Abstract
This study reports the effect of topography, stubble grazing, tillage and the addition of fertilizer on the organic carbon content and structural stability of a typic Hapludoll topsoil under mixed agricultural production. The organic carbon content was significantly higher in the lower area of the slope when harvest residues were not grazed and when conservation tillage was performed. The interaction tillage x residue showed the highest carbon content to be attained with reduced tillage and no stubble grazing, and the lowest to be attained with conventional tillage with stubble grazing. Comparisons with minimally altered soil showed the loss of organic carbon to oscillate between 80% with conventional tillage when residues were grazed and 77% when conservation tillage systems were used. With respect to quantities of water-stable aggregates available (four diameter ranges), minimal alteration led to the highest percentages of the most coarse aggregates, while with the different treatments the finest and most coarse aggregates showed the highest percentages. The exception was under direct seeding where the distribution was similar to that for minimal soil alteration, though the percentage of the most coarse aggregates was lower. A linear, positive relationship was found between organic carbon and macroaggregate content. These results may help in the choice of technologies that can improve soil quality.
Highlights
The natural, seasonal change in the condition of soils has been modified by Man, largely through the replacement of wild vegetation and by tillage
Larson et al (1972), Black (1973) and Ressia et al (1998) found that removing crop residues for animal feed or for fuel led to a decrease in soil organic carbon (OC) content
They indicate that this phenomenon might be potentiated in semi-arid and subhumid regions where, since biomass production is low, a fall in soil OC content cannot be avoided when the removal of crop residues is extensive
Summary
The natural, seasonal change in the condition of soils has been modified by Man, largely through the replacement of wild vegetation and by tillage. This has led to reductions in soil chemical, physical and biological functions, the extent depending on the soil’s resistance to change (Herrick and Wander, 1998). The organic matter content of mineral soils is linked to factors involved with soil formation, such as climate, the vegetation and other organisms present, topography, starting material and time. The climate and mineralogy of the soil have a very marked influence on the accumulation and storage of organic matter since temperature and humidity affect the amount of biomass produced and the ability of the mineral components to retain it (Carter and Stewart, 1996)
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