氮锌复合作用对混播系统白三叶生长与固氮及氮转移的影响

Influences of the compound effects between nitrogen and zinc on growth,N-fixation and transfer of fixed nitrogen of white clover in mixed culture

选用南方草地土壤——山地黄棕壤进行盆栽试验 ,研究了氮锌复合作用对混播系统白三叶生长、根瘤发育、固氮及固氮产物转移的影响。结果表明 ,氮锌复合作用对白三叶生长、根瘤发育、固氮及氮转移在白三叶不同生长阶段、不同氮锌施用范围表现出不同的效应。生长前期氮锌复合作用对白三叶茎叶及根系产量的协同效应表现在氮 0～ 30 mg/kg、锌 0～ 6mg/kg的范围内 ,而生长后期协同范围扩大到氮 0～ 90 mg/kg与锌 0～ 2 0 mg/kg的不同组合处理中 ;在高于上述氮锌施用范围 ,氮锌之间表现为拮抗效应。与不施氮相比较 ,施氮显著降低了白三叶根瘤数量及生长前期固氮百分数 ,但适量施氮 ( 30 mg/kg)显著增加了白三叶根瘤重量及生长后期固氮百分数。在所有施氮水平中 ,施锌 6mg/kg显著增加了根瘤数量、根瘤重量及固氮百分数。与茎叶及根系生长氮锌协同范围相比较 ,氮锌对根瘤发育与固氮作用的协同范围较小。固氮产物转移与白三叶根瘤衰败有密切相关。试验为我国南方牧场科学施肥提供理论依据。

The area of pasture in the southern China is about 60 million hectare, which is an important husbandry base in China. The experimental soil is collected from Bailihuang demonstration pasture in Yichang county, Hubei Province of China , typical subtropical middle mountain pasture of the southern China. The soil type is yellow brown earth and deficient in nitrogen, phosphorus and zinc, therefore the application of nitrogen, phosphorus and zinc is an important measurement in increasing output and quality of herbage. The large amount of phosphorus application results in the fixation of zinc. There are more researches on the relationship between P and Zn, but in fact short of the studies of the relationship between N and Zn. The influences of the compound effects between nitrogen and zinc on growth, nodules, N-fixation and transfer of fixed nitrogen by white clover to ryegrass in mixed culture are studied in this paper. This study will provide guidance for fertilization of the pasture in the southern China. ;The tests contained two factors and four levers, adopted 4×4 complete design by pot experiments. The levels of nitrogen ( 15N-(NH 4) 2SO 4) were 0, 30, 90, 150mg/kg ( 15N abundance was 5.00%). The levels zinc (ZnSO 4) were 0, 6, 20, 40 mg/kg . In the whole growth period, two harvests were made. The first harvest was in thriving growth stage and the second harvest was in the beginning of the winter. The experiment contained two series of ryegrass in mono-culture and ryegrass-white clover in mixture. There were 20 plants in each pot and the ratio of ryegrass to clover was 4 to 1. The mono-culture of ryegrass was used as a control for calculation of nitrogen fixation and transfer of fixed nitrogen by white clover to ryegrass in mixture. The main results showed as follows: The influences of the compound effects between nitrogen and zinc on growth, nodule development, N-fixation and N-transfer of white clover had different effects on various growth stages of white clover and various ranges of applied nitrogen and zinc. The synergism between nitrogen and zinc on the growth of shoot and root was in the range of different combination applied 0～30 mg/kg N and 0～6 mg/kg Zn in the first growth stage, and enlarged to the range of different combination of applied 0～90 mg/kg N and 0～20mg/kg Zn in the late growth stage. For higher quantities of applied nitrogen and zinc than above range, there were antagonism effects between nitrogen and zinc on the growth of white clover. In comparison with no applied nitrogen, the application of nitrogen significantly decreased the percentage of nitrogen fixation in the early growth stage and the number of nodules in both growth stages, but suitable amount of applied nitrogen (30mg/kg) significantly increased the percentage of nitrogen fixation in the late growth stage and the fresh weight of nodules per plant in both growth stages. In all treatments with applied nitrogen, zinc applied 6mg/kg significantly increased the number of nodules as well as the percentage of nitrogen fixation. In comparison with the synergism range between nitrogen and zinc on shoot and root growth, the range of synergism effects between nitrogen and zinc on nodule development narrowed down. There was close relationship between the transfer of fixed nitrogen by white clover to ryegrass and the declination of nodules.