Rate and pattern of tillage erosion by rotary cultivator on the steep land of purple soil
[Background] The process mechanism and conservation technology of tillage erosion are the key research domains of science and technology for soil and water conservation at current stage in China. Most of researches on the tillage erosion have focused on the effect of towed or hanging mechanized tillage and manual or animal-powered non-mechanized tillage on soil translocation and soil loss. However, there is few researches about the processes and factors of soil redistribution by the direct-connected rotary cultivator tillage. [Methods] The magnetic tracer method was used to label soils of 84 experimental plots with different gradients ranging from 5.7% to 30.9%, and to quantitatively evaluate the rate and pattern of soil redistribution by rotary cultivator tillage on the steep land of purple soil in Sichuan Basin,southwestern China. Ilmenite powder was selected as magnetic tracer, because its contrasting color distinguished from the surrounding soil and high level of magnetic strength, and it could be closely adsorbed on soil surface and move simultaneously with the eroded soil. In order to determine effects of tillage speed and directions on tillage erosion rate, three tillage directions of i) parallel to the contour ii) downward along the slope and iii) upward along the slope, and two tillage speeds of high and low gear for each tillage direction were set up in the study. [Results] The results showed that at each tillage direction, any single tillage by rotary cultivator caused soil moving in both upslope and downslope simultaneously, and net translocation of soil was in the downslope direction due to gravity. While at different tillage speeds, the net translocation rates were significantly correlated with slope gradient incontour and upward tillage (P < 0.01), respectively, but not significantly correlated in downward one (P >0.05). Net soil translocation rate decreased in the order: contour at high gear (11.53 kg/ m),downward at high gear (11.40 kg/ m), upward at high gear (7.59 kg/ m), downward at low gear (7.33kg/ m), contour at low gear (6.87 kg/ m), and upward at low gear (6.29 kg/ m). Tillage erosion rates induced by upslope-downslope alternative were less than those by contour at high gear operation, however, they were equivalent at low gear operation. Tillage erosion rate (4.54 - 7.68 t/ hm2 under downslope parcel length of 15 m conditions) by rotary cultivator was much lower than by traditional farming implements (52.89 and 53.06 t/ hm2 for hoeing tillage and ox-drawn ploughing, respectively),i. e. , more than 85% erosion rate decreased. [Conclusions] Therefore the expanding application of rotary cultivator should play a critical role in reducing tillage erosion and preventing soil from degradation on the sleep land of purple soil.
Li Erhuan, Shen Jun, Ju Jing, Hu Haibo, Lu Xiaozhen
Distribution characteristics of salinity and nutrient at the estuary in coastal saline soil of north Jiangsu
[Background] Systematically understanding the distribution of saline soil nutrients and salts on both sides of the mouth of Huai River is important in establishing strategies for soil salinity management. [Methods] In this paper, the spatial distribution characteristics of soil nutrient indexes, i. e. , soil organic matter (SOC), available nitrogen (AN) and available phosphorus (AP), and salinity mass fraction for various depth layers (0 -10 cm, 10 -20 cm, 20 -50 cm, 50 -100 cm, 100 -150 cm, 150 -200 cm, 200 -250 cm, 50 -300 cm and 300 -350 cm) at the estuary of Huai River were analyzed by the application of Outdoor survey and sampling as well as indoor analysis, including cluster analysis and correlation analysis. [Results] 1) The research area was generally lacking in SOC and AN, the amounts of SOC and AN presented a slow increasing trend with the increasing distance from the estuary, while the amount of AP was appropriate in general. Soil nutrients showed an obvious surface aggregation phenomenon, compared with the floodplain, the variation depths of SOC and AN in the soil on the dike outer were low, while the difference of AP was not obvious. 2) The amounts of salinity in the research area presented a slow increasing trend with the increasing distance from the estuary. The critical desalinization positions of the north floodplain, south floodplain, north dike outer and south dike outer were respectively located at 3200 m, 2800 m, 3400 m and 600 m from the estuary. The salinity profile types were obviously classified into the types of surface accumulative, bottom accumulative and balanced,the distributions were concentrated and respectively located in the severe salinization zone, moderatesalinization zone, mild salinization zone and desalinization zone. 3) SOC and AN presented highly significant positive correlation, and the two had significant negative correlation with the soil salinity, while AP was not significantly correlated with the other three indexes. [Conclusions] The research results can serve as a theoretical and practical reference to the partition, amelioration, management and rational utilization of saline soils in the estuary of Huaihe River.
