Abstract:【Objective】In Xinjiang, an arid region, water scarcity has promoted extensive use of drip irrigation under plastic film mulch in agricultural production as an effective water-saving technique in this region. However, Xinjiang is also a region where soil salinization is common. With the extensive replacement of conventional irrigation with drip irrigation, the benefit of the former washing salts off the soil disappeared. Moreover, the irrigation water in this region is quite high in mineralization and ready to supply the soil with salt. So, although the effect of drip irrigation saving water and increasing yield is quite obvious, long-term adoption of the technique may lead to salt accumulation in the soil, thus lowering soil quality. This paper is oriented to explore impacts of 15-year long-term drip irrigation on soil salinity or soil salt content of the field in an attempt to provide certain scientific basis for management of soil salt under mulched drip irrigation in this region. 【Method】A tract of farmland, around 224 km2 in area was delineated in Regiment 147, Division Eight of the Xinjiang Production and Construction Corp, in the Manas River Basin, North Xinjiang for the study. The data of salt contents and soil available nutrient contents in the plow layer accumulated during the years from 1996 to 2010 of the tract of farmland were analyzed statistically with the aid of GIS technology to characterize variation of soil salt in the plow layer and relationship between soil salt and other soil indices in the plow layer relative to irrigation history. 【Result】Results show: (1) soil salt content in the plow layer decreased from 3.13 g kg-1 to 3.00 g kg up>-1 or by 4.2% in the first 3 years of drip irrigation, but it rose back up to 4.81 g kg-1 or 53.7% at the end of the study; (2) after 15 years of drip irrigation, soil salt content in the plow layer of the study region increased significantly, varying mainly in the range of 4 ～ 10 g kg up>-1, and a large proportion of the plow layer soil could be sorted as moderately or heavily salinized soil; and (3) long-term mulched drip irrigation in the arid region led to redistribution of soil salt in the plow layer, approaching to normal distribution in the scope of the regiment as a whole. 【Conclusion】Under the condition of the study, long-term mulched drip irrigation has led to salt accumulation in the plow layer, because the water used in drip irrigation carries some salt, which may serve as supplement to soil salinity. It is, therefore, recommended to flood the field to wash soil salt off every two or three years in areas under long-term mulched drip irrigation, and to build up soil fertility and soil organic matter content, which may play a positive role in controlling soil salt accumulation due to drip irrigation in this region.

Abstract:The technology of image spectroscopy has been widely used in soil attribute mapping in the past few decades.However,vegetation cover seriously affects the acquisition of soil spectral information, leading tomisestimating of soil attributes by visible and near-infrared (vis-NIR) spectroscopy. The traditional solution dealt with vegetation cover interfering soil spectra by masking out the areas with high vegetation coverage, thus resulting in absence of soil information for these areas. Some researchers also tried to use vegetation indices to estimate soil attributes, with results showing that the general applicability and transferability of these vegetation indices was limited by study areas and crop varieties. Therefore, how to remove the influence of vegetation on soil spectrum has become a crucialissue in estimating soil components, such as salt content over partially vegetated surfaces. The residual spectral unmixing method was previously used to separate different components of a mixedspectrum, however, the percentage of each component had to be known as a prerequisite. Recently blind source separation (BSS), a method previously often used in signal separation analysis, has successfully been appliedto separating soil spectral information from vegetation spectral information. In order to verify the effectiveness of BSS, in theHuanghai Raw Seed Growing Farm in Dongtai of Jiangsu, was selected as an experiment site, with its field delineated into plots diversified in soil salt content by amending the soil with salt and vegetated sparsely by seeding in different densities The experiment eventually had a total of 50 plots, 5 levels in soil salt content and 10 in sowing density. Then spectra, photos and soil samples of each plot were collected regularly until the soil surface was fully covered by vegetation. A total of 189 groups of field spectral reflectance of the plots various in vegetation coverage, soil salinity and growing season, were analyzed for influences of vegetation on estimationof soil salt content, and effectiveness of BSS removing the interference of vegetation. Results show that vegetation cover seriously affected accuracy of the estimation of soil salt content with R2cv=0.53, RMSEcv=3.54 g kg-1, RPDcv=1.47, R2p=0.50, RMSEp=3.33 g kg-1 and RPDp=1.41. However, the BSS algorithm, based on equation z=tanh(y), effectively eliminated the interference of vegetation on soil spectral reflectance, and improved accuracy of the estimation of soil salt content in the over partially vegetated areas using vis–NIRspectroscopy, with R2cv =0.66, RMSEcv=3.10 g kg-1, RPDcv=1.70, R2p=0.63, RMSEp=2.89 g kg-1 and RPDp=1.57. However, the effectiveness of BSS weakened when vegetation coverage was getting high, because it was unable to capture enough soil information from the mixed spectra. Additionally, choosing a suitable number of source spectra was essential to the results, and two was the best choice in this case. The method proposed here is expected to broaden the use of spectroscopy, which is usually limited to bare soil, and facilitates wider application of remote sensing images to map soil salinity overpartially vegetated surfaces.

Abstract:Salt contents in soils different in cultivation age in Qitai County of Xinjiang were investigated for analysis of rules of the variation of soil salt content, types of soil salinity profiles and their affecting factors, using the cluster analysis method and some other related methods. Results show that along with the transformation of wasteland into farmland (at least 5 years in cultivation history), characteristics of soil salt content distribution in the soil profiles varied and fell into four types, i.e. surface accumulation profiles (SAP), even distribution profiles (EDP), oscillation profiles (OP) and bottom accumulation profiles (BAP). Uncultivated land high in salt content is typical of salinized soil, with an apparent phenomenon of surface salt accumulation; and the salt in the surface layer (0~20 cm) accounted for 34.31% of the tatol in the soil profile. Farmlands, 5 or 10 years old, are mostly of the type of BAP. With the farming operation going on and on, soil salt content in various salt-containing layers varied in activity degree showing an order of active layer (AL), sub-active layer (SAL) and relatively stable layer (RSL), and the relationship between soil salt content and soil organic matter content gradually turned from extremely positive one into extremely negative one, while the correlation between soil salt content and soil pH went the other way round. Under farming activities, soil salinization developed reversely. The average salt content in farmlands 10 years old was only 20.90% as much as in wasteland. The desalination rate was reducing with the farming operation going on from 0.156% a-1 in the first three years of farming down to 0.004% a-1 in the years beyond 5.