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Two soils at the University of Ife (Nigeria) research farm were evaluated for their physical and chemical properties under long‐term pasture, bush fallow, and arable cultivation that involved three tillage techniques and two fertility levels. The cultivated plots were adjacent to the fallow plots, which were at least 1/2 ha in size. Differences in soil properties between fallow and cultivated soils were considered to be due to soil changes resulting from continuous cropping.The percentage of water stable aggregates (> 2.36 mm) in the 0‐ to 15‐cm soil depth was highest and more stable under fallow than under bush. Stability values were 95 and 80%, respectively, under grass and bush. About 76% and 80% of these aggregates were destroyed after 5 years of continuous cropping, and 88% after 10 years. Aggregate stability of the cultivated soils ranged from one‐fifth to one‐third those of fallow soils. The average bulk densities were 1.24 and 1.52 g/cm3 for fallow and cultivated soils, respectively, while the reductions in porosity and saturated hydraulic conductivity were more than proportionate to the increases in bulk density of the cultivated soils. The fallow soils were about four‐times higher in organic matter than the cultivated soils, which had an average organic matter content of 0.8%. The fallow soils were also higher in nitrate‐nitrogen, exchangeable bases, and CEC than the cultivated soils.Soil deterioration in decreasing order was: Plow‐disk‐harrow > plow > no‐tilage. Fertilizer treatments had no efect on soil deterioration after 10 years of continuous cropping.

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The study was aimed at identifying the soil properties responsible for maize yield decline on eroded soils and at quantifying their relationship with yield. Topsoil was artificially removed to incremental depths of 0, 5, 10, 15 and 20 cm to simulate various degrees of erosion. Maize growth and yield were monitored on the plots and soil physical and chemical properties were determined after two years (4 seasons) of cultivation. Soil pH was significantly higher on the control plot and decreased with increased depth of topsoil removal. Bulk density (BD) increased with depth of topsoil removal from a mean value of 1.38 g cm )3 under control to 1.55 g cm )3 at 20 cm depth of removal, while cone index of penetrometer resistance (CI) correspondingly increased from 1.09 g cm )2 to 1.37 g cm )2 . Maize yield significantly decreased in the first year from 3.2 t ha )1 on the control plot to 0.12 t ha )1 where 20 cm of topsoil was removed and correspondingly from 1.85 to 0.09 t ha )1 in the second year of cropping. Maize yield decreased exponentially with increase in depth of topsoil removal (r 2 =0.99, P < 0.01) with an average of 55% yield loss on the removal of just 5 cm topsoil. Soil organic carbon (SOC), BD, CI, field capacity (FC), pH and exchangeable Mg 2+ were significantly correlated to maize yield parameters. However, factor analysis showed that the combination of SOC and exchangeable Mg 2+ with soil physical properties (BD, FC, CI and depth of topsoil removal) explained 99% of variation in maize grain yield. The need for conservation farm practices is recommended on the soil to prevent soil degradation.

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