Driving factors and spatiotemporal dynamics of carbon storage of a Pinus massoniana plantation in reddish soil erosion region with ecological restoration
[Background] Measures such as closing hillsides for forest recovering and artificial afforestation can improve the ecological environment of soil erosion area, yet its accompanied benefits from carbon sink have not been given due attention for a long time. [Methods] Taking the ecological restoration area with a project of soil and water conservation in Changting County, Fujian Province as the study area, we quantitatively analysed the spatial and temporal patterns in carbon storage and the carbon sink enhancement dynamics of afforested Pinus massoniana forest since ecological restoration in 2000. Based on the Landsat satellite image sets from 2000 to 2013, forest subcompartment survey, on-sitemeasurement, and the statistical yearbook of history, we extracted three periods of distribution maps for carbon storage of the P. massoniana forest from 2000 to 2013 and the different terrain characteristics (including height and slope), and then discussed the effects of main factors on the carbon sink enhancement with the method of the principle component analysis. [Results] 1) The inversion model (y =1.243 2e8.399 7x ) of carbon storage of the P. massoniana forest, established by the vegetation index (MNDVI), has been proved to be effective by the practice test (R2 = 0.869 2, RE =4%) in this study. 2) The carbon storage of the P. massoniana forest grew up from 127.01 *104 t in 2000 to 189.63*104t in 2013, accompanied by an increase of carbon density from 27.95 t/ hm2 to 41.72 t/ hm2 during theperiod. The average annual growth rate of carbon storage was 3.52%, much higher than that in the non-ecologica-restoration areas with only an average annual growth rate of 1.76%. 3) The increasing of carbon storage of the P. massoniana forest mainly occurred in the area with an altitude of below 600 m and a slope of lower than 25 particularly in the last seven years from 2000 to 2013, with respective annual growth rate of 41.6% and 50.9%. 4) The results of the principle components analysis showed that the driving factors of carbon storage dynamics of the P. massoniana forest were the implementation of ecological restoration policy, the adjustment of economic structure and increased income of peasant households, especially that the ecological restoration by government policy and subsistence allowance played a pivotal role in the carbon sink enhancement of the P. massoniana forest in the study area. By contrast, the physical environment factors, such as temperature and precipitation, were insignificant. [Conclusions] There was a significant increase of the carbon sink of the P. massoniana forest in the soil and water conservation area after ecological restoration, and the carbon density of P. massoniana forest grew with the increasing of elevation and slope, showing that in the flat areas where always densely populated, there still has a great potential for forest carbon sequestration to be improved. This paper might provide some essential scientific basis for revealing the potential of carbon sequestration in reddish soil erosion region, quantifying the carbon storage that accumulated in the historical period of ecological management in China, as well as undertaking effective measures to enhance the accumulation of carbon storage in deteriorated lands.
