The soil water retention curve (SWRC) is the basic parameter of soil hydraulics to study soil water movement and soil water balance, which is closely related to soil physical and chemical properties. But the parameters of model is difficult to estimate. In this study, black soil samples with different erosion intensity were collected in the black soil region of Northeast China, and soil moisture under 7 soil water suction, mechanical composition, organic matter and bulk density were measured. We used Rosetta model to estimate the parameters of Van Genuchten (VG) model and compared the estimated soil moisture with the measured soil moisture. And then the simulation accuracy of different soil physical and chemical indexes and the suitability of the method to the black soil in Northeast China were evaluated. The results showed that there had little effect for the residual water content (θr) and saturated water content (θs) between 4 or 6 soil properties index, but had large difference for the scale parameter (α) and shape parameter (n). When the 6 indexes were used, shape parameter n decreased with the increased of scale parameter α. The relationship between the shape parameters m and n of the VG model was further modified, which improved the accuracy of model fitting obviously. The results of the 6 indexes were better than the 4 indexes. But the estimated values were different from the measured values and the estimated values were larger than the measured, which means soil moisture estimation need to be corrected according to the estimated value of relatively large degree. The fitting precision of Rosetta model for lightly and moderately erosion black soil was higher, and the precision of severely erosion black soil was lower. The model was suitable for sand content less than 46%, the clay content more than 28% of black soil in Northeast China.
In order to promote the management of soil fertility and precision agriculture effectively, provide some guidance for the soil and water conservation. A sloping cropland (0.91 km2) located in Heshan farm in Heilongjiang Province was selected as the research area,101 samples were collected by vertical and horizontal 100 m interval, for the study of spatial distribution of soil organic matter of the 0-15 cm top layer soil and the relation with soil erosion by the GIS and geostatistics math methods. The results showed that the average content of soil organic matter in typical black soil area was 4.13%, higher than the average level of Heilongjiang Province, and the proportion of organic matter content concentrated in the 3%-5%. Spatial variability of organic matter significantly which was mainly affected by soil erosion. High erosion area corresponds to low organic matter, erosion area in the corresponding medium organic matter content areas and sedimentary areas correspond to areas with high organic matter content. When the slope planted with an average gradient of 2.2°, per 1 000 t/km2 soil erosion increased, accompanied with the content of organic matter will be reduced by 0.8%. The spatial variability of organic matter could be described by the spherical model, showed significantly spatial autocorrelation, further suggested that soil erosion causes the redistribution of soil organic matter. When the sampling interval is 200 m which based on the range, the interpolation of spatial distribution can accurately reflect spatial variability of organic matter content, to provide precision fertilizer sampling basis.
Emamectin benzoate is one of the most efficiently semi-synthetic antibiotic pesticides. However, little is known about the responses of composition, structure and biodiversity of soil animal community to the application of emamectin benzoate. In order to reveal the effects of emamectin benzoate on soil animal community, a field experiment was carried out in a typical black soil farmland area of Hulan district, Harbin city, Northeast China. Based on fixing-plot investigation in 2012, the plots were treated by different concentrations of emamectin benzoate, and then the soil samples were collected from different stratification (i.e. 0-5 cm, 5-10 cm, 10-15 cm and 15-20 cm) in May, July and September. In total, 5772 individuals belonging to 4 classes, 11 orders were captured, and all of them were divided into 31 groups. The results showed that under emamectin benzoate treatment (1) individual densities and group numbers of soil animal decreased significantly, and the decreasing trends of individual densities and group numbers were more obviously with increasing concentrations of emamectin benzoate; (2) the vertical distribution structures of soil animal communities were changed obviously, and most individuals and groups of soil animals preferred to gather in the 5-15 cm soil layer rather than in the 0-5 cm soil layer; (3) the diversities of soil animal communities were changed, but the contributions of different groups to community diversity were different, in which contributions of soil mites and springtails were relatively large than those of other groups; (4) the soil chemical properties of topsoil were changed significantly. However, responses of soil animal groups to soil environmental change were groups-specific, in which soil mites and springtails exhibited a stronger adaptive ability than those of the others. In a word, emamectin benzoate treatment can significantly change the community structure, vertical pattern and diversity of soil animal community in a typical black soil farmland area. It is emphasized that the concentration of emamectin benzoate might be an important indicator when we assess the influence of emamectin benzoate on soil animal community. It is suggested that we should prudently assess the ecological consequences when using the emamectin benzoate in farmland ecosystems.
