Changes in properties of tropical ferruginous soils under long-term fertility management and continuous cultivation

Soil fertility is an important resource to enhance crop productivity and meet global food demand. The present work investigated the impact of long-term fertility management and continuous cultivation on selected soil properties of ferruginous soils. 8 plots of the experimental research plot situated behind the Agricultural Extension Research and Liaison Services (AERLS) building in Samaru, Zaria, Nigeria,were subjected to different fertility treatment for over 50 years. These treatment were: control (C); nitrogen (N); nitrogen & potassium (NK); nitrogen & phosphorus (NP); nitrogen & phosphorus & potassium (NPK); dung & potassium (DP); dung & nitrogen (DN); and dung & nitrogen & phosphorus (DNP). Using a completely randomized design (CRD) sampling technique, triplicate soil samples were collected from each fertility plot from the first 300 mm of the soil surface and analysed for selected properties. Results showed that the soils were majorly sandy loam. Sand component of the fertility plots was significantly (P<0.05) higher compared to the Control, while silt was observed to have reduced in the experimental plots. Soil organic carbon (SOC) was significantly (P<0.05) higher in the Control. Soils with dung as part of its fertilizer treatment showed slightly higher organic carbon content, with the DNP treatment having the highest value (0.76%), while lowest OC (0.36%) was recorded in the soils treated with inorganic fertilizer of NPK combinations. The OC content (0.35%-0.78%) recorded in soils of the various fertility plots was well below the 2% critical level required to guarantee soil structural stability. The pH values of treated soils were from 5.1–6.1 and significantly (P<0.05) higher in the Control. Bulk density was highest (1620 kg/m3) in the Control, while the plot under DP showed the least value of 1520 kg/m3. The different fertility treatments were observed to have reduced the plasticity of the soils from highly plastic recorded in Control to medium plastic observed in most of the other treatments. It is suggested that measures to enhance the soil OC be implemented as that will not only enhance the soil aggregate stability, but reduce the risk of soil erosion.