Temporal and vertical dynamics of carbon accumulation potential under grazing-excluded grasslands in China: The role of soil bulk density.

Despite the progress made in understanding relevant carbon dynamics under grazing exclusion, previous studies have underestimated the role of soil bulk density (BD), and its implications for potential accumulation of soil organic carbon (SOC), especially at regional scale over long term. In this study, we first constructed a database covering a vast majority of the grasslands in northwestern China based on 131 published literatures. A synthesis was then conducted by analyzing the experimental data to comprehensively investigate the mechanisms of vegetation recovery, carbon-nitrogen coupling, and the importance of changed soil BD in evaluating SOC sequestration potential. The results showed that although the recovery of vegetation height and cover were both critical for improving vegetation biomass, vegetation height required a longer recovery period. While the SOC accumulation was found to be greater in surface layers than deeper ones, it exhibited a reduced capacity for carbon sequestration and an increased risk of SOC loss. Grazing exclusion significantly reduced soil BD across different soil profiles, with the rate of change influenced by soil depth, time, geographical and climatic conditions. The potential for SOC accumulation in the top 30 cm of soil based on data of 2003-2022 was 0.78 Mg ha-1 yr-1 without considering BD effects, which was significantly underestimated compared to that of 1.16 Mg ha-1 yr-1 when BD changes were considered properly. This suggests that the efficiency of grazing exclusion in carbon sequestration and climate mitigation may have been previously underreported. Furthermore, mean annual precipitation represented the most relevant environmental factor that positively correlated to SOC accumulation, and a wetter climate may offer greater potential for carbon accumulation. Overall, this study implies grazing exclusion may play an even more critical role in carbon sequestration and climate change mitigation over long-term than previously recognized, which provides essential scientific evidence for implementing stepwise ecological restoration in grasslands.

Detrimental Effects of Induced Soil Compaction on Morphological Adaptation and Physiological Plasticity of Selected Multipurpose Tree Species.

Soil compaction has become a global problem affecting soil worldwide. With an increased population, more demands for food and wood have resulted in intensive cultivation and increased mechanization of our farmlands and irrigated plantations. The use of heavy machinery results in soil compaction, which affects the entire soil ecosystem. This study was conducted to analyze the impact of compacted soil on germination and initial growth stages of four major agro-forest trees of central Punjab, Pakistan. Morpho-physiological traits of all selected species (Eucalyptus camaldulensis, Albizia lebbeck, Vachellia nilotica, and Zyziphus mauritiana) were measured against soil compaction. Results indicated that the root and shoot length, biomass, root-shoot ratio, diameter at root collar, no. of leaves and branches, leaf area, germination, and survival %, and physiological traits (i.e., photosynthetic rate, transpiration rate, stomatal conductance, internal CO2 concentration, and photosynthetic water use efficiency) were significantly affected by the induced soil compaction. Eucalyptus camaldulensis Dehnh. performed better and exhibited 96% germination percentage under (1.40 mg m-3) compaction level and gradually decreased by 11% with the increase of compaction level (1.80 mg m-3). It shows that the shorter roots developed due to soil compaction decreased water use efficiency, photosynthesis, and whole-plant physiological performance. The findings concluded that judicious use of machinery is highly desired for sustainable and good-quality wood production from farm trees.

Phosphorus deficiency is the main limiting factor for re-vegetation and soil microorganisms in Mu Us Sandy Land, Northwest China.

