Conservation Agriculture in Zambia: Effects on Selected Soil Properties and Biological Nitrogen Fixation in Soya Beans (Glycine max (L.) Merr)

Conservation agriculture has been promoted in Zambia as a strategy to mitigate some of the negative effects arising from conventional tillage practices. Conservation agriculture offers several potential benefits on soil properties. However, these benefits and impacts vary across agro ecological regions and management practices. This study investigated changes, over time, associated with the practice of conservation agriculture in selected soil chemical, physical and biological properties, including an assessment of the effects on soil respiration, nodulation and biological nitrogen fixation in soya beans (Glycine max (L.) Merr). Six paired soil samples were collected from conservation agriculture and conventional tillage fields. Fields under conservation agriculture were 4, 7 and 16 years old while those under conventional tillage had been cultivated for over 18 years. Changes in soil properties due to conservation agriculture practice were determined using published laboratory procedures and compared using the paired t-test at 95% confidence level. The results indicated significantly higher soil pH, soil organic carbon, nodulation and biological nitrogen fixation under conservation agriculture than conventional tillage after seven years of practice. The study also showed significantly higher total porosity, soil microbial biomass, soil respiration and lower soil bulk density after sixteen years of practice. Based on these results, the practice of conservation agriculture has potential to improve crop productivity by improving the different aspects of soil fertility, the length of time before this is realized notwithstanding. Further studies that compare several conservation agriculture systems are recommended in other agro-ecological zones of the country to validate these findings.