For dairy farmers, an increase in soil organic matter could lead to improved soil carbon sequestration, leading to a lower carbon footprint. Roughly half of all organic matter is made of carbon. To determine the amount of carbon sequestration (soil carbon), measurements must be taken.
Measurement challenges
“Accurately measuring soil carbon is difficult,” says WUR’s Jan Peter Lesschen. “The topsoil can store approximately 50 to 100 tonnes of carbon per hectare, but it’s not always distributed evenly across the plot. At the moment, dairy farmers take plot samples once every four years. A carbon sequestration of 0.5 tonnes represents a virtually insignificant change in this stock (0.5-1%), which is often less than the accuracy with which the soil is analysed. Geographical and weather factors also impact the degree of carbon sequestration, such as differences in altitude, the presence of peat layers, and the effects of temperature and moisture.”
Monitoring system
An alternative is to use scientific models to calculate soil carbon. Here, too, differences exist per farm; for example, because it’s difficult to estimating the amount of carbon generated by crop residue.
Lesschen and his colleagues at Wageningen Environmental Research and Wageningen Livestock Research developed a monitoring system that’s accurate enough to generate a reliable result for multiple plots and farms. The current approach undertaken by the 33 participating companies contributes to a 2% reduction in CO2 emissions on average, with no active management of carbon sequestration. The researchers propose supplementing the models with additional field measurements taken over several years, combined with annual soil samples.
Fine-tuning the scientific model
“We want to take frequent soil carbon measurements on a large number of plots,” explains Lesschen. “We also want to centrally document activities such as fertilisation, grassland renewal, and crop rotation on these plots. As more measurement data becomes available, we can fine-tune our scientific model and make more accurate calculations for individual plots.”
In the meantime, dairy farmers will focus on taking measures that have been proven to help carbon sequestration, such as minimising grassland renewal and maximising the supply of carbon from manure and crop residues.
Read the report: edepot.wur.nl/526420