Hydrothermal Process Of Cold Paddy Field And Water-saving And Heating Irrigation Mode In Sanjiang Plain

Sanjiang Plain is one of China's nine major commodity grain bases, playing animportant role in the country's food security.10billion kg grain are currently plannedto add in Heilongjiang Province, therefore, paddy acreage of Sanjiang Plain willcontinue to expand. And under the premise of the increase of cultivated area,increasing yields is also an important way to ensure food security. Exploitation ofunderground water resources in Sanjiang Plain has reached its limit, then how to solvethe contradiction between water supply and demand is an urgent problem to be solvedfor the sustainable agricultural development of Sanjiang Plain. From the perspectiveof regional sustainable development, wetland protection point of view, and irrigationcosts to consider, developing water-saving and yield-increasing irrigation mode willbe the forward way. Water exchange, evapotranspiration and heat balance of coldpaddy field at Sanjiang Plain are systematically studied, and then the irrigation modeof shallow water warming irrigation in the early stage combined with intermittentirrigation in the middle and late stage (control irrigation I and control irrigation II) isinnovatively proposed and studied, because soil warming of paddy field is slow andwater temperature of well irrigated paddy field is low, resulting in low fieldtemperature and soil temperature, affecting the growth of rice. The followingconclusions are obtained.(1) Water and heat exchange of cold paddy filed at Sanjiang PlainEvaporation and seepage, most of which have no value for rice growth, accountfor the vast majority of water consumption of cold paddy field in Sanjiang Plain.Evaporation and seepage accounted for62%of the total water consumption in2010.The maximum paddy field evapotranspiration appeared in the period of strongevaporation or the period of strong transpiration. The maximum paddy fieldevapotranspiration, appearing in the period of strong evaporation, was7.0mm/d in2010, while the maximum paddy field evapotranspiration, appearing in the period ofstrong transpiration, was7.2mm/d in2011. The average paddy filed evapotranspiration was5.7mm/d,5.5mm/d in2010,2011. The evapotranspiration oftraditional flooding irrigation paddy field is mainly affected by meteorological factors.The correlation coefficient r of evapotranspiration with net radiation, air temperatureand vapor pressure was0.59,0.64and0.62. Evapotranspiration was significantlyrelated to net radiation, air temperature and vapor pressure at the0.05confidencelevel. It was showed that most of solar net radiation was assigned to the latent heatcaused by evapotranspiration exchange through the study of the heat balance of coldtraditional flooding paddy field in Sanjiang Plain.(2) Evaluation of actual evapotranspiration estimation methodEstimation evapotranspiration by Bowen ratio energy balance method was9.1%lower than measured evapotranspiration, but estimation evapotranspiration by Bowenratio energy balance method was overall well correlated with measuredevapotranspiration. Estimated evapotranspiration of the middle stage and the endstage by Penman-Monteith model combined with the corrected crop coefficient Kc(PM-Kc method) were all10%less lower than measured evapotranspiration of thesame stages, while estimated evapotranspiration of the early stage by PM-Kc methodwas19.3%higher than measured evapotranspiration of the same stage. With theincreasing interval, there were decreasing trends of RMSE and MAE and increasingtrends of d. The7-day mean data estimated by PM-Kc method perfomed best.(3) Water-saving potential of the irrigation mode of shallow water warmingirrigation in the early stage combined with intermittent irrigation in the middle andlate stageThe results of this research showed that the irrigation mode of shallow waterwarming irrigation in the early stage combined with intermittent irrigation in themiddle and late stage could drastically reduce water consumption of rice bysignificant reducing evaporation and soil percolation, as the water layer of intermittentirrigation was shallow, and the field exposure was emphasized; hence, soil watercontent was reduced, and then evaporation and soil percolation was significantlyreduced. The total evapotranspiration of cold paddy field under control irrigation I andcontrol irrigation II was lower than that of flooding irrigation by9.6%~10.3%and 15.2%~15.8%, respectively, while the total water consumption of cold paddy fieldunder control irrigation I and control irrigation II decreased by14.0%~18.7%and20.5%~23.4%, respectively. And the drainage water of cold paddy field under controlirrigation I and control irrigation II was reduced by14.4%~30.4%and19.5%~43.5%,respectively.(4) Warming and yield-increasing potential of the irrigation mode of shallowwater warming irrigation in the early stage combined with intermittent irrigation inthe middle and late stageShallow water layer or non-water layer was beneficial for the increase of0~15cm soil temperature. The average soil temperature of paddy field under shallowwater warming irrigation in the early stage was0.5℃~1.2℃higher than paddy fieldunder flooding irrigation at the sunny day of early rice growth stage, which wasbeneficial for the growth of cold rice. The irrigation mode could promote the materialproduction of effective tillering of rice, bringing about high percentage ofearring-tillers, thus forming the reasonable high-yield group, while it could controlineffective tillering to make photosynthetic product of rice for the growth of panicles,bringing about increase of filled grains per panicle, thus producing a more reasonableyield structure, with increase of aboveground biomass and seed yield. The actual yieldof rice under control irrigation I and control irrigation II was8.6%~9.4%and11.9%~12.7%higher than that under continuous flooding irrigation.