Study On Soil Substrate Micro-environment Coupling Model Of Grape Greenwood Cutting Seedlings

The cuttage with greenwood is one important method that nursery stocksreproduce of grape. In the process of rooting, the greenwood cuttings make a greaterimpact on water diffusion and heat transfer in the seedbed, and the cuttings rootorganizations are in the developmental stages, without the root absorption function.These features make the movement of the environmental factors changed in theseedbed. However, a large number of experimental results show that a reasonablecontrol of rooting temperature and humidity is the key to ensure a successful cuttingbreeding. Therefore, in order to provide a good rooting environment for the cuttings,we should study the migration and coupling rules of the heat and moisture in theseedbed, there is a great practical significance for us to seek for these rules.The soil matrix is one typical porous medium, there is a remarkable characteristicin thermal physics of the soil matrix, considering the phase transformation of flow,heat transfer and mass transfer calculations and by the pure thermal conductivitymodel falls far short of the forecast results. It is necessary to consider the mutualinfluence between the heat and moisture. So far, the researches on heat and masstransfer in soil medium can be divided into two directions, one is about heat andmass transfer in soil bed without plant, the other is about soil - plants - atmosphericcontinuum. These research results have played an important role in the area ofagricultural production. As greenwood cutting propagation using the branches withgreen leaves and without the function of root absorption, the mechanism of heat andmoisture migration in the greenwood cuttings seedbed is different from themechanism in bare soil medium and also different from the mechanism in the soil ofSPAC. Compared with the bare soil bed, the branches will make a great impact onwater vapor diffusion and heat transfer in the greenwood cutting seedbed;Compared with SPAC, root organ has not yet formed, the greenwood cuttings don,thave the function of root absorption, and can not absorb water in the soil like normalplant, therefore the moisture content distribution in the soil and the intensity of leafblade transpiration are dissimilar. As a result of these characteristics,in order toprovide a reasonable rooting environment for the cuttings, the impact whichgreenwood cuttings make on the environment factors in the seedbed must beconsidered.The equations of micro-porous media flow and heat transfer based on the method of volume average which was created by Whitaker and Slattery. Though, withoutusing this method, we can obtain some equations from the macroscopic forcebalance of fluid interior, we can understand the assumptions related to the modelwhich is based on the method of average volume more thoroughly and themathematical description is also more rigorous, especially for the internalmomentum and heat transfer problems of Porous Media.In order to explore the mechanism of heat and moisture migration in thegreenwood cutting-seedbed in depth, a mathematical model used to describe themechanism is built, based on the continuity-media dynamics and the local-volumeaveraging method, considering the impact that the greenwood cuttings produce tothe factors of heat and moisture.According to the characteristics of this research, we emphatically studied themechanism of heat and moisture migration in the grape greenwood cutting-seedbed,and we designed the corresponding calculation software using Visual Basic 6.0programming language for numerical simulation. The main conclusions of the studyare as follows:Leaf area index has effect on the thermal characteristics parameter of soil matrixstrongly, and the different thermal characteristics parameters enable the effect ofheat and moisture migration to change, the unsteady state characteristic displaysobviously.Because of the green branches, the temperature fluctuation scope in thegreenwood cutting seedbed is narrower than the one in the bare soil bed, (especiallyfor the part of 0-15cm depth), and the temperature change has the hysteresis qualityslightly, beside, the evaporation Rate of the greenwood cutting-seedbed is alsosmaller.If the humidity of the seedbed is enough to compensate the consumption of waterevaporation, the hydraulic conductivity of top soil is high, and the evaporation rateis relatively stable, the evaporation is mainly controlled by the atmosphericevaporative power. Because of water evaporating, the soil moist degree and theevaporation frontal area will drop unceasingly if there is no external water source.Once the soil moisture is outside the critical range value, the growth of roots organwill be seriously affected. This stage is an important period to accommodate themoisture content of the seedbed.The model which is built in this paper is used to describe the heat and moisturemigration mechanism of greenwood cutting-seedbed in the natural condition. It can also play a role in other conditions such as the rainfall or the irrigation. If theseedbed is influenced by a large number of external water, from the modelgoverning equations, we can judge that the seedbed matrix will turn to wet saturatedinstantly because of a rapid invasion of external water. So when we adjustment themoisture content of seedbed we should control the capacity of water supply, andavoid keeping the rooting substrate being in wet saturated condition for a long timeas a result of too much water staying in the seedbed.We studied the impact, which greenwood cuttings influence on the environmentalfactors in the seedbed instead of studying the one which environmental factorsinfluence on the greenwood cuttings in the past. It would provide a more scientificbasis for the environmental factors control in the process of cuttings rooting.