滴灌点源施肥灌溉对土壤氮素分布影响的试验研究

利用室内试验,研究了点源施肥灌溉条件下硝态氮和铵态氮的分布规律。试验土壤为砂壤土,滴头流量的变化范围为0.6～7.8L/h、灌水量为6～15L、肥液(NH₄NO₃)浓度为100～700mg/L。销态氮在距滴头17.5cm范围内呈均匀分布,其浓度随肥液浓度的增加而增加;在湿润边界上硝态氮产生累积;肥液浓度是影响硝态氮分布的主要因子。在距滴头15cm范围内,滴头流量和灌水量对土壤中硝态氮分布的影响不明显,在此范围以外,随滴头流量的增大或灌水量的减小,硝态氮浓度增加。铵态氮浓度在滴头附近出现高锋值,肥液浓度越高,锋值越大,且施肥灌溉对铵态氮分布的影响范围较小,一般在距滴头10cm范围以内

Nitrogen Distributions in Soil Under Fertigation From a Point Source

Simultaneous distributions of water, nitrate-N and ammonium-N in a sandy loam soil from a point source discharging an ammonium nitrate (NH₄NO₃) solution were measured using the gravimetric method. The variables affecting water and solute distributions, including application rate varying from 0.6 to 7.8 L/h, input concentration from 100 to 700 mg/L, and applied volume from 6 to 15 L, were investigated and their effects on the distributions of nitrate-N and ammonium-N were presented in this article. A uniform distribution of nitrate-N concentration in the soil was found a radius of 17.5 cm around the point source for a given input concentration. For any input concentration, the accumulation of nitrate at the boundary of the wetted volume was observed. The nitrate-N concentration in the soil was primarily affected by the input concentration. There was an increased nitrate-N concentration with a higher input concentration. The effects of application rate and applied volume on nitrate distribution were not significant up to a radius of 15 cm, beyond which either a higher application rate or a smaller applied volume resulted in a higher nitrate concentration in the soil. The results of ammonium-N distribution measurements indicated that there existed an extremely high ammonium-N concentration in the proximity of the point source (about 2.5 to 7.5 cm from the source). An increased input concentration produced a higher ammonium concentration around the point source. Results also demonstrated that the influence of fertigation on the ammonium-N distribution was restricted in a small volume, about 10 cm around the point source. Beyond this range, input concentration, application rate, and total applied volume had insignificant effects on ammonium-N distribution. The information obtained from this research is useful in the design, operation, and management of a fertigation system with drip irrigation.