Zhu Liping, Cai Yongmao, Kang Manchun, Zhao Guangliang, Chen Zuosinan, Zhang Zhiqiang
Characteristics of soil organic carbon for Pinus tabuliformis and Acer truncatum plantations in rocky mountainous area of northern China
[Background] The soil organic carbon storage and its temporal and spatial variation in forest ecosystem are not only of significance for global carbon cycle and carbon balance study, but also the crucial for developing sustainable forest management measures. To comprehensively understand the characteristics of soil organic carbon ( SOC) and accurately assess the soil carbon stock of the plantations, and therefore, provide evidence for plantation management in this region, This study was carried on the Pinus tabuliformis and Acer truncatum plantations of different stand density in rocky mountainous area of northern China. [Methods] We examined the SOC content, SOC density and SOC storage and their vertical distribution between 0 -100 cm soil depth of P. tabuliformis and A. truncatum two plantations with different stand densities in the rocky mountainous region of northern China and also discussed the correlations of SOC content and soil physicochemical properties, i. e. , soil density, pH,total nitrogen, and available potassium. [Results] The results showed that the average SOC content and SOC density of A. truncatum plantations were both higher than these of P. tabuliformis plantations, indicating that under the similar climate and soil condition, the soil of A. truncatum plantations had greater carbon sequestration than the P. tabuliformis plantations. Meanwhile, the quantity of humus and plant roots in soil layers decreased with the increase of soil depth, both the SOC content and SOC density in 0 -10 cm layer were the highest among the 0 -100 cm soil depth and decreased with the increase of soil depth. The SOC content of the A. truncatum plantations showed no difference between the high and low stand densities, while the SOC density of the A. truncatum plantations in high density was greater than lower ones. However, both of the SOC content and SOC density of the P. tabuliformis plantations in the middle density was much higher than that in the high and low density ones. Specifically, the SOC density was the highest, when the stand density was 1 700 and 2 350 stems per hm2 for the P. tabuliformis plantations and the A. truncatum plantations, respectively. The SOC content of the P. tabuliformis and A. truncatum plantations showed significant negative correlation with soil density, while highly positive correlation with the total nitrogen and available potassium. Nevertheless, only the SOC content of the P. tabuliformis plantations was affected by soil pH value. [Conclusions] In this study the SOC content had the most significant relation with the soil total nitrogen among all the measured soil physicochemical properties in both of the P. tabuliformis and A. truncatum plantations. In summary, the A. truncatum plantations had greater potential for carbon sequestration than the P. tabuliformis plantations in rocky mountainous area of northern China, both SOC content and SOC density were greatly influenced by tree species and stand density.
Liu Ying, He Kangning, Xu Te, Wang hui, Liu Yujuan
Impact of water stress on leaf water potential, photosynthetic parameters and water use efficiency of Potentilla fruticosa
[Background] The rapid development of urbanization have put forward higher requirements on the country road greening and landscape. But the high latitudes, low temperature and drought problemrestrain the growth and breeding of many kinds of flowers in the cold and arid Qinghai Province. So a number of scholars began to study the advantages of the local wild species, trying to pick out plant species domesticated from local flowers for landscaping and road greening. [Methods] In order to solve the problem of the cultivation and domestication of greening plants in the cold and arid Qaidam regions, Qinghai Province, explore the photosynthetic physiological characteristics of Potentilla fruticosa and its quantitative relations with soil moistures, provide a scientific basis to the scientific irrigation management of P. fruticosa, and improve the water use efficiency of alpine and arid regions in addition, 17 P. fruticosa seedlings (2 years old) were taken as the research object under a pot experiment to study its rules of response to drought stress and rewatering. Leaf water potential, photosynthetic parameters and photosynthetic diurnal variation process were investigated. Quantitative relations between net photosynthetic rate, transpiration rate, water use efficiency and soil water content were explored to determine the suitable soil moisture thresholds of photosynthesis and water use efficiency of P. fruticosa. [Results & Conclusions] The main results are as follows: 1) With the lowering of soil moisture to 5.97%, more than half of the leaves dried up, and the wilting moisture content of P. fruticosa was about4.02%. 2)The effects of soil moisture content on leaf water potential and photosynthetic parameters had threshold, too high and too low soil moisture content would inhibit the physiological activity of P. fruticosa. The morning leaf water potential, net photosynthetic rate, and transpiration rate of P. fruticosa had obvious threshold response to the changes of soil moisture. The morning leaf water potential would decrease if the soil moisture was lower than 19.48%, and when the soil moisture varied from 17.03% to14.37%, the morning leaf water potential would come down at the maximum speed and amplitude, indicating that this range of soil moisture content would significantly improve the water absorption and drought resistance of P. fruticosa. When the net photosynthetic rate reached its maximum the soil moisture content was 20.83%, the soil moisture content of highest water use efficiency was 13.82%, and the hydration compensation point was 4.38%. 3) Under the condition of sandy loam, the net photosynthetic rate could keep above 70% of its maximum unless the soil moisture went down to 12.71%. When the soil moisture content was about 8.33% the water use efficiency could keep 70% of its maximum, and the change speed of water use efficiency would slow down. So soil water content varing from 8.33% to 12.71% could not only satisfy the basic need for the growth of P. fruticosa, but also improve the efficiency of water use to the largest extent. 4) During the growing season of P. fruticosa in Qinghai Province (July) without any rain, the irrigation should be conducted once every two weeks for good growth. P. fruticosa is able to recover from 2 -3 weeks' drought after irrigation, but will die of the drought stress which lasts over one month.
