Study on Physical Properties and Related Spectral Characteristics of Composited Soil with Different Ratio of Feldspathic Sandstone and Sand

Juan LI,Jichang HAN

1.Shaanxi Province Land Engineering Construction Group,Xi’an 710075,China;

2.College of Forestry,Northwest A&F University,Yangling 712100,China;

3.Key Laboratory of Degraded and Unused Land Consolidation Engineering,the Ministry of Land and Resources of China,Xi’an 710075,China

Responsible editor:Yong XU Responsible proofreader:Xiaoyan WU

Population increase and environmental damage make the global desertification degree become more and more serious,agricultural arable land resources face critical shortage,and the sustainable development of agriculture severely restricted.How to increase the area of arable land and improve land utilization has become the focus problem of economic development in the world today[1-4].Many scholars have being engaged in the research of the agricultural in desertified region,and strive to explore soil desertification control measures and ways to increase arable land with the aim to solve the shortage of land resources and desertification expansion and ease the pressure of land resources caused by population increase and social development[5-7].

The southern margin of Maowusu Sandyland is located in the west farming-pastoral zone in north China,which belongs to the typical multi-level transition zone in geology and has weak ecotope,making it one of the area with most serious desertification in north China where the contradiction between people and land is very outstanding.Since 1987 when large-scale management of Maowusu Sandyland began,comprehensive treatment has been conducted to this area through the measures of afforestation and grass breeding to seal sand,ecological restoration,chemistry,physics,and adjusting measures to differing conditions[8-12],which have got certain achievements,but it fails to change the trend of desertification fundamentally.

In view of resources,feldspathic sandstone and sand are the 2 most important resources in Maowusu Sandyland.The research results of YIN et al.[13],LI et al.[14]and WANG et al.[15]show edthat the mass fraction of chemical stable components in feldpathic sandstone reached 84.9%,and most of feldpathic sandstone existed in the form of between parent material and soil.However,feldspathic sandstone tended to become cement in dry status,and the volume-weight was usually 1.50-1.55 g/cm3,which greatly affected its permeability,air permeability and the crop roots stretching.When encountering water,the feldspathic sandstone would expand rapidly with the total porosity reaching up to 45.91%,and because of its good water retaining property,it can be used as water retaining material; with no structure,aeolian sandy soil could keep good water permeability under wet and dry conditions,but it has poor water retaining property.Therefore,the two were complementary to each other,and the alternative distribution of the two in the Maowusu Sandyland could generate interaction after mixing.Through the study on the interactions in the land resources of the feldspathic sandstone area,it could improve the physical and chemical properties,which could realize the reclamation of Maowusu Sandyland[16].In this study,based on field plot experiment and laboratory analysis,different proportions of feldspathic sandstone and sand were mixed into composited soil,and the composited soil texture,soil water storageand related spectral characteristic changes were analyzed to screen out the optimal mixture ratios of feldspathic sandstone and sand with the aim to provide scientific basis for the agricultural planting in Maowusu Sandyland by using composited soil technology in large-scale.

Materials and Methods

General situation of the test station

Located in Chuyuan Village,Ducun County,Fuping Town,Weinan City,Shaanxi Province(109°11′30″ E,34°42′11″ N),the test place belonged to warm temperate semi humid climate zone,with the characteristics of the following:average annual rainfall of 472.97 mm,rainfall in July to September accounting for 49% of the total,annual evaporation amount of 1 000-1 300 mm,frost-free season of 225 d,annual average temperature of 13.4℃,summer maximum temperature of 41.8 ℃,winter minimum temperature of -22 ℃,annual total light radiation amount of 12.39 - 127.8 kca/cm2,and the climatic conditions could meet the needs of crop growth.

