• Authors:
    • Parton, W. J.
    • Mueller, T.
    • Molina, J. A. E.
    • Li, C.
    • Komarov, A. S.
    • Klein-Gunnewiek, H.
    • Kelly, R. H.
    • Jensen, L. S.
    • Jenkinson, D. S.
    • Frolking, S.
    • Franko, U.
    • Coleman, K.
    • Chertov, O. G.
    • Arah, J. R. M.
    • McGill, W. B.
    • Powlson, D. S.
    • Smith, J. U.
    • Smith, P.
    • Thornley, J. H. M.
    • Whitmore, A. P.
  • Source: Geoderma
  • Volume: 81
  • Issue: 1-2
  • Year: 1997
  • Summary: Nine soil organic models were evaluated using twelve datasets from seven long-term experiments. Datasets represented three different land-uses (grassland, arable cropping and woodland) and a range of climatic conditions within the temperate region. Different treatments (inorganic fertilizer, organic manures and different rotations) at the same site allowed the effects of differing land management to be explored. Model simulations were evaluated against the measured data and the performance of the models was compared both qualitatively and quantitatively. Not all models were able to simulate all datasets; only four attempted all. No one model performed better than all others across all datasets. The performance of each model in simulating each dataset is discussed. A comparison of the overall performance of models across all datasets reveals that the model errors of one group of models (RothC, CANDY, DNDC, CENTURY, DAISY and NCSOIL) did not differ significantly from each other. Another group (SOMM, ITE and Verberne) did not differ significantly from each other but showed significantly larger model errors than did models in the first group. Possible reasons for differences in model performance are discussed in detail.
  • Authors:
    • Kohl, D. H.
    • Shearer, G.
    • Lockeretz, W.
  • Source: Science
  • Volume: 211
  • Issue: 4482
  • Year: 1981
  • Summary: A small minority of farmers in the Midwest produces crops on a commercial scale without using modern fertilizers and pesticides. On the basis of a 5-year study, it appears that these farmers have more in common with the majority of farmers in the region than with certain stereotypes of organic farmers. Their farming practices (other than chemical use), the size and labor requirements of their farms, and the production and profitability they achieve differ from those of conventional farmers by considerably less than might be expected on the basis of the fundamental importance of chemicals in modern agricultural production. Compared to conventional methods, organic methods consume less fossil energy and cause less soil erosion, but have mixed effects on soil nutrient status and grain protein content.