Soil salinity prediction in the Lower Cheliff plain(Algeria) based on remote sensing and topographic feature analysis

Soil salinity and ground surface morphology in the Lower Cheliff plain(Algeria) can directly or indirectly impact the stability of environments. Soil salinization in this area is a major pedological problem related to several natural factors, and the topography appears to be important in understanding the spatial distribution of soil salinity. In this study, we analyzed the relationship between topographic parameters and soil salinity, giving their role in understanding and estimating the spatial distribution of soil salinity in the Lower Cheliff plain. Two satellite images of Landsat 7 in winter and summer 2013 with reflectance values and the digital elevation model(DEM) were used. We derived the elevation and slope gradient values from the DEM corresponding to the sampling points in the field. We also calculated the vegetation and soil indices(i.e. NDVI(normalized difference vegetation index), RVI(ratio vegetation index), BI(brightness index) and CI(color index)) and soil salinity indices, and analyzed the correlations of soil salinity with topography parameters and the vegetation and soil indices. The results showed that soil salinity had no correlation with slope gradient, while it was significantly correlated with elevation when the EC(electrical conductivity) values were less than 8 d S/m. Also, a good relationship between the spectral bands and measured soil EC was found, leading us to define a new salinity index, i.e. soil adjusted salinity index(SASI). SASI showed a significant correlation with elevation and measured soil EC values. Finally, we developed a multiple linear regression for soil salinity prediction based on elevation and SASI. With the prediction power of 45%, this model is the first one developed for the study area for soil salinity prediction by the combination of remote sensing and topographic feature analysis.     

Responses of soil nitrogen,phosphorous and organic matter to vegetation succession on the Loess Plateau of China

Revegetation is a traditional practice widely used for soil protection. We evaluated the effect of natural revegetation succession on soil chemical properties and carbon fractions(particulate organic carbon(POC), humus carbon(HS-C), humic acid carbon(HA-C) and fulvic acid carbon(FA-C)) on the Loess Plateau of China. The vegetation types, in order from the shortest to the longest enclosure duration, were:(a) abandoned overgrazed grassland(Ab G3; 3 years);(b) Hierochloe odorata Beauv.(Hi O7; 7 years);(c) Thymus mongolicus Ronnm(Th M15; 15 years);(d) Artemisia sacrorum Ledeb(At S25; 25 years);(e) Stipa bungeana Trin Ledeb(St B36; 36 years) and(f) Stipa grandis P. Smirn(St G56; 56 years). The results showed that the concentrations of soil organic carbon, total nitrogen and available phosphorus increased with the increase of restoration time except for Th M15. The concentration of NH4-N increased in the medium stage(for Th M15 and At S25) and decreased in the later stage(for St B36 and St G56) of vegetation restoration. However, NO3-N concentration significantly increased in the later stage(for St B36 and St G56). Carbon fractions had a similar increasing trend during natural vegetation restoration. The concentrations of POC, HS-C, FA-C and HA-C accounted for 24.5%–49.1%, 10.6%–15.2%, 5.8%–9.1% and 4.6%–6.1% of total carbon, respectively. For Ab G3, the relative changes of POC, HS-C and FA-C were significantly higher than that of total carbon during the process of revegetation restoration. The higher relative increases in POC, HS-C and FA-C confirmed that soil carbon induced by vegetation restoration was sequestrated by higher physical and chemical protection. The increases of soil C fractions could also result in higher ecological function in semiarid grassland ecosystems.     

Effects of long-term fertilization on oxidizable organic carbon fractions on the Loess Plateau,China

The effects of long-term fertilization on pools of soil organic carbon(SOC)have been well studied,but limited information is available on the oxidizable organic carbon(OOC)fractions,especially for the Loess Plateau in China.We evaluated the effects of a 15-year fertilization on the OOC fractions(F1,F2,F3 and F4)in the 0–20 and 20–40 cm soil layers in flat farmland under nine treatments(N(nitrogen,urea),P(phosphorus,monocalcium phosphate),M(organic fertilizer,composted sheep manure),N+P(NP),M+N(MN),M+P(MP),M+N+P(MNP),CK(control,no fertilizer)and bare land(BL,no crops or fertilizer)).SOC content increased more markedly in the treatment containing manure than in those with inorganic fertilizers alone.F1,F2,F4 and F3 accounted for 47%,27%,18% and 8% of total organic carbon,respectively.F1 was a more sensitive index than the other C fractions in the sensitivity index(SI)analysis.F1 and F2 were highly correlated with total nitrogen(TN)and available nitrogen(AN),F3 was negatively correlated with p H and F4 was correlated with TN.A cluster analysis showed that the treatments containing manure formed one group,and the other treatments formed another group,which indicated the different effects of fertilization on soil properties.Long-term fertilization with inorganic fertilizer increased the F4 fraction while manure fertilizer not only increased labile fractions(F1)in a short time,but also increased passive fraction(F4)over a longer term.The mixed fertilizer mainly affected F3 fraction.The study demonstrated that manure fertilizer was recommended to use in the farmland on the Loess Plateau for the long-term sustainability of agriculture.     

