黄土高原典型土壤有机氮矿化过程

Organic N mineralization in typical soils of the Loess Plateau

以黄土高原从北向南不同地区典型土壤类为对象,采用Bremner淹水培养法,研究黄土高原典型土壤有机氮的矿化过程。结果表明,淹水培养期间矿化出的部分NH4+-N会被粘土矿物固定,固定量因土壤不同而异,因此在测定有机氮矿化量时,只有考虑这一部分氮素,才可获得可靠结果。不同土壤有机氮量矿化明显不同,表现为土垫旱耕人为土>黄土正常新成土>简育干润均腐土>干润砂质新成土,从南到北氮素矿化量呈减小趋势。添加C/N低(C/N比为21.7)的紫花苜蓿(Medicago stativa)茎叶有利于促进土壤有机氮矿化,而添加C/N高(C/N比为43.3)的长芒草(Stipa bungeana)会促进矿质氮的生物固定;不同类型植被土壤间在培养20、40d和60d时的矿化量差异显著(p值分别为0.0177、0.0109和0.0073),均表现为均为林地土壤>裸地土壤>草地土壤>农田土壤;从平均看,加(NH4)2SO4后有机氮矿化量有一定减少。在不同培养阶段,不同土类间氮素矿化率不同,在20d和40d时存在显著差异(p分别为0.0092和0.0381),60d时差异不显著,不同土类氮素矿化率的大小顺序为干润砂质新成土>黄土正常新成土>土垫旱耕人为土>简育干润均腐土,这一结果说明在淹水条件下,黄土高原土壤从南到北易矿化氮所占全氮比例呈增加趋势。

The objective of this experiment was to improve our understanding of soil organic N mineralization in the Loess Plateau. Typical soils were sampled from north to south in the Loess Plateau and soil organic N mineralization was measured in the soils using the Bremner incubation method. The soils were incubated for 60 d. The results showed that part of NH4^＋ - N released during mineralization was fixed by clay minerals in these soils, so in order to get reliable results, we must consider this when determining total organic N mineralization. The amount of organic N mineralization was significantly different among the soil types. Specifically, the amount of mineralization decreased in the order Eum-Orthic Anthrosols 〉 Los-Orthic Entisols 〉 Hap-Ustic Isobumisols 〉 Ust-Sandiie Entisols. The amount of organic N mineralization decreased from south to north across the Loess Plateau. The addition of Medicago sativa residue, which has a low C： N ratio （C/N = 21.7）, increased the amount of organic N mineralization. In contrast, the addition of Stipa bungeana residue, which has a high C：N ratio （C/N =43.3）, increased microbial immobilization of soil mineral N. There were significant differences in the amount of organic N mineralization at 20d （p = 0.0117 ）, 40d （p = 0.0109）, and 60d （p = 0. 0073 ） depending on the type of vegetation growing on the soil at the time the samples were collected. The amount of organic N mineralization tended to decrease in the order： forest soil 〉 bare land soil 〉 grassland soil 〉 farmland soil. The addition of （NH4）2SO4 to the soil resulted in a decrease in the N mineralization rate at 20d （p = 0.0037） , 40d （p = 0. 0033 ） , and 60d （p = 0. 0027 ） compared to soils which did not receive （NH4 ）2SO4. There was a significant difference in the N mineralization rate among the different soil types when incubated for 20d （p = 0. 0092） and 40d （p = 0. 0381 ）, however, there was no significant difference in mineralization rates among the soils （when incubated for 60d. Organic N mineralization rates tended to decrease in the order： Ust-Sandiie Entisols 〉 Los-Orthic Entisols 〉 Eum-Orthic Anthrosols 〉 Hap-Ustic Isohumisols. The results showed that total organic N mineralization rates increased from south to north in the Loess Plateau.