Life in the Soil

Abstract

The soil is host to many and varied groups of organisms and countless individuals that make up complex food webs, decomposing the primary production of plants and recycling materials and energy. It is becoming clearer that the most effective basis for the farming of the future is likely to be husbandry and propagation of these biological systems, and we need to understand them. The crotovinas (infilled burrows) that are a conspicuous feature of chernozem are made by various large burrowing animals, but the chief architects and builders of the chernozem are invertebrates, especially earthworms. In ploughed chernozem in Moldova, the worm population ranges from 140,000 to 280,000/ha; in pristine chernozem, there are more than 1 million/ha and they make up about half of the invertebrate population. Their casts are a conspicuous feature of the soil profile. Worms augment soil porosity, aeration and water infiltration and drainage; the contributions of this unseen workforce to agriculture and the development of whole landscapes were perceived by Darwin in the nineteenth century but neglected by agricultural science till quite recently. Moving down in size but up in numbers, the total number of micro-organisms in the upper 20 cm of the chernozem is 6 or 7 million/ha. Cellulose-decomposing bacteria and actinomycetes play an essential role in the formation of humus and ammonifiers in the nitrogen cycle. Although the nitrogen-fixing Azotobacter are numerous, especially in the south, they fix only 5–6 kg of nitrogen per hectare annually and they cannot replace the nitrogen-fixing role of legumes in agriculture.