Analysis On Soil Evaporation Of Spatial And Temporal Variability Of Abandoned Cropland And Bare Land In Arid Area

This paper discussed the measurement accuracy influence factors of micro-lysimeters (MLS) , and its feasible soil changing period in field experiment way. Based on correlation between daily soil evaporation and soil moisture, this study founded the function of estimating spot soil evaporation, analyzed the spatio-temporal variability of sandy bared soil evaporation before and after one irrigation. Simulated six rainfall intensities from flurry to super heavy rain in filed, combined non-rain control and natural rain treatments, the research studied soil evaporation law of different rain styles and different rain intensities, discussed the relationship among soil evaporation, moisture and ground temperature, divided typical water supply layer of 0 to 120cm soil layers. Results were as follows:(1)In the experiment period, each MLS treatment had high measurement accuracy, and the highest one had come to 97.40%. Whether the inner cylinder is drilled or not do not affect obviously the measurement accuracy. The accuracy of the drilled outside cylinder is higher than the undrilled ones, and the drilled holes are better to be equally distributed, further more, the number is less than 36 with the diameter of 3mm. The sealed outside cylinder can lower the measurement accuracy. The thinner material of sealed inside cylinder is and the more ventilative function is, the higher accuracy will be achieved. Moreover, when the space between inside and outside cylinder is smaller, the measurement accuracy also becomes higher.(2)The study discussed whether it was reasonable to change soil in 8d, 11d, 13d under 21 original soil moisture, by combinning 6 styles original soil moisture and 3 soil changing period. The results showed that MLS could change soil in 8 days when the original soil moisture content was less than 20%. When it was more than that value, the soil changing period could extend to 11 days. The measurement accuracies were high up to 80% both under the former two soil changing period. Average accuracies of them were separately 90.53% and 92.26%.(3)soil evaporation before one week and after three weeks of the irrigation have distinct correlativity , but other stages do not . Whereas, the evaporation before irrigation differs much , and space relationship is weak , but after irrigation it reverses. Moreover, the spatial conjunction is controlled more by space self-correlation but spatial heterogeneity in this stage. Also the spatial distribution of soil evaporation changed over time and space. Because of vegetation and landform of the study area , the evaporation of west zone was larger than east one week after irrigation, while the other two stages have no marked differences in the west and east. In time sequence, the evaporation of north region was stronger than south zone before irrigation. But one week after irrigation, the southern part was stronger, and it changed over again three weeks after irrigation.(4)different treatments had the same soil evaporation process which could be divided into three stages, namely fall evaporation speed stage, fluctuating stage and stabilization stage. The whole time of them were separately 6, 7 and 7 days. But the soil evaporation also had some obvious differences. For one thing, soil evaporation increased in logarithm function way when rainfall intensities enhanced. The accumulative total soil evaporation of the super heavy rainfall treatment was 5.12 times more than it of flurry treatment. For another, the ratio of evaporation to rainfall declined with rainfall intensities enhanced. The ratio of flurry treatment was 0.89, but it decreased to 0.15 when the rainfall intensity became super heavy rainfall. The correlation between soil evaporation, moisture content and ground temperature indicated that different treatments had the same law of soil water and heat transmission. They were strong correlative to surface and deep soil layer, but weak to middle layer. Consequently, the soil layer of 0cm to 120cm could be divided into three typical water and heat coupling action section planes. The first section plane was straight evaporation layer(0 to 15cm). Its soil water was evapored a lot. The second section plane was water transportation layer (15 to 40cm), which soil moisture was in homeostasis. The third one was water supply layer (40 to 120cm), which soil moisture descended day by day.