水稻根际固氮量及根系不同部位的固氮活性

采用乙炔还原法测定水稻根际原状土粒的固氮活性,以3∶1的换算比例推算为田间固氮量。每季水稻根际固氮量早稻为0.4-0.45斤氮/亩/66天;晚稻为0.6-0.79斤氮/亩/72天。其中早稻80—90%的氮素在抽穗至成熟期固定,而晚稻在这段期间固定的氮素占总数的40—52%。经多次测定表明:水稻根系不同部位固氮活性的趋势是,埋入土中带根基茎段2.5厘米活性最高,根基以下3厘米根段次之,3厘米以下根段活性很低,水稻根系结合的腐生性细菌以固氮菌占优势,同时也含有少量的丁酸固氮梭菌。

AMOUNT OF NITROGEN FIXED IN RHIZOSPHERE OF RICE PLANT AND NITROGEN FIXATION ACTIVITIES AT DIFFERENT PARTS OF ROOT

The nitrogen fixation,activities in soil cores of rice rhizosphere were measured by the acetylene-reduction method.As calculated according to the theoretical value of the ratio of acetylene reduced to N fined (3:1),the amount of nitrogen fined in paddy field of early rice ranged from 200-226 g per mu for 66 days and that of late rice from 301-398 g per mu for 72 days respectively,in which about 80-90% of N₂ was fined from the heading to ripening stages for early rice and 40-52% of N₂ was fixed during the same growing period for late rice.The results of experiments showed that the nitrogen fixation activity in rice rhizosphere varied with different parts of root.The highest activity was found at the basal part of stem connect with root system buried in soil about 2.5 cm,the lower was at the roots below basal stem about 3 cm in soil and the lowest was at the roots near root tip.Among the heterotraphic bacteria associated with rice plant routs,nitrogen-fixing organisms was dominant,with a few Clostridium butyricum.