Effect Of Soil Water Potential Research Articles

A general framework for jointly modelling thermal and hydric constraints on developing eggs

Abstract Eggs are a vulnerable stage because they are sensitive to thermal and hydric conditions and yet cannot behaviourally avoid stressful environments. A general mechanistic model of egg development in natural nests requires microclimatic predictions of temperature, humidity, radiation (if above ground) and water potential (if buried in soil) to be integrated with models of heat and water exchange of the egg and the metabolism of the developmental process. Although all the required pieces for such a model now exist, they have not been integrated into a general modelling framework. We developed such an integration using NicheMapR package for mechanistic niche modelling. Specifically, we took an existing general model of egg water exchange and connected it with the microclimate model in NicheMapR to simulate nest thermal and hydric environments, including the effects of soil water potential on liquid and vapour exchange and moisture‐mediated soil thermal conductivity on heat exchange. We then used the Dynamic Energy Budget model within the ectotherm model of NicheMapR as the mechanistic engine for the developmental process, allowing the explicit computation of the dynamics of metabolic heat production and all aspects of mass exchange. We illustrate the modelling framework using existing laboratory and field data on reptiles, insects, and birds. We show that it can capture laboratory observations of water exchange and metabolic heat production and how it can be used to map potential development and water uptake under natural conditions at the continental scale. The modelling framework can be used to interpret laboratory experiments and allows strong inferences to be made about the abiotic constraints on egg development in natural nests under past, present, and future environmental change.

Combined Effects of Induced Water Deficit and Foliar Application of Silicon on the Gas Exchange of Tomatoes for Processing

The beneficial effects of silicon (Si) on plants have been widely reported for its fruit qualitative improvements, growth gains, and protection against abiotic and biotic stresses. This study aimed to evaluate the combined effect of soil water potential (Ψs) (−30 and −60 kPa) and the foliar application of Si (0.0 (control), 1.0, 2.0, 3.0, and 4.0 g L−1) in the development of tomatoes grown in a greenhouse. We evaluated the biometric parameters and gas exchange in three periods (20, 34, and 48 days after planting). The rates of transpiration (E), stomatal conductance (gs), and net photosynthesis assimilation (An) were lower when the plants were subjected to water deficit. The foliar application of Si attenuated the effect of the water deficit in both levels applied to the crop. A high response was observed at −60 kPa, regardless of the evaluated period. However, a significant effect was not observed on the relative chlorophyll index and biomass accumulation when Si was applied. A foliar application up to 2.8 g L−1 promotes increases in An,gs, and E. It is highlighted that Si can promote improvements in gas exchange when plants are affected by a water deficit.

Effects of white-tailed deer and invasive plants on the herb layer of suburban forests.

Lack of hunting and predators and proximity to human communities make suburban forests prone to high deer abundance and non-native plant invasions. I investigated these likely drivers of community structure in the herb layers of six suburban forests in one region of New Jersey, USA. In 223 plots I assessed the herb layer response to 2.5 years with or without deer fencing and the early stage of invasion from seed additions of Microstegium vimineum, an invasive, annual grass. Non-native plants and herbaceous native plants were affected very little by fencing or M. vimineum invasion. In contrast, across all forests the combination of deer access and M. vimineum addition had a strongly negative effect on woody native percent cover. Forests differed in overall fencing effects on woody natives; their cover was greater in fenced plots in just three forests, suggesting greater deer pressure in those forests during the experiment. The early invasion by M. vimineum was greatest in two of these same forests, but was not influenced by fencing. Multi-group structural equation modelling compared two groups of forests that differed in vegetation abundance and other characteristics. It paralleled the results above and also showed no negative influence of non-native cover on native cover, even in the forests where non-native cover was greater. It identified a positive effect of light level on herb layer plants in the forests with less vegetation, and also revealed a positive effect of soil water potential (SWP) on non-native plants in the forests with more vegetation, which had higher SWP. These suburban forests within a common region varied widely in native and non-native herb layer abundance, the early success of M. vimineum invasion and the herb layer's response to early invasion and protection from deer.

