Studies have shown that adding biochar to soil can improve soil fertility, increase nutrient utilization in plants, improve soil’s water-holding capacity, increase crop yield and reduce emissions of greenhouse gases.
However, if you are a potato grower, your joy may be short-lived. Biochar and potatoes do not go very well together—at least not if you are aiming at saving water, according to results from Aarhus University in Denmark.
During her Ph.D. studies, Caixia Liu from Aarhus’s Department of Agroecology investigated the effect of adding biochar produced from wood on potato growth, yield, nutrient uptake and water utilization when three other factors were also taken into consideration: irrigation methods, phosphorous fertilization and inoculation with a certain class of beneficial fungi. The aim was to investigate the interactions between biochar and the fungi on the growth of potatoes.
Potatoes are rather sensitive to drought and phosphorous deficiency because of their relatively small root system. It would be easy to merely suggest irrigate and fertilize in plentiful amounts, but since both phosphorous and water are limited resources, it is important to use them optimally.
Earlier studies at Aarhus have shown that much water can be saved by irrigating alternately on each side of the potato ridge and letting the other side remain dry—the so-called alternating partial root zone-drying irrigation.
It is also possible to save phosphorous. In the course of her studies, Liu found that inoculation of potatoes with a certain type of beneficial fungi—arbuscular mycorrhizal fungi (AM fungi)—can improve potatoes’ utilization of phosphorous, make utilization of water more efficient, and increase potato yield in crops that are stressed due to drought or phosphorous deficiency.
The question was, What happens when you combine biochar and inoculation with AM fungi? Would there be a double win? The answer was no.
Liu carried a series of studies with various combinations of irrigation (either full irrigation or alternating partial root zone dehydration), phosphorous fertilization (none or 0.11 mg P/g soil), inoculation with AM fungi (inoculation or no inoculation) and addition of biochar (addition or no addition).
Biochar inhibited the growth of potatoes. If the crop is irrigated fully, the soil is given no phosphorous at all, and the potatoes are not inoculated with AM fungi, then addition of biochar can increase potato yield. This was the only case in the studies; in all other cases, addition of biochar to the soil had the opposite effect.
The negative effect on potato growth was especially pronounced when phosphorous was added, alternating partial root zone drying irrigation was used, and the potatoes were inoculated with AM fungi. Addition of biochar inhibited the growth and vigor of young potato plants, some of the young potato plants even died.
“I would recommend that the farmer refrains from adding biochar produced on the basis of wood to an AM system, where the soil has been fertilized with phosphorous or if the soil is prone to drought,” says Liu. “Biochar remains in the soil for a long time. so there is no going back.”
Source: EurekAlert!