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 (2400m.a.s.l., 08 degrees 57'N, 39 degrees 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 (22m 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 modi. cations may be required to. fit to the prevailing cropping system and soil characteristics.