Rice Water Requirement Base On BP ANN And Studies On Irrigation Program

The intensification of air contamination forms mass acid rain, in the form of acid snow inwinter. Particular attention has been pain to acid snow damage to soil environment, water andecological environment in the world and the research on water, heat and solute transport in themelting process of snowpack is the theoretical foundation of evaluating and predicting acidsnow influence. Snow pack directly influences soil temperature, freezing and thawing depths,freezing speed and upward migration courses of water, evaporation and infiltration courses inthawing processs etc. In this paper, the transport rule of several main anions and cations oftenappeared in snow cover during thawing process of snow, and the effects of different thicknessof snow pack on the freezing characteristics and moisture and heat condition of fluvo-aquicbrown soil in freezing and melting courses are studied by field and laboratory experiments.The results show that:(1) The maximum or average concentration of each ion profile increase with the increaseof the length of snow thawing and the decrease of the thickness of snow cover. In theprevious period of snow thawing, the ions mainly concentrate in the top layer; in the lateperiod of snow thawing, the ions mainly concentrate in the bottom layer; in the late period ofsnow thawing, the ions mainly concentrate in the bottom layer; in the middle period of snowthawing, there are some fluctuations in the profiles of ion, and the maximum concentration ofeach ion occurs between the top and bottom layer. The order of leaching of anion is: SO₄^2-＞PO₄^3-＞Cl^-＞NO₃^-; the order of leaching of cation is: K⁺＞NH₄⁺ when the snow is new, andNH₄⁺＞K⁺ when the snow is old. The order of leaching of anion and cation in 2005 is: K⁺＞NH⁺＞SO₄²ï¼žCl^-＞NO₃^-. The order of leaching of anion and cation in 2005 is: NH⁺＞K⁺＞SO₄²ï¼žPO₄^3-＞Cl^-＞NO₃^-.(2) When the average daily air temperature is less than 0℃, the soil surface temperatureincrease and fluctuate less with the air temperature with in increase of the thickness of snowcover. From the comparison with bare soil, it is obvious that the effect of snow cover continueuntil the snow cover disappear because of melting. When the snow cover is heaped up in the1st or 2nd 10-days of Dec., the effect of snow thickness on the freezing and thawing velocityand the maximum frozen depth of soil is obvious, and all of them decrease with the increaseof snow cover depth apparently.(3) The situation of water and heat migration controls the soil frost heave amount. Whenthe snow cover exist, these 2 factors is influenced by the heat preservation function of it,hence influence the frost heave of soil obviously. In the other hand, the dead weight of snowcover cause a pressure on the soil surface, this pressure increase the soil water potential. andunfrozen water content, hence influence the heat and water transfer processes of soil;meantime, the pressure resist the frost heave of soil moving toward up side, and the bigness ofthe pressure or this resistance increase with the thickness of snow cover.(4) when snow thickness is thicker than 30 cm and daily average close ground airtemperature is about -5℃, the change of meteorological condition does little impact on theheat state of soil under the snow pack; and the thicker the snow cover, the smaller the degreeof soil temperature is influenced by outside environment. In the course of freezing, the exist of snow pack retains ground temperature, decreases freezing speed of soil, and increases thevelocity of transport water. The migration amount of non-frozen water in bare soil is largerthan in the one with snow cove apparently. In thawing course, ice of frezen soil layer meltsfrom both of the ground surface and the underground interface of frozen and unfrozen soil.Because it is prevented by non-melted frozen soil layer below, water in surface layermassively evaporates, and the water in the underground thawed layer seeps into deep layer,therefore in the treatment of bare soil, water content profile appears that bigger in the middle,and smaller in the top and lower soil layer immediately after the whole frozen soil zonecompletely melted. But in the treatments with snow pack, the water content of surface soil isbigger due to the infiltration of melted snow water. For the solutes content and undergroundwater level is alike, the unfrozen water content in frozen soil is mainly influenced by soiltemperature, soil texture, initial and total water contents of soil, the higher the soiltemperature, the finer the soil texture, the bigger the initial or total water contents of soil, thehigher the unfrozen water content in frozen soil is.