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.
Highlights
Rice is the main food crop in China, and its planting area has increased from25.4 million∙hm2 to 31.4 million∙hm2 with per unit yield that has increased from1.9 t to 6.3 t in the past 50 years [1]
Results showed that, compared with CK, both NPK and NPKM significantly increased the contents of nitrogen forms in topsoil, especially nitrate nitrogen ( NO3− -N) content increased by 70% (NPK) and 111% (NPKM), respectively
Compared with CK, the soil total nitrogen (TN) content in NPK and NPKM treatments increased by 64% and 59%, soil alkali-hydrolysable nitrogen (AN) increased by 65% and 61%, soil NO3− -N content increased by 70% and content increased by
Summary
Rice is the main food crop in China, and its planting area has increased from25.4 million∙hm to 31.4 million∙hm with per unit yield that has increased from1.9 t to 6.3 t in the past 50 years [1]. Rice is the main food crop in China, and its planting area has increased from. When nitrogen supply is sufficient, the roots and tillers of rice will increase rapidly, so nitrogen plays a key role in the yield and quality of rice [2]. Excessive chemical fertilizer may cause nutrient loss and reduce fertilizer use efficiency, which is not conducive to higher crop yield and soil fertility [3]. Rational application of nitrogen fertilizer has been a key measure to obtain higher target yield in crop production in the world, and it is of great significance to alleviate the problems of soil quality degradation, rice yield and quality decline, environmental pollution and so on [4]
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