Fallow Research Articles

Influence of land-use on properties of a ferralitic soil under low external input farming in southeastern Swaziland

An assessment of changes in soil properties associated with land-use and management practices is vital for the selection and establishment of appropriate sustainable practices under different agroecosystems. This study compared soil properties between land located on an abandoned kraal site (KS), under fallow (FL) and one that was continuously cropped to maize (CC) for over 12 years. Aggregation and aggregate stability as measured by both dry and wet sieving showed large differences between land-use systems. The soil under CC had a higher proportion (26.4%) of micro aggregates (<0.25 mm) compared with that of FL (10.1%) and KS (6.9%). The dry mean weight diameter (DMWD) was larger in KS (3.03 mm) than in FL (2.17 mm) and CC (1.38 mm). Soil aggregates in CC were the least stable with a wet mean weight diameter (WMWD) of (1.61 mm) compared with those of FL (2.18 mm) and KS (2.89 mm). Reduced stability of aggregates in CC is likely due to the lower organic carbon content of soil in this land-use (1.7%) compared with that of FL (2.5%) and KS (3.2%). The soil under KS had lower bulk density (BD), penetration resistance (PR) and aggregate tensile strength (ATS) than that of FL and CC. Soil moisture content (MC) and available water capacity (AWC) showed an opposite trend. The soil in KS had a higher concentration of total N (TN), available P and exchangeable K, Ca, Mg and Zn. Soil on CC, on the other hand, had a higher concentration of Mn than that from FS and KS possibly because of its acidic nature. There were significant strong correlations between soil organic carbon and BD (−0.86 ∗∗∗), PR (−0.61 ∗), MC (0.82 ∗∗), ATS (−0.62 ∗), WSA (0.79 ∗∗∗), AWC (0.91 ∗∗∗), pH (−0.61 ∗∗) and TN (0.76 ∗∗∗). Grain yields of maize were highest in KS followed by FL and least in CC. The high yields were attributed to improved soil properties in plots of KS compared with both FL and CC. In conclusion, the findings suggested that organic matter had a major influence on soil properties and fertility.

Comparison of population density of plant parasitic and free‐living nematodes in earthworm casts and adjacent soils of fallow and cultivated land in South Eastern Nigeria

SummaryNumbers of nematode species, juveniles, females and males in earthworm casts and in adjacent soils were studied in fallow (FL) and in cultivated lands (CL). In the FL each cast had an average of 5.6 different species of nematodes, while a soil sample of equal weight to the cast and within a 10 cm radius of the cast averaged 2.5 species. The difference between these means was highly significant. In the CL there were 4.7 species/cast and 2.9 species/soil sample. The difference between these two means was also highly significant.A total of 16 plant parasitic species, five omnivorous, two predacious and eight free‐living nematode species were observed in the casts and in the adjacent soils of both FL and CL. The results partially contradicted the widely held view that earthworm casts are beneficial because the casts harboured numerous plant parasitic nematodes.