连作大豆根际土及根系、冠部三要素含量变化动态的研究

通过对轮、连作大豆根际土及根系、冠部氮、磷、钾三要素含量的定期测定，发现根际土中，速效氮含量连作区略高于轮作区；速效磷含量变异程度大且无规律；速效钾含量连作区低于轮作，差异达显著水平（ｔ＝４．４７８，ｔ０．０５＝４．３０３）。根系和冠部的全氮含量连作区均高于轮作区，冠部除鼓粒期外差异均达到显著水平；全磷含量鼓粒前连作区低于轮作区，盛花期差异达显著水平，鼓粒后基本无差异；全钾含量连作区均低于轮作区，差异达极显著水平（ｔ＝８．００９，ｔ０．０１＝３．１６９）。由此认为氮素不是限制连作大豆产量的因素；连作大豆快速生长期植株缺磷，应及早补施磷肥；大豆连作可导致缺钾，应增施钾肥。

STUDIY ON THE TRI-ELEMENT CONTENT IN RHIZOSPHERE SOIL, ROOTS AND CANOPY OF CONTINUOUS CROPPING SOYBEAN

The content of nitrogen, phosphorus and potassium in rhizosphere soil, roots and canopy was estimuted on difinste periods. Soil of effective nitrogen was higher in continuous cropping plot than that of rotational cropping plot and the vaviation of effective phosphorus was not regulative while the effective potassium of continuous cropping plot was lower than that of rotational cropping plot. The results reached significant level (t=4. 478, t0.05= 4.303).The total content of nitrogen in both roots and canopy was higher in continuous cropping plot than that in rotational cropping plot. The difference of nitrogen content in canopy and roots reached significant level except on pod- filling stase. The content of phosphorus was lower in continuous cropping plot than that in rotational cropping plot before pod -filling period,and tecance significant in full- blooming period,but there was no differece after pod filling stage. The total content of potassium in every stage was lower in continuous cropplng plot than that in rotational eropping plot,and the difference reached significant level (t=8.009,t0.05= 3.169). On this basis,we think tha nitrogen is not the limiting factor of soybean yield under the condition of continuous cropping. Soybean plant under continuous cropping condition will be deficient of potassium and phosphorus in rapid growth stage and corresponding fertilizer should be applied on time.