Long-term drought induced by low rainfall leads to environmental degradation of land in arid and semi-arid regions. In past decades, re-vegetation of degraded sandy soils to prevent soil erosion has been widely employed, including in Mu Us Sandy Land, which suffers from severe soil erosion. However, it remains unclear how re-vegetation affects soil properties and soil microbes after long restoration periods. In this study, typical plots planting Artemisia ordosica and Salix psammophila were selected to investigate the influence of plant types on soil properties; an area of bare sandy land was used as a control. The results show that re-vegetation increased soil organic carbon (C), total nitrogen (N), soil microbial carbon, microbial nitrogen and soil organic acid, while decreasing soil total phosphorous (TP) content significantly, resulting in increased C/P and N/P ratios. Correlation analysis showed that TP was negatively correlated with oxalic acid (OA) and acetic acid (AA), indicating that increased AA and OA content could accelerate the active utilization of phosphorus and induced low TP in soil. Re-vegetation with A. ordosica significantly decreased the microbial diversity of topsoil. The redundancy analysis showed that TP was main index in affecting microbes. These results that lower P content, higher C/P and N/P ratio and influence of TP on microbes suggest that phosphorus is the main limiting factor for re-vegetation and growth of soil microorganisms. In the future, strategies for the development of sustainable ecosystems in regions suffers from severe soil erosion should consider phosphorus supplementation.

The Impact of Using Different Doses of Biomass Ash on Some Physical Properties of Podzolic Soil under the Cultivation of Winter Oilseed Rape.

This two-year study was focused on the effect of the application of different biomass ash doses on selected soil physical properties, i.e., soil moisture (SM), bulk density (BD), penetration resistance (PR), and soil stability in water measured by the content of readily dispersible clay (RDC), following control and mineral NPK fertilization in the cultivation of winter oilseed rape (Brassica napus L. var. napus). A one-factor field experiment conducted on podzolic soil (control, NPK, 100, 200, 300, 400, 500 kg K2O·ha-1) showed that the use of biomass combustion ash significantly improved soil moisture at all depths and variants, and especially at a depth of 30-35 cm in the 500 kg·ha-1 variant, i.e., by 2.99% v/v, compared to NPK. In turn, the moisture content in the 30-35 cm layer increased by 3.19% v/v in all variants in both years compared to the control. In 2020 and 2021, bulk density in the 0-5 cm layer treated with a dose of 500 kg·ha-1 exhibited a positive 0.15 and 0.12 Mg·m-3 decrease, respectively, compared to the control. In both years, the BD values in the 30-35 cm layer were reduced by 0.14 and 0.16 Mg·m-3 compared to the control. The PR values decreased in the treatments with doses of 300, 400, and 500 kg·ha-1, especially in 2021. The RDC content was found to decline in both years, i.e., 2020 and 2021, upon the application of even the lowest dose (100 kg·ha-1) in all the analysed layers. The reduction in the RDC content, especially in the 0-5 cm layer, is very important for soil structure stability and to protect the soil environment. This layer is most susceptible to crusting, which results in poor aeration and weak plant emergence during drought and/or periods of excessive moisture. It may also increase surface runoff and intensify soil erosion processes.

Spatial distribution of soil bulk density and its relationship with slope and vegetation allocation model in rehabilitation of dumping site in loess open-pit mine area.

Studies of soil bulk density (BD) spatial variations of land reclaimed after mining have become a focus of land reclamation and ecological restoration research. However, there have been few studies on the relationship among the reconstructed BD, terrain conditions, and vegetation growth. We examined the southern dumping site of the Pingshuo Antaibao open-pit coal mine located in a loess area in China. Field sampling data, digital elevation models (DEMs), and high-definition images were obtained, and indoor testing, geostatistics, and inverse distance weighting (IDW) were applied. This paper aims to analyze the spatial distribution law of the reconstructed BD and focus on its relationship with slope and vegetation allocation models. We demonstrated that (1) BD increased with soil depth and varied moderately within each layer. (2) The BD variation amplitude of the top 0-20-cm soil layer in both the east-west and south-north directions was small and more similar in the east-west direction than in the south-north direction, which was affected by herbaceous root systems. In the next four layers from 20 to 60 cm, the variation in BD in the east-west direction was far larger than that in the south-north direction, which was affected by vegetation classification. (3) On the whole, BD decreased with increasing slope, but when the slope was between 0° and 21°, BD exhibited a specific change law. (4) From the perspective of vegetation classification, the orders of magnitude of BD in the 0-20-cm and 20-60-cm layers differed. Overall, BD in areas vegetated with Korshinsk Peashrub was the lowest, and BD was moderate in areas with mixed vegetation, while BD was the highest in areas without vegetation or only vegetated with Black Locust. The mixed grass-bush-tree or bush-tree mode attained the best effect in regulating BD. These results can improve the basic principles of land reclamation in mining areas and provide a basis for further optimizing land reclamation technology in practice.

