洞庭湖平原典型水稻土氮素固持动态及氮的残留形态

以洞庭湖平原2个典型水稻土（红黄泥和紫潮泥）为对象，采用¹⁵N示踪技术，研究了淹水培养条件下稻草+硫铵配施（S+¹⁵NA）和单施硫铵（¹⁵NA）土壤微生物和粘土矿物对化肥氮的固定与释放及氮的残留形态.结果表明，淹水培养条件下B_N（SMBN）总体变化趋势是在培养前期达到峰值，而后逐渐下降，最后趋于稳定.固定态铵在整个试验期间变化相对较小，但也随培养时间的延长而减少.淹水培养条件下， B_N 以原有B_N为主.标记底物B_N的比例红黄泥为0.30%～6.67%；紫潮泥为1.00%～3.47%.微生物同化的标记底物硫铵氮的比例红黄泥为0.15%～20.65%，紫潮泥为2.06%～15.93%；有机无机配施处理(S+¹⁵NA)均大于单施化肥(¹⁵NA)，红黄泥S+¹⁵NA处理平均为6.78%，高于红黄泥¹⁵NA处理；紫潮泥S+¹⁵NA处理（10.78%）也高于紫潮泥¹⁵NA处理.粘土矿物对标记底物氮的固定率，红黄泥为2.48%～10.57%，紫潮泥为12.55%～30.04%.红黄泥S+¹⁵NA处理平均为7.14%，低于红黄泥¹⁵NA 处理；紫潮泥S+¹⁵NA处理（21.53%）也低于紫潮泥¹⁵NA处理.淹水培养条件下底物硫铵氮的残留率均大于30%，有机无机配施处理提高了无机氮的残留率.红黄泥底物氮的残留形态主要为酸解有机氮（>72%），而紫潮泥以酸解有机氮(44.0%～53.2%)和固定态铵(35.2%～37.5%)为主，两种土壤底物氮矿质氮形态残留在10%～20％之间.研究表明土壤对外源无机氮的固定与释放是一个动态的过程，施肥方式和土壤粘土矿物组成对该过程有重要影响.化肥和秸秆配合施用能增强微生物对无机氮的同化，降低土壤粘土矿物对无机氮的固持.有机无机配施处理在降低化肥氮损失的同时提高了酸不溶性氮态的残留率，降低了无机氮形态(固定态铵和矿质氮)的残留.

Dynamics of Labeled Substrate N by Microorganism and Soil Clay Immobilized and Its Residue Fractions in Typical Paddy Soils in Dongting Lake Floodplain

Dynamics of immobilization of the labeled substrate N by microorganism and soil clay and its residue fractions in soils from the plough layers of two subtropical paddy soils (Reddish clayey soil, Purple alluvial soil) in the Dongting Lake floodplain were studied. A laboratory-flooded incubation experiment was composed of three treatments: control(CK), labeled ammonium sulphate group (¹⁵NA) and the combined of labeled ammonium sulphate and rice straw group (S+¹⁵NA). During the incubation, microbial biomass N (B_N) increased firstly and then those decreased and tended to stable subsequently, while the content of fixed ammonium changed little. Native B_N acted as the major N pool because the percentage of labeled substrate B_N in reddish clayey soil and purple alluvial soil were 0.30%-6.67% and 1.00%-3.47%, respectively. The combined application of rice straw and chemical fertilizer (S+¹⁵NA) improved the immobilization of inorganic N by microorganism, because the immobilization ratio of substrate N in reddish soil and purple alluvial soil were 6.78% and 10.78%, respectively, for S+¹⁵NA treatment, higher than those for ¹⁵NA treatment. The immobilization ratio of substrate N by soil clay in reddish clayey soil and purple alluvial soil were 2.48%-10.57% and 12.55%-30.04%, respectively. However, the immobilization ratio of substrate N by soil clay in the two soils were 7.14% and 21.53%, respectively, for S+¹⁵NA treatment, lower than those for ¹⁵NA treatment. The incorporation of chemical fertilizer and rice straw increased the N remain percent. The main residue formation of the labeled substrate N was total hydrolysable N (>72%) in Reddish clayey soil, while it was total hydrolysable N (44.0%-53.2%) and fixed ammonium (35.2%-37.5%) in Purple alluvial soil. The residue of mineral nitrogen ranged 10%-20% in the two soils. In conclusion, fertilization method and the type of soil clay had important effects on the immobilization and mineralization of substrate N. The combined application of chemical fertilizer and straws increased the immobilization of inorganic nitrogen by microorganism and decreased immobilization of inorganic nitrogen by soil clay. The combined application of chemical fertilizer and straws decreased the loss of chemical fertilizer N, increased residue of nonhydrolysable N, and decreased residue of mineral nitrogen.