Gravimetric Soil Water Content Research Articles

Microscopic deformation and fragmentation energy consumption characteristics of soils with various moisture contents using discrete element method

Increased soil moisture content commonly leads to higher resistance and energy consumption during agricultural operations. However, the impact of moisture content on soil microscopic deformation and fragmentation energy consumption characteristics remains unclear. In this study, discrete element models of sandy clay loam with different gravimetric water contents (15.0%, 18.8%, 21.6%, 24.1%, and 27.3%) were constructed for simulation experiments using coupled contact method (Hertz-Mindlin with bonding and Hertz-Mindlin with JKR). The degree of soil fragmentation and the rate of crack propagation were investigated. The results indicated that at fixed gravimetric water content, fissure rate exhibited a pattern of slow increase, rapid increase, and eventual stabilization with increasing compression displacement, while the fissure transfer coefficient showed a pattern of first increase and then decrease. At a fixed compression displacement, the increase in moisture content led to a decrease in both fissure rate and fissure transfer coefficient. The analysis of soil stress-strain characteristics and energy dissipation patterns found that soil with a gravimetric water content of 27.3% (close to soil liquid limit) exhibited no compression yield point; at a soil gravimetric water content of 15.0%, the minimum crushing energy (Udmin) was achieved (1.32 J), with a maximum elastic strain energy (Uemax) of 1.83 J. Similarly, at a soil gravimetric water content of 24.1%, the minimum crushing energy (Udmin) was reached (2.17 J), with a maximum elastic strain energy (Uemax) of 2.25 J. The comparison between actual and simulated results revealed low relative errors (<6%) in Udmin for all the above soil gravimetric water contents, suggesting the feasibility of our coupled discrete element model for assessing soil crushing energy consumption. This study revealed microscopic deformation and instability fragmentation mechanisms of soils with various moisture contents under vertical axial loads. Our findings provide novel method and strategy for developing the high-efficiency low-consumption soil fragmentation model.

Interseeded cover crops in wide‐row corn: An opportunity for northern cropping systems

AbstractCover crops are an effective way to reduce soil erosion and promote soil health. However, in North Dakota and other northern climates where corn (Zea mays L.) is an important commodity crop, killing frosts generally occur before harvest, leaving little opportunity for cover crop planting. By interseeding cover crops into corn during the growing season, the cover crops are given a longer period to establish. The purpose of this study was to identify the impact cover crops interseeded into wide‐row (60‐inch) corn have on soil water content and corn productivity. Two experimental sites were established in 2020 near Leonard and Rutland, ND. Both sites were organized into randomized complete block designs, with three cover crop treatments in Leonard (n = 9) and four cover crop treatments in Rutland (n = 16). Cover crops were no‐till drilled into the corn at the V4 growth stage. The cover crop treatments were diverse mixes developed to either provide pollinator habitat, overwinter, or winter‐kill. Throughout the growing season, soil gravimetric water content and cover crop biomass was monitored. At the end of the growing season, dry cover crop biomass ranged from 189 to 1445 lb ac−1. The presence and type of interseeded cover crops did not have a statistically significant effect on soil water content or corn yield. It is suspected the above average precipitation during the month of July led to adequate amounts of soil water for the entirety of the cover crop growing season, limiting the difference between treatments.

Microbial resistance and resilience to drought and rewetting modulate soil N2O emissions with different fertilizers

Future climate models indicate an enhanced severity of regional drought and frequent rewetting events, which may cause cascading impacts on soil nitrogen cycle and nitrous oxide (N2O) emissions, but the underlying microbial mechanism remains largely unknown. Here we report an incubation study that examined the impacts of soil moisture status and nitrification inhibitor (DCD) on the N2O-producers and N2O-reducers following the application of urea and composted swine manure in an acid soil. The soil moisture treatments included 100 % water-holding capacity (WHC) (wetting, 35.3 % gravimetric soil water content), 40 % WHC (drought, 7 % gravimetric soil water content), and 40 % to 100 % WHC (rewetting). The results showed that N2O emissions were significantly decreased under drought conditions and were significantly increased after rewetting. The resistance of ammonia-oxidizing bacteria and nosZII, which was inhibited by urea or manure application, modulated N2O emissions under drought conditions. The resilience of the functional guilds modulated their dominant role in N2O emissions with rewetting. Ammonia-oxidizing bacteria, nirS-type denitrifying bacteria and nosZI showed significant resilience in response to rewetting. Significant negative relationships were observed between N2O emissions and nosZII clade under wetting condition and between N2O emissions and nosZI clade after rewetting. Our results highlighted the importance of microbial resistance and resilience in modulating N2O emissions, which help to better understand the dominant way of N2O emissions, and consequently make efficient mitigation strategies under the global climate change.

