燥红土微咸水滴灌下水盐运移规律的试验研究

Study of movement of water and salts in dry red soilunder drip irrigation with brackish water

为了探讨燥红土地区微咸水滴灌的水盐运移规律,对该地区容重为1.2 g·cm^(-3)的红壤土,进行了不同灌水矿化度(2.88 g·L^(-1),4.86 g·L^(-1),8.33 g·L^(-1))的单、双点源入渗试验及不同滴头流量(2.68 L·h^(-1),3.74 L·h^(-1),4.68 L·h^(-1))的单点源入渗试验,采用室内三维土箱入渗,分析滴头流量及矿化度对该地区红壤土水盐运移规律的影响。结果表明:单点源入渗试验中,矿化度一定(2.88 g·L^(-1))的条件下,灌溉时间在150 s后, 3.74 L·h^(-1)滴头流量下湿润锋运移速率快且稳定,平均推进速率达1.65 cm·s^(-1),最终推进深度达22 cm,可以达到灌溉要求,优于4.68 L·h^(-1)滴头流量的综合性能且节省灌溉水;在滴头流量一定(3.74 L·h^(-1))的条件下,湿润锋推进深度随矿化度的增加而增加,其速率排序为:2.88 g·L^(-1)<4.86 g·L^(-1)<8.33 g·L^(-1),其推进深度分别为21.5、22.4、22.78 cm。双点源试验中,矿化度为8.33 g·L^(-1)和4.86 g·L^(-1)的滴头正下方及交汇部分含水率均达到0.4 g·g^(-1)左右;但8.33 g·L^(-1)矿化度下含盐量可达0.4%,不适合作物生长,而矿化度为4.86 g·L^(-1)的微咸水灌溉时,在交汇部分会形成一个含盐量0.1%左右的适合作物生长的低盐区域。在滴头流量为3.74 L·h^(-1)时,将单、双点源入渗试验的同一入渗深度处进行对比分析发现,随着矿化度增大,地表湿润比由87%增加到90.8%;8.33 g·L^(-1)矿化度下交汇时间比2.88 g·L^(-1)矿化度下提前16 min;矿化度为8.33 g·L^(-1)时在0～15 cm土层,交汇区含盐量相对于相同湿润位置处单点源的含盐量增加了37%,而矿化度不大于4.86 g·L^(-1)时,含盐量增加比率几乎为负值,可知矿化度为4.86 g·L^(-1)的土壤积盐不显著且含水率高。在灌溉水资源匮乏的云南燥红土地区推广应用微咸水滴灌时,可参考滴头流量3.74 L·h^(-1),微咸水矿化度≤4.86 g·L^(-1)用于作物栽培实践。

In order to better understand the water and salt transport of brackish water drip irrigation in dry red soil region,single and double point source infiltration experiments with different irrigation salinity(2.88 g·L^-1,4.86 g·L^-1 and 8.33 g·L^-1)and single point source infiltration experiments with different dripper discharge(2.68 L·h^-1,3.74 L·h^-1,4.68 L·h^-1)were carried out on red soil with a bulk density of 1.2 g·cm^-3.The effects of dripper discharge and salinity on water and salt transport in red loam soil were analyzed.The results showed that under the fixed salinity(2.88 g·L^-1),the movement rate of wetting front was fast and stable after 150 seconds,and the average advancing rate was 1.65 cm·s^-1 under 3.74 L·h^-1 dripper discharge.The final wetting depth was 22 cm,which meets the irrigation requirements.Its comprehensive performance was better than 4.68 L·h^-1 dripper discharge and effectively saved irrigation water.Under certain conditions(3.74 L·h^-1),the propulsive depth of wetting front increased with increasing salinity,and its velocity was 2.88 g·L^-1<4.86 g·L^-1<8.33 g·L^-1,and the propulsive depth was 21.5 cm,22.4 cm and 22.78 cm,respectively.In the double point source experiment,the water content of the dripper with salinity of 8.33 g·L^-1 and 4.86 g·L^-1 was about 0.4 g·g^-1,while the salt content of the dripper with salinity of 8.33 g·L^-1 was about 0.4% ,which was not suitable for the cropgrowth.When the water salinity of 4.86 g·L^-1 was irrigated,a low salinity area with salinity of about 0.1% was formed in the intersection part.When the dripper flow rate was 3.74 L·h^-1,comparing the same infiltration depth of single and double point source infiltration tests,it is found that increasing salinity made the surface wetting ratio increase from 87% to 90.8% .The intersection time at 8.33 g·L-1 salinity was 16 minutes earlier than that at 2.88 g·L^-1 salinity.The salinity at 0~15 cm soil layer at 8.33 g·L^-1 of drip water salinity at the same wetting position increased by 37% over that at the single point source.When the salinity was not more than 4.86 g·L^-1,the salt content increase ratio was almost negative.While the irrigation salinity was at 4.86 g·L^-1,salt accumulation was not significant and the water content was high.When using drip irrigation with brackish water in dry red soil area of Yunnan Province where irrigation water resources are scarce,the drip flow rate of 3.74 L·h^-1 with≤4.86 g·L^-1 salinity of brackish water can be used for crop cultivation practice.