Threshold friction velocity influenced by soil particle size within the Columbia Plateau, northwestern United States

Wind erosion is a geomorphic process in arid and semi-arid areas and has substantial implications for regional climate and desertification.In the Columbia Plateau of northwestern United States,the emissions from fine particles of loessial soils often contribute to the exceedance of inhalable particulate matter(PM)with an aerodynamic diameter of 10μm or less(PM10)according to the air quality standards.However,little is known about the threshold friction velocity(TFV)for particles of different sizes that comprise these soils.In this study,soil samples of two representative soil types(Warden sandy loam and Ritzville silt loam)collected from the Columbia Plateau were sieved to seven particle size fractions,and an experiment was then conducted to determine the relationship between TFV and particle size fraction.The results revealed that soil particle size significantly affected the initiation of soil movement and TFV;TFV ranged 0.304-0.844 and 0.249-0.739 m/s for different particle size fractions of Ritzville silt loam and Warden sandy loam,respectively.PM10 and total suspended particulates(TSP)emissions from a bed of 63-90μm soil particles were markedly higher for Warden sandy loam than for Ritzville silt loam.Together with the lower TFV of Warden sandy loam,dust emissions from fine particles(<100μm in diameter)of Warden sandy loam thus may be a main contributor to dust in the region's atmosphere,since the PM10 emissions from the soil erosion surfaces and its ensuing suspension within the atmosphere constitute an essential process of soil erosion in the Columbia Plateau.Developing and implementing strategic land management practices on sandy loam soils is therefore necessary to control dust emissions in the Columbia Plateau.

Gross nitrogen transformations and N2O emission sources in sandy loam and silt loam soils

The soil type is a key factor influencing N(nitrogen)cycling in soil;however,gross N transformations and N_(2)O emission sources are still poorly understood.In this study,a laboratory 15N tracing experiment was carried out at 60%WHC(water holding capacity)and 25℃to evaluate the gross N transformation rates and N_(2)O emission pathways in sandy loam and silt loam soils in a semi-arid region of Heilongjiang Province,China.The results showed that the gross rates of N mineralization,immobilization,and nitrification were 3.60,1.90,and 5.63 mg N/(kg·d)in silt loam soil,respectively,which were 3.62,4.26,and 3.13 times those in sandy loam soil,respectively.The ratios of the gross nitrification rate to the ammonium immobilization rate(n/ia)in sandy loam soil and silt loam soil were all higher than 1.00,whereas the n/ia in sandy loam soil(4.36)was significantly higher than that in silt loam soil(3.08).This result indicated that the ability of sandy loam soil to release and conserve the available N was relatively poor in comparison with silt loam soil,and the relatively strong nitrification rate compared to the immobilization rate may lead to N loss through NO_(3)–leaching.Under aerobic conditions,both nitrification and denitrification made contributions to N_(2)O emissions.Nitrification was the dominant pathway leading to N_(2)O production in soils and was responsible for 82.0%of the total emitted N_(2)O in sandy loam soil,which was significantly higher than that in silt loam soil(71.7%).However,the average contribution of denitrification to total N_(2)O production in sandy loam soil was 17.9%,which was significantly lower than that in silt loam soil(28.3%).These results are valuable for developing reasonable fertilization management and proposing effective greenhouse gas mitigation strategies in different soil types in semiarid regions.

Migration process of ammonium ion in saturated silty sand and sandy loam

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Effects of a new nitrification inhibitor 3,4-dimethylpyrazole phosphate(DMPP) on nitrate and potassium leaching in two soils

In this study, soil column was used to study the new nitrification inhibitor 3,4-dimethylpyrazole phosphate （DMPP） on nitrate （NO3^-- N） and potassium （K） leaching in the sandy loam soil and clay loam soil. The results showed that DMPP with ammonium sulphate nitrate （ASN） （（NH4）2SO4 and NHaNO3） or urea could reduce NO3^--N leaching significantly, whereas ammonium （NH4^＋-N） leaching increased slightly. In case of total N （NO3^--N＋NH4^＋-N）, losses by leaching during the experimental period （40 d） were 37.93 mg （urea）, 31.61 mg （urea＋DMPP）, 108.10 mg （ASN）, 60.70 mg （ASN＋DMPP） in the sandy loam soil, and 30.54 mg （urea）, 21.05 mg （urea＋DMPP）, 37.86 mg （ASN）, 31.09 mg （ASN＋DMPP） in the clay loam soil, respectively. DMPP-amended soil led to the maintenance of relatively high levels of NH4^＋ -N and low levels of NO3^--N in soil, and nitrification was slower. DMPP supplementation also resulted in less potassium leached, but the difference was not significant except the treatment of ASN and ASN＋DMPP in the sandy loam soil. Above results indicate that DMPP is a good nitrification inhibitor, the efficiency of DMPP seems better in the sandy loam soil than in the clay loam soil and lasts longer.

Aeolian Facies Belts in the Taklimakan Desert

At least at the beginning of the last glacial epoch, the facies belts of dune sand, sandy loam and loess formed by winds had existed in the Taklimakan desert and areas south of it. There were no appreciable changes in the NE and NW wind systems and their wind fqrces that deposited dune sand, sandy loam and loess in the global cold stage since the last glacial epoch (accordingly no marked shifts of the boundaries of these aeolian facies belts took place. In the global warm stage since then, the climate in the Taklimakan desert and areas south of it became warm and dry, resulting in ablation of substantial volumes of ice and snow in their surrounding mountains and thus forming alluvial and diluvial deposits in the region. The alluvial-diluvial actions, however, failed to change the general framework of aeolian facies belts.