Response of soil water dynamics to precipitation years under different vegetation types on the northern Loess Plateau,China

Implementation of the Grain-for-Green project has led to rapid land cover changes and resulted in a significantly increased vegetation cover on the Loess Plateau of China during the past few decades. The main objective of this study was to examine the responses of soil water dynamics under four typical vegetation types against precipitation years. Soil water contents(SWCs) were measured in 0–4.0 m profiles on a hillslope under the four vegetation types of shrub, pasture, natural fallow and crop in a re-vegetated catchment area from April to October in normal(2010), dry(2011), wet(2014) and extremely wet(2013) years. The results indicated that precipitation and vegetation types jointly controlled the soil water temporal dynamics and profile characteristics in the study region. SWCs in 0–4.0 m profiles of the four vegetation types were ranked from high to low as cropfallowpastureshrub and this pattern displayed a temporal stability over the four years. In the extremely wet year, SWC changes occurred in the 0–2.0 m layer under shrub and pasture while the changes further extended to the depth of 4.0-m deep layers under fallow and crop. In the other three years, SWCs changes mainly occurred in the 0–1.0 m layer and kept relatively stable in the layers deeper than 1.0 m for all the four vegetation types. The interannual variation in soil depth of SWCs was about 0–2.0 m for shrub and pasture, about 0–3.4 m for fallow and about 0–4.0 m for crop, respectively. The dried soil layers formed at the depths of 1.0, 0.6, 1.6 and 0.7 m under shrub, and 1.0, 1.0, 2.0 and 0.9 m under pasture, respectively in 2010, 2011, 2013 and 2014. The infiltrated rainwater mostly stayed in the 0–1.0 m layer and hardly supplied to soil depth 1.0 m in normal, dry and wet years. Even in the extremely wet year of 2013, rainwater recharge depth did not exceed 2.0 m under shrub and pasture. This implied that soil desiccation was difficult to remove in normal, dry and wet years, and soil desiccation could be removed in 1.0–2.0 m soil layers even in the extremely wet year under shrub and pasture. The results indicated that the natural fallow was the best vegetation type for achieving sustainable utilization of soil water and preventing soil desiccation.     

不同原料好氧堆肥过程中碳转化特征及腐殖质组分的变化

为探讨不同畜禽粪便（牛粪和羊粪）为主料,添加不同作物秸秆（玉米秸秆和小麦秸秆）为辅料在堆肥过程中的碳转化特征及腐殖质组分的变化规律,采用条垛式好氧堆肥研究了不同原料组合（T1：牛粪+玉米秸秆;T2：牛粪+小麦秸秆;T3：羊粪+玉米秸秆;T4：羊粪+小麦秸秆）在堆肥过程中总有机碳（TOC）、可溶性有机碳（DOC）和腐殖酸含量的碳转化特征以及胡敏酸（HA）和富里酸（FA）的含量变化规律。结果表明：所有处理的TOC含量随堆肥过程的推进而下降,至堆肥结束时T1~T4处理的TOC含量分别下降了22.1%、21.5%、23.6、23.7%;DOC含量也随堆肥过程的推进而降低,至堆肥第15天时降低至最低,T1~T4处理分别降低至6.57、5.47、4.73 g·kg^-1和4.93 g·kg^-1,但不同处理的变化规律明显不同：以牛粪为主料的T1和T2处理在第10天以前几乎无变化,而以羊粪为主料的T3和T4处理从一开始就迅速下降至最低值,至堆肥第15天时T1~T4处理的降幅分别为32.4%、36.5%、51.8%和39.3%;总腐殖酸(THA)含量的增加始于堆肥的第10天,第15天时达到最高值,最高值分别为25.5%、22.5%、29.8%和30.0%,整个堆肥过程中T3和T4处理显著高于T1和T2处理（P＜0.05）。随堆肥过程的推进,游离腐殖酸(FHA)含量逐渐降低,堆肥结束时降幅为7.6%~18.0%; HA含量逐渐增加,至堆肥结束时增幅为65.4%~197.8%,堆肥过程提高了胡敏酸态碳。T3和T4处理的FHA和HA含量在整个堆肥过程中始终高于牛粪组合T1和T2处理。FA含量随堆肥进程推进逐渐下降,至堆肥结束时降幅为44.9%~54.9%。羊粪中较高含量的纤维素、半纤维素和HA可能是堆肥产品中THA和HA含量较高的主要原因,在以牛粪为主料的堆肥配料中适当加入羊粪可以提高堆肥产品的腐殖酸含量和胡敏酸态碳。     

黄土高原子午岭油松林管理方式对黑碳和颗粒有机碳积累的影响

对黄土高原子午岭油松林不同管理方式下土壤的黑碳(BC)、有机碳(POC)和活性有机碳(LOC)的空间分布和积累进行了研究.结果表明,各种管理方式的油松林其POC、LOC和BC由表层至下层均呈显著的降低规律性.各种管理方式油松林0～10cm土层以BC>POC>LOC,10～20 cm土层中,天然油松林和粗放管理型油松林B...     

