Soil organic matter pools and crop yields as affected by the rate of farmyard manure and use of biodynamic preparations in a sandy soil

One aim of organic and biodynamic agriculture is to improve soil fertility. Our objectives are to (1) explain previously reported differences in the soil organic matter levels between soils receiving farmyard manure (FYM) with or without biodynamic preparations (BD), (2) quantify the effect of three levels of FYM applications on microbial biomass and soil organic matter (SOM) pools with different stability, and (3) relate SOM pools to crop yields in a long-term experiment on a sandy soil at Darmstadt, Germany. Soils of the BD-FYM treatments had significantly higher Corg contents compared to soils of the FYM treatments. However, soil fractionation indicated that there was a greater storage of Corg in the intermediate and passive pools of the BD-FYM treatments, and the temporal course of Corg contents suggested a slow convergence of Corg stocks between FYM and BD-FYM with time. Thus, the observed differences between BD-FYM and FYM treatments were likely to have existed since the beginning of the experiment. Contents of labile C (70-114 g [kg Corg],-1 turnover time 462 days) and labile N (35-49 g [kg Nt]-1, turnover time of 153 days) were strongly related to the application rate and also to crop yields. Yield of potatoes, winter rye, and clover significantly increased in proportion to the application rate of FYM, while BD had no effect. Overall, the study showed that increasing rates of FYM increased C and N availability independent of the use of BD. Nevertheless, efficiency of C sequestration in a more stable form (intermediate pool) decreased with increasing rate. © 2011 Springer Science & Business Media BV.