The number of humans on the planet is continuing to grow. Sub-Saharan Africa has the fastest population growth in the world, and this trend is expected to continue in the coming decades. Consequently, crop production in this area must increase as well.
“In these areas, there is a need for climate-smart agricultural practices that increase the climate resilience of food production systems,” PhD candidate José Luis Munera-Echeverri says.
In his doctoral thesis, Munera-Echeverri has examined the use of biochar as a part of conservation farming in Zambia. Biochar is charcoal used as a soil amendment. It is a stable solid, very rich in carbon, and made from biomass via pyrolysis. Munera-Echeverri explains that applying biochar to crop soils have many advantages.
“It binds carbon, improves soil fertility and it makes use of resources that otherwise would have gone to waste,” he says.
“The goal has been to contribute to the development of climate-smart agricultural practices.”
Climate-smart agricultural practices are the ones offering the adaptation to the negative effects of climate change on crop production and mitigation of the emissions of greenhouse gases to the atmosphere.
Increase yields and decrease emissions
Conservation farming and the addition of biochar to the soil have been suggested as climate-smart agricultural practices. Conservation farming involves minimum tillage, crop residue retention in soil and crop rotation; while biochar is a carbonized material made of agricultural wastes with the purpose of being used as a soil amendment.
“Both agricultural practices have the potential of sequestering carbon in soils,” he comments.
“They increase yields and decrease emissions of greenhouse gases to the atmosphere. In the case of biochar, it is nitrous oxide.”
“However, there is little research on the combined effects of both practices in Sub-Saharan Africa, where climate change is already affecting negatively agriculture.”
“I have developed a method for cation exchange capacity of biochar, which is highly reproducible and uses inexpensive reagents.”
The application of this method in different types of biochar revealed that some biochars may have a large capacity of retaining nutrients while others not. Biochar properties differ greatly depending on the feedstock used, and the temperature in the charring process.
“Having reliable estimates of cation exchange capacity is crucial for predicting the effects of biochar on crop production and soil fertility,” he explains.
Higher levels of carbon
Munera-Echeverri has evaluated the effects of seven years of conservation farming. The results showed higher levels of carbon (several forms), and nitrogen mineralization rates, as compared to conventional tillage. The increase of soil organic carbon was attributed to greater root biomass.
Increased soil carbon
He has analyzed the effect of soil management practices and biochar addition on the amount and quality of soil organic matter. The biochar that was used in the field trials was made of pigeon pea (Cajanus cajan) stems, which is a leguminous shrub that fixes nitrogen and whose seeds are edible.
“Biochar increased soil organic carbon in a highly stable form.”
Conservation farming increased nitrogen mineralization and soya yield as compared to conventional farming in a maize-soya-maize rotation that involved the addition of mineral fertilizer to maize crop only.
“The field trials did not show any effect of biochar on nitrogen mineralization, nitrous oxide emissions or crop yields,” he says.
Emissions related to nitrate concentration
The doctoral thesis also investigated the factors involved in the emissions of nitrous oxide, a potent greenhouse gas, from agricultural soils under conservation and conventional farming.
“My results show that nitrous oxide emissions were related to the concentration of nitrate in soil and the nitrification rates measured in-situ,” Munera-Echeverri says.
Nitrate and nitrous oxide differed between conservation and conventional systems despite receiving the same nitrogen input, which deserves further research.
Positive when fertilizer levels are low
His results suggest that conservation farming has a positive effect on yield compared to conventional farming when little or no fertilizer was added. However, this effect disappeared when ample amounts of fertilizer were supplied.
“Biochar was effective sequestering carbon in soil, but it did not have any other agronomic benefits,” he comments.
Increasing food security
Munera-Echeverri’s research is part of the ongoing development of climate-smart practices that offset anthropogenic emissions of CO2 while providing stable yields. This is particularly important in Sub-Saharan Africa where climate change is already affecting food security.
José Luis Munera-Echeverri defends his PhD thesis” Effects of conservation farming and biochar on carbon and nitrogen cycling in light textured soils in the sub-humid tropics” on Friday 7 June, 2019.