Test design

The trial was carried out from September 2010 to June 2013.In order to simulate the land conditions with the mixture of feldspathic sandstone and sand in the Maowusu Sandyland of the project experimental area,the thickness of the filling matrix in the test region was 70 cm (crop tillage layer generally was about 30 cm).The soil layers of this test were designed as follows:topsoil of 0-30 cm was the mixture of feldspathic sandstone(or loess)and sand,soil layer of 30 -70 was completely filled with sand,and both the feldspathic sandstone and sand came from the Dajihan Village,Xiaojihan County,Yuyang District,Yuyang.The mixture volume ratio of 1:2 of feldspathic sandstone and sand was the turning point for the decrease of saturated hydraulic conductivity of the mixture soil becoming slow.When the mixing ratio increased,the saturated hydraulic conductivity became decreased gently[17].Therefore,4 treatments were set in this test with the mixing volume ratio of feldspathic sandstone and sand of 1:1 (C1),1:2(C2) and 1:5 (C3),and the CK used loess soil and sand.The test plot area was 2 m × 2 m = 4 m2,and with there replicates,there were 12 test plots in total,which were laid out in a line from south to north.

Test materialsThe tested materials were wheat Xiaoyan 22.

Test plot managementThe fertilization amounts of all test plots were as follows:N of 255 kg/hm2,P2O5of 180 kg/hm2,K2O of 90 kg/hm2.The applied nitrogen fertilizer,phosphate fertilizer,potash fertilizer were urea,diammonium phosphate and potassium chloride,and all fertilizers were base fertilizer.

Before sowing winter wheat,the application amount of the fertilizers was calculated according to the plot area,which was applied through manual work.The soil should be prepared to make it flat and the fertilizers evenly distributed.The wheat was sown manually in line with the sowing amount of 150 kg/hm2and row spacing of 20 cm.No fertilizer was applied during the growth period of wheat,and before tilllering,the wheat was irrigated once.The irrigation amount of the 12 test plots was the same,and the other management was the same as that of the local fields.

The wheat sowing time of the three planting seasons were September 18,2010,Septermeber 20,2011 and September 24,2012,and the corresponding harvest time was June 8,2011,June 10,2012 and June 5,2013.

Testing items and methods

Measurement of soil moistureAfter the harvest of winter wheat,the earth boring auger was used to take soil samples,which was used to test the soil moisture content in the depth of 0 -60 cm by using oven drying method,and soil sampling interval was 10 cm.

Measurement of soil textureAfter the wheat harvest,soil samples in the depth of 0-30 cm were collected,from which the coarse roots and small stones were removed.Quartering method was used to take the testing soil samples,which were then dried naturally and meshed by the 0.149 mm mesh.Master-sizer 2000 was used to determine the soil texture,and according to the United States agricultural soil texture classification system of the US[18],the soil grains were classified into sand (grain diameter of 2 -0.05 mm),silt(grain diameter of 0.05-0.002 mm)and clay (grain diameter of smaller than 0.002 mm).

Determination of wheat spectraIn 2013,5 representative wheat plants were selected from each test plot during the winter wheat jointing stage and filling stage in sunny days to determine the canopy reflectance at 10:30-13:30 using ASD FiedlSpec4 high spectrometer (wavelength range of 350-2 500 nm,spectral sampling interval of about 1.5 nm,spectral resolution of 3.5 nm with the standard ASD spectrometer configuration of 7.5°field angle).During the determination,the sensor probe was vertically downward at about 10 cm above the top of the leaf.Every 10 spectral samples was a group,and each time 2 groups were determined,and the mean value was used as the canopy spectral reflectance of each plot.In order to reduce the influence of weather change,standard blank was corrected before and after the measurement of each group.

Determination of soil spectraIn 2013,3 spots were selected from each test plot after winter wheat harvest in sunny days to determine the soil spectral reflectance at 10:30-13:30 using ASD FiedlSpec4 high spectrometer(same parameters as above).During the determination,the sensor probe was vertically downward at about 15 cm above the soil.Every 10 spectral samples was a group,and the mean value was used as the soil spectral reflectance of each plot.In order to reduce the influence of weather change,standard blank was corrected before and after the measurement of each group.

Data calculation and statistical analysis

W=Wi×Di×Hi×10/100

Where,Wis soil water storage;Wi is the soil water content of the ithlayer;Dit is the soil bulk density of the ith layer;Hiis the soil layer thickness of the ith layer s.

Microsoft Excel 2010 was used to process all data,charts,and graphs,and SPSS (PASW Statistics 18) was used for the statistical analysis.Duncan new repolarization difference method (SSR) was used for multiple comparisons.

