A Laboratory Simulation For The Effects Of Earthworm Cast On Soil Evaporation And Infiltration

Moisture is an important factor which restricts crop production and vegetation restoration in arid and semi-arid region in the northwestern of China.Improving water use efficiency is of great significance to the efficient development of agriculture and the reconstruction of ecological environment.As one of the most typical large soil animals,earthworm has great potential for direct effect on soil function.The earthworm cast has good physical,chemical and biological characteristics,so it is widely used in crop seedling,soil fertility,pollution remediation and crop disease control.Earthworm cast contains a large amount of humus,which can improve the soil structure,while earthworm cast covering the ground could increase the surface roughness,thus affecting the soil water movement process.In this study,earthworm cast was used as the research object,and the indoor soil column simulation experiment was used to analyze the influence of earthworm cast on the process of water evaporation and infiltration on the surface and soil.Exploring the influence mechanism of earthworm cast on the process of soil water movement and clarify the effect of earthworm cast on the soil physical and chemical properties,to broaden the application range of earthworm cast..The main results and conclusions were as follows:1 For a given mulching coverage,In terms of the ratio of soil evaporation to atmospheric evaporation,the treatments exhibited an order of?4 cm<2.5 cm<1 cm<bare soil?in mulching thickness,both the cumulative and daily evaporation of soil decrease with the increasing of earthworm cast mulching thickness.For a given mulching thickness,soil cumulative evaporation decreases with increasing of earthworm cast coverage,90%coverage of earthworm cast treatment,the ratio of soil evaporation to atmospheric evaporation was significantly smaller than that of the other treatment.The daily evaporation of different mulching treatments increased first and then decreased with time,but the effect of mulching coverage on evaporation is not significant due to compaction of the surface soil.Earthworm cast is quite high in organic matter content,and hence higher in soil water retention capacity.That is to say,cast mulching is able not only to increase soil organic matter content,but also to retain soil water.Besides,the mulch can also reduce influences of the external factors,such as climate,thus making soil evaporation and its variation lower.2 The movement rate of water in earthworm cast was higher than that in the control soil.The coverage of earthworm cast on the surface was beneficial to rainfall infiltration.However,in the case of heavy rainfall,the precipitation can quickly pass through the earthworm cast to the subsoil,effectively increase the soil surface moisture content after rain,and thus has a weak retarding effect on rainfall.After the rainfall infiltration,the soil moisture content in different layer of the treated earthworm cast is lower than that of the bare soil in a short time,but the water content of the 5¹5 cm soil layer is increasing and gradually higher than the bare soil.It indicates that earthworm cast cover can delay rainfall infiltration and affect the process of soil water redistribution,which can promote the increase of water below the surface layer after rainfall and conducive to improving the utilization rate of precipitation.3 Results show that the application of 50 g kg^-11 earthworm cast in the 0¹0 cm soil layer promotes downward movement of the wetting front while the application of 100 g kg^-1earthworm cast in the 10²0 cm soil layer significantly inhibits movement of the wetting front depth.The cumulative infiltration of 10²0 cm mixed earthworm cast treatment is less than 0¹0 cm.The application of 75 g kg^-11 and 100 g kg^-11 can significantly reduce the cumulative infiltration when applied at 5⁸ cm and 10¹3 cm depth,but 100 g kg^-1when aearthworm cast was applied by layer is not significant effect on the infiltration process.The Kostiakov infiltration model was adopted to fit temporal variation of the measured cumulative infiltration.In the experiment,water content in the soil-cast mixed layer and the soil layer right underneath increased correspondingly,but with cast application rate being beyond 75 g kg^-1,water content in the deep soil layer?16²0 cm?might decrease.4 The addition of earthworm cast has effect on soil evaporation,the phreatic water recharge and soil water holding capacity obviously.But the effects were different depending on the application amounts of earthworm cast and the size of particle.10%application of small particle size earthworm cast could reduce soil water evaporation.The cumulative evaporations was higher in the treatments than in the control and risen with increasing additions of big particle size earthworm cast?bare soil<10%<15%<20%?.The deep water recharge increased with the increasing amount of earthworm cast addition and declined with the particle size of earthworm cast.The soil water holding capacity of earthworm cast with different particle sizes was as follows:bare soil<10%<15%<20%,while earthworm cast with small particle size had greater impact than that with big particle size.