Nowadays many incentives are focusing on replacing fossil fuels with renewable energy sources to become “carbon neutral”. As such these incentives are engaged in the use of biogenic materials (such as biomass) for energy production to lower CO2 emissions compared to fossil fuel use. However, often the greater ecological importance of CO2 and carbon for biological processes is overlooked. The importance of CO2 and carbon for biological processes even is considered to go far beyond the calorific value of materials. Instead of focusing on CO2 emissions, let’s have a look at CO2 capture and reuse instead.
Topsoil is crucial in balancing the global carbon cycle as it represents a long-term accumulator of carbon and sequesters CO2 from the atmosphere. Topsoil is the topmost layer of the earth’s crust, ranging from 0.3 -1 meter in depth. Topsoil consists of mineral particles, organic matter, water and air and is inhabited by living organisms all together forming an extremely complex living medium. Topsoil is a non-renewable resource and performs many vital functions such as food, biomass production, storage, filtration and transformation of many substances including carbon and nitrogen. Topsoil directly affects food and feed security as also energy and resource security for industries.
CO2 is an important nutrient for the growth of plants; carbon is a structural essential element in all living systems. Plants fixate carbon in biomass via plant growth by a process called photosynthesis: the formation of biomass by photosynthesis captures more CO2 from the atmosphere than any other process on earth. Each year one seventh of the earth’s CO2 stock in the atmosphere is photosynthetically fixated by plants. Biomass is no a stable sink of carbon but can become one after different decomposition processes. The search is for technologies and processes contributing to decomposition of biomass into long term carbon-sequester such as the fertile humus fraction in topsoil. Humus is the major component of soil organic matter (SOM) in soils and contributes to 65-75% of the total. Humus is brown to black in color and decomposes slowly under natural conditions. In combination with soil minerals, soil humus can even persist for several hundred years in soils.
Soil degradation (e.g. erosion, loss of organic matter, compaction, salination, landslides, contamination and sealing) is accelerating at alarming rates, with negative effects on human health, natural ecosystems and climate change. Land degradation endangers agricultural food production and thereby food security and an estimated 20 million km2 of land are affected worldwide. Every year up to 70,000 km2 of agricultural land is lost worldwide due to intensive agriculture, deforestation, overgrazing and sealing. This is an area nearly the size of the Benelux states. Soil organic matter containing humus and soil organic carbon can get lost (emitted) when management practices are not maintaining it. Depending on the region, topsoil loss occurs at a rate of 16-300 times faster than it can be rebuilt.
The decrease in soil organic carbon content can be reversed by adjusted farming practices that focus on land use which is a net carbon-sink, instead of a net carbon source. A conversion of only about 7% of the terrestrial plants (grown in one year) into a stable biomass carbon material (such as humus) would be sufficient to carbon offset the entire amount (nearly 9.7 Gt C a-1) of CO2 emitted into the atmosphere annually from the use of fossil fuels. Currently soil fertility management practices that increase soil carbon and soil organic matter are, for example: compost, green manure, intercropping, livestock manure and no-tillage as well as biochar. Other options are to focus more on the use of perennial crops, shrubs, trees and palms in improved farming systems.
From a Cradle to Cradle® perspective we look at CO2 and carbon as valuable resources for the generation of biomass and the (re)generation of precious topsoil. By changing our viewpoint and practices topsoil can be rebuilt and will no longer be a carbon emitter but a carbon sink instead again.
 the amount of energy contained in food and fuel