Results and Analysis

Change of soil texture of composited soil in 0-30 cm soil layer

Due to the influence of soil fertility,climate,crop root and biological activities,soil texture would also change with the increase of planting year,including the content of sand,silt and clay.After the winter wheat harvest in 2011,2012 and 2013,in the composited soil with different proportions of feldspathic sandstone (or loess) and sand,the changes of soil grain levels in 0-30 cm soil depth (Fig.1,2,3 and 4) indicated that with the increase of planting year,all composited soil mixed with feldspathic sandstone and sand showed decrease in the proportion of and and incrase of silt;the composited soil mixed with loess and sand showed decrease in clay and increase in sand.

After the wheat harvest in 2011,compared with other composited soils,treatment CK showed the highest clay content in the depth of 0-30 cm,and the content of clay increased with the increase of soil depth,while the content of both silt and sand decreased(Fig.1a),which was mainly because of the interactions between the root system and soil fertility during the early stage of crop planting,which could form cementation between the soil layers.With the increase of planting year,the proportion of silt increased in every treatment soil,and after wheat harvest in 2013,the soil silt content of treatment CK in the depth of 0-30 cm reached up to 26.07%,which was 73.49% and 47.25% higher than that in 2011 and 2012.The soil texture composited with feldsapthic sandstone and sand showed uniform trend the content of sand decreased significantly,while the content of silt increased and gathered on surface soil,and the content of clay showed no significant change (Fig.2,3 and 4).After wheat harvest in 2013,treatment C1,C2 and C3 in soil depth of 0-30 cm showed that the content of sand decreased by 13.41%,12.73% and 8.45%than that of 2011;in the 3 treatments,the content of sand increased with the increase of the proportion of sand,respectively,69.21%,76.69%and 78.94%,and all treatments showed significant differences (P＜0.05);in all treatments,the changes of silt contents were the same as that of sand that treatment C1 in the soil depth of 0-30 cm showed the average silt content of 24.99%,which was 6.27% and 8.25% higher than that of the treatment of C2 and C3,and all treatments were significantly different from each other (P＜0.05).In the soil depth of 0-15 cm of treatment C1,sand gathered together reaching up to 34,22,which might cause greater soil surface evaporation,resulting in water loss.After wheat harvest in 2013,all treatments showed that clay content decreased with the increase of soil layer depth and decreased with the increase of the mixing proportion of sand in the soil.In the soil depth of 0-30 cm of treatment C1,C2 and C3,the average clay contents were 5.80%,4.70% and 4.15%,respectively,and all treatments were significantly different from each other(P ＜0.05).

To sum up,after wheat harvest in 2013,treatment CK along the soil depth of 0-30 cm showed the average clay content decreased by 62.60% to that of 2011,the fast decrease of clay content increased soil porosity,which was easy to accelerate water evaporation and reduce effective utilization rate.Treatment C1 along the soil depth of 0-15 cm showed the accumulation of silt,which increased the surface soil porosity,making it easy to cause high soil water loss rate,which was not favorable to water and fertilizer retention.In treatment C3 along the soil depth of 0=30 cm,the average sand content was 79.17%,which was not favorable for water conservation.Treatment C2 along the soil depth of 0-30 cm showed coordinated proportions of clay and silt,which was suitable for crop production and soil water conservation,ensuring the growth and development of winter wheat.

Moisture storage of composited soil in 0-60 cm soil layer

After winter wheat harvest in 2011,2012 and 2013,the water storage in the soil layer of 0-60 (Table1)showed that the annual water storage amount of treatment C2 was higher than hat of the other treatments,indicating that the soil water storage of composted soil in 0-60 cm soil layer would decrease no matter the proportions of feldspathic sandstone was too low or too high.In 2011,the soil water amount of CK and C1 in 0-60 cm soil layer showed significant differences from the other treatments (P ＜0.05),and the water storage amounts in 0-60 cm soil layer were in the order of C2 ＞C3 ＞C1 ＞CK.The soil water storage of C2 in 0-60 cm soil layer was 20.31%,7.97%and 1.79%higher than that of CK,C1 and C3.In 2013,the soil water storage of C2 in 0-60 cm soil layer showed significant difference with the other treatments (P ＜0.05),and the order was the same as that in 2011.The soil water storage of C2 in 0-60 cm soil layer was 20.05%,18.90% and 6.62% higher than that of CK,C1 and C3.In 2013,the soil water storage of C2 in 0-60 cm soil layer was 19.06%,8.59%and 3.62%higher than that of CK,C1 and C3,respectively.

