In the integrated livestock-forest system, each component contributes more to one form of carbon than the other. While the forest component tends to contribute more to particulate, the pasture component influences mineral-associated carbon. Since most carbon is in the mineral-associated form, pasture management within these systems plays a central role in soil storage.
“For trees to contribute more, it would be necessary to increase the quantity and diversity of tree species. We also found that soils in integrated livestock-forest systems can store as much carbon as permanent pastures, provided nutrients are replenished and grazing intensity is controlled,” explains the agronomist.
On the other hand, the agronomist explains, “practices such as plowing and harrowing during the implementation of these systems can delay their recovery.”
In addition to integrated livestock-forest systems, integrated crop-livestock (ILP) systems were also evaluated in two situations where they were present. In both, ILP systems reduced soil carbon, unlike integrated livestock-forest systems.
To understand what was behind this difference, the microbial community and chemical characterization of functional groups of soil carbon forms were analyzed. “We used various tools, such as microbial biomass quantification, enzymatic activity, and DNA sequencing, and confirmed that soil fertility and grazing management are fundamental to ensuring storage in permanent pastures and those integrated with trees or crops,” underlines Rosemery dos Santos.
In one of the study locations, the integrated livestock-forest system showed soil carbon loss. However, in this system, the chemical composition of the mineral-associated element was still similar to that of permanent pasture, even with a lower quantity in this fraction. This confirmed that the loss was linked to decreased pasture productivity due to degradation. Low enzymatic activity, microorganism abundance, soil fertility, and particulate carbon reinforced the diagnosis of loss associated with degradation of the pasture component in the integrated livestock-forest system.
In integrated crop-livestock systems, the situation was different. A more active and diverse microbial community was found, even with carbon loss. The addition of residues from various crops, combined with fertilization of grain crops, higher pasture productivity, and more intense grazing, created a situation of lower nitrogen availability for microorganisms. Without sufficient nitrogen, microorganisms sought this nutrient from organic forms already present in the soil, resulting in this loss.
“Our study showed that pastures can be important allies in addressing the climate crisis, both in simple systems and those integrated with trees, as long as degradation of these areas is avoided. In systems that alternate grain cultivation with land use for cattle, special care is needed, especially regarding grazing intensity,” emphasizes the agronomist. “Moreover, it will be essential to seek strategies to supplement nitrogen without additional cost to the producer. A promising possibility is the consortium of grasses and forage legumes.”