黄土高原的植被演替研究现状及发展趋势

从地质、历史时期黄土高原植被演替研究和现存植被的群落演替及群落结构特征 演化研究两方面论述了黄土高原的植被演替研究现状及发展趋势,认为黄土高原植被演替研 究对黄土高原的生态建设尤其是退耕还林还草工程建设具有重要意义,建议基于黄土高原的 植被演替规律进行仿自然植被林草建设。     

The impact of land use change on soil organic carbon and labile organic carbon stocks in the Longzhong region of Loess Plateau

Land use change (LUC) is widely recognized as one of the most important driving forces of global carbon cycles. The soil organic carbon (SOC) and labile organic carbon (LOC) stores were investigated at arable land (AL), artificial grassland (AG), artificial woodland (AW), abandoned arable land (AAL) and desert steppe (DS) in the Longzhong region of the Loess Plateau in Northwest China. The results showed that conversions from DS to AL, AL to AG and AL to AAL led to an increase in SOC content, while the conversion from DS to AW led to a decline. The differences in SOC content were significant between DS and AW at the 20-40 cm depth and between AL and AG at the 0-10 cm depth. The SOC stock in DS at the 0-100 cm depth was 39.4 t/hm 2 , increased by 28.48% after cultivation and decreased by 19.12% after conversion to AW. The SOC stocks increased by 2.11% from AL to AG and 5.10% from AL to AAL. The LOC stocks changed by a larger magnitude than the SOC stocks, which suggests that it is a more sensitive index of carbon dynamics under a short-term LUC. The LOC stocks increased at 0-20 cm and 0-100 cm depths from DS to AW, which is opposite to that observed for SOC. The proportion of LOC to SOC ranged from 0.14 to 0.20 at the 0-20 cm depth for all the five land use types, indicating low SOC dynamics. The allocation proportion of LOC increased for four types of LUC conversion, and the change in magnitude was largest for DS to AW (40.91%). The afforestation, abandonment and forage planting on arable land led to sequestration of SOC; the carbon was lost initially after afforestation. However, the carbon sink effect after abandonment may not be sustainable in the study area.     

陇中旱地不同保护性耕作方式表层土壤结构和有机碳含量比较分析

在陇中黄土高原半干旱区进行保护性耕作定位试验,研究了不同保护性耕作措施对表层土壤结构和有机碳含量的影响。结果表明:与传统耕作(T)、传统耕作结合秸秆还田(TS)相比,免耕秸秆覆盖(NTS)土壤容重在作物生长期保持稳定;虽然两种序列NTS处理土壤总孔度较低,但其>30μm的非毛管孔度显著高于其它三种处理,W→P→W序列(2002年小麦→2003年豌豆→2004年小麦)NTS处理分别比T处理、TS处理和NT处理提高3.605%、4.749%、3.338%;P→W→P序列(2002年豌豆→2003年小麦→2004年豌豆)NTS处理分别比T处理、TS处理和NT处理提高2.834%、4.023%、2.728%;就大团聚体(>0.25 mm)含量而言,W→P→W序列下T处理、TS处理、NT处理和NTS处理分别为7.412%、9.493%、9.098%、10.577%,P→W→P序列下分别为7.600%、10.027%、8.085%、9.933%,且统计分析表明两种序列下NTS处理均与T和TS两处理差异显著。同时发现,NTS处理可显著增加土壤有机碳含量,两种序列下分别比T处理增加0.958 g/kg和1.045 g/kg,而单一的免耕(NT)或覆盖(TS)效果并不显著。     

黄土高原表土有机碳和无机碳的空间分布及碳储量

选取位于干旱-半干旱区的黄土高原陕西境内表土样品为研究对象,对其有机碳(Soil organiccarbon,简称SOC)和无机碳的空间分布及陕西省碳储量进行初步研究。结果表明:黄土高原陕西境内有机碳和无机碳的平均值分别为5.41g/kg和17.04g/kg,有机碳的空间分布是自北向南呈现出增加的趋势,这也与所处环境相符,无机碳的空间分布特征沿着纬度呈现自北向南逐渐增加的趋势,特别是北纬36o以北;将每一区域内CaCO3含量的平均值与相对区域的降雨量和温度分别进行一元线性拟合,其拟合系数分别为R=0.338和0.182,碳酸盐含量与降雨量和温度的相关性并不显著。陕西省表土有机碳和无机碳储量分别为0.272Pg和0.856Pg,无机碳储量远大于有机碳储量,这与其所处干旱环境有关。