3. Results and discussion
3.1. Soil characteristics
The soil physicochemical characteristics changed significantly
after 3 years with different fertilization (Table 2). Versus the CK
treatment, the water-holding capacity after CP treatment increased
markedly. This was probably due to the improved pore size
distribution of soils by the continuous incorporation of commercial
compost (Shiralipour et al., 1992). In contrast, the water-holding
capacity of chemically treated soils decreased significantly. The pH
values of CF were lower than that of CK, indicating that soil
acidification occurred in these plots. An intensive microbial
nitrification process often results in soil acidification when large
amounts of synthetic ammonium fertilizers are applied as
demonstrated by the greatest concentrations of nitrate in the
soils treated with CF (Stamatiadis et al., 1999). The application of
compost is known to increase the content of soil organic C (SOC;
Achiba et al., 2010), and a similar result was obtained in this study.
The residues of crops and increased microbial populations may
explain why the SOC content in CF soils were larger than those in
the CK treatment group.
Positive effects of both fertilization treatments were observed
for soil total nitrogen (TN). The largest mean value (1.22 g kg1) for
CP was obtained after three years of successive commercial
compost application. There were no apparent differences in the
NH4
+-N concentrations among all the three treatments, and similar
results were observed by Dong et al. (2014) and Zhao et al. (2014).
The intense accumulation of NO3
-N in CF was attributed to the
urea stimulatory effects on nitrification. However, the N release
from the
finished compost was relatively slow, and the NO3
-N
concentrations in CP soils were much lower than that in CF. This
indicated that the application of compost might decrease the
possibility of ground water contamination and reduce nitrate