基础肥力不同的玉米田土壤有机碳组分数量对施氮水平的响应
为阐明三种不同基础肥力土壤有机碳组分数量对施氮水平的积极响应，文章以玉米长期定位施肥试验地为供试对象，采用化学分析法，系统比较了不同施氮水平（不施氮、70?Cc优化施氮、优化施氮、130?Cc优化施氮和农民习惯性施氮）对不同肥力土壤0~20cm耕层有机碳及其活性组分数量的差异影响。结果表明：（1）施氮水平对三种不同基础肥力土壤有机碳（SOC）含量的影响规律不一。在肥力较差区域，增氮会加剧土壤退化的程度；（2）适宜氮素用量（0~240 kg/hm2）有利于较高肥力土壤易氧化有机碳（ROC）含量的提升；（3）贫瘠土壤难氧化有机碳（DOC）抵御外源氮素干扰的能力较差，施氮能加速其矿化，大幅降低SOC的氧化稳定性，不利于肥力的保蓄；（4）施氮有助于高肥力地块SOC的年轻化，抑制轻、重组有机碳含量的提高，而在中、低肥力区域，重组有机碳含量均经历着“先增后减”的变化规律，后者更有助于该组分的累积。
英文摘要:
To clarify the positive response of the organic C components of soils with three basic fertilities to different nitrogen (N) application levels, the experimental field of corn with long-term fixed fertilization serves as our object of study. The method of chemical analysis was adopt to compare the differences systematically among the effects of different levels of N (no N, 70?Ccoptimized N, optimized N, 130?Ccoptimized N, habitual N of ordinary farmers) on organic C and its labile fractions in the farmland surface soil (0-20cm) with different basic fertilities. The results showed that: (1) the influenced rules of N levels applied in the soils with three different basic fertilities on their SOC were different. In the barren area, the increasing N application would aggravate the degree of soil degeneration; (2) the appropriate adjustment of N dosage in the range of 0~240 kg/hm2 could enhance the amount of readily oxidizable organic C (ROC) of soil with high fertility; (3) the ability of difficultly oxidizable organic C (DOC) in barren soil resisting the exogenous nitrogen interference was poor. The N application could accelerate the mineralization of DOC and then reduce the oxidation stability of SOC greatly, which was bad for the maintenance of soil fertility; (4) The N application could make the SOC of plot with high fertility younger, which could inhibit the enhancement of organic C amounts in the light and heavy fractions. In the condition of moderate and low fertility, both of the organic C in the heavy fractions experienced a similar rule that DOC was increased first and then decreased, in which the N application was more helpful to accumulate the DOC of barren soil.
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