Epsilon Archive for Student Projects

Abstract

During the last century mankind has been able to boost food production with fertilization
and improved cultivation techniques. Crop biomass production has been increased both,
above and below ground. Due to this fact it is expected that highly yielding crops may also
influence the soil organic carbon pool in the subsoil through increasing root production.
The goal of this thesis was to investigate the impact of low and high yields (no N vs high N
fertilization) on (1) the soil organic matter pool (2) soil stability and (3) related chemical and
physical interactions.

Soils of three Swedish long-term field experiments (Fors, Kungsängen and Örja) were
sampled to a depth of 0.40 m and analyzed. The organic carbon content decreased with
depth at all three sites. Nitrogen addition through organic manure and inorganic fertilizer
slightly increased the soil organic carbon content (SOC) in the topsoil, but in the subsoil
(0.30-0.40 m) only the soil from Fors showed higher SOC contents in N fertilized
treatments. Nitrogen fertilization (organic and inorganic) resulted in lower pH values
compared to control without fertilization at all three experimental sites. Manure had an
important influence on aggregate stability at the site Fors. The soil treated with manure
showed a higher soil aggregate stability (SAS) and a lower amount of readily dispersible clay
(RDC) than no manure treatment. At Kungsängen, the soil stability was governed by the
high clay content of 56%. No stabilizing effect of fertilization was detected. The acidifying
effect of biological N fixation was observed in Örja soil. Samples with lower pH showed
lower stability. Inorganic N fertilizer significantly stabilized the Örja surface soil layer (0-
0.20 m). Multiple regressions revealed that the factor clay seems to have the most impact
on soil stability.

In conclusion, it has been shown that small differences in soil management practices
(organic and/or inorganic fertilization, cultivation of N fixing plants) have an impact on soil
properties in the long-term with a much greater degree in the topsoil than in the subsoil.