Effects of compaction on lead availability in contaminated soils with contrasting texture.

The effects of soil compaction on porosity (α), bulk density (ρs), and saturated hydraulic conductivity (Ksat) can create a physical barrier in the soil, reducing the vertical movement of toxic elements in the soil profile. However, the indirect effects of compaction in altering the forms and availability of heavy metals in soil have not been well-studied. This study examined the influence of compaction on forms of lead (Pb) in soils with contrasting texture. Four levels of compaction were imposed on a sandy loam and a clayey soil, which were artificially contaminated based on their maximum Pb adsorption capacity. Compaction had different effects on Pb forms depending on soil texture. In the sandy loam soil, compaction had a dual beneficial effect in mitigating the impact of Pb contamination, since it decreased Ksat, reducing metal transport to deeper soil layers, and also prevented transformation to more available Pb forms (soluble and exchangeable). Instead, there was an increase in the most environmentally stable forms of Pb (inner sphere adsorption on iron and manganese oxides). In the clayey soil, compaction caused a significant increase in soluble and exchangeable Pb, accompanied by a significant reduction in environmentally stable Pb (inner sphere adsorption on gibbsite and kaolinite). In addition, studies about Pb contents under compacted soil layers should be investigated, mainly in clayey soils with edible crops, and environmental remediation practices that involve the machines traffic (for example, phytoremediation-successive cultivation of Pb-hyperaccumulating plants) should be used with care to minimise the compaction of clayey soils.

The additive effect of biochar amendment and simulated nitrogen deposition stimulates the plant height, photosynthesis and accumulation of NPK in pecan (Carya illinoinensis) seedlings.

This work investigated the effective doses of biochar (BC) amendment with simulated nitrogen deposition on the stimulation of pecan (Carya illinoinensis) growth. A total of nine conditions combining three levels of BC-BC0, 0 t ha-1 year-1; BC20, 20 t ha-1 year-1; and BC40, 40 t ha-1 year-1-and three levels of simulated nitrogen deposition-N0, 0 kg N ha-1 year-1; N50, 50 kg N ha-1 year-1; and N150, 150 kg N ha-1 year-1-were applied throughout 1 year on the pecan-grafted seedlings of cultivar 'Pawnee'. The growth, photosynthesis, chlorophyll and nutrient content in the seedlings were measured. The soil bulk density, pH, nitrogen content and enzymatic activities were also measured. Biochar amendment reduced soil bulk density and elevated soil pH. Meanwhile, aided by BC amendment, the inorganic nitrogen content and enzyme activities increased with increasing doses of nitrogen. In the absence of BC amendment, the seedlings' height, photosynthesis and chlorophyll pigments were only stimulated by a low level of simulated nitrogen deposition (N50), whereas a high level of simulated nitrogen deposition (N150) impeded the growth. The seedlings improved the most under the combined treatment of BC20N150, wherein the seedling heights, photosynthesis and total chlorophyll improved by 22 %, 70 % and 40 %, respectively, compared to those treated solely with BC20. Further increase of nitrogen retention in the soil by the BC40 did not further improve the growth of the seedlings, suggesting the possible mechanisms involve nutrient uptake and usage dynamic in the seedlings. The BC amendment alleviated the antagonist effect from simulated nitrogen deposition that suppressed the absorption of phosphorus, potassium and iron. The effect of applying both BC amendment and simulated nitrogen deposition to the growth of seedlings was additive at fertilizing tree species.

Assessing the impacts of log extraction by typical small shovel logging system on soil physical and hydrological properties in the Republic of Korea.

