularly positive effects here. However, possible desorption of heavy metals with significant and relatively short-term changes in soil properties (e.g., pH) cannot be ruled out. Pesticides and herbicides are also immobilized by the adsorptive effect of biochar with a protective effect on the groundwater, the soil and its soil fauna [ 73 ].