The objective of the study was to evaluate the effects of long-term fertilization of a sandy soil with differentiated doses of cattle slurry as well as its after-effect action on the possibilities of migration of dissolved organic carbon (DOC) and dissolved nitrogen (DNt) down to deeper layers of the soil profile. DOC and DNt were extracted with borate buffer and 0.004M CaCl 2 solution. Evaluation of effects of cattle slurry on the content of DOC and DNt was done in comparison with mineral fertilization. It was shown that the use of cattle slurry in the doses of 100 and 200 m 3 /ha caused a significant increase of labile organic matter in the 0-25 and 25-50 cm layers of soil. As compared with mineral fertilization the application of slurry increased also the amounts of extracted DNt, but only in the surface layer. The DNt content in the deeper soil horizons did not depend on the kind of fertilization. Concentrations of DOC and DNt in the extracts depended not only on their content in soil but it was also modified substantially by the extractant used.
Summary
The impact of fertilizer application on soil aggregate stability is of increasing interest to soil scientists. Aggregate water stability depends primarily on soil organic matter. We studied silty loam and loamy sand aggregates from three long‐term fertilizer treatments (control, pig manure and NPK) which significantly altered the quantity of organic matter. A new approach to examining aggregate stability was used: soil aggregates were immersed in methanol‐water solutions with methanol at 0, 20, 40 and 60% concentration (C), and non‐disrupted aggregates were separated after 30 minutes. The aggregate resistance R(C) against each solution was taken as the percentage of stable aggregates. Overall resistance of the aggregates was taken as the Rtot parameter given by the product of four R(C) values. The R(C) values of all aggregates were positively correlated with C. The R(60) values were independent of the applied fertilizer. The R(0) value for silty loam aggregates ranged from 28% (pig manure) to 7% (NPK), while that for loamy sand equalled 7–9% in all cases. The R(20) values were most effective at differentiating the soils and the fertilizer treatments. However, the Rtot value was a better indicator of aggregate stability. Greater differences in stabilities of aggregates were noted in loamy sand. Mineral fertilizer application seemed to decrease aggregate resistance in both soils. Total organic carbon and nitrogen content in all non‐disrupted aggregates were negatively correlated with methanol concentration (C) of the solution applied for aggregate separation. The largest decrease was for the pig manure treatment, and the smallest was for the control. Porosity and pore size distributions of the aggregates were derived from micro‐tomography and approximated to lognormal pore size distributions. Larger porosities and pores were found in water‐stable aggregates than in methanol‐stable aggregates. It seems that the dominant mechanisms for aggregate instability during fast wetting were not related only to the pore air compression, but to weakening of attractive forces between aggregate particles by water.
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