Typical small shovel logging system, using manual felling and extraction by small crawler excavator with grapple and crawler carriers, is the predominant logging method in the Republic of Korea, due to the associated high productivity. The trails with ground pressure and one more passes of the shovel and carriers may lead to soil compaction. However, impacts of these bunching-extraction technologies on physical and hydrological properties of soils are not well known. The main objectives of this study were to: (1) determine the bulk density, porosity, and saturated hydraulic conductivity of soils in logging operation areas with three different disturbance types (i.e., undisturbed areas [UAs], bladed trails [BTs], and skid trails [STs]), and (2) compare soil compaction between these disturbance types. The most intense compaction occurred within BTs and STs, with increased bulk density and reduced porosity and hydraulic conductivity. Soil bulk density increased by 27-53% at all depths in BTs and STs compared to UAs, while porosity decreased by 23-49%. On average, saturated hydraulic conductivity at depths of 0-20 cm decreased from 337.5 mm h-1 to 30.5 mm h-1 in the most compacted sections of BTs and STs. Skid trails, which are characterized by trail construction and frequent vehicle movement, also caused greater impacts on soil compaction than BTs. This study provides useful insights to aid forest consultants and field managers in planning more environmentally sound mechanized logging operations.

Soil acidification of the soil profile across Chengdu Plain of China from the 1980s to 2010s.

Soil acidification is a major environmental issue associated with intensive agricultural land use. Rapid urbanization has inevitably caused great changes in agricultural land use around urban areas. However, the effects of agricultural land-use change and soil parent material on the pH dynamics of the whole soil profile remain poorly understood. Based on a paired soil resampling campaign in the 1980s and 2010s, this study evaluated the effects of agricultural land-use change and parent materials on the pH dynamics of the soil profile across the Chengdu Plain of China. The results showed that soil pH significantly decreased by 1.20, 0.72, 0.66 and 0.68 units at the 0-20, 20-40, 40-60 and 60-100 cm soil depths, respectively. Conversions of traditional rice-wheat/rapeseed rotations to rice-vegetable rotations and afforested land significantly increased the magnitude of pH decline at the 0-60 cm soil depth. Soils formed from Q4 grey-brown alluvium and Q4 grey alluvium, which had a lower soil bulk density (BD) and higher sand content, showed a much higher magnitude of pH decline than soils formed from Q3 (Quaternary Pleistocene) old alluvium, and significant acidification of deep soils only occurred in soils formed from Q4 (Quaternary Holocene) grey-brown alluvium and Q4 grey alluvium. These results suggested that agricultural land-use change aggravated acidification in the soil profile and the soil acidification degrees were parent material-dependent; in particular, significant acidification of deep soils was more inclined to occur in soils with lower soil BD and higher sand content due to their effects on the downward movement of acids and the penetration resistance of plant roots. More attention should be given to minimizing or preventing acidification of both topsoil and deep soils aggravated by agricultural land-use change across urban agricultural areas.

[Effects of straw returning combined with nitrogen fertilizer on spring maize yield and soil physicochemical properties under drip irrigation condition in Yellow River pumping irrigation area, Ningxia, China]. / æ»´çŒæ¡ä»¶ä¸‹ç§¸ç§†è¿˜ç”°é æ–½æ°®è‚¥å¯¹å®å¤æ‰¬é»„çŒåŒºæ˜¥çŽ‰ç±³äº§é‡å’ŒåœŸå£¤ç†åŒ–æ€§è´¨çš„å½±å“.

