Tillage for soil fertility before fertilizers

The present concern for decreased tillage in crop production systems makes it interesting to look back 300 years to when Jethro Tull introduced his system of intensive tillage for cereals and fodder crops. His experiments in England, at a time when landowners started paying more attention to farming, established that frequent tillage with plows could substitute for manure or fallow in continuous cropping of wheat. The general understanding was that exposed soil absorbed plant nutrients from the atmosphere; therefore, it was important to turn over lower layers and to leave the soil in a loose condition where more surfaces were exposed. In addition to controlling weeds, a probably equally important factor was speeding up mineralization of organic matter through increased aeration. This would account for the increased yields even where weeds were not present, and the ability to substitute tillage for fallow. Tull's system of cultivating wheat grown in rows, sometimes on ridges, was vehemently debated in the 18th century and was not widely accepted. The benefits would have diminished as organic matter content of soils decreased, and was probably not effective on all soils. Key words: Horse-hoeing husbandry, mineralization, ploughing, Jethro Tull