渭北旱原小叶杨苗期的施肥效应

对小叶杨采用盆插土培法辅以田间育苗施肥实验．结果表明：在渭北旱原土壤条件下，N、P、K三要素对于培育小叶杨壮苗都是必不可少的，N素的施用效果最好，凡不施用氮肥的处理，其苗木高生长量、叶面积和干物质量显著降低，且封顶早生长期短，单施氮肥或配合施用氮肥的各个处理则相反，都能有效地提高苗高生长量、叶面积和干物质量．延长了苗木的生长期，并且有避免单施磷、钾所引起蒸腾强度大、耗水多的良好作用；磷肥的施用效果仅次于氮，居第2位．但是磷在小叶杨苗木的径生长中．却起着主导作用；氮、磷、钾或氮、磷配合施用效果为最好，因施用钾肥对小叶杨苗木影响不明显，但它与氮、磷配合施用却显示出了积极的效果．

Fertilization Effect on Populus simonnii Carr in Weibei Loess Plateau in Its Seedling Stage

The experiment of fertilizing Populus sirnonnii Carr seedlings indicates N, P and K are necessary for cultivating strong Populus sirnonnii Casseedlings on Weibei Loess Plateau. The best fertilization effect is from N fertilizer. Either N fertilizer or mixed with other fertilizers can effectively increase seedling height growth, leaf area and dry matter, prolong seedling developing time. and avoid high transpiration and water wasting resulted from only applying P or K fertilizers. The better fertilization effect is from P fertilizer. It plays a dominant role in promoting Populus simonnii Cart seedling diameter growth. The effect comes best with P mixed with N or N and K. Only with K fertilizer the fertilization effect is not obvious. But it is good when K mixed with P and N.