稻秆（^（15）N）和尿素（^（15）N）单施或混施时，水稻对标记氮的吸收与1

￣(15)N ABSORPTION BY RICE AND NITROGEN BALANCE SHEET WHEN SINGLY OR MIXEDLY APPLYING RICE STRAW(15N)AND UREA(15N)

水稻盆栽试验表明，稻秆或尿素做基肥，单独施用时稻秆１５Ｎ的当季利用率（＜１８．６％）低于尿素，但有较高的土壤残留（＞４５．８％）；增加稻秆用量，水稻对其１５Ｎ的利用率无显著差异，增加尿素用量则会显著增加水稻对其１５Ｎ的吸收。在最高分蘖期，水稻已吸收了其能利用的尿素氮的大部分和稻秆氮的一半左右。两种肥料混合的Ｃ／Ｎ比为１５时，尿素用量增加，其１５Ｎ水稻利用率变化不大。添加尿素使稻秆１５Ｎ的利用率显著增大，而它的土壤残留率和损失率则有所减少；随混合把料用量的增加，稻秆１５Ｎ的利用率没有显著的变化，但其损失率则呈现显著下降的趋势。

A rice pot experiment showed when 15N labeled rice straw or urea was singly appliedbefore seedings transporting,1.lower 15N utilization efficiency(NUE,<18.6%)buthigher 15N residual effect in soil(>45.8%)of applied rice straw than those of corres-ponding values for urea were observed;2.the increase of rice straw did not signifi-cantly change its own 15N uptake by rice,but contrary result was obtained byincreasing urea application, 3.before maximum tillering stage,most of the urea 15Nand about half of the rice straw 15N it could utilize would already have been absorbedby the rice plant.When both fertilizers were mixed and basely applied in a C/N ratio15,the NUE of urea did not change much with the increase of urea applicationwhile maintaining the fixed C/N ratio;added urea enabled more absorption of ricestraw 15N by rice,but less remained in soil or was lost. Increase of mixed fertilizerdid not change the rice straw NUE much,but 15N loss tend to be lower.