TITLE:
Effects of Long-Term Fertilization on Different Nitrogen Forms in Paddy along Soil Depth Gradient
AUTHORS:
Xinyue Li, Bing Li, Changquan Wang, Yulan Chen, Peng Ma
KEYWORDS:
Long-Term Fertilization, Soil Depth Gradient, Total Nitrogen, Nitrogen Form
JOURNAL NAME:
American Journal of Plant Sciences,
Vol.11 No.12,
December
14,
2020
ABSTRACT: The combined application of organic fertilizer and chemical
fertilizer is an effective measure to increase nutrient content of soil plough layer,
which must have a profound impact on the deep soil nutrients, especially the contents
of nitrogen forms. The purpose of this study was to explore the characteristics
of soil nitrogen forms in plough layer and along depth gradient in different fertilization
treatments, so as to evaluate the soil quality in spatial dimension, further providing a theoretical basis for scientific
fertilization and improvement of paddy soil fertility. Here, a 34-year field experiment
was conducted with three treatments: without any fertilizer (CK), pure chemical
fertilizer (NPK) and chemical fertilizer combined with organic fertilizer (NPKM).
We analyzed the content of nitrogen forms in 0 - 100 cm soil depth and their ratios
to total nitrogen (TN), and discussed the correlation between nitrogen forms contents
and pH, CEC. Results showed that, compared with CK, both NPK and NPKM significantly
increased the contents of nitrogen forms in topsoil (soil layer of 0 - 20 cm), especially
nitrate nitrogen (NO3--N) content increased by 70%
(NPK) and 111% (NPKM), respectively. Although the contents of different nitrogen
forms decreased gradually along soil depth gradient, NPKS slowed down the decline
rate of TN and alkali-hydrolysable nitrogen (AN) in 0 - 60 cm soil layer, compared
to CK. Compared to NPK, NPKM significantly increased the NO3--N/TN ratio in 0 - 20 cm soil
layer, but also decreased the content of -N in 20 - 40 cm, which was beneficial to reduce the
risk of nitrogen leaching caused by nitrate leaching into deep layer. The increase
of soil pH in NPKM treatment obviously alleviated the problem of soil acidification
caused by long-term application of chemical fertilizer. Correlation analysis showed
that there was a significant positive correlation between soil nitrogen forms and
cation exchange capacity (CEC), but no significant correlation with soil pH. In
conclusion, NPKM ensured the nutrients of soil plough layer (0 - 20 cm), also reduced
the risk of nitrogen infiltration and nitrogen loss, thus ensuring the fertility of soil profile.