【摘要】 <正> 绿肥作物,特别是豆科绿肥,不仅是土壤有机质的重要来源,更是作物氮素的良好给源。绿肥的后一作用,历来受到人们的重视。许多研究者研究了绿肥中氮素对当季作物的有效性以及影响氮素有效性的因素。已经知道,除土壤性质和作物种类外,绿肥作物的化学组成,特别是C/N比值和木质素含量是影响其氮素有效性(对当季作物)的关键因素。各种绿肥中能被当季作物吸收利用的氮素一般仅占其总氮量的25.3±5.0%,其余更多还原

【Abstract】 The nitrogen balance and the availability of residual nitrogen of green manures in relation to their chemical composition were studied in pot and incubation experiments.Azolla, milk-vetch and common water hyacinth were used as green manures and labelled by the fertilization of (¹⁵NH₄)₂SO₄.Result obtained are summarized as follows:1.Although plant materials having lower C/N ratio usually give more available nitrogen and the C/N ratio of azolla was lower than that of milk-vetch, yet azolla contained high lignin about 20%, and consequently the percentage recovery of nitrogen by rice plant from azolla was much lower than that from milk-vetch.2.The loss of nitrogen from azolla during the growing period of rice plant was more than that from milk-vetch. It may be due to chemodenitrification.3.Judging from the nitrogen availability ratio （defined as the percentage of nitrogen originated from plant residues mineralized or absorbed by crop divided by the percentage of soil native nitrogen of the same performances）, the residual nitrogen availability of azolla was equal to, or slightly lower than that of soil native organic nitrogen, while that of milk-vetch and common water hyacinth was usually higher.It seems that the effect of green manures on the improvement of soil organic matter varied with their chemical composition.Green manures with a higher lignin content usually yielded a lower amount of "active organic matter".Previously translated as Wen Chi-hsiao.更多还原