Soil organic carbon and related properties under conservation agriculture and contrasting conventional fields in Northern Malawi

Conservation agriculture (CA) is widely promoted as an agro ecology-based approach for soil conservation. Several studies focused on effects of CA on crop yields and moisture dynamics, with limited focus on total soil organic matter (SOM) and its associated fractions. We collected representative soil samples from 30 paired farms under CA and conventional tillage in Mzimba district, north of Malawi to determine effects of tillage and soil depth on soil physicochemical properties, total SOM, and organic matter fractions. Undisturbed soil cores were collected for bulk density measurements. Different soil organic matter (SOM) pools were determined using the soil fractionation method, while soil physicochemical analyses were conducted using standard laboratory methods on disturbed soil samples. Soil organic matter content ranged from 0.7-3.1% in CA plots. Significantly lower concentrations of 0.6-2.6% SOM were measured under conventional tilled plots Tillage and soil depth had significant interaction effects on SOM. For example, larger concentrations of SOM were measured at depths of 0-10 cm compared to 10-30 cm under CA plots. Soil depth had significant effects of most soil properties compared to tillage. Examples include C-Heavy POM fraction, C-MAOM, Heavy POM, MAOM, N-MAOM and N-Light POM fraction. These were larger in the 0-10 cm soil depth than in the 10-30 cm soil depth. In contrast, tillage only had significant effects on C-Heavy POM fraction and C-MAOM. These were larger under CA than conventional tilled plots. Conservation agriculture showed capacity to improve total SOM and its associated fractions, a finding relevant towards understanding effects of land management on carbon storage. However, challenges of competing residue use as feed, mulch, and fuel continue to impede mulching under CA. Longer term studies and use of alternative mulching options could be employed to recognise noticeable changes in other SOM pools under CA systems.