Summary

Annual mouldboard ploughing (CMP) is a major driver of land degradation in semi-arid tropics with serious impacts on food security. Conservation Agriculture (CA) is regarded the key to soil rejuvenation without fallowing. This study assessed the effects of CA on micro fauna diversity and soil physical properties in Southeast Lowveld (SELZ) and Kadoma during the 2008/2009 agricultural season.CA trials, involving different crop residue amounts, were compared against farmer practices. Four trials under sorghum (in SELZ) and 3 under maize (in Kadoma) were setup; each treatment was replicated 4 times per farmer. Macro fauna specimens were handpicked from collected monoliths; identified and then counted to determine abundance (N).Shannon-Weiner diversity (H) and evenness (E) indices were then computed. Infiltration tests were done on red clay soils in Kadoma using double ring infiltrometers. The infiltration data was tested for conformity to known infiltration models. Soil sampling for moisture assessment was done thrice in SELZ and twice in Kadoma, at 15cm intervals to 45cm depth.

The study results showed positive changes in N as land management changed from CMP to CA system. Significantly higher (p<0.05) mean N was observed in CA with residues (CA+2t/ha; CA+4t/ha and CA+6t/ha) than systems without residues (CMP and CA without residues), in both SELZ and Kadoma. However, increase in residue amount, after CA+2t/ha, did not result in significant (p>0.05) increase in N. Diversity (H) increased significantly on changing from CPM to CA without residues (CA+0t/ha) on high clay content soils. On two sites located on vertisols, H increased from 0.2 to 1.3 and 0.2 to 1.2 while it increased from 0.6 to 1.4 on red clay soil. However, a decline in H, though not significant was observed on sandy soil upon changing from CMP to CA+0t/ha.Evenness (E) exhibited patterns similar to those of H. Under natural ecosystems ,abundance (N) was 409,514 and 595 organisms per m² for communal, resettlement and national park respectively. The respective H indices for communal; resettlement and national park were 0.9,1.0 and 1.8 while the corresponding E indices were 0.6,0.5 and 1.0 .On average ,mean N was relatively higher in CA (at 714 organisms per m²)than natural ecosystems (506 organisms per m²).However ,H and E were higher in natural ecosystems than CA systems ,indicating richer micro fauna communities in natural ecosystems than cropping systems, in terms of diversity and evenness. Termites contributed over 80% of N in most treatments and their abundance was significantly correlated (p<0.05) to residue amount. Initial rates of infiltration were highly significant (p=0.003), however significance of the differences diminished after 30 minutes. No clear relationship was observed between infiltration rate and residue mount but infiltration was dependent on initial topsoil moisture content; with drier soils recording faster rates. Although N was significantly and positively correlated (p<0.05) to infiltration, the correlation was weaker than that of top-soil moisture. Residue amount did not have a significant effect on in-season moisture storage before crop maturity. However, after crop maturity ,moisture storage was higher in CA than CMP on both vertisols and sandy soils of SELZ,an effect attributed to crop water uptake during the season. Grain yield was only significantly correlated (p<0.05) to moisture storage on a site with better early weed control. It was, therefore, concluded from the study that CA had significantly positive effects on N; however, the effects on H and E were significantly negative. The lower N but higher H and E in natural than cropping systems indicated better stability of the systems.

The hypotheses that CA and non-cropping land uses had significant effects on micro fauna diversity and soil properties were therefore accepted, hence CA has a role in revitalizing soils through its influence on increasing soil micro fauna activity and improving soil physical properties.