ABSTRACT

Land use and soil management practices, affect soil physical quality indicators. Ten plots from the long-term DNPK trial field of Samaru were selected and soils analyzed to assess the hydrological and physico-chemical properties after a long period of cultivation and fallow. The plots were subjected to different fertilization regime from 1950 to 1998 under continuous cultivation. Surface and subsurface (0-15 cm and 15-30 cm) soil properties of these ten plots were studied under different rates and combination of fertilizer regime.These plots include inorganic fertilizers Nitrogen (N), Phosphorus (P), Potassium (K) in combination with organic fertilizer Dung (D) that is (D+NPK), (D+N), (D+P), (D+K), NPK only and a Control,that received no fertilizer NPK nor D.Sand fractions were found to be more dominating than any other fraction. On the surface soil, plots treated with N (1.29%), DNPK (1.24%) and DP (1.23%) were found to be recording higher values of total soil organic carbon than other selected plots.Bulk density rangedfrom 1.84 Mg m-3(DNPK) to 1.34 Mg m-3(N) across all the plots. Plots amended with DK, P and K recorded a near neutral soil pH values of 7.2, 7.13 and 7.15 respectively. More water conducting pores were observed in plots treated with organic manure singly or in combination with inorganic fertilizer among others. Mean weight diameter (MWD) indicates higher water stable aggregates of 1.26 and 1.25 mm in N and DNPK than in other plots, and low dry macroaggregates of 0.34 mm for control and DN plots.Most of the moisture was retained in soils with histories of dung treatments and the control, while it was lowest for single inorganic fertilizer treated plots across all the matric suction points. Evaluation of three infiltration models showed the Kostikov's model to be more efficient and proved to be excellent predictor of infiltration over Philip's and Horton's model,because Kostiakov's model gave coefficient of determination r2, close to unity (0.99). Relational expression otherwise pedo-transfer functions(PTFs) were generated between field capacity moisture content (FC), moisture contentat permanent wilting point (PWP), available water holding capacity (AWHC) and dry mean weight diameter (DMWD) and small macroaggregate stability (SMS) because of the significant relationship between them (p<0.05). Soil organic carbon content was found to increase over time with increased rates of organic matter application, both during cultivation and over the fallow period. The complimentary application of organic and inorganic fertilizer over a long period of time is viewed to have excellent potentials of improving soil quality for sustainable agricultural production.