土壤和植物营养研究部主要研究有关影响养分和水分供应的因素以及土壤管理措施对橡胶树的影响。看来,在Boralu土壤上更新胶树(PB86)需要的养分(尤其是钾素)比目前推荐的水平要高些。而且,RRIC100组无性系需要的氮和钾也比PB86高。一般来说,施用氮、磷、钾有增产的迹象,记录表明产量比不施肥区增加5—27％。 最近八年进行的一项试验的产量资料表明:尿素作为一种氮源,对种植在Boralu土壤上的成龄树与硫酸铵一样有效。其它的试验也有类似的趋势。至于磷源,Eppawela磷灰石粉对幼龄胶树与进口磷矿粉一样有效。不论使用何种磷肥,增加磷的用量不一定能增加肥效。硫酸镁、水镁矾和白云石粉这三这镁源中,看来即使象白云石这样一种缓效的镁肥也能用于更新胶树。基于这些研究结果,为了利用尿素和白云石(斯里兰卡本国有最便利的氮和镁肥),推荐的肥料名单已作了修改。 覆盖作物的一些管理措施,如建立豆科覆盖作物及对其施磷肥,继续显示出对成龄胶树生长和产胶有长期有利的影响。然而,钾肥直接对胶树施用,看来比施给覆盖作物更有效;至少在更新胶树早期阶段如此,特别是缺钾的土壤。 土壤保持措施的研究表明,在新植或更新胶园建立起良好的豆科覆盖作物之前,死覆盖是一种很好的农业措施。一旦建立起良好的豆科覆盖,土壤流 Soil and Plant Nutrition Research focuses on factors affecting nutrient and water supply and the impact of soil management practices on rubber trees. It appears that the nutrients (especially potassium) needed to renew gum tree (PB86) in Boralu soils are higher than currently recommended. Moreover, RRIC100 clones required higher nitrogen and potassium than PB86. In general, there is evidence of increased N, P and K production and records indicate a 5-27% increase in yield over the non-fertilized area. Yield data from one trial conducted in the last eight years show that urea as a nitrogen source is as effective as ammonium sulfate grown on Boralu soil. Other experiments have similar trends. As for the phosphorus source, Eppawela apatite powder is as effective for young gum trees as imported phosphate rock. No matter what type of phosphate fertilizer used, increasing the amount of phosphorus does not necessarily increase fertilizer efficiency. Among the three magnesium sources, magnesium sulfate, hydrosulphate and dolomite, it seems that even a slow-acting magnesium fertilizer like dolomite can be used to renew the gum tree. Based on these findings, the list of recommended fertilizers has been modified to utilize urea and dolomite (Sri Lanka’s most convenient nitrogen and magnesium fertilizers). Some of the management practices that cover crops, such as the establishment of leguminous cover crops and their application of phosphate fertilizer, continue to show long-term beneficial effects on the growth and production of gum trees. However, application of potash directly to the gum tree appears to be more efficient than application of the cover crop; at least in the early stages of renewing the gum tree, especially potassium-deficient soil. Studies of soil conservation practices show that dead coverage is a good agricultural practice before new legume cover crops are established or renewed. Once well established legume coverage, soil flow