涌泉根灌不同浓度肥液入渗特性及土壤湿润体模型研究

为了研究涌泉根灌肥液入渗特性及湿润体水氮运移的变化规律,在陕北米脂山地微灌枣树示范基地原状土上进行了涌泉根灌肥液入渗试验。结果表明:累积入渗量与入渗时间之间符合Kostiakov幂函数关系(R20.9,P0.01);涌泉根灌入渗能力与增渗效果均随肥液浓度增大而增大;水平湿润锋与竖直湿润锋运移距离均随肥液浓度增大而增大,且均与入渗时间呈显著的幂函数关系,水平方向和竖直方向的湿润锋运移距离的拟合值与实测值的相对误差在–3.84%～5.20%以内。肥液浓度的不同对于湿润体大小略有影响。提出了涌泉根灌肥液入渗湿润体内土壤含水率和NH_4~+-N浓度分布的数学模型,即在一定浓度范围内,单位含水率的变化可引起的肥液浓度变化,且模型的计算精度较高(模拟值与实测值相对误差在10%以内),并符合湿润体内土壤含水率和NH_4~+-N分布规律,可对不同位置处土壤含水率及NH_4~+-N含量进行估算。水分分布情况对肥液浓度条件敏感性较低,NH_4~+-N分布情况对肥液浓度条件敏感性较高。研究可为涌泉根灌水肥高效利用提供参考。

Infiltration characteristics and wetting body model of bubbled-root irrigation under different fertilizer concentration

Bubbled-root irrigation is an effective method of irrigation that transports water and fertilizer to roots of fruit trees. This study investigated the infiltration characteristics of the bubbled-root irrigation and the changes of water and nitrogen transport in the wetting body. A field experiment was carried out in Yulin city, Shanxi. During the experiment, water was supplied by a Markov bottle. The emitter flow rate was 5 L/h. The irrigation amount was 30 L. The nitrogen-fertilizer was urea with nitrogen not less than 46.4%. The fertilizer concentration was 5, 10 and 20 g/L. The irrigation without fertilizer was as control. The cumulative infiltration was determined and it dynamic change was fitted by a Kostiakov model. The infiltration-increasing rate was calculated by difference between cumulative infiltration of fertilizer treatments and that of control dividing by the cumulative infiltration of control. In addition, the water content and ammonium N content were measured. Soil samples along the profile 0-100 cm (in an interval of 10 cm) were collected from the position where the emitter was, at the distance of 12.5 and 25 cm away from the emitter, respectively. The sensitivity of water distribution and nitrogen distribution in soils was assessed by comprehensive sensitivity coefficient when the fertilizer concentration increased by 100 g/L or decreased by 50 g/L. The results showed that the cumulative infiltration increased with infiltration time following a Kostiakov power function model (R2>0.9). The infiltration rate decreased with time. The cumulative infiltration and infiltration-increasing rate both increased with increasing fertilizer concentration. The wetting front shift distance increased with infiltration time. When the fertilizer concentration increased, the horizontal wetting front shift distance increased slightly but the vertically upward and downward wetting front shift distance increased greatly. Models of wetting front shift distance based on fertilizer concentration and infiltration time were established. It had a high accuracy and the relative error between measured and simulated value was -3.84%-5.20%. The fertilizer concentration could slightly affect the volume of wetted body. Models were established to estimate soil water content and NH4+-N concentration of bubbled-root irrigation under different fertilizer concentrations. Both of the models had the high accuracy with the relative error between measured and estimated values less than 10%. The models could estimate the soil water content and NH4+-N content at different locations. Within the wetted body, the relationship between soil water content and NH4+-N content could be described by power functions, while in the outside of the wetted body, the ratio of initial fertilizer concentration to initial soil water content was a constant. The change of fertilizer concentration could be caused by the change of unit water content within a certain concentration range. At the end of irrigation, NH4+-N content decreased with increasing the distance away from the emitter at the same buried depth of emitter. It increased with the increase in the fertilizer concentration. The NH4+-N content increased greatly before 3 h and the increase amplitude gradually decreased after 3 days. The comprehensive sensitivity coefficient of water distribution to fertilizer concentration change was 0.029-0.076 while that of NH4+-N distribution was 0.148-0.662. It indicated that the water distribution was less sensitive to fertilizer concentration, and the distribution of NH4+-N was more sensitive to fertilizer concentration.