层状土壤质地对地下滴灌水氮分布的影响

Water and nitrogen distribution under subsurface drip fertigation as affected by layered-textural soils

以均质砂土(S)、均质壤土(L)和上砂下壤层状土壤(SL)为对象,采用室内土箱试验,研究了土壤质地及其层状结构和地下滴灌灌水器流量对水分、硝态氮和铵态氮分布的影响。结果表明,SL层状土壤中,砂-壤界面增加了水分的横向扩散而限制了水分的垂向运动,致使界面下部形成水分和硝态氮积聚区。土壤硝态氮分布还受肥料溶液浓度和土壤初始硝态氮浓度影响,对试验采用的土壤初始硝态氮浓度较低而肥料溶液硝态氮浓度较高的情况而言,灌水器周围的硝态氮浓度与肥料溶液的硝态氮浓度相近,随着离开灌水器距离的增加,土壤硝态氮浓度减小。灌水器周围的土壤含水率和硝态氮浓度随灌水器流量的增大而增大。施肥灌溉使灌水器周围5～10cm范围内的铵态氮浓度出现峰值,而土壤质地和灌水器流量对铵态氮浓度分布没有明显影响。因此地下滴灌水氮管理措施的制定应综合考虑土壤质地及其结构、初始土壤水氮状况、灌水器埋深及流量、灌水量、肥液浓度等因素。

Laboratory experiments were conducted using a plexiglass box to investigate the effects of soil textures,layed structure and emitter discharge rates on the distribution of water nitrate nitrogen and ammonium nitrogen from a buried source.A uniform sandy（S）,a uniform sandy loam（L）,and a sandy-over-sandy loam（SL）soil were tested.The results indicated that the sandy-loam interface existing in the SL soil limited the downward movement of water while increased the horizontal water movement,resulting in an accumulation of water and nitrate nitrogen in the sublayer soil underneath the interface.The distribution of nitrate nitrogen concentration was also controlled by input concentration and initial concentration of soil nitrate nitrogen.A nitrate nitrogen concentration approximating the input nitrate nitrogen concentration was found in the proximity of the buried source and the concentration decreased as the distance from the source increased under the tested conditions that input nitrate nitrogen concentration was substantially higher than the initial nitrate nitragen concentration.For both uniform and layered soils,an increasing emitter discharge rate resulted in greater water content and nitrate nitrogen concentration around the source.Measurements of ammonium nitrogen showed that there existed an extremely high ammonium nitrogen concentration in the 5-10 cm proximity of the buried source because of the adsorption.No significant influence of soil texture and emitter discharge rate on ammonium nitrogen distribution was found.The results obtained from the study suggest the importance of thoroughly considering soil texture and layed-structure,initial conditions of water and nitrogen,buried depth and discharge rates of emitters,water and fertilizer applied,and input concentration in the design and management of subsurface drip irrigation systems.