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Significant differences in soil structure and soil physical properties were detected on a red earth (Oxic Paleustalf) which had grown four different winter crops in rotation with wheat in Wagga Wagga, N.S.W., Australia. At the end of the fourth season (after two cycles of 1:1 wheat:alternate crop rotation), soils which had been under lupin (Lupinus angustifolius) and canola (Brassica napus) were more porous and had lower shear strength than those which had been under field pea (Pisum sativum) and barley (Hordeum vulgare). Penetrometer measurements suggested that differences extended to 0.18 m depth. The soil under barley had the highest bulk density and shear strength, but water stability was similar to that of lupin and canola. Soil which had been under field pea had the lowest water stability. These differences were also detectable after only one season under the four different crops in a field core experiment. The different effects of the various alternate crops appear to be related to their different abilities in promoting soil structure formation and soil structure stabilisation. Evidence is also presented suggesting the crops' different abilities in modifying a range of soil biological and chemical properties, namely microbial biomass, dissolved carbon and soluble cation concentrations. Under conventional cultivation regimes, effects of the different alternate crops in terms of water stability and soil strength tend to be transient. |
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