The Study On Water Consumption Characteristics Of Poplar Sheltbelts System In The Cropland Of North China Plain

With the thermal dissipation probe(TDP) method and the Penman-monteith modle, the transpiration of 24-year-old poplar (Populus tomentosa Carr.)and the crop(Triticum aestivum L. & Zea mays L.) were measured and estimated in the poplar sheltbelts over a period from April to September in the Cropland of North China Plain.Meanwhile,the parameter of microclimate in the sheltbelts were observed by the automatic weather station system.The water consumption characteristics of the poplar-crop systems in the cropland of North China Plain were analyzed form three aspects:1,The rules of the variation of the poplar belt's transpiration and the mechanism of its influence:In the main growing months(from April to September), the transpiration(Tr) the poplar belt demonstrate that: after sunrise the Tr begins ascending at 6:30–8:30,and 40 minutes lagges to the solar radiation;Tr reaches peak at 13:00-15:30, then drops rapidly and becomes slowly at 19:30,and the Tr is faint before the next sunrise. Tr is demonstrated single-peak curve in fine and cloudy day,but in the overcast day, it is demonstrated several-peak in the main growing seasonsThe daily or seasonal variations of the transpiration (Tr)is characterized with that it rises gradually in April, and reaches a peak during May,June and July, falls down readily in August and September. In the growing seasons(4-9) ,the total Tr(ToTr) is 488.02mm, and the ratio of the monthly transpiration to the ToTr is 11.17%,18.71%,19.30%,19.29%,16.66%,14.88% In every month during the growing seasons of 2007,Tr showes significantly compound correlated with the solar radiation(Q), air temperature(Ta), air relative humidity(RH) and wind speed(V) (α=0.01),and Ra is the most important meteorology factor effecting on Tr though comparing the partial coefficient. In the growing months(4-9),the multivariate linear model between Tr and the meteorological factors is:Tr=0.240*Ta-0.035*RH+0.007*Q+0.0260*V-0.734 R2=0.822 And the relationship between Tr and the poplar's LAI is described by the power function: Tr=0.2568LAI1.8392 ,R2=0.8337. 2,The variation of the crop's transpiration(Tr) in the sheltbelts and in the open cropland:For the wheat, the variations of the Tr in the sheltbelts is consistent with the Tr in the open cropland in different growth period. The Tr is lower in the shooting phase,and reaches the highest in the grain-filling phase, decreases in the mature phase. Concretely, the daily mean Tr in the sheltbelts and in the open cropland is 2.45mm/d and 3.23mm/d respectively in the shooting phase, 2.68mm/d and 3.90mm/d in the graining-filling phase,2.61mm/d and 3.20mm/d in the mature phase.And the rate of the Tr to the main growth period in sheltbelts and in open cropland is 33.18% and 31.97% respectively in shooting phase, 51.46% and 48.30% in the graining-filling phase, 18.52% and16.57% in the mature phase. From the shooting to the mature phases, the Tr of the wheat in the sheltbelts and the open cropland are 212.14mm and 155.18mm respectively, the intercropping significantly reduces the Tr by 26.85%(α=0.01) compared with monoculture system.For the maize, the variations of the Tr in the sheltbelts is also consistent with the Tr in the open cropland in different growth period. The daily mean Tr is character with the model of parabola which is lower in the seeding phase,and increases in the shooting ,reaches the highest in the grain-filling phase, decreases in the mature phase. Concretely, the daily mean Tr in the sheltbelts and in the open cropland is 1.29mm/d and 1.46mm/d respectively in the seeding phase, 4.15mm/d and 4.78mm/d in the tasseling phase,2.89mm/d and 3.28mm/d in the mature phase.And the rate of the Tr to the main growth period in sheltbelts and in open cropland is 4.33% and 4.30% respectively in seeding phase, 25.33% and 25.55% in the tasseling phase, but lower than that in filling phases which is 30.81% and30.65%,and in the mature phase, it is 19.42%,19.31%. In the whole growth period, the Tr of the summer maize in the sheltbelts and the open cropland are 374.29mm and 327.78mm respectively, the intercropping reduces the Tr by 12.43%(α=0.01) compared with monoculture system.The horizontal variations of the crop's transpiration (Tr) in the sheltbelts is characterized with that it increases gradually with the augment of the distance to the southern belts, the Tr's maximum is in the middle of the sheltbelts where the distance neither to the southern nor to northern belts was 6H, the crop's Tr dramatic decreases for the effect of the northern belts.The minimum of the Tr is in the range from 0.5H to H which is the distance to the northern belts.3,The relation of water consumption proportion between belt and the crop: In the main growing months(4-9), the water consumption ratio of the winter wheat to the poplar belts is 4.8:1,for the summer maize,it's 8.9:1,it showes that the water consumption ratio of the crop is the main features of the poplar-crop system,and it is feasible to develop the broad-row poplar-crop system in the cropland of North China.