农田NO排放的时间变异性

Temporal Variability of NO Emission from Croplands *

在采用基于箱法的自动观测技术对苏州地区一个完整的冬小麦生育期的麦田ＮＯ排放进行全天候连续观测的基础上，讨论了ＮＯ排放的季节变化和日变化特征及其温度和植物生长的影响．观测实验研究发现，苏州地区冬小麦田的ＮＯ排放具有极其显著的季节变化规律性，冬季以前的小麦苗期和返青至淹水种稻之前的春季，ＮＯ排放量分别为０．１５６—０．７５８ｍｇ·ｍ－２·ｈ－１和１．２２９—１０．８０２ｍｇ·ｍ－２·ｈ－１，前者是全生育期排放总量的１．５％—１０．５％，后者为８３．０％—９３．８％．温度是决定其季节变化格局的首要因素，虽然施氮肥可以使ＮＯ排放增大５—７倍，但却不能改变其季节变化格局．在植物生长活动较弱的阶段，ＮＯ排放的日变化格局与温度一致，即日排放极大值发生在午时左右．但是，在植物旺盛生长的季节，由于根系与土壤微生物竞争土壤ＮＨ＋４－Ｎ，导致与温度完全相反的ＮＯ排放日变化格局，即日排放极大值发生在夜间１８—２４时，午时左右出现的却是日排放极小值．

No emission from the croplands of Suzhou suburban,in which winter wheat following rice was planted,was continuously measured with an automated system based on static chamber techniques.The discussion of this paper focuses on the seasonal and diurnal variation of NO emission and the influcences of temperature,fertilization and plant activity.The NO emission from the wheat fields shows high seasonal variability.Amounts of released NO in the seedling stage and during the period from wheat reviving in spring till flooding fields for rice planting was observed to be 0 156—0 758 and 1 229_10 802mg·m -2 ·h -1 ,respectively.The former only accounts for 1 5%_10 5% of the seasonal total,and the later 83 0%_93 8%.It is temperature that determines the seasonal variation pattern of NO emission.Even though N fertilization may significantly intensify the seasonal NO emission by 5—7 times,it is not able to modify the seasonal variation pattern.Under suitable temperature,the diurnal variation pattern of NO emission from crop fields depends on the activities of plants.When wheat growth activity is relatively lower,the diurnal pattern of NO emission is very similar with that of temperature,with the maximum appears at about 12∶00.When wheat in the fields luxuriates,the competition of NH + 4 up take by wheat roots and NH + 4 oxidation by nitrifers leads to a night peak pattern of diurnal variation,with the maximum emission occurring at 18∶00_24∶00 and the minimum at about 12∶00.