Abstract
Long-term cultivation of crops has been found to cause soil physico-chemical and biological quality (SQ) degradation for sustainable agricultural production practices in Akwanga, Nigeria. Understanding the dynamics of SQ change under different land use types is desired. The present study was carried out to assess soil physico-chemical indicators (based on land evaluation approach) and biological SQ (based on agro-ecological approach) for sustainability of cereal, arable and plantation land uses and management systems. Quantitative and qualitative indicators were defined based on chronosequence of soils under different land use types: 3-month cereal cropping of Rice); 7-month root cropping (yam/cassava/vegetable intercrop); 10-year plantation (orange/pineapple orchard); and >22-year oil palm plantation. Their respective management practice is Tillage + NPK fertilization; Tillage + NPK fertilizers + Organic manure; No tillage + mulch; and no tillage + Farm yard manure + Legume cover as live mulch. Each age class was replicated at least three times and their sensitivity to change was sought. The statistical mean values of the bio-physical and chemical properties of soil quality indicators (SQI) under the various types of land use (LUT) show that the most sensitive soil quality indicators (P ≤ 0.001) were soil pH, total organic C, available phosphorus (P), CEC, bulk density, total porosity, and PWAC, and earthworm population. Moderately sensitive indicators (0.001 < P ≤ 0.01) include total N, P and K, and exchangeable K. Weaker indicators of SQ (0.01 < P ≤ 0.05) include percentage BS. Soil texture and clay/silt ratio were of no value as soil quality indicators (SQI) for these soils. SQI improvements were related to their management practices; hence LUT4 had the best SQ, followed by LUT3. The worst management was that in LUT1. Qualitative assessments based on farmers’ perception of SQ showed the following order of importance for their cropping systems: Soil organic matter, fertility, topsoil thickness, soil structure, moisture retention, earthworm abundance, compaction, soil erosion, and the incidence of weeds. Farmer observations of SQ changes were generally in good agreement with the quantitative assessments. To ensure adoption of improved management practices for more sustainable production system, qualitative soil quality information obtained from on-farm surveys should be used to supplement the quantitative data obtained through soil analyses. These would serve as effective diagnostic tools for evaluating soil quality for long-term sustainability of crop productivity
Key words: Soil quality indicators, land evaluation, agro-ecological approach, guinea savanna, Nigeria.
