BIODYNAMIC VS CONVENTIONAL FARMING EFFECTS ON SOIL-STRUCTURE EXPRESSED BY SIMULATED POTENTIAL PRODUCTIVITY

Effects of alternative farming systems on soil structure need to be qu antified to judge the sustainability of the systems. This study was co nducted to compare two farming systems by converting ''static'' basic soil properties into a ''dynamic'' assessment using simulation modelin g. Increasingly popular biodynamic farming systems use no commercial f ertilizers and pesticides but apply organic manure and compost. Soil c onditions on four fields on two farms where biodynamic and conventiona l soil management had been practiced for about 70 yr were investigated with morphological and physical methods. Soils (loamy, mixed, mesic T ypic Fluvaquents) were pedologically identical. Four procedures were u sed to express differences in soil structure as a function of differen t management: (i) morphological description; (ii) measurement of basic and static soil parameters such as bulk density, organic matter, and porosity; (iii) measurement of soil hydraulic characteristics; and (iv ) determination of simulated water-limited yields. The latter procedur e provides a criterion that is quantitative, is directly related to a practical aspect of soil behavior, and reflects the highly nonlinear s oil-water processes. The WAVE simulation model was used to predict wat er-limited potato (Solanum tuberosum L.) yields with climatic data of 30 yr. Basic static soil parameters were not significantly different b ut simulated yields were significantly different and were 10200 and 10 300 vs. 9400 and 9700 kg dry matter tuber yield ha(-1) yr(-1) for the biodynamic and the conventional fields, respectively. Simulation model ing of crop yields thus provides a relevant expression for the product ion potential of the two different farming systems.