Cogon grass biochar amendment and Panicum coloratum planting improve selected properties of sandy soil under humid lowland tropical climatic conditions

Biochar amendment improves the physical,chemical and biological characteristics of different soil types under different climatic and environmental conditions.In this study,effects of biochar or live pasture plants existing alone or co-existing on selected soil properties of sandy loam soil under humid lowland tropical climatic conditions were investigated.The changes measured in the amended soil,with or without plants,were compared to the unamended and unplanted soils.Biochar amendment with or without pasture improved moisture retention,lowered bulk density,increased pH and kept the electrical conductivity within ranges conducive for pasture growth.Generally,contents of all the nutrients increased following biochar amendment,however pasture establishment without amendment resulted in depletion of available potassium and magnesium.Under all treatment conditions,soil organic carbon and soil organic matter were significantly depleted.Cogon grass is invasive under all land use systems and contributes to greenhouse gas emissions through slash-and-burn.Using biomass from the grass instead of burning would mitigate CO2 emissions from the tropics.

Effects of digestate application depth on soil nitrogen volatilization and vertical distribution

This study investigated the effect of the digestate application depth on soil nitrogen volatilization and vertical distribution in black loam soil and sandy loam column.The contents of soil moisture,TKN(total Kjeldahl nitrogen),ammonium nitrogen,nitrate nitrogen,and the extent of ammonia volatilization were tested by applying digestate at depths of 0 cm,2 cm,6 cm,10 cm,15 cm and 20 cm,respectively.The experimental results showed that ammonia volatilization mainly occurred in the first 10 days and reduced significantly when the application depth was deeper than 10 cm.At the same application depth,compared with the black loam,the nitrogen loss in sandy loam through ammonia volatilization was less,and the penetration depth of nitrate nitrogen and ammonium nitrogen were all deeper.In the same soil,nitrate nitrogen penetrated deeper than ammonium nitrogen at all application depths.

Monitoring the variation of soil quality with sewage sludge application rates in absence of rhizosphere effect

Agricultural soils in semi-arid regions have frequently been degraded due to adverse climatic conditions,organic matter depletion,and poor farming practices.To enhance soil quality,this study examines the reuse of sewage sludge(SS)as an available source of organic matter in a typical Mediterranean sandy-loam soil.Accordingly,we studied the cumulative effect of two annual applications of 40,80 and 120 tons of sludge per ha on soil quality in absence of vegetation.The dose-dependent improvement of organic matter content was the most significant event that reflected sludge application rates,and consequently influenced other soil properties.Accordingly,soil structural stability increased by 13.3%,28.8%and 59.4%for treatments SS-40,SS-80 and SS-120 respectively as compared to unamended control.Structural stability improvement was also confirmed by the dose-dependent variation of other edaphic factors including calcium content,the microbial quotient as well as Welt and C:N ratios.These param-eters are involved in cementing soil aggregates by cation bridging,the formation of microbial mucilage,and clay-humic complexes.Soil magnetic susceptibility(SMS)was measured in situ as a possible rapid tool to evaluate soil condition.SMS showed significant correlation with sludge dose and stability amelioration testifying to the aggregation role that can play Al2O3 and particularly Fe2O3 minerals added by the hematite-rich sludge.Besides,analytical results and field observations revealed no trends of soil salinization or acidification by excessive sludge amounts.By avoiding the rhizosphere effect,outcomes could reflect the resilience and intrinsic capacity of the soil to cope with excessive sludge loads.

Urease activity and nitrogen dynamics in highly weathered soils with designer biochars under corn cultivation

The application of designer biochar has the potential to impact soil enzyme activity and soil nitrogen dynamics.However,very little is known about the mechanisms responsible for biochar-enzyme-nitrogen interaction in highly weathered soils.The objective of our 3-year(2016-2018)field experiment was to evaluate the effectiveness of designer biochars(DB)in enhancing urease activity(UA),total nitrogen(TN),total inorganic nitrogen(TIN),and nitrogen uptake(NU)at different growth stages(GS)of corn in a highly weathered soil of southeastern Coastal Plain region,USA.Experimental treatments have consisted of the control,100%pine chips(100PC),100%poultry litter(100PL),2:1 blend of PC and PL(PCPL),100%raw switchgrass(Panicum vaginatum,L;100RSG),and 2:1 blend of PC and RSG(PCRSG).All the designer biochar treatments were applied at the rate of 30,000 kg ha^(−1)to a Goldsboro loamy sand in 2016.Urease activity,TN,TIN,and NU varied remarkably with DB(p≤0.0001)at different GS(p≤0.0001)of corn.Soils treated with 100PL had the greatest UA(28.18μg N g^(−1)h^(−1)),TN(0.087%),and TIN(14.53 mg kg^(−1))while the least UA,TN,and TIN of 20.55μg N g^(−1)h^(−1),0.063%,and 5.42 mg kg^(−1),respectively,were observed from the control.The three-year TN average increase over the control was in the order:100PL(36.8%)>100RSG(25.8%)>PCRSG(25.3%)>PCPL(23.9%)>100PC(7.1%).The greatest NU of corn of 140.4 kg N ha^(−1)was from soils treated with 100PL while the least amount of NU was from 100PC.Overall,our results showed promising significance for the treatment of highly weathered soils since the application of DB did enhance UA and improve TN and TIN in the soils.