Temporal Variability of Soil Physico-chemical Properties under a Long-term Fertilizer Trial at Samaru, Northern Guinea Savanna of Nigeria

Studies on the effect of long term land use management practices on the temporal variability of soil properties are limited. This study addressed the temporal variability of soil properties under a long term fertilizer trial in a northern guinea savannah of Nigeria. The long-term dung (D), nitrogen (N), phosphorus (P), potassium (K) trial popularly referred to as DNPK experiment at Samaru is about the oldest manure and mineral fertilizer experiment in West Africa modeled after Rothamstead long-term trials in the United Kingdom. It has been under continuous cultivation from 1950 to 2008 from when it was fallowed up till now. Data on soil physico-chemical properties from previous studies conducted on DNPK experiment were synthesized for this work as well as data from the present work to create a time series graph using Microsoft excel to monitor trend of variability of each property over a long term. The contribution of dung to organic carbon appears to supersede any other treatment across all the years. Soil pH showed a decreasing trend with time with increasing rates of Nitrogen fertilization than other treatments. No significant influence of fertilizer management was observed for soil bulk density of the plots across the study years. Saturated hydraulic conductivity and aggregate stability improved when the plots were under cultivation for all fertilization regimes than when they were under fallow due to compacted soil aggregates. This study highlighted the sustainability of integrated nutrient management in sequestering carbon as well as maintaining soil quality over time, and it is therefore recommended as a sustainable management practice for tropical soils.