1.Institute of Agricultural Resources and Regional Planning,Chinese Academy of Agricultural Sciences National Engineering Laboratory for Improving of Arable Land;2.Red Soil Experiment Station of Chinese Academy of Agricultural Science in Hengyang/National Observation and Research of Farmland Ecosystem in Qiyang,Hengyang
The National Natural Science Foundation of China (No 42077098) and Basic Scientific Research Service Funds of Central Level Public Welfare Research Institutes (No 1610132021023),
不同形态的土壤氮素是作物吸收氮素的主要来源，而土壤肥力不仅影响氮素的含量，也影响氮素的有效性，进而影响作物对氮素的吸收利用。明确不同肥力红壤中各形态氮素的变化及其对作物吸氮量的贡献，可为阐明氮素循环机制和沃土培肥提供理论依据。2019年5月在湖南祁阳红壤实验站选取低肥力、中肥力和高肥力红壤进行田间微区试验，设置不施氮（N0）和常规施氮（N1）两个处理。分析了2020年玉米（该试验的第三季作物）种植前和收获后土壤矿质氮（MN）、固定态铵（FN）、微生物生物量氮（SMBN）和可溶性有机氮（SON）含量的变化及其与玉米地上部吸氮量的关系，并通过结构方程模型（SEM）建立了各形态氮库与吸氮量的关系模型。结果发现，N0条件下高肥力土壤的籽粒产量约为中肥力土壤的4.6倍，但在N1条件下，高肥力土壤的玉米产量和生物量与中肥力土壤无显著差异，但其吸氮量显著高于中肥力土壤。与种植前相比，N0条件下，收获后中肥力土壤FN含量显著提高了63%，低肥力和高肥力土壤分别增加了47%和11%。与其相反，土壤MN、SMBN和SON含量均有所降低。土壤MN含量降低了0.4~4 mg·kg-1；SMBN降低了18%~44%且土壤肥力间无显著差异；SON减少了55%~84%。N1条件下，土壤MN含量降低了约22~38 mg·kg-1; SMBN降低了32%~72%；而SON的减少量在高肥力土壤中可达99 mg·kg-1，分别为中肥力土壤和低肥力土壤的2.0倍和9.3倍。相关分析结果表明，地上部吸氮量与SMBN、SON和NH4+减少量存在显著正相关关系。结构方程模型结果进一步表明，SON和NH4+含量直接影响吸氮量，SMBN通过影响SON和MN间接影响玉米地上部吸氮量。总体而言，SON和SMBN可直接或间接影响玉米对氮素的吸收利用，是土壤中重要的氮素存在形态，应进一步加强对其形态转化的机制研究，可促进红壤培肥和氮素高效利用。
【Objective】Soil nitrogen (N) is an important resource for N uptake by crops. The availability of soil N is dependent on soil fertility to a high extent, which in turn affects the absorption and utilization of N by crops. Understanding the various N forms in red soils with different fertility and their contribution to crop N uptake can provide a theoretical basis for clarifying the N cycle mechanism and cultivating high-yield and high-N efficiency soils.【Method】In May 2019, low-fertility, medium-fertility and high-fertility red soils were selected for the field micro-area experiments, and two treatments, no nitrogen fertilizer (N0) and conventional fertilization (N1) were set up. We determined the contents of soil mineral nitrogen (MN), fixed ammonium (FN), microbial biomass nitrogen (SMBN) and soluble organic nitrogen (SON) before planting and after harvest of 2020 maize (the third crop of the experiment). The relationship model between each form of N form and the quantity of N uptake was established through structural equation modeling (SEM).【Result】The grain yield of high fertility soil under N0 treatment was about 4.6 times that of medium fertility soil. Under N1 treatment, the maize yield and biomass of high fertility soil had no significant difference with that of medium fertility soil. Meanwhile the N uptake of high fertility soil was significantly higher than that of medium fertility soil. Compared with before planting, the FN content in the medium-fertility soil after harvest was significantly increased by 63% under N0 treatment. The FN of low and high fertility soil increased by 47% and 11%, respectively, while the contents of MN, SMBN and SON in the soil were reduced. The MN content of the soils were decreased by between 0.4~4.0 mg·kg-1. SMBN was decreased by 18%~44% and there was no significant difference in soil fertility. Also, the SON was decreased by 55%~84%. Under N1 treatment, the content of MN was decreased by 22~38 mg·kg-1 and the content of SMBN was reduced by 32%~72%. The SON was reduced by 99 mg·kg-1 in high-fertility soil, which was 2.0 times higher than medium-fertility soils and 9.3 times higher than low-fertility soil. The correlation analysis results revealed a significant positive correlation between the amount of N uptake by the aboveground biomass and the decrement of SMBN, SON and NH4+. The structural equation model results further showed that the content of SON and NH4+ directly affected the amount of N uptake, while SMBN indirectly affected the N uptake by maize by changing SON and MN.【Conclusion】SON and NH4+ can directly regulate the maize N uptake. The SMBN and FN indirectly affect maize N uptake through the MN and SON. In the future, it is crucial to strengthen the research on the mechanism of soil N form transformation to promote red soil fertility and high-efficiency utilization of N.
ZOU Hongqin, LI Dejin, REN Keyu, WANG Boren, CAI Zejiang, XU Ming-gang, DUAN Yinghua. Contributions of various forms of nitrogen to nitrogen uptake by maize in red soil with different fertilities[J]. Acta Pedologica Sinica,,[In Press]