The average water storage amount of treatment CK,C1,C2 and C3 in 0-60 cm soil layer was 47.32,51.46,57.42 and 55.26 mm,respectively,indicating that treatment C2 was most beneficial to soil water conservation,which could better ensure the smooth germination and growth of wheat seeds.

Spectral characteristics of wheat in different growth stages

The canopy reflection spectral curves at the different stages of wheat growth in the composited soil with different proportions of feldspathic sandstone and sand were also different.In 2013,the spectral reflection curve characters were similar for all treatment of winter wheat at the jointing stage and filling stage along the fullwave band (350-2 500 nm),and the reflectance was higher in the jointing stage than the filling stage (Fig.5a and 6a).For all treatments,the canopy reflection spectra in the visible region(400-1 000 nm)first increased gradually and then decreased,and then increased greatly and then decreased(Fig.5b and 6b).The reflection peak was found around 550 nm,a part of green light wave band,and when the light band was over 800 nm,the reflectance tended to be stable,forming a reflection platform.Treatment C2 showed the highest canopy reflectance at the jointing stage of 0.21%,which was significantly different from the other treatments (P ＜0.05),indicating that under treatment C2,the crops showed good growth conditions,and the overall difference in leaves was small,which was mainly because during this period,the wheat canopy reflectance was greatly influenced by the soil reflectance,and the effect of soil reflectance on canopy reflectance was smaller when the wheat grew well.At the wavelength region of 680-820 nm,the wheat canopy reflectance of all treatments presented negative correlation with the wavelength in jointing stage,that is,with the increase of wavelength,the reflectance decreased.At the filling stage,the wheat canopy reflectance of all treatments was in the order of C3 ＞C1 ＞CK ＞C2,which may because the effect of soil reflectance on wheat canopy reflectance was small in this stage,which was mainly related with the chlorophyll content in the leaf.Treatment C2 showed the lowest reflectance at this stage,indicating that under treatment C2,the crops showed good growth conditions,and the content of canopy chlorophyll content was high.

Soil spectral characteristics

Different soil texture showed different light reflectance.In 2013,all treatments showed similar spectral curve characters at the wavelength of 350-1 750 nm after winter wheat harvest(Fig.7).The relative reflectance of soil increased during 350-1 750 nm wave length along with the increase of sand proportion.Under the treatment CK,C1,C2 and C3,the soil average reflectance was 0.317%,0.303%,0.321% and 0.339%,respectively.At the 350-750 nm band,for treatment CK,C1,C2 and C3,the soil spectral reflectance (y) and wave length (x)presented highly correlated relationship,and the correlation equations were as follows:y = 0.187 1ln (x) -0.979 4,y = 0.158 7 ln (x) - 0.801 2,y= 0.177 1ln (x) - 0.910 8 and y =0.184 5ln(x)-0.944 5.And the correlation coefficient was 0.653,0.553,0.653 and 0.672,respectively.At the wave length of 1 350-1 450 nm band,soil reflectance had an obvious peak,but it was not suitable for data analysis,for the wave length was mainly caused by water vapor absorption caused,which was very sensitive to water[19].