Irrigation and lithothamnium fertilization in bell pepper cultivated in organic system

ABSTRACT For proper plant growth and achievement of satisfactory yield, it is essential to replenish water and nutrients, in the right amount and time. Therefore, the aim of this study was to evaluate the effects of soil water potential and lithothamnium doses on the growth and yield of bell pepper fruits in an organic production system. The experimental design was randomized blocks in a 5 x 4 factorial scheme, with four replicates. The treatments were five lithothamnium doses (0, 0.5, 1, 2 and 4 g dm-3) and four soil water potentials (-6, -24, -42 and -60 kPa). Increasing lithothamnium doses and irrigations based on increasing soil water potentials produced linear increase in plant growth and fruit production. The maximum economic efficiency of the lithothamnium fertilizer was obtained with the application of 0.54 g dm-3, corresponding to the fruit yield of 491.26 g plant-1. More frequent irrigations favor the increase in growth and yield of bell pepper in organic system.

Effects of Soil Water Potential and Nitrogen Fertilization on Characteristics of Photosynthesis and Chlorophyll Fluorescence Induction in Schisandra chinensis Baillon

Management of soil water and fertilization is known to primarily affect physiological properties and yield in plant. The effect of soil water potential and nitrogen application on characteristics of photosynthesis and chlorophyll fluorescence in Schisandra chinensis Baillon was investigated on a sandy loam soil. Net photosyntheis rate and transpiration rate increased as a photon flux density and was highest at -50kPa of soil water potential. Light compensation point (<TEX>$1.5{\mu}molm^{-1}s^{-1}$</TEX>) and dark respiration (<TEX>$0.13{\mu}molCO_2m^{-1}s^{-1}$</TEX>) was lowest at -50 kPa but maximum photosynthesis rate (<TEX>$13.10{\mu}molCO_2m^{-1}s^{-1}$</TEX>) and net apparent quantum yield (<TEX>$0.083{\mu}molCO_</TEX><TEX>2m^{-1}s^{-1}$</TEX>) was highest at -50 kPa. As results of chlorophyll fluorescence by OJIP analysis, maximum quantum yield (Fv/Fm) of photosystem II (PSII) and PIabs was higher in treatments of -50 kPa and -60 kPa respectively, which reflects the relative reduction state of PSII. But the relative activities per reaction center such as ABS/RC and DIo/RC were low with decreasing soil water potential. Net photosyntheis rate and transpiration rate were highest at treatment of soil testing 1.0 times (<TEX>$92kgha^{-1}$</TEX>). Application of nitrogen resulted in high Fv/Fm, <TEX>$PI_{abs}$</TEX> and low ABS/RC, DIo/RC. This result implies that -50 kPa of soil water potential and nitrogen fertilizer may improve the efficiency of photosynthesis through controlling a photosystem in Schisandra chinensis Baillon.

Effects of soil water potential on germination of co-dominant Brigalow species: Implications for rehabilitation of water-limited ecosystems in the Brigalow Belt bioregion

Rehabilitation of disturbed and degraded land is a critical legal and ecological requirement to achieve stable and non-polluted ecosystems. In some semi-arid climates, such as the Brigalow Belt Bioregion in Eastern Australia, extensive areas have been affected by open-cut mining. With erratic rainfall patterns and clayey soils, the Brigalow Belt is a unique biome which is representative of other water-limited ecosystems worldwide. Direct seeding and native plant germination on post-mining land may be an effective and economically viable solution to re-establishing plant communities. Germination is governed by the amount of water the seed can imbibe, which is a function of the soil water potential and hydraulic soil properties rather than soil water content. The question remains how soil water potential triggers germination of Brigalow Belt plant species.We used six replicates of 50 seeds of three co-dominant native species from the Brigalow Belt Bioregion – Eucalyptus cambadgeana, Eucalyptus populnea, and Casuarina cristata – to investigate germination in relation to water potential as environmental stressor. Solutions of polyethylene glycol (PEG 6000) were applied to expose seeds to nine osmotic water potentials ranging