Comparative study on particle size distribution of eroded sediment by laser method and pipette method in black soil region of Northeast China
[Background] Soil particle size distribution (PSD) is one of the important indicators of soil physical properties, is also a key parameter in erosion and sediment nutrient enrichment research. In recent years, as a relatively new method of measuring particle size distribution(PSD) compared to the classical method of the pipette method, the laser method has been widely applied to the PSD of soil and river sediment, and gradually applied to the PSD of eroded sediment. [Methods] In order to obtain thedifferences and transformation relations between the PSDs determined by the two methods in the Black Soil Region, 18 eroded sediment samples of a small watershed during the snow melting were measured and analyzed by the laser method and pipette method. In the present study, the S3500 manufactured by the US Microtrac company were used for measuring the samples of laser method. [Results] Results showed that the D50 (Median Diameter) and MWD (Mean Weight Diameter) using the laser method were obviously higher than those using the pipette method, which was consistent with the conclusion of the sediment size distribution curve. Although the D50 and MWD measured by two methods varied widely, significant relationships were found between the two methods for the D50 and MWD: yD50 =1.609xD50 -13.743(R² = 0.960, P < 0.001), yMWD = 0.962xMWD - 0.002 (R² = 0.999, P < 0.001). The PSD was analyzed according to the US soil texture classification system. The sand and clay contents using the laser method was under-estimated by 2.6% and 31.5% respectively compared to that using the pipette method, while the silt content of the laser method was over-estimated by 34.1% compared to that of the pipette method. However, significant linear transformation relationships were observed between the laser method and the pipette method for the clay content, silt content and sand content of the eroded sediment: ysand = 0.864xsand + 3.844 (R² = 0.965, P < 0.001), ysilt = 0.725xsilt - 11.858(R² = 0.897, P <0.001 8), yclay = 0.879xclay + 32.772(R² = 0.918, P < 0.001). According to the US soil texture classification, the sand content was further classified into the above medium, fine and very fine, while the silt content into the coarse and fine. The laser method obviously caused the over-estimation of the content of the fine silt by 34.1%, while there were not significant differences between the two methods for the other four contents. There were significant linear transformation relationships between the two methods for the above medium sand: y1 =0.948x1 +0.092 (R² =0.996, P <0.001), fine sand: y2 =0.943x2 - 0.234 (R² = 0.912, P < 0.001), coarse silt: y4 = 0.730x4 + 3.407 (R² = 0.924, P <0.001), and fine silt: y5 =0.517x5 -1.088(R² =0.896, P <0.001), except the very fine sand: y3 =0.699x3 +4.436 (R² =0.764, P <0.001). [Conclusions] The laser method cannot be used for directly measuring the PSD of eroded sediment, as obvious difference existed between two methods. However,significant linear transformation relationships for each grade were observed between two methods, thus the laser method can be effectively used to measure the PSD of eroded sediment, which can save our time when it comes to sedimentation, pipet samplers, drying and so on.