Soil compaction and nutrient deficiency are common problems in Ningxia Yellow River pumping irrigation area, which adversely affect crop yield. A two-year (2017-2018) field experiment of straw returning combined with nitrogen fertilizer were designed. Four nitrogen application levels (pure N with 0, 150, 300 and 450 kg·hm-2) were set under the condition of full smashing of maize straw (12000 kg·hm-2) returning, with the conventional nitrogen application (pure N with 225 kg·hm-2) without straw returning as the control (CK) to investigate the effects of straw returning combined with different amounts of nitrogen fertilizer on soil physical and chemical properties and maize yield under drip irrigation condition. The results showed that, compared with no-straw returning treatment, the treatments of straw returning combined nitrogen fertilizer with 300 and 450 kg·hm-2 reduced soil bulk density (0-20 cm) by 3.3% and 5.4%, but increased soil porosity by 3.7% and 7.1%, respectively. Straw returning combined with nitrogen with 300 kg·hm-2 and 450 kg·hm-2 was the best treatment which increased soil organic matter content, available K, P, alkaline N and total N in 0-40 cm soil layer. Compared with the non-returning treatment, straw returning combined with nitrogen fertilizer 300 kg·hm-2 significantly increased soil water storage by 13.6% and 22.1%, increased maize yield by 31.1% and 46.0 % in 2017 and 2018, respectively. The analysis of yield components showed that the high maize yield was achieved mainly by increasing grain number and the100-grain weight. Curve fitting showed that the optimum amount of nitrogen fertilizer was 260 kg·hm-2. Our results provide important basis for soil fertility improvement and sustainable production.

[Impact of Biochar on Soil Bulk Density and Aggregates of Lou Soil].

The effect of biochar on the bulk density and aggregate stability of Lou soil was evaluated and compared after biochar was applied for 2 years and 5 years through a field-positioning experiment. Five biochar amounts were applied in this study, as follows:0 t·hm-2 (B0), 20 t·hm-2 (B20), 40 t·hm-2 (B40), 60 t·hm-2 (B60), and 80 t·hm-2 (B80). The biochar was produced by pyrolysis of stems and branches from fruit trees at the temperature of 450℃ with limited oxygen apply. At the beginning of the study, biochar was mixed thoroughly with the surface soil (0-20 cm). After 5 years, the soil bulk density and aggregate stability of 0-30 cm soil layers (0-10, 10-20, and 20-30 cm) were measured and compared with the results obtained after 2 years with the purpose of observing the long-term and persist effects of biochar application. The results showed that:① compared with the results after 2 years of application, the effect of biochar on the aggregates at depths of 0-10 cm and 10-20 cm after 5 years were less distinct, and the effect on soil aggregates at depths of 20-30 cm was significantly enhanced; ② compared with the 2 year application, the aggregate stability and the content of the>0.25 mm aggregate size fraction were significantly increased at 0-10 cm depths after 5 years of biochar application at a rate of 40 t·hm-2, while bulk density was significantly decreased; at 10-20 cm and 20-30 cm soil depths, the stability of aggregates and the content of the>0.25 mm aggregate size fraction was significantly increased, while the bulk density was significantly decreased after 5 years of biochar application at a rate of 60-80 t·hm-2;③ when the biochar application rate was 60 t·hm-2, the increase in soil organic carbon was the highest after 5 years. After biochar was applied for 5 years, its effect was more significant lower in the soil profile; the soil bulk density was significantly reduced, and aggregate stability and the content of>0.25 mm aggregates were significantly increased at depths of 20-30 cm. Based on a comprehensive evaluation of the improvement effects and economic benefits, the most suitable biochar application rate was found to be 40-60 t·hm-2. It was further concluded that the effect of biochar on soil aggregates was gradual and sustainable.

Soil compaction and the architectural plasticity of root systems.

Soil compaction is a serious global problem, and is a major cause of inadequate rooting and poor yield in crops around the world. Root system architecture (RSA) describes the spatial arrangement of root components within the soil and determines the plant's exploration of the soil. Soil strength restricts root growth and may slow down root system development. RSA plasticity may have an adaptive value, providing environmental tolerance to soil compaction. However, it is challenging to distinguish developmental retardation (apparent plasticity) or responses to severe stress from those root architectural changes that may provide an actual environmental tolerance (adaptive plasticity). In this review, we outline the consequences of soil compaction on the rooting environment and extensively review the various root responses reported in the literature. Finally, we discuss which responses enhance root exploration capabilities in tolerant genotypes, and to what extent these responses might be useful for breeding. We conclude that RSA plasticity in response to soil compaction is complex and can be targeted in breeding to increase the performance of crops under specific agronomical conditions.

Effects of polyester microfibers on soil physical properties: Perception from a field and a pot experiment.

