施用氮肥对提高旱地作物利用土壤水分的作用机理和效果

The Mechanism and Effects of N Fertilization in Increasing Water Use Efficiency

在年降水丘４５０～５１０ｍｍ的半湿润易旱地区的壤质红垆土上，以春玉米为供试作物进行了大田试验。玉米生长期间，每隔１０天分别测定不同栽培和施氮量处理的蒸腾强度，叶面积，伤流量，伤流液成分，叶水势，叶片糖分含量，并刈割玉米地上部分，测定生长量，分层采取２ｍ土层的土壤，测定含水量，以研究施用Ｎ肥对提高旱地作物利用土壤水分的作用机理和效果。试验表明，施用氮肥促进了作物根系发育，扩大了作物觅取水分和养分的土壤空间，增大了蒸腾强度和伤流量，降低了叶水势，提高了伤流液中氨基酸含量，使根系活性增强，作物吸取和运转土壤水分的能力提高。利用直接测定的结果计算，施肥不仅提高了作物蒸腾量，减少了土壤水分蒸发量，增高了Ｔ／ＥＴ比值，而且提高了蒸腾效率，增加了叶片的糖分含量，使蒸腾的水分得到了更有效地利用。施氮区与无氮区相比，消耗的土壤水分无明显区别，但由于施肥区显著增产，水分的利用效率明显提高。用蒸散量计算出来的水分利用效率，ＷＵＥ（ＥＴ），随施氮量增高而增高；用蒸腾量计算出来的水分利用效率，ＷＵＥ（Ｔ），因产物而不同：籽粒的水分利用效率与施氮量成直线关系，而干物质的水分利用率不因施氮量而变化，表明施肥对提高经济产物的水分利用效率更?

Field experiments were conducted in a subhumid area prone to drought with a loamy red-lou soil,using maize as an indication plant.During the crop growth period,transpiration intensities,leaf areas,bleeding sap and amino acid in it,leaf water potentials and sugar contents in leaf,thebiomass of maize, and the soil water contents in a zone from 0 to 200 cm were all determined for treat- ments with different rates of N fertilizer and cropping systems once every ten days in order to investi-gate the mechanism and effects of application of N fertilizers in increasing water use efficiency.The re-sults obtained show that applying N fertilizer promoted root growth,and therefore extend the rootspace in soil for plant to take up more nutrients and water,raised the transpiration intensity and theamounts of bleeding sap with the increase of the amino acid contents in it,and reduced the leaf waterpotential.As a result, the root activity was increased,and the water uptake and transfer from roots toabove- ground parts increased.The results also show that the application of N fertilizer did not onlyraise the transpiration rates,reduce water evaporation rates from soil,increase the T/ET ratio,but alsoincreased transpiration efficiency and sugar contents in the leaves. consequently,the water transpiredwas used more effectively,crop production. compared to the soil with no N fertilization, the waterlost from that with N application was almost the same,However,due to high yields obtained with Napplication,the water use efficiency(WUE) was substantially increased.The WUE obtained from e- vapotranspiration water was linearly increased with the increase of N rates,using either grain or drymatter for calculation.In contrast,the WUE obtained from transpiration water was different with dif- ferent products:for dry matter,it was not significantlychanged with N rates; but the reverse was truefor the grain,indicating that application of N fertilizer was more advantageous to increasing the WUE ofthe economic product.