Tillage effects on sediment enrichment, soil quality, and crop productivity in Ethiopian Highlands

The promotion and adoption of new tillage practices requires that their potential on-site, off-site, and economic effects are acceptable. Consequently, a field experiment was conducted at Caffee Doonsa (2400m a.s.l.; 08 degrees 57'N, 39 degrees 06'E) in the Central Highlands of Ethiopia for 6 years (1998 - 2003) to evaluate the effects of tillage practices on sustainable productivity and quality of the soil. Four tillage methods [ broad bed and furrows (BBF), green manure ( GM), ridge and furrows (RF), and reduced tillage (RT)] were arranged in a randomised complete block design with 3 replications on permanent plots (22m by 6 m). Three crops comprising durum wheat ( Triticum durum Desf.), lentil ( Lens culinaries Medik), and tef (Eragrostis tef), were sown in rotation. Relative crop productivity index (RPI), financial profitability, the nutrient enrichment ratio (ER) of the eroded sediment, and soil quality index (SQI) were used as performance indicators. With its highest RPI, the use of BBF significantly increased the grain yield of lentils by 59% compared with the control, and RT resulted in the highest grain yield of wheat and tef. Economically, BBF was the most pro. table option for lentils with 65% increase in gross margin, whereas RT resulted in 11% and 8% increase in that of wheat and tef, respectively. The ER indicated that the nutrient and organic matter content of the eroded sediment was always greater than that of surface soil, but there were no consistent effects associated with the treatments. The SQI showed a positive trend for GM, BBF, and RT, but differences were not statistically different at P <= 0.05. Overall, none of the tillage treatments was superior, but we encourage use of BBF and RT because of their positive productivity and economic trends. Further research is needed to tap the potential soil quality improvements anticipated for the GM treatment. To optimise the overall benefits, a complete system has to be developed, perhaps using BBF for lentils followed by RT for wheat and tef.