APPLICATION OF FRACTAL THEORY IN QUANTIFYING SOIL AGGREGATE STABILITY AS INFLUENCED BY VARYING TILLAGE PRACTICES AND COVER CROPS IN NORTHERN GUINEA SAVANNA, NIGERIA

Abstract

Background. Soil aggregate stability varies with management practices like tillage and soil organic matter management. Objective. The objectives of this study were to (i) Explore a fractal theory to investigate the extent of soil fragmentation in soil of Samaru, Northern Nigeria, subjected to different tillage practices and covers crops for the purpose of improving soil aggregate stability (ii) Establish a relationship between fractal dimension (D) and mean weight diameter (MWD). Methodology. A three years field trials was conducted with three tillage practices (no-till, reduced till and conventional till) as main treatments and four cover crops (Centrosema pascuorum, Macrotyloma uniflorum, Cucurbita maxima and Glyine max), and a bare/control (no cover crop) as sub treatments. The trial was laid out in randomized complete block design, split plot arrangement and replicated three times. Soil samples were collected at 0-15 cm prior to trial establishment for routine soil physical and chemical properties and at depths 0-5, 5-10, 10-15 and 15-20 cm at the end of each cropping season each year for soil aggregate stability test. Results. No-till soils had 12.58% better soil aggregate stability than soils under reduced and conventional tillage systems. Also, no-till soils had 2.40 % less fragmented soil aggregates than Reduced and Conventional till soil as indicated by the fractal dimension of soil aggregates. Soils under Macrotyloma uniflorum cover crop, were on the average 2.33% less fragmented than soils under Centrosema pascuorum, Glycine max and Cucurbita maxima but 4.56% less fragmented than soils with no cover crops. Implication, No-till and reduced till systems; and cover cropping better enhanced soil aggregate stability due to better accumulation of organic matter emanating from crop residues return to soil in these practices. Conclusion. Conservation tillage and the use of cover crops lowered soil aggregate fragmentation relative to conventionally tilled system and bare soil with no cover crop. The strong linear relationship established between MWD and fractal dimension showed over 80% dependency, suggesting that fractal dimension is another useful index for evaluating soil aggregate stability..