Mid-season drain severity impacts on rice yields, greenhouse gas emissions and heavy metal uptake in grain: evidence from on-farm studies

Context or ProblemFlooded rice systems produce an important staple crop but are a source of methane (CH4) and arsenic (As) exposure. Introducing non-continuous flooding events can decrease seasonal CH4 emissions and grain As concentration. A single mid-season drain (MD: a 7-to 10-day soil drying period during the mid-season) is easier for farmers to manage than multiple drain events (e.g. alternate wetting and drying). Previous research has shown that a MD can accomplish these goals without yield reduction. However, depending on soils and precipitation, the soil drying severity during a MD can vary substantially. Objective or Research QuestionThe objectives of this study were to compare a MD to the farmer practice under on-farm conditions with respect to yields, greenhouse gas (GHG) emissions and As and cadmium (Cd – which can increase with non-continuous flooding). Second, to quantify the relationship between soil drying severity during the MD and the reduction in CH4 emissions and grain As. MethodsA three-year study with seven on-farm trials was implemented. Each trial had two treatments: a MD and the farmer practice. Grain yields, GHG emissions, and grain As and Cd concentrations were quantified for each treatment. ResultsGrain yields were similar between treatments. The MD decreased seasonal CH4 emissions by 20–77% (average of 52%), with the magnitude of reduction being related to soil-drying severity during the MD. Combining previous on-station data with this on-farm data, indicates that for every 1% reduction in soil gravimetric water content (GWC), seasonal CH4 emissions were reduced by 2.5% (r2 = 0.47). With MD, N2O emissions increased (average = 0.25 kg N2O-N ha−1), but accounted for only 3% of the global warming potential. The MD decreased grain As concentration (by 20% on average, but not related to soil drying severity), and there was no effect on grain Cd concentrations. ConclusionsGiven these results, an MD has similar GHG mitigation potential to other non-continuous flooding practices that require more drain periods and may be more difficult to implement. These results indicate that a MD is a viable on-farm management practice for GHG mitigation and reducing grain As concentration with limited risk of yield reduction. Implications or SignificanceThis is the first research that has documented the relationship between soil drying severity and reduction in CH4 emissions across soils. This relationship is a potentially useful tool for on-farm monitoring, but will need to be developed further across more locations.

Bacterial denitrification drives elevated N2O emissions in arid southern California drylands.

Soils are the largest source of atmospheric nitrous oxide (N2O), a powerful greenhouse gas. Dry soils rarely harbor anoxic conditions to favor denitrification, the predominant N2O-producing process, yet, among the largest N2O emissions have been measured after wetting summer-dry desert soils, raising the question: Can denitrifiers endure extreme drought and produce N2O immediately after rainfall? Using isotopic and molecular approaches in a California desert, we found that denitrifiers produced N2O within 15 minutes of wetting dry soils (site preference = 12.8 ± 3.92 per mil, δ15Nbulk = 18.6 ± 11.1 per mil). Consistent with this finding, we detected nitrate-reducing transcripts in dry soils and found that inhibiting microbial activity decreased N2O emissions by 59%. Our results suggest that despite extreme environmental conditions-months without precipitation, soil temperatures of ≥40°C, and gravimetric soil water content of <1%-bacterial denitrifiers can account for most of the N2O emitted when dry soils are wetted.

The Effects of Hedgerows Shading on Soil Temperature and Gravimetric Soil Water Content

This study sets out to examine the effects of hedgerow shading on soil physical properties, specifically soil gravimetric water content and soil temperature. Analyses of both soil parameters were conducted at two locations with different shade proportion. The aim of the study was to address the links between hedgerow shading and basic physical soil properties which could be significant both for agricultural production and for ecological processes in agroecosystems. At both locations, soil samples and measurements were taken at different distances from hedgerow and in different time intervals. Diurnal shading variation at certain distances from the hedgerow on Location 1 and 2 was calculated with the software toll for Arboriculturists. At Location 1 shading is consistently high throughout the year, ranging from 76 to 100%. In contrast, shading at Location 2 varies from 1 to 25%. The results reveal that hedgerows at Location 1, do not have a statistically significant impact on gravimetric soil water content and soil temperature across the entire plot surface. Additionally, the percentage of shading is only marginally decreases with distance. Conversely, Location 2 exhibits an increase in soil temperature and a slight but (non-significant) decrease in soil gravimetric watercontent as the distance from the hedgerow increases., The total mean shading at Location 2 is considerably lower compared to Location 1, and the shading percentage declines more at the distance from the hedgerow increases. Overall, lower soil temperatures and higher gravimetric soil water content where observed at the more shaded Location 1. The research outcomes are helpful in agricultural production planning as well as in the evaluation of hedgerows for the needs of agricultural policy.

Link between the aboveground and belowground biomass allocation with growing of Tamarix sp. seedlings in the hinterland of Taklimakan Desert, China.