Zhao Ke, Ding Man, Hua Dangling, Gao Wei, Yang Qiuyun, Wang Daichang, Liu Shiliang
Effects of lignite-based amendments on lead chemical speciation in calcareous soil organo-mineral complexes
[Background] In order to remediate heavy metal-contaminated calcareous soil, a comparative research on the effect of lignite-based materials on heavy metals speciation of different organo-mineral complexes were conducted for screening out highly effective amendments andunderstanding the restoration mechanism of pollution degradation. [Methods] All these materials weremixed with lead-contaminated soiland incubated for 120 days at 25 and 65% relative humidity,thereafter organo-mineral complexes were extracted, and mass fraction of different Pb chemical speciationof soil complexes were assessed. [Results] The results indicated that water-stable complexes were increased with the application of lignite organic materials,the treatments with humic acid,lignite,nitrified lignite and sulphonated lignite transformed more of G1 and G2 complexes from G0, and other results were as follows:1) The distributions of 6 Pb chemical speciation (ion-exchangeable Pb, Fe-Mn-oxide-bound Pb, carbonate-bound Pb, organics-weakly-bound Pb, organics-strongly-bound Pb, and residual Pb)varied in the different complexes G0(water-dispersing complex), G1 (NaCl-dispersing complex),and G2 (NaCl-grinding-dispersing complex ). For all amendments, the order of the abundance for ion-exchangeable Pb, Fe-Mn-oxide-bound Pb, and carbonate-bound Pbwas G0 > G1 > G2; the ion-exchangeable Pb decreased 8.74% - 32.22% from G0 to G1, and 2.73% - 26.74% from G1 to G2; organics-weakly-bound Pb, organics-strongly-bound Pb, and residual Pb in G1 and G2 complexes were more than that in G0. 2) Applying organic materials decreased the content of ion-exchangeable Pb averagely 2.73% - 32.22% in 3 complexes, while increased the organics-weakly-bound Pb at a maximum of 51.23% and organics-strongly-bound Pb at a maximum of 67.65%, no significant effect on residual Pb. Organics-weakly-bound Pb in G0 was less significantly affected than that in G1 and G2 by these organic materials, and the content of organics-weakly-bound Pb in G1 complexes treated with lignite, humic acid, nitrified lignite and sulphonated lignite were higher than original soil in the range of 35.06% -51.23%, and in G2 higher in the range of 27.11% - 41.35%. All lignite-based materials increased the content of organics-strongly-bound Pb in the range of 5.44% - 38.29%, but had no significant effect on residual Pb of G0, G1 and G2. 3) Compared with raw lignite, the treatments with humic acid, active charcoal, alkalization and calcium-loaded lignite decreased markedly the content of ion-exchangeable Pb in G0 group, but all modified lignite increased ion-exchangeable Pb content in G2 group, as well as sulphonation and demineralization increased ion-exchangeable Pb in G1 remarkably. Except humic acid,many modified lignite-based materials resulted in lower content of organics-strongly-bound Pb in all three groups of complex. There were no significant differences on content of carbonate-bound Pb in all complexes between original and modified lignite. Alkalization and calcium-loaded lignite markedly decreased residual Pb in G0, and the same changes in G1 and G2. Simultaneously, alkalization and calcium-loaded lignite increased significantly Fe-Mn-oxide-bound Pb in G1. [Conclusions] In conclusion, applying lignite-based amendments is effective in increasing water-stable complexes and prompting more organically-bound Pb speciation in contaminated soil, decreasing the fraction of ion-exchangeable Pb, thus it helps establish stable soil structure, enhance the capacity of resisting soil erosion, and decrease the environmental exposure risk by surface runoff and deep percolation. Organic lignite-based amendments improve remarkably content of organically-bound Pb, nevertheless, organic matter has little effect on Fe-Mn-oxide-bound, residual and carbonate-bound Pb. Taking immobilization and economy efficiency into account, raw lignite, humic acid, active charaoal, nitrified lignite and sulphonated lignite are recommended for remediating Pb-contaminated soil.
Issues and countermeasures in the comprehensive management of small watershed in China
[Background] Small watershed management aiming at the prevention of soil erosion has a long history in China. After 30 years of exploration and practices on the comprehensive management of soil erosion using small watershed as a unit, a set of management system including management notion and governance measures suitable for specialized situation in China has been gradually earned, and great achievements with significantly ecological, social and economic benefits have been acquired. [Methods] Since 1980s, China has taken comprehensive measures on millions of watersheds covering 380,000 km2. However, with the socioeconomic development and increasing needs of people on environmental quality, some issues emerged in the comprehensive management of small watershed, including management notions and objectives cannot meet the demand of the public, the mechanism of management is not complete, and the fund input should be improved urgently, et al. [Results] In the new era, small watershed management cannot only be limited to the original ideological framework, based on the inheritance of management experience, it is revitalized by adding new connotation according to the national economic and social development, and then it better serves for people with the increasing needs of living, production and environment. [Conclusions] In the current management of small watershed, we should focus on the needs of local people, design proper prevention system based on local condition, and gradually adjust governance contents, measures and objectives; moreover, we should improve the funding input and management systems, and build the related laws and regulations to adapt to the continuing development of our society.
