28 December 2023

New soil fertilizers can be made from pulp waste


Adding biosolids to conventional fertilizers can reduce greenhouse gas emissions and improve soil quality, according to a Canadian study. A circular solution that is good for plants and the environment

by Matteo Cavallito


Pulp processing waste can be turned into organic fertilizers capable of replacing at least part of their conventional counterparts, thus reducing the overall environmental impact. This is supported by research from the University of Alberta. The circular solution identified by the scientists would also improve soil and tree health.

According to Scott Chang, lead author of the study and a professor in the Canadian university’s Faculty of Agricultural, Biological and Environmental Sciences, quoted in a statement, the findings provide new insights into the effects biosolids could have if they were redirected into the same tree plantations that feed the forestry industry.

The study on fertilizers

The investigation, whose findings were published in the Journal of Environmental Management, took place over two years on a 2.4-hectare experimental site of hybrid poplar trees located in northern Alberta. Researchers compared the effects of three different applications-biosolids, conventional urea-based fertilizers and a combination of both-on emissions of carbon dioxide, methane and nitrous oxide from the soil.

“We found that the addition of biosolids increased soil CO2 and N2O emissions by 21 and 17%, respectively, while urea addition increased their emissions by 30 and 83%, respectively,” the study states.

Moreover, the researchers noted with some surprise how the combined use of the two types of fertilizers had not produced an increase in emissions. “The addition of urea did not affect soil CO2 emissions when biosolids were also applied,” the research says.

The role of microorganisms

The study showed how the application of biosolids, either alone or with conventional fertilizers, proves beneficial for plant growth in the soil. Use of cellulose waste, in particular, increased levels of dissolved organic carbon and microbial biomass capable of decomposing organic matter. All of this promotes the release of nutrients into the soil.

In addition, the study points out, “The addition of biosolids and biosolids + urea increased soil dissolved organic carbon (DOC) and microbial biomass C (MBC), while urea addition and biosolids + urea addition increased soil inorganic N, available P and denitrifying enzyme activity (DEA).”

Moreover “the CO2 and N2O emissions were positively, while the CH4 emissions were negatively associated with soil DOC, inorganic N, available phosphorus, MBC, microbial biomass N, and DEA. In addition, soil CO2, CH4 and N2O emissions were also strongly associated with soil microbial community composition.”

Fertilizers in the crosshairs

The study assumes significance by bringing out a strategy to mitigate the impact of traditional fertilizer use in global soils. In 2021, FAO’s Global Assessment of Soil Pollution report showed that in 2018 the Planet’s soils had absorbed 109 million tons of synthetic nitrogen fertilizers. This came alongside the growing use  of pesticides (more 75 percent on a global scale between 2000 and 2017).

The problems, however, are not confined to soils. A study by a group of scientists at Nagoya University in Japan, for example, showed how nitrogen from the soil is a major contributor to contamination of waterways. And not without consequences.“Nitrate is an essential nutrient for plants and phytoplankton,” the authors explain. “But excessive nitrate levels in streams can damage water quality, cause eutrophication (the over-enrichment of water by nutrients), and pose health risks to animals and humans.”