Soil moisture is an important impact factor of agricultural production and regional ecosystem. The No. 2 small watershed in Heshan farm of Heilongjiang Province was selected as the study area, the characteristics of the dynamic of soil moisture and soil water profile in different land use types were analyzed in this article. The results showed that: the soil moisture of embankment was the maximal, and the woodland’s was the least. The variation trends of soil moisture content of different land use types were as same as the variation trend of precipitation in the observation period, and they showed a reduced trend, but there were some differences between the soil moisture variation curves of different land use types, the soil moisture cures could be divided into three types: two peaks and three troughs type (wheat field, soybean field, woodland and field road), two peaks and two troughs type (embankment), two peaks and one trough type (grassland). The soil moisture variation in the observation period was divided into relatively stable period, consumption period, and supply period. The influence of land use type on the water content of soil profile increased with soil depth, and the soil moisture of different land use types showed different variation trends with soil depth. Among them, because of the presence of plow pan, the soil moisture of wheat field and soybean field increased first and then decreased; the soil moisture of woodland decreased gradually with the soil depth; the soil moisture of grassland and field road for the difference soil property reason presented the trend of increased first and then decreased, but the max soil moistures of these two land types appeared in different depth; because of the soil property did not change with soil depth, the soil moisture of embankment increased gradually with the soil depth. In addition, there is also a seasonal diversity in the water content change of soil profile in every land use type. The water content variation of soil profile in wheat field appeared an obvious seasonal diversity, but with the increase of soil depth the diversity decreased; the seasonal change of soil moisture in soybean mainly in the depth of 0-70 cm, and the seasonal change was not obvious under the depth of 70 cm; the seasonal diversity of soil moisture change in each section of soil profile in woodland is the largest; the top layer and the layer in the depth of 70-80 cm which was composed by peat were the layers that seasonal diversity of soil moisture in grassland mainly happened, and the diversities of other layers were small; because of there were not any plants on the field road, and the soil moisture variation subjected only to the influences of rainfall and evaporation, the seasonal diversity of soil moisture in field road mainly appeared in the top layer of soil, but the diversity in deeper layer were not obvious; the seasonal diversity of soil moisture in embankment was as same as field road, but the reasons that leaded this phenomenon were that the soil property were all the same from top to bottom, and the soil moisture of top layer was effected by the plants, precipitation and evaporation. Besides the land use types, slope position and direction, soil texture, topography are all the important influence factors for the dynamic changes of soil moisture, further studies are needed to determine the interaction of these factors above and the main control factors.
Soil on slopes of the gentle hilly black soil region in Northeast China, one of the most important bases of cash rice, degraded seriously after dozens of years of intensive cultivation. The thickness of soil humus layer becomes thinner and less fertile year after year. So it is very essential to deepen the researches of soil restoration and improvement after severe soil erosion. Analysis of main reasons for black soil degradation revealed that the cultivation activities halted the accumulation of organic matter and then baffled the soil development which cannot compensate the decrease of the thickness of soil humus layer caused by soil erosion. Soil developing process and conditions are the most important foundation for soil restoration. So the developing history of black soil and chernozem was reconstructed and the geomorphological and climatic factors, which were the key factors affecting the formation of black soil, were analyzed through studying both the formation time of the underlying strata and the local climate change history since the late Pleistocene. The conclusion is that black soil and chernozem formed in different periods, from early period of late Pleistocene and the beginning of Holocene respectively. The former period was warm and wet, while the latter period was warm and dry. And they formed in different places, the black soil was mainly distributed on the second and the third terraces and the chernozem on the first terrace of the Nenjiang River, which is lower than the distributing places of black soil and can accept more carbonate from the highland to form the characteristic illuvial layer. The processes of the soil formation were very slow, so it is hard to restore. These results provide important basis for forulating policies to improve the quality of soils in the region.