Impact of spatial data on the accuracy of watershed hydrological simulation of SWAT model
The simulation accuracy of watershed hydrological model depends largely on the description of the watershed characteristics of the input data. High resolution input data can accurately describe the watershed characteristics, and at the same time increase the difficulty of data collection and processing. So it is meaningful to study the response of the model simulation results to spatial data resolution, which would help to improve model running efficiency without reducing model simulation accuracy. Based on the previous studies, taking the SWAT for example, we review the impact of data quality on the accuracy of watershed hydrological simulation, mainly including the resolution of DEM (digital elevation model),the delineation of watershed, the quality of land use/ land cover (LU/ LC) and soil maps, the number and distribution of weather and precipitation gauge stations. The main conclusions are as follows: 1) Threshold of resolution of spatial data exists in the simulation of different subjects (runoff, sediment, nutrient, etc. ), and too high or too low resolution of spatial data could result in the decrease of simulation accuracy. 2) The impact of DEM resolutions on the relative error of flow simulation results is far less than the relative error of sediment simulation, and the simulation results of inorganic nitrogen and organic phosphorus are consistent with the results of flow and sediment, respectively. 3) Further improvement of DEM resolution does not always result in the improvement of simulation accuracy after the resolution reaching certain accuracy, while the decrease of slope degree caused by the decrease of DEM resolution would decrease the flow production and delay the summit of peak flow. 4) The number of subwatersheds has little impact on the simulation of flow, but significantly influences the simulation of sediment. The number of subwatersheds and HRUs has significant impact on the upstream sediment yield, while it has little impact on the sediment load at the outlet of the watershed. 5) Effects of resolution of spatial landuse data and soil data on the simulation results of the model mainly result from their impact on the generation of HRUs. 6) The spatially distributed precipitation data could increase the accuracy of surface runoff simulation, because the distributed precipitation data could embody the locally intensified rainfall events that could significantly influence the surface runoff. The results could provide references for the development, application and improvement of watershed hydrological model and increase the accuracy of hydrological model simulation.
Zhang Jiaqiong, Yang Mingyi, Liu Zhang, Zhang Fengbao
A review of tillage erosion research
Very few studies have so far focused on tillage translocation and erosion although they have presented since humans cultivation activity started. Tillage translocation and erosion were discovered in the middle of the 20th century but have attracted limited attention among researchers. Scientists rediscovered these processes by the end of the 20st century when visible changes occurred in slope farmlands and systematic research on these processes started since then. Tillage translocation and erosion are triggered by tillage and are mostly influenced by gravity force. They are the main processes that cause the redistribution of soil in farmlands on hill slopes, and are among the main processes for soil erosion on slopes. They also greatly influence the evolution of slope landform, soil properties and nutrients, land productivity, and carbon pool. Based on the results of previous research, the present study summarized the processes and mechanisms, influencing factors, research methods and techniques, and erosion rates of tillage erosion, and then discussed the weakness of the previous work as well as possible research aspects in the future. Unlike wind and water erosions, tillage erosion is caused by human activity on hill slopes, but not by wind or rainfall. Therefore, tillage erosion is different from wind and water erosions on most aspects. Tillage erosion is influenced by both anthropogenic and natural factors. The anthropogenic factors refer to the tillage management of farmlands, which acts as the dynamical conditions of tillage erosion. Such factors mainly include the characteristics of tillage tool, plough direction, speed, and depth. The natural factors mainly include the shape and size of the tilled area, the terrain and gradient of slope and soil properties, in which slope is the terrain base of tillage erosion. Strong erosion by tillage usually occurs at areas near the top of a slope and areas where slope curvature greatly changes. The study methods for tillage erosion differ from those of water and wind erosions owing to the great difference in their characteristics. Tillage erosion is mainly studied using tracer methods and model simulations. Limited number of reports can be found on the erosion rates of water and tillage erosions, and few reports on wind and tillage erosions so far. Further study on erosions by water, wind and tillage at crisscross regions is important to determine the erosion processes and mechanisms at these multiple-force erosion regions. The main obstacle is the lack of general study methods for these processes. Nevertheless, radionuclide tracing techniques (e. g. 137Cs) could be well applied to tillage, water, and wind erosions, providing a possibility to separate the rate and contribution of each erosion processes from the total erosion in crisscross erosions by erosion forces.
