Teklu Erkossa

Indexing soil quality: a new paradigm in soil science research

Soil quality indexing is a new approach in spatial and temporal evaluation of land management systems effects on soils’ capacity to function. A field experiment was conducted at Caffee Doonsa (2400 m a.s.l., 08°57′N, 39°06′E) for 6 years (1998–2003) to compare the effects of land preparation methods on soil quality (SQ) and to test the use of the Soil Management Assessment Framework (SMAF) in assessing SQ under the Ethiopian Central Highlands conditions. Four methods of land preparation [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 (22 m by 6 m). Physical, chemical, and biological SQ indicators were determined and scored, and a soil quality index (SQI) was developed using the SMAF procedures. Seven SQ indicators including microbial biomass carbon (MBC), bulk density, aggregate stability (AGG), soil organic carbon (Corg), pH, available water capacity (AWC), and available phosphorus were selected as a minimum dataset. The scored values of the indicators ranged from 0.21 for AGG and 0.97 for pH, both under BBF. Compared with RF (control), all the alternatives (GM, BBF, and RT) increased the scores of Corg and MBC. Moreover, BBF and GM increased the score values of AWC and AGG, respectively. Consequently, there was a non-significant increase in SQI due to the use of GM, BBF, and RT compared with the control. As a result, the land preparation methods may be preferred in a decreasing order GM ≥ BBF ≥ RT ≥ RF for the management goal of crop production. The study indicated that SMAF could be a robust tool to assess the performance of land management methods on soil quality in the study area, but some modifications may be required to fit to the prevailing cropping system and soil characteristics.

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 (2400 m a.s.l.; 08°57′N, 39°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 (22 m 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 profitable 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.

Tillage effects on physical qualities of a vertisol in the central highlands of Ethiopia

In the highlands of Ethiopia, tillage methods and frequency affect drainage, soil erosion, moisture conservation, weeding and harvesting of crops. This is through their effects on soil physical, chemical and biological qualities. In this study, four tillage methods for land preparation, “broad bed and furrows”,” green manure”, “reduced tillage “and the traditional tillage “ridge and furrows” were evaluated for their effects on soil physical quality indicators. The study was superimposed on the field experiment conducted on a vertisol area at Caffee doonsa for five years (1998 to 2002) in the central highland of Ethiopia. Penetration resistance (PR), aggregate stability, water-holding capacity, crust strength and thickness, texture, porosity, saturated hydraulic conductivity, bulk density and water holding capacity were the soil physical quality indicators considered. The result indicated that only PR was significantly (p<0.05) affected, where as the other parameter have shown a slight changes that are consistent with the effects on the bio-chemical parameters as previously reported. Broad bed furrows, and reduced tillage resulted in the highest and the lowest PR, respectively under both the moist and dry soil conditions. Green manure increased aggregate stability and reduced surface crust strength, which was linked to its increased organic matter content and consequent improved microbial activities.