Long-term management impacts on soil C, N and physical fertility

Manure is a source of plant nutrients and can make a valuable contribution to soil organic matter (SOM). Two experimental sites were studied on a Halpic Phaeozem soil near Bad Lauchstadt in Germany. The first experiment, called the static experiment, commenced in 1902. The impact of fresh farmyard manure (FYM) (0, 20 and 30 t ha −1 2 year −1 ) combined with P, K and N fertiliser application on total organic C (C T ), labile C (C L ), non-labile C (C NL ), total N (N T ), mean weight diameter (MWD) and unsaturated hydraulic conductivity ( K unsat ) was investigated. The second experiment commenced in 1984 and investigated the effect of extreme rates of fresh FYM applications (0, 50, 100 and 200 t ha −1 year −1 ) and cropping, or a continuous tilled fallow on the same soil properties. At both sites a nearby grassland site served as a reference. On the static experiment, FYM application increased all C fractions, particularly C L , where application of 30 t ha −1 2 year −1 increased C L by 70% compared with no FYM application. Fertiliser additions to the static experiment had a positive influence on C fractions while N T increased from both FYM and fertiliser application. MWD increased as a result of FYM application, but did not reach that of the grassland site. Both fertiliser and FYM application increased K unsat (10 mm tension) on the static experiment. In the second experiment application of 200 t ha −1 year −1 of FYM increased concentrations of C L by 173% and of C NL by 80%, compared with no FYM application to make them equivalent to, or greater than the grassland site. A continuously tilled fallow resulted in significant decreases in all C fractions, N T and MWD compared with the cropped site, while K unsat (10 mm tension) was increased on the 0 and 50 t ha −1 year −1 treatments as a result of a recent tillage. There was no difference in K unsat between the cropped and the continuous tilled fallow at FYM applications of 100 and 200 t ha −1 year −1 . There were similar significant positive correlations of all C fractions and N T with MWD on both experimental sites but the relationships were much stronger on the extreme FYM experiment. Weaker relationships of C fractions and N T with K unsat (10 mm tension) occurred for the static experimental site but these were not significant for the extreme FYM experimental site. The strongest relationship between C fractions and K unsat was with C L . This research has shown that applications of FYM can increase SOM and improve soil physical fertility. However, the potential risk of very high rates of FYM on the environment need to be taken into consideration, especially since the application of organic materials to soils is likely to increase in the future.