稻—萍—鱼系统中红萍氮素吸收利用及有效性研究

本文报道以红萍为饵料,鱼类对红萍氮素消化吸收、转化情况。试验结果表明:草鱼和尼罗罗非鱼对红萍氮素的消化和吸收率约为60％,其中30％红萍氮素转化为鱼体动物蛋白,另外约30％氮素排出体外。在田间条件下,尼罗罗非鱼摄食红萍,每季平均增长率约为41—40％。稻田养鱼,以萍喂鱼,鱼粪肥田,萍体氮素得以吸收利用,效益明显。在稻萍鱼体系中,当季红萍氮素的总利用率可达45—50％,而红萍单作肥料处理其利用率仅为30—36％,第二季作物对红萍残留氮素回收率可达7.83—9.64％,比红萍单作肥料处理高3.33—4.11％。第二季残效明显优于红萍压施处理,晚季稻谷产量的增产率可达13—25％,比压施红萍作肥料处理高7—8％。

STUDY ON UTILIZABILITY AND AVAILABILITY OF AZOLLA- NITROGEN IN THE "RICE-AZOLLA-FISH" SYSTEM OF PADDY FIELD

Azolla is a good fodder to fish. The Azolla-N can be uptaken availably by fish. When Azolla was used as fodder for fish, 60% of Azolla-N were utilized, a half of such Azolla-N uptaken being incorporated into fish body (Clenopharyn idellus and Tilapia nilotica) and another half being excreted as fish feces. The weight of T. nilotica increased by 41-48% during early season under the condition of paddy field, where Azolla (60kgN/ha) was put into rice-Azolla-fish ecosystem as the fish fodder. After that, the Aazolla-N could be utilized for cycling so that it had a good effect on rice growth. The total rate of 15N recoveried by fish and rice as 45-50% of availability in the rice-Azolla-fish system, but the rate of 15N recoveried as only 30-32% when Azolla was incorporated into soil as a green manure. In the cropping season, the residual rate of Azolla-N is about 7.83-9.64%, being 3.33-4.11% higher than that for the treatment of Azolla as manure. In this system, the ecosystem of paddy field is greatly improved, and the avilable nutrients in the fish feces are much and have a good effect on rice growth. The rice yield is similar to that for the treatment of Azolla as green manure, but its residual effect on rice yield is better than latter, the increasing rate of rice yield in the next cropping season beeing up to 13-25% and 7-8% higher than the latter.