Understanding soil physical properties is essential for soil quality management and sustainable land use. With the growing accumulation of microplastics in soils, a better understanding of the impact of microplastics on soil physical properties is crucial to conserve and manage soil quality. This study explored the effects of polyester microfiber (PMF) concentrations (0, 0.1% and 0.3%) on bulk density, porosity, aggregation and hydraulic conductivity of a clayey soil from a field experiment (1 year) and a pot experiment (6 wet-dry cycles). Polyester microfibers significantly increased the volume of >30 µm pores and reduced the volume of <30 µm pores compared to the control treatment. However, there were no detectable changes in the soil bulk density and saturated hydraulic conductivity between the PMF treatments and the control treatment. Interestingly, we observed that polyester microfibers significantly increased the contents of water stable large macroaggregates (>2 mm) in the 0.3% PMF (44%) and 0.1% PMF (39%) treatments compared to the control treatment (31%) in the pot experiment, but this was not true in the field experiment. The efficient interaction between polyester microfibers and fine soil particles and the frequent wet-dry cycles enhanced the formation and stability of macro-aggregates induced by polyester microfibers in the pot experiment. Overall, our results provide valuable evidence for microplastic influences on soil physical properties. Because microplastics are long-term anthropogenic contaminants, it is necessary to further study the impacts of microplastics on soil quality for terrestrial ecosystem sustainability.

[Comparison of soil organic matter, bulk density and clay content in small watersheds under different ecological managements of Loess Plateau, China]. / 黄土高原不同生态治理小流域土壤有机质、容重及黏粒含量的对比.

To explore the effects of small watersheds with different ecological managements on soil properties, the spatial differences of soil organic matter (SOM), bulk density (BD), and clay content (CC) in the four facets, including slope aspect, slope position, zone, and soil layer, were analyzed between Yangjiagou (YJG, artificial Robinia pseudoacacia forest watershed) and Dongzhuanggou (DZG, closed grassland watershed). The results showed that SOM, BD and CC were 12.78 g·kg-1, 1.24 g·cm-3, 19.2% for YJG and 11.13 g·kg-1, 1.21 g·cm-3, 18.2% for DZG, respectively. The values for YJG were slightly higher than those for DZG, but the difference was insignificant. All indices in the east slope were bigger than those in the west slope. Across different slope positions, the variation of BD was small, SOM and CC showed increasing trends from top to bottom. BD and CC declined downward the watershed, whereas SOM changed in an opposite trend. From the soil surface down to 60 cm soil depth, BD and CC increased and SOM decreased. The spatial sensitivity followed CC > SOM > BD, and the effects of the spatial factors can be ordered as soil layer > zone > slope aspect > slope position. There were significant differences in CC of the upper reaches, BD and CC of the middle reaches between the two basins. The sensitivity of each index to slope position, zone and soil layer in YJG was lower than that in DZG.

Variations of organic carbon storage in vegetation-soil systems during vegetation degradation in the Gahai wetland, China.

Qinghai-Tibet Plateau wetland, an important component of terrestrial ecosystem, plays an essential role in global carbon cycling. To understand the variation of organic carbon storage in vegetation-soil system during vegetation degradation in the Gahai wetland we examined aboveground litter, root biomass and soil organic carbon content in different degradation stages (CK: no degradation, SD: light degradation, MD: moderate degradation, HD: heavy degradation). The results showed that except for HD, carbon storage of aboveground biomass was 99.58-205.64 g·m-2 and that of root biomass (0-40 cm) was 56.96-754.37 g·m-2. The carbon stocks of aboveground and roots decreased significantly with degradation. Soil bulk density increased first and then decreased with degradation. Soil bulk density of each layer under degraded wetland was greater than that of the control. The carbon storage of litter was 17.29-35.69 g·m-2, which was significantly higher in CK than in MD and HD. The carbon storage in the soil (0-40 cm) was 7265.06-9604.30 g·m-2, with the order of MD＞CK＞SD＞HD. The carbon storage in CK and MD as significantly higher than that in SD and HD. The total carbon storage in the vegetation-soil system was 7265.06-10389.94 g·m-2 under different degradation stages. The largest was in CK, followed by MD, SD, and HD. Organic carbon was mostly stored in soil, which accounted for over 90% of the storage. Moderate interference might benefit carbon sequestration of the alpine wetland ecosystems.

Effects of conservational tillage on water characteristics in dryland farm of central Gansu, Northwest China.

Productivity is low and unstable in dryland farms of central Gansu, Northwest China. Conservational tillage is an important way for the sustainable development of agriculture. The effects of different tillage measures on soil moisture infiltration, evaporation, crop yield and water use efficiency (WUE) were investigated in this study based on a long-term experiment since 2001 in Longzhong. There were six treatments, i.e. conventional tillage with no straw (T), no-till with straw cover (NTS), no-till with no straw cover (NT), conventional tillage with straw incorporated (TS), conventional tillage with plastic mulch (TP), and no-till with plastic mulch (NTP), with annual rotation of spring wheat and pea. The results showed that compared with T, soil bulk density of NTS decreased and total porosity of soil increased significantly in wheat and pea land. Compared with conventional tillage, conservation tillage reduced soil infiltration rate in 0-5 cm in the pea field by 56.2%. Conservational tillage siginificantly increased soil saturated water conductivity in both wheat and pea lands. Compared with T, the saturated water conductivity in NTS was significantly increased by 52.8%-107.1%. Conservational tillage siginificantly reduced soil evaporation during growing season. Compared with T, the evapotranspiration of NTP, TP and NTS was significantly reduced by 14.4%-50.8%. The soil evaporation after rain was also decreased. Conservational tillage improved crop yield and water use efficiency by 9.5%-62.8% and 0.4%-50.9%, respectively. Therefore, conservational tillage could increase water use efficiency and crop yield in dryland farming area of central Gansu, Northwest China.

[Effects of soil bulk density on growth, physiology and quality of Glechoma longituba].

Through the determination of the growth, physiological and active components of Glechoma longituba, the effect of soil bulk density on growth and quality of G. longituba was explored. Through pot experiment, six different bulk density treatments were set for 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 g·cm⁻³ , the growth index, physiological index and the content of active components were determined. The results showed that the growth indexes and biomass of G. longituba firstly increased and then decreased with the increase of soil bulk density. The dry weight of G. longituba achieved the maximum 5.70 g in the treatment of 1.0 g·cm⁻³ . The photosynthetic pigments, soluble sugars and free amino acids firstly increased and then decreased with the increase of soil bulk density. The suitable soil bulk density was beneficial to the accumulation of photosynthetic pigment, soluble protein and free amino acid synthesis. The content of malondialdehyde increased gradually with the increase of soil bulk density. The contents of ethanol-soluble extractives of G. longituba were greater than 25%, meeting its quality criterionin Chinese Pharmacopoeia 2015, achieved the maximum of 40.66% in the treatment of 1.0 g·cm⁻³ . The total flavonoids content of G. longituba increased gradually with the increase of soil bulk density, triterpenic acid and phenolic acids decreased gradually with the increase of soil bulk density. Soil bulk density has a significant effect on the growth and quality of G. longituba, and it is conducive to the growth and its medicinal quality at the soil bulk density of 1.0 g·cm⁻³.

Experimental Determination of TDR Calibration Relationship for Pyroclastic Ashes of Campania (Italy).

Time domain reflectometry (TDR) is one of the most widely used techniques for indirect determination of soil volumetric water content (θ). TDR measures the relative dielectric constant (εr) which, in a three-phase system like the soil, depends on water, air, and solid matrix dielectric constants. Since dielectric constant of water is much larger than the other two, εr of bulk soil mainly depends on water content. In many cases, the application of TDR requires a specific calibration of the relationship θ(εr) to get quantitatively accurate estimates of soil water content. In fact, the relationship θ(εr) is influenced by various soil properties, such as clay content, organic matter content, bulk density, and aggregation. Numerous studies have shown that pyroclastic soils often exhibit a peculiar dielectric behavior. In Campania (Southern Italy) wide mountainous areas are covered by layered pyroclastic deposits of ashes (loamy sands) and pumices (sandy gravels), often involved in the triggering of landslides induced by rainwater infiltration. Reliable field measurements of water content of such soils are therefore important for the assessment of landslide risk. Hence, in this paper, the θ(εr) relationship has been experimentally determined on samples of typical pyroclastic soil of Campania, collected around Sarno, reconstituted with different porosities. The aim of the study is to identify specific calibration relationships for such soils based not only on empirical approaches. In this respect, a three-phase dielectric mixing model with a variable exponent is introduced, and the variable value of the exponent is related to the different dielectric properties of bond and free water within the soil pores.

Effects of soil bulk density on growth, physiology and quality of Glechoma longituba / 中国中药杂志

Through the determination of the growth, physiological and active components of Glechoma longituba, the effect of soil bulk density on growth and quality of G. longituba was explored. Through pot experiment, six different bulk density treatments were set for 0.8, 0.9, 1.0, 1.1, 1.2, 1.3 g·cm⁻³ , the growth index, physiological index and the content of active components were determined. The results showed that the growth indexes and biomass of G. longituba firstly increased and then decreased with the increase of soil bulk density. The dry weight of G. longituba achieved the maximum 5.70 g in the treatment of 1.0 g·cm⁻³ . The photosynthetic pigments, soluble sugars and free amino acids firstly increased and then decreased with the increase of soil bulk density. The suitable soil bulk density was beneficial to the accumulation of photosynthetic pigment, soluble protein and free amino acid synthesis. The content of malondialdehyde increased gradually with the increase of soil bulk density. The contents of ethanol-soluble extractives of G. longituba were greater than 25%, meeting its quality criterionin Chinese Pharmacopoeia 2015, achieved the maximum of 40.66% in the treatment of 1.0 g·cm⁻³ . The total flavonoids content of G. longituba increased gradually with the increase of soil bulk density, triterpenic acid and phenolic acids decreased gradually with the increase of soil bulk density. Soil bulk density has a significant effect on the growth and quality of G. longituba, and it is conducive to the growth and its medicinal quality at the soil bulk density of 1.0 g·cm⁻³.

A multi-year study of tillage and amendment effects on compacted soils.

Constructing roads and buildings often involves removal of topsoil, grading, and traffic from heavy machinery. The result is exposed, compacted subsoil with low infiltration rate (IR), which hinders post-construction vegetation establishment and generates significant runoff, similar to impervious surfaces. Our goal was to assess tillage and adding amendments for improving density and maintaining perviousness of subsoils compacted during construction. The effects of tillage with and without amendments on (1) soil compaction, (2) IR, and (3) vegetative growth at five sites in North Carolina, USA were evaluated over a period of up to 32 months. The sites, representing a range of soil conditions, were located at three geographic regions; one in the Sandhills (located in Coastal Plain), one in the mountains, and three in the Piedmont. Amendments varied by site and included: (1) compost, (2) cross-linked polyacrylamide (xPAM), and (3) gypsum. Bulk density (BD) and soil penetration resistance (PR) tests were used to characterize soil physical condition. The IR was measured using a Cornell Sprinkle Infiltrometer. Vegetative growth was evaluated by measuring shoot mass and vegetative cover at all sites and root density at the Piedmont sites. Tillage decreased BD and PR compared to the compacted soil at four out of five sites for observations ranging from 24 to 32 months. Compost was applied to four sites prior to tillage and reduced BD in two of them compared to tillage alone. The IR in the tilled plots was maintained at about 3-10 times that of the compacted soil among the five sites over the monitoring periods. Adding amendments did not increase IR relative to tillage alone except at one Piedmont site, where compost and xPAM increased IR at 12 months and compost at 24 months after site establishment. Vegetative responses to tillage and amendments were inconsistent across sites. Results suggest that tillage is a viable option to reduce bulk density and increase infiltration for areas with compacted soils where vegetation is to be established, and that the effect is maintained for at least several years.