Conservation agriculture (CA) practices are being widely promoted in many areas in sub-Saharan Africa to recuperate degraded soils and improve ecosystem services. This study examined the effects of three tillage practices [conventional moldboard plowing (CT), hand hoeing (MT) and no-tillage (NT)], and three cropping systems (continuous maize, soybean–maize annual rotation, and soybean/maize intercropping) on soil quality, crop productivity, and profitability in researcher and farmer managed on-farm trials from 2010 to 2013 in northwestern Ghana. In the researcher managed mother trial, the CA practices of NT, residue retention and crop rotation/intercropping maintained higher soil organic carbon, and total soil N compared to conventional tillage practices after four years. Soil bulk density was higher under NT than under CT soils in the researcher managed mother trails or farmers managed baby trials after 4 years.

In the researcher managed mother trial, there was no significant difference between tillage systems or cropping systems in maize or soybean yields in the first three seasons. In the fourth season, crop rotation had the greatest impact on maize yields with CT maize following soybean increasing yields by 41 and 49% compared to MT and NT maize, respectively. In the farmers’ managed trials, maize yield ranged from 520 to 2700 kg ha-1 and 300 to 2000 kg ha-1 for CT and NT, respectively, reflecting differences in experience of farmers with NT. Averaged across farmers, CT cropping systems increased maize and soybean yield ranging from 23 to 39% compared with NT cropping systems. Partial budget analysis showed that the cost of producing maize or soybean is 20–29% cheaper with NT systems and gives higher returns to labor compared to CT practice. Benefit-to-cost ratios also show that NT cropping systems are more profitable than CT systems.

The impact of NT, CT and cropping systems on soil quality and crop productivity was measured during four seasons under researcher and farmer managed conditions. In the researcher managed mother trial, the results showed that the CA practices of NT, residue retention and crop rotation/intercropping can maintain higher soil quality compared to conventional practices. The higher SOC and TNC contents under NT suggest that switching from conventional moldboard plowing to NT can maintain or improve soil organic carbon. No significant increase in soil quality indicators was detected in farmers’ fields mainly due to insufficient biomass production, difficulty in residue retention and the practice of removing all soybean plants for threshing outside the fields. Our results showed that in the researcher managed mother trial, tillage and cropping systems did not have a significant impact on maize or soybean yields in the first three seasons. Crop rotation had the greatest impact on maize yields in 2013 with CT rotations increasing maize yields compared to NT maize. In the farmers’ managed trials, CT crop rotation increased maize and soybean yield compared with CA practice of NT and crop rotation.

The results suggests that rotation should be an integral part of farmers’ cropping practices and thus for the full benefits of CA to be achieved farmers need to move from continuous mono-cropping to rotations that include legumes. Although our results show a yield advantage of CT cropping systems over NT cropping systems, partial budget analysis showed that the cost of producing maize or soybean is cheaper with NT systems and earns more than double returns to labor than with CT practice. Benefit-to-cost ratios also show that continuous NT soybean and NT soybean–maize rotations are more profitable than CT systems. We conclude that with time, implementation of CA practices involving crop rotation and intercropping of maize and soybean and NT along with crop residue retention presents a win-win scenario due to improved crop yield, increased economic return, and trends of increasing soil fertility. Thus farmers are more likely to adopt NT cropping systems than CT cropping systems. Indeed adoption studies carried out in 2014 showed that 60% of farmers who participated in the on-farm trials adopted the NT and soybean– maize rotation with crop residue retention. For non-participating farmers, the adoption rate was 50%. The average acreage under no-till adoption was found to be 3 acres among all the adopters

The authors conclude that with time, implementation of CA practices involving NT, crop rotation, intercropping of maize and soybean along with crop residue retention presents a win– win scenario due to improved crop yield, increased economic return, and trends of increasing soil fertility. The biggest challenge, however, remains with producing enough biomass and retaining same on the field.

Research article by Jesse B. Naabi, George Y. Mahama1, Iddrisu Yahaya1 and P. V. V. Prasad abstracted from the Agroecology and Land Use Systems, a section of the journal Frontiers in Plant Science