Discussion

As an important physical characteristic,texture is subject to the influence of many factors like parent material,climate,topography,groundwater hydrology and so on.,making it present certain regularity and constitutive property in special distribution.Soil texture affects the migration,distribu-tion and utilization efficiency of soil nutrients,and,therefore,research on its spatial variation is of great significance to soil improvement,irrigation,fertilization and eco agricultural regionalization[18].The test results of this study showed that after the winter wheat harvest in 2011,2012 and 2013,in the composited soils with different mixing proportions of feldspathic sandstone(loess)and sand in 0-30 cm soil layer,with the increase of planting year,treatment C1,C2 and C3 showed decrease in sand but increase in silt,while treatment CK showed decrease in clay but increase in sand.After planting crops for 3 seasons,the sand content in 0-30 cm soil layer of treatment CK showed an increase of 43.44% to that of the early stage; the sand content in 0-30 cm soil layer of treatment C1,C2 and C3 decreased by 13.41%,12.73% and 8.45%,respectively,and silt content increased by 14.53%,13.16% and 8.82%,respectively,which presenting significant differences among all treatments (P ＜0.05).Soil texture directly affects soil water retention,permeability and retention.The test results of this study showed that with the increase of planting year,the soil texture was better in ventilation and water permeability.The average sand,silt and clay content in the 3 planting seasons of treatment C2 in 0-30 cm soil layer was respectively 76.69%and 18.72%and 4.70%,which was more suitable for plant growth.Due to differences in soil texture,treatment CK,C1,C2 and C3 showed significant difference in water storage in 0-60 cm soil layer,which first increased with the increase of sand proportions,and then decreased with the increase of sand proportions after treatment C2 showed the maximum water storage.The average water storage in 0-60 cm soil layer of treatment C2 was 57.42 mm.

Table1 Soil water storage in 0-60 cm soil layer under different treatments(2011-2013)

There have many studies on crop canopy characteristics but with different conclusions.The application of spectroscopy overcomes the disadvantage of time-consuming and damage to the crop,achieving efficient management and production[20].This study analyzed the canopy reflectance of winter wheat at jointing stage and filling stage in 2013,and the canopy reflectance of all treatments at the jointing stage was higher than that at the filling stage.The canopy reflectance of all treatments first increased and then decreased,and the reflection peak was found around 550 nm,a part of green light wave band.Treatment C2 showed the highest canopy reflectance at the jointing stage and lowest in the filling stage,which was mainly because with the advance of the growth period of wheat,the photosynthetic capacity increased,the influence of soil reflectance on canopy reflectance decreased,the absorption of visible light gradually increased,and the reflectance gradually decreased.The reason why the canopy reflectance at jointing stage higher than at filling stage was that the proportions of leaves with high chlorophyll content in the crop canopy of wheat decreased at the filling stage,while the proportions of wheat awns in canopy increased,which decreased the reflectance in near infrared region.In the mean time,the effects of diseases and pests on wheat became obvious at the filling stage,which could also decrease the reflectance[21-22].

Soil spectral character is also affected by many factors like soil moisture,soil organic matter content,iron oxide,soil texture and so on.After three seasons of crops planting,the soil spectrum of each treatment was determined in 2013 after wheat harvest,and the results showed that all treatments had similar spectral characters at the 350 -1 750 nm wave length,and the soil spectral reflectance increased with the increase of sand proportions,which was mainly caused by the differences in soil texture.The increase in sand proportions would intensity the cementation and interaction between particles,which could increase the spectral reflectance.Bowers et al.[24]studied the effect of mechanical composition on the energy of soil reflection,and the results showed that soil spectral reflectance presented exponential growth with the soil particles becoming small,which was especially more obvious when the diameter of soil particles was less than 0.4 μm.The study of Alabbas et al.[25]found that soil clay content presented negative correlation with soil spectral reflectance,which was consistence with the results of this study that under treatments C1,C2 and C3,with the decrease of clay content in soil texture,the spectral reflectance increased.During 350-1 750 nm wave length,for treatment CK,C1,C2 and C3,the soil spectral reflectance(y)of different soils and wave length(x)showed good logarithmic relationship as follows:y = 0.187ln (x)-0.979,y=0.159ln(x)-0.801,y=0.177ln(x)-0.911 and y=0.185ln(x)-0.945.

Composing feldspathic sandstone with sand according to different proportions could replace the traditional methods of soil improvement.Combining the complementarity of feldspathic sandstone and sand with scientific planting technology combination,the composited soil could be superior to the soil improved by traditional method to a certain extent,and experimental study shows that the mixing proportion of 1:2 can increase the soil moisture storage capacity,which is conducive to the growth of crops.This study only investigated the differences of soil texture,moisture and spectral characteristics,and further study is required to learn the the effects of other soil index and crop yield.

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