The morphological characteristics and biomass allocation can reflect plant adaptive strategies to the environment. Tamarix sp. is an excellent shrub species used for windbreaks and fixing sand in the desert of northwest China. The successful establishment of Tamarix sp. seedlings and their growth into mature individuals require their adaptation to various environmental conditions, which is the key to naturally regenerating the Tamarix population. To clarify the root morphological characteristics, leaf structural characters, and biomass allocation of Tamarix sp. seedlings in response to drought conditions, we took the Tamarix sp. seedlings at the Daryaboyi oasis in the hinterland of Taklimakan Desert as the object of study, analyzed rooting depth, root dry weight (RDW), specific root length (SRL), root surface area (RA), specific root area (SRA), leaf area (LA), specific leaf area (SLA) and root: shoot ratio (R:S ratio). The gravimetric soil water content varied from 5.80% to 25.84% in this study area. The taproots of Tamarix sp seedlings with small basal stem diameters were shallower and had few lateral root branches and Tamarix sp. seedlings with large basal stem diameters had more obvious taproots and lateral roots. With the growth of Tamarix sp. seedlings, the taproot deepened, and the values ranged from 4.5 cm to 108.0 cm; the SRL, SRA, and SLA decreased, and the ranges of the values were 28.92-478.79 cm·g-1, 1.07-458.50 cm2·g-1, and 24.48-50.7 cm2·g-1; the RDW, RA, and LA increased, the ranges of the values were 0.16-21.34 g, 3.42-328.04 cm2, and 2.41-694.45 cm2; the more biomass was allocated to the aboveground parts, and the mean R: S ratio was 0.76. In better soil water conditions, the root growth rate decreased as Tamarix sp. seedlings grew, and more biomass was allocated to the aboveground. This further showed that stable surface water is highly significant to the biomass allocation strategy of Tamarix sp. seedlings.

Estimating soil water and salt contents from field measurements with time domain reflectometry using machine learning algorithms

Soil water and salt contents are key soil physical parameters that play a crucial role in soil-related hydrological, ecological, environmental, and agricultural processes. Time domain reflectometry (TDR) is commonly used to measure in-situ soil water and salt contents, and provide possible solutions to quickly obtain soil bulk density (BD). However, the measurement accuracy is greatly influenced by the interaction of soil water and salt contents on the measured soil dielectric constant and electrical conductivity, especially for salinized soils. To accurately estimate the soil gravimetric (GWC) and volumetric (VWC) water contents, soil salt content (TS), and BD based on the TDR measurements, we designed different model input schemes to quantify the effect of different soil factors, and applied eight machine learning algorithms to map the non-linear relationship between model inputs and each target soil property. Results of a case study in Hetao Irrigation District in Northwest China indicated that soil particle-size fractions (psfs) are important inputs to predict all the above soil properties. Furthermore, BD mainly contributes to the prediction of soil GWC, and soil surface temperature (T) is effective in improving the GWC and TS estimations. Among eight machine learning algorithms used, extreme gradient boosting (XGB) and gradient boosting regression tree (GBRT) showed good robustness and strong learning capacity. It is recommended to apply XGB to precisely estimate GWC and BD, which resulted in the coefficients of determination (R2) of 0.80 and 0.69, respectively. On the other hand, GBRT precisely estimated the VWC and TS with R2 of 0.71 and 0.84, respectively. The evaluation of spatial distribution characteristic indicated that it is reliable to obtain the spatial distributions of the above soil properties from the TDR measurements based on the recommended model input schemes and machine learning algorithms.

Responses of Trollius chinensis to drought stress and rehydration: From photosynthetic physiology to gene expression

Drought stress occurs more frequently in recent years due to the global climate change. Widely distributed in northern China, Mongolia, and Russia, Trollius chinensis Bunge has high medicinal and ornamental values and is often exposed to drought stress, while the mechanism underlying its drought response is still unclear. In this study, we applied 74–76% (control, CK), 49–51% (mild drought), 34–36% (moderate drought), and 19–21% (severe drought, SD) of the soil gravimetric water content to T. chinensis, and measured leaf physiological characteristics on the 0, 5th, 10th, 15th day after the soil reaching the set drought severities, and on the 10th day after rehydration. The results showed that many physiological parameters, such as chlorophyll contents, Fv/Fm, ΦPSⅡ, Pn, and gs decreased with the deepening of severity and duration of drought stress and recovered to some extent after rehydration. On the 10th day of drought stress, leaves in SD and CK were selected for RNA-Seq, and 1649 differentially expressed genes (DEGs) were found, including 548 up-regulated and 1101 down-regulated DEGs. Gene Ontology enrichment found that the DEGs were mainly enriched in catalytic activity and thylakoid. Koyto Encyclopedia of Genes and Genomes enrichment found that DEGs were enriched in some metabolic pathways such as carbon fixation and photosynthesis. Among them, the differential expression of genes related to photosynthesis process, ABA biosynthesis and signaling pathway, such as NCED, SnRK2, PsaD, PsbQ, and PetE, might explain why T. chinensis could tolerate and recover from as long as 15 days of severe drought conditions.

