Tillage effect on macroporosity and herbicide transport in percolate

Changes in topsoil C content were measured in 60 experiments on soddy-podzolic soils in the Russian Federation, Belarus, Ukraine, Lithuania and Latvia with different management characteristics. The data were compiled with a range of actual climatic parameters for the years of the experiments. The combined impact of different management practices (inorganic fertilizers, organic manure and different rotations), climate gradients and soil properties (initial soil C, clay content) was analysed using a static model. The importance of initial C level interactions with the soil and climatic variables are demonstrated as one of the major factors of soil organic matter (SOM) dynamics. The effect of different treatments for seven long-term experiments at the same site (Barybino, the Moscow Region) was explored using both static and dynamic modeling approaches. The SUNDIAL dynamic model was used to estimate the dynamics of different C pools for the whole 35-year experimentation period. Some adjustments to parameters were necessary to obtain satisfactory results. The management practices tested lead to changes not only in total SOM but also in SOM quality parameters. This was established using a complex of chemical and biological methods. For cropping systems with 50% of row crops manure application increased steady state C values by about 0.2%. High inorganic N fertilization decreased the steady state C values. The negative effect of high inorganic N fertilization was seen to be more pronounced on soil with a higher C content. This influence might be a result of increased organic C mineralization after autumn application of mineral N where there may be no crop present to utilize the fertilizer, resulting in adverse changes in SOM quality. The mineral fertilization contributes significantly to the formation of labile humic substances at the expense of Ca-forms of SOM which are more resistant to microbial decomposition and act as the binding agents of aggregate stability.