Some biochemical and physical properties of Tokomaru silt loam under pasture and after 10 years of cereal cropping

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Abstract
Some biochemical and physical properties were measured on Tokomaru silt loam that was either under permanent pasture or continously cropped with cereals for 10 years. Total carbon (C), nitrogen (N), microbial biomass, earthworms, and mineralisable N were all significantly lower in soil under cropping, particularly for the last three parameters. On average, the annual decline in total N under cropping has been 130 kg N/ha in the top 23 cm depth. Apart from markedly lower water stability of macro-aggregates under cropping which appeared to be close to a new equilibrium level, differences in other soil physical properties measured under pasture and cropping were less discernable. Penetrometer resistance indicated no development of a plough pan even after 10 years of continuous cropping. The decline in macro-aggregate stability under cropping was more closely related to the predicted decline in microbial biomass C than a similar model prediction for total organic C. Under a management of continuous cropping and minimal return of above-ground residues, it is likely to be several decades before a new equilibrium level for organic C is established. The more labile microbial biomass and earthworm fractions are predicted to be close to their new lower equilibria after cropping for 10 years.