Vineyard floor management intensity impacts soil health indicators and plant diversity across South Australian viticultural landscapes

Throughout the last thirty years, major shifts in vineyard floor management have been observed. Challenges initially posed by intensive tillage included high rates of soil erosion and the degeneration of soil structure and soil organic matter, which lead viticulturists to depend more heavily on herbicide use as an effective weed control strategy. However, an increase in herbicide persistence and toxicity in water, soils, and grapevines, increasing resistance of common weeds; and pressure from consumers and regulators to reduce their use is directing a shift towards an overall reduction in herbicide usage. This has led to more frequent tillage to manage vegetation in vineyards, while in some instances, cultural practices including slashing and animal grazing are used solely or in conjunction. However, little is known about the holistic effects of these varying practices on vineyard soils and biodiversity across landscapes in Australia. Thus, to comparatively assess the environmental impacts of different floor management practices, soil health indicators and plant dynamics were seasonally measured in the mid- and under-vine rows at twenty-four vineyard sites and four native sites in the Barossa Valley, Eden Valley, and McLaren Vale, all located in South Australia, where different intensities of floor management were implemented. Vineyard sites were categorised based on the frequency of herbicide and/or tillage passes particularly in the under-vine area into Low (no annual management passes), Medium (one annual management pass), and High (two to four annual management passes) intensity groups. Findings revealed similarities in the vineyard mid-rows across the management intensities, yet the under-vine rows displayed many differences; in particular, there were more plant species, higher plant coverage, and greater plant biomass in the Low management intensity group. Furthermore, as management intensity decreased, the relative richness of ruderal plant species also decreased, giving way to a plant community mainly comprised of slow-growing, perennial Poaceae and Fabaceae species in the Low-intensity management group. These differences in plant dynamics drove a suite of soil responses including faster water infiltration, higher soil ammonium-N and total nitrogen, and a tendency of higher soil gravimetric water content at the time of sampling. These results suggest that after an initial period of establishing these more extensive vineyard floor management practices, low levels of soil disturbance in the under-vine rows may contribute positively to improving natural ecosystem synergy and functionality between soil and plants. Therefore, our findings lend insights into how the varying intensity of floor management practices, rather than differing management ideologies per se, across a viticultural landscape can be intrinsic supporters of agroecosystem resilience under South Australian conditions.

Mixed-species plantations alleviate deep soil water depletion and facilitate hydrological niche partitioning compared to pure plantations

Understanding the effects of different silvicultural patterns on soil water reservoirs and how silvicultural species adjust their water use strategies and plant function traits is critical to guiding future silvicultural activities toward the sustainable development of plantations. We continuously monitored soil gravimetric water content (SWC), soil and plant isotopes, leaf water potentials at predawn and midday (Ψpd and Ψmd), and plant morphological traits in pure Populus simonii tree plantations (PPs), pure Amorpha fruticose shrub plantations (PAf), and mixed P. simonii-A. fruticose plantations (Msf) during the 2021 growing season. The study showed that the average SWC of the deep layer (80–200 cm) was Msf > PAf > PPs. P. simonii in the Msf increased the water use proportion of the deep layer compared to that in the PPs, especially during the vigorous growth period of June-July, and shifted the major water use from shallow (0–40 cm) to deep layers on average. A. fruticose mainly used shallow soil water during the growing season. The leaf-level water use efficiency of the same species did not change in the Msf compared to that in the PPs or PAf. Based on the slope (σ) of the linear equation of Ψpd-Ψmd, P. simonii and A. fruticose exhibited isohydric (σ < 1) and an-isohydric (σ > 1) behavior under varying soil water conditions, respectively. The wood density was higher and specific leaf area (SLA) was lower in the PPs than in the Msf for P. simonii, while the ratio of stem sapwood area to leaf area was higher and SLA was lower in the PAf than in the Msf for A. fruticose. These findings reflected that mixed tree-shrub plantations alleviate deep soil water depletion compared to pure plantations, facilitate hydrological niche segmentation of co-occurring species, and reduce carbon investment in xylem and leaves to resist water stress and possibly devote more resources to growth.

Impacts of alpine meadow degradation on the soil moisture and hydrological processes in the three river source region on the Qinghai Tibetan plateau

AbstractTo explore the effects of mattic epipedon (ME) on soil moisture and hydraulic properties in the alpine meadow of three‐river source region, the soil moisture, water infiltration, evapotranspiration, soil bulk density and soil water holding capacity of original vegetation (OV), light degradation (LD), moderate degradation (MD) and severe degradation (SD) was conducted in this study, respectively. The results showed that: (1) the alpine meadow degradation reduced the soil moisture in the shallow layer (0–10 cm) and had no significant effects on the soil moisture in the deep layer (20–30 cm). (2) The effects of alpine meadow degradation on infiltration was depend on the presence of ME or not, when the ME existed on the land surface (from OV treatment to MD treatment), the alpine meadow degradation had no significant effects on infiltration. Once the ME disappeared on the land surface (from MD treatment to SD treatment), the alpine meadow degradation mainly increased the infiltration. (3) With the aggravation of alpine meadow degradation, the daily evapotranspiration first decreased and then significantly increased when the gravimetric soil water content at 0–5 cm in SD treatment (GWC5) was exceeded 19.5%, the daily evapotranspiration gradually decreased when GWC5 ranged from 9.3% to 19.5%, and had no significant changes on the evapotranspiration when GWC5 was less than 9.3%. Considering the characteristics of precipitation in alpine meadow, it was concluded that the alpine meadow degradation accelerated the evapotranspiration during the plant‐growing season. (4) The effect of alpine meadow degradation on soil bulk density and saturated water capacity was concentrated at 0–10 cm. With the aggravation of alpine meadow degradation, the bulk density at 0–10 cm was first stable and then significantly increased and the saturated water capacity at 0–10 cm was first gradually increased and then significantly decreased. Our results suggested that the ME is vital for water conservation of alpine meadow and the protection of ME should be emphasized to promote the sustainable development of the ecosystem and the water supply of water towers in China.

宁夏河东沙区刺槐和丝绵木水分利用策略

PDF HTML阅读 XML下载 导出引用 引用提醒 宁夏河东沙区刺槐和丝绵木水分利用策略 DOI: 10.5846/stxb202202100330 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（31760236，42161013）；宁夏自然科学基金项目（2022AAC03094） Water use strategies of Robinia pseudoacacia and Euonymus bungeanus in the east sandy land of the Yellow River in Ningxia, China Author: Affiliation: Fund Project: The National Natural Science Foundation of China (31760236,42161013);The National Natural Science Foundation of Ningxia,China(2022AAC03094) 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:刺槐和丝绵木混交林是宁夏河东沙区防护林建设的主要模式，了解刺槐和丝绵木的水分利用策略，能为区域植被恢复和防护林林分结构调整提供科学依据。以宁夏河东沙区刺槐（Robinia pseudoacacia）和丝绵木（Euonymus bungeanus）混交林为研究对象，通过监测微气象、树干液流和土壤质量含水量，结合大气降水、土壤水、植物木质部水同位素组成，采用Granier及其校正公式，运用贝叶斯混合模型（MixSIAR）和相似性比例指数（PS）研究2个树种的蒸腾耗水、水分来源和水分利用关系。结果表明：刺槐和丝绵木的蒸腾耗水量在生长季中期较高，前期和后期较小，刺槐的蒸腾耗水量是丝绵木的1.55倍；影响刺槐蒸腾耗水的主要环境因子为饱和水汽压差、太阳辐射、0-40 cm土壤质量含水量和40-120 cm土壤质量含水量；影响丝绵木蒸腾耗水的主要环境因子为饱和水汽压差、太阳辐射、平均气温、0-40 cm土壤质量含水量和40-120 cm土壤质量含水量；蒸腾耗水较高时，刺槐主要吸收利用中层土壤水，丝绵木主要吸收利用浅层土壤水，蒸腾耗水较低时，刺槐主要吸收利用浅层土壤水，丝绵木主要吸收利用中层土壤水；在土壤水分含量较小的月份，刺槐和丝绵木主要通过水分利用空间上的差异来应对干旱，维持自身的蒸腾耗水；土壤水分含量较高的月份，刺槐和丝绵木的相似性比例指数最大，存在较强的水分竞争关系；浅层土壤水分含量较高可能反映了沙区植物根系对土壤水分再分配作用下植物在水分和养分需求之间的平衡。 Abstract:The mixed forest of Robinia pseudoacacia and Euonymus bungeanus is the typical shelterbelt construction mode in the east sandy land of the Yellow River in Ningxia, China. Research on the water use strategies of Robinia pseudoacacia and Euonymus bungeanus could provide scientific basis for restoration regional vegetation and stand structure optimization allocation of shelter forest. In this study, the sap flow of Robinia pseudoacacia and Euonymus bungeanus was monitored continuously to clarify the characteristics of water consumption by transpiration which calculated by Granier and its correction formula, as well as simultaneous records of micro-meteorological factors and gravimetric soil water content. Combined with stable hydrogen and oxygen isotope analysis of rainfall, soil water and plant xylem water, the water source and water use relationship among symbiotic trees were quantitatively analyzed by Bayesian mixture model (MixSIAR) and the proportional similarity index (PS). The results showed that the water consumption of Robinia pseudoacacia and Euonymus bungeanus were higher in the middle growing season, but lower in the early and late growing season. The water consumption of Robinia pseudoacacia was 1.55 times larger than Euonymus bungeanus. The main environmental factors affecting water consumption of Robinia pseudoacacia were vapour pressure deficit, solar radiation, 0-40 cm gravimetric soil water content and 40-120 cm gravimetric soil water content. The main environmental factors affecting water consumption of Euonymus bungeanus were vapour pressure deficit, solar radiation, average temperature, 0-40 cm gravimetric soil water content and 40-120 cm gravimetric soil water content. Robinia pseudoacacia mainly used the middle layer soil water and Euonymus bungeanus mainly used the shallow layer soil water in the season with high water consumption. While the shallow layer soil water and the middle layer soil water were ultilized by Robinia pseudoacacia and Euonymus bungeanus separately in the season with lower tree water consumption. In addition, Robinia pseudoacacia and Euonymus bungeanus was able to deal with drought and maintain their own water consumption mainly through the spatial difference of water use strategy under drought seasons. In the seasons when gravimetric soil water content was higher, the proportional similarity index (PS) of Robinia pseudoacacia and Euonymus bungeanus was the highest, and there was a strong water competition relationship. The higher of shallow layer gravimetric soil water content might reflect a trade-off between water and nutrient requirements of plants under the effect of soil water redistribution by plant roots in the sandy land. 参考文献 相似文献 引证文献

Trade-off between agronomical and energetical performances during barley sowing varying adjustable parameters in a tractor-tire-tool system

Soil compaction on seedbed, resulted from the traffic of a tractor-tire-tool system, alters soil structure and harmfully impacts crop production. Soil conservation during sowing operations and the optimization of energy consumption of tractor-tire-tool system, form the focus of the global agriculture policies and farmers under the energetical and the agroecological transitions. The present study aims to find a trade-off between the agronomical and the energetical performances, during a sowing operation of spring barley (Hordeum vulgare), varying adjustable parameters (controlled factors) in tractor-tire-tool system (i.e. tractor speed, axle load distribution, inflation pressure and soil working depth). The adjustable parameters have been chosen as to be adjustable by a regular tractor operator. The study was carried out on a silty loam soil (with an average soil gravimetric water content of 23.4%) located in Northern-France. The used tractor-tire-tool system consisted of a Four-Wheel Drive tractor (140 HP of power) equipped with 480/70 R28 front tires and 580/70 R38 rear tires, and hitched to an air seeder. Agronomical performance is evaluated via the conservation of soil physical properties, and via the success of the sowing operation. The energetical performance is evaluated via the optimization of energy consumption. The conservation of soil physical properties was assessed via soil bulk density (BD) and air permeability (ka). The success of the sowing operation was assessed via barley seedling, counting the emerged plants at one to two leaves stage, and crop yield. Energy consumption was assessed via the consumption of fuel per hectare. BD and ka were negatively correlated (ρ = −0.56 and p-value<0.001), but ka was significantly more influenced by the controlled factors and their combinations showing higher sensitivity of pore continuity to the structural disturbance than pore space. Crop seedling and yield were slightly influenced by the variation of the controlled factors and their combinations. All these agronomical indicators depended significantly on the combination between the four factors showed as single treatment. Fuel consumption decreased significantly with the equal load distribution and increased with tractor speed and soil working depth solely. Nonetheless, it showed higher dependence on the combinations between the factors. As a conclusion, soil physical properties could be conserved, better barley seedling and yield could be obtained, and energy consumption could be optimized by equally distributing the axle load, accelerating tractor at 14 km/h, working the soil at 10 cm of depth and inflating tires at 140 or 80 kPa of inflation pressure.

Flexible drought deciduousness in a neotropical understory herb.

PremiseAdaptive divergence across environmental gradients is a key driver of speciation. Precipitation seasonality gradients are common in the tropics, yet drought adaptation is nearly unexplored in neotropical understory herbs. Here, we examined two recently diverged neotropical spiral gingers, one adapted to seasonal drought and one reliant on perennial water, to uncover the basis of drought adaptation.MethodsWe combined ecophysiological trait measurements in the field and greenhouse with experimental and observational assessments of real‐time drought response to determine how Costus villosissimus (Costaceae) differs from C. allenii to achieve drought adaptation.ResultsWe found that drought‐adapted C. villosissimus has several characteristics indicating flexible dehydration avoidance via semi‐drought‐deciduousness and a fast economic strategy. Although the two species do not differ in water‐use efficiency, C. villosissimus has a more rapid growth rate, lower leaf mass per area, lower stem density, higher leaf nitrogen, and a strong trend of greater light‐saturated photosynthetic rates. These fast economic strategy traits align with both field‐based observations and experimental dry‐down results. During drought, C. villosissimus displays facultative drought‐deciduousness, losing lower leaves during the dry season and rapidly growing new leaves in the wet season.ConclusionsWe revealed a drought adaptation strategy that has not, to our knowledge, previously been documented in tropical herbs. This divergent drought adaptation evolved recently and is an important component of reproductive isolation between C. villosissimus and C. allenii, indicating that adaptive shifts to survive seasonal drought may be an underappreciated axis of neotropical understory plant diversification.

Soil organic matter, texture, and drying temperature effects on water content

AbstractA balance between soil water and air is needed to optimize soil microbial activity in laboratory incubations. Some fraction of water holding capacity (WHC) is often used to optimize water during controlled laboratory incubations, and yet this level may differ among soils. This study was undertaken to develop relationships among gravimetric and volumetric water content, WHC, and water‐filled pore space (WFPS) among a variety of soils, representing eight soil orders, 46 subgroups, total soil N from 0.46 to 4.68 g kg–1, and clay concentration from .072 to .491 kg kg–1 (5–95% range). Gravimetric soil water content was determined for each sample under the following sequence of conditions: (a) from dry storage, (b) when dried at 55 °C, (c) near saturation, and (d) when drained to WHC. Gravimetric water content was calculated at 50% WFPS (.50 m3 m–3). Like that of WFPS, WHC varied strongly with soil clay and total N concentrations. To achieve 50% WFPS, water content was 69 ± 10% of WHC and 58 ± 3% of near saturation. Although drying soil to only 55 °C for routine soil microbial processing led to overestimation of soil bulk density by 0.012 ± 0.006 Mg m–3, it was a bias. Soil water content calculations are important for obtaining best estimates of soil‐test biological activity and other soil C and N fractions to assess soil health, and this research demonstrated that using drying temperature of 55 °C was practical but created a small and consistent bias.

Quantification and mitigation of nitrogen leaching in a maize silage cropping system

Nitrogen (N) leaching is a major source of groundwater contamination. We used a series of lysimeters and suction cups to measure total N leaching losses in a high N maize crop system on a long-term maize paddock in the Waikato.&#x0D; The goal of the study was to 1) quantify N leaching losses under maize silage, 2) determine the effectiveness of a cut-and-carry annual ryegrass catch crop (RG) in mitigating N leaching losses and 3) determine an appropriate depth for measuring N leaching losses under maize.&#x0D; At least 200 kg/ha more fertiliser N than calculated plant requirements was applied to the maize crop to ensure surplus soil N after maize.&#x0D; Nitrogen leaching losses were measured in a maize-RG and maize-fallow rotation over two seasons (October 2018 - September 2020). Less than 10 % of N leaching losses occurred during the maize growing season. This is likely due to evapotranspiration exceeding rainfall in summer.&#x0D; The greatest leaching losses were observed in the maize-fallow rotation, averaging 60 kg N/ha and 88 kg N/ha for the 2018/19 and 2019/20 seasons. This was despite 2020 winter being drier than 2019. The greater 2019/20 leaching losses can be attributed to a greater soil N concentration (+15 mg N/L) in 2020.&#x0D; The importance of catch crops as a N leaching mitigation tool after maize was evident over the two years, resulting in leaching reductions &gt;85% in the maize-RG than the maize–fallow plots. The catch crop removed &gt;200 kg N/ha from the soil, significantly reducing the soil N concentration, which appear to be the main driver of leaching losses in our study. Additionally, RG also increased gravimetric soil water content by 7.3 % in the top 30 cm.&#x0D; When N leaching was measured at 70 cm, losses in fallow plots were almost three times higher than the 41.6 kg N/ha recorded at the 120 cm soil depth, our default maize rooting depth. &#x0D; A similar amount of isotopic 15N (1.2 %) was observed in maize grain at maturity when 15N was inserted to 60 cm or 120 cm soil depth. This was greater than the background values obtained when standard urea was applied to the plots (0.37 %), indicating 15N interception at depth. &#x0D; It is speculated that provided fertiliser rates match crop N demand and catch crops are used, N leaching losses in maize crops should be much lower than values reported here, irrespective of soil type and season.

Single midseason drainage events decrease global warming potential without sacrificing grain yield in flooded rice systems

Rice (Oryza sativa L.) cultivation is an important part of global food security, yet it is also responsible for a significant portion of agricultural greenhouse gas (GHG) emissions, particularly methane (CH4). Midseason drainage of flooded rice fields can decrease CH4 emissions, but the magnitude of CH4 reduction and its effect on grain yield are variable due to variation in the timing and soil-drying severity of drainage across studies. Therefore, in this two-year study, we aimed to quantify the effect of timing and severity of a single midseason drainage event on seasonal GHG emissions and grain yields, compared to a continuously flooded (CF) control. Treatments varied in terms of soil-drying severity (low, medium, and high, corresponding to approximately 5, 8, and 12 days of drying, respectively) and the timing of when drainage events occurred (between 34–49 and 45–59 days after seeding, or roughly between tillering and panicle initiation). Soil moisture parameters (perched water table, volumetric water content, gravimetric water content (GWC), and soil water potential), soil mineral nitrogen, CH4 and nitrous oxide (N2O) emissions, grain yield, and yield components were all quantified. Midseason drainage reduced seasonal CH4 emissions by 38–66%, compared to the CF control. Seasonal CH4 emissions decreased with increasing drain severity, and for every 1% reduction in soil GWC during the drainage period, seasonal CH4 emissions were reduced by 2.5%. The timing of drainage had no significant impact on CH4 emissions. Emissions of N2O were low (average = 0.035 kg N2O-N ha−1) and accounted for only 0.5% of the seasonal global warming potential (GWP) across all drainage treatments. Within each year, drainage did not significantly affect grain yield compared to the CF control. Additionally, midseason drainage reduced both GWP and yield-scaled GWP by approximately the same amount as seasonal CH4 emissions, as N2O emissions were minimal and yields were similar across treatments. These results indicate that midseason drainage may be a viable GHG mitigation practice in flooded rice systems with limited risk for yield reduction, however, this practice should also be further tested under a broad range of soil types and different environments to determine its widespread adoptability.

Performance of field‐scale lab vs in situ visible/near‐ and mid‐infrared spectroscopy for estimation of soil properties

AbstractComparison of laboratory versus in situ visible/near‐ (visNIR) and mid‐infrared (MIR) spectroscopy for prediction of various soil properties is required to demonstrate trade‐offs between accuracy and efficiency. Field measurements were made on an arable field in Germany (silt loam Haplic Luvisol) using visNIR (ASD FieldSpec 3 Hi‐Res) and MIR (Agilent Technologies 4300 Handheld FTIR) and material was collected for lab visNIR (Foss XDS Rapid Content Analyzer) and MIR (Bruker‐TENSOR 27) measurements on dried and ground soil and determination of total, labile (&gt;63 μm light), stabilized (&gt;63 μm heavy + &lt;63 μm oxidizable) and resistant organic carbon (OC) content, total nitrogen (Nt), pH and texture. Partial least squares regression models were calculated for five repeated partitions of the dataset (n = 238) into training (75%) and test (25%) sets. Lab spectral models outperformed in situ models for total OC (root mean squared error [RMSE] = 0.24–1.0 g kg−1), Nt (RMSE = 0.026–0.088 g kg−1), pH (RMSE = 0.12–0.28) and texture (RMSE = 0.53–1.5%). For both lab and field spectra, the accuracy of visNIR models was comparable or slightly better than MIR for sand, silt and clay. Spectral estimations for labile (RMSE = 0.34–0.47 g kg−1) and stabilized OC (RMSE = 0.41–0.85 g kg−1) were slightly (lab spectra) to substantially (field spectra) inferior to estimations from multiple linear regressions using total OC, Nt, clay and pH as predictors. Variable importance in the projection scores elucidated differences in spectral prediction mechanisms by spectrometer and OC fraction, and found mineral spectral signatures were highly important. For this field‐scale study with 14% median soil gravimetric water content (GWC), the loss of accuracy from lab to field measurement was lower for visNIR than MIR. Analysis of the driest soils (&lt;9% GWC) found field MIR outperformed field visNIR for OC and Nt estimation and vice versa for the wettest soils (&gt;18%), demonstrating the moisture dependence of performance rankings.Highlights Lab vs field visible/near‐ (visNIRS) and mid‐infrared (MIRS) spectroscopy require comparison for prediction of soil C fractions, N, pH and texture. Lab MIRS prediction of C, N and pH were superior, while texture estimations were comparable or slightly inferior to lab visNIRS. At 14% median soil water content, the loss of accuracy from lab to field measurement was lower for visNIRS than MIRS. The ranking of field visNIRS vs MIRS performance for C and N estimation is moisture dependent.

Spatial Heterogeneity and Driving Factors of Soil Moisture in Alpine Desert Using the Geographical Detector Method

Soil moisture is a vital factor affecting the hydrological cycle and the evolution of soil and geomorphology, determining the formation and development of the vegetation ecosystem. The previous studies mainly focused on the effects of different land use patterns and vegetation types on soil hydrological changes worldwide. However, the spatial heterogeneity and driving factors of soil gravimetric water content in alpine regions are seldom studied. On the basis of soil sample collection, combined with geostatistical analysis and the geographical detector method, this study examines the spatial heterogeneity and driving factors of soil gravimetric water content in the typical alpine valley desert of the Qinghai–Tibet Plateau. Results show that the average value of soil gravimetric water content at different depths ranges from 3.68% to 7.84%. The optimal theoretical models of soil gravimetric water content in 0–50 cm layers of the dune are different. The nugget coefficient shows that the soil gravimetric water content in the dune has a strong spatial correlation at different depths, and the range of the optimal theoretical model of semi-variance function is 31.23–63.38 m, which is much larger than the 15 m spacing used for sampling. The ranking of the influence of each evaluation factor on the alpine dune is elevation &gt; slope &gt; location &gt; vegetation &gt; aspect. The interaction detection of factors indicates that an interaction exists among evaluation factors, and no factors are independent of one another. In each soil layer of 0–50 cm, the interaction among evaluation factors has a two-factor enhancement and a nonlinear enhancement effect on soil gravimetric water content. This study contributes to the understanding of spatial heterogeneity and driving factors of soil moisture in alpine deserts, and guidance of artificial vegetation restoration and soil structure analysis of different desert types in alpine cold desert regions.