Totalinnehåll och djupfördelning av organisk substans i mångåriga plöjningsdjupsförsök

In two long-term experiments (started in 1978) on day loam soils each with four randomized blocks, four different ploughing depths had been compared during a fifteen year period on sites previously ploughed to a depth of ab out 25 cm. During the whole experimental period, fertilizing, crop residue management and other treatments had been equal for all ploughing depths. Deep ploughing had resulted in a few percent higher accumulated yields than shallow ploughing, probably because of higher weed infestation (Elymus repens, (L.) Gould) for shallow ploughing. In two treatments (mouldboard ploughing to about 31 cm and 16 cm) an investigation was made in 1993 on bulk soil properties and penetration resistance and on concentration and total amount of organic matter and nitrogen. Depending on the ploughing depth used, sampling was done in two layers for deep ploughing and three layers for shallow ploughing. The first layer from the ground surface to present ploughing depth and the second layer (shallow ploughing) from present to previous ploughing depth. The bottom layer is a shallow transition layer between topsoil and subsoil. Bulk density and degree of compactness were higher and porosity lower in deeper layers. There was a plough pan in both treatments but at different depths. Total amount of organic matter in the soil was equal for both treatments, but the vertical distribution of organic matter differed between the ploughing depths. The concentration of organic matter was about 0.5 % higher in the upper layer in shallow ploughing than in deep ploughing