红萍在稻田氮素平衡中的作用

应用１５Ｎ示踪法研究了红萍在稻田氮素平衡中的作用。红萍作基肥，当季水稻的１５Ｎ－红萍Ｎ素利用为２７．８％；第二季５．３８％；土壤残留３６．１％。红萍可排出体内１２％以上的氮素。红萍的排氮和吸氮有助于调节稻田的氮素平衡，稻田养萍抑制藻类生长，降低ｐＨ值和ＮＨ浓度，减少ＮＨ３挥发损失，以及减少蓝藻（颤藻）反硝化反应释放的Ｎ２Ｏ，提高化学肥料１５Ｎ的回收率：它比１５Ｎ－尿素不养萍处理１５Ｎ回收率增加４．２５％，比１５Ｎ－尿素追肥不养萍处理１５Ｎ回收率增加８．３５％～２５．１１％。

THE EFFECT OF Azolla ON NITROGEN BALANCE IN PADDY FIELD

The effect of Azolla on N halance in paddy field was studied by 15N tracer technique. Us-Ing 15N Labclled Azolla as basal dressing,27.8%and 5.38%of 15N were utilized by early andlate rice respectively, while 36.10%of 15N were residued in the soil.AzoIla dressed werc re-duced 15N loss by 9.1%as comparing with an equal of N from urea. 12%of total N of Azollawas excreted through its root system,In addition,inoculation with Azolla could inhibit thegrowth of blue-green algae ln the field and decrease the pH value,amount of NH -N in wa-ter of paddy field’ammonia volatilization and denltrification caused by the algae, Inocula-tion with Azolla in paddy field increased 4.25%of recovery from urea-15N as basal dressingand 8. 35%and 25.11% 15 N recovery from urea-15N as top dressing,compared with tketreatments without Azolla inoculation.These results suggested that inoculation with Azollainto rice field may be not only bcneficial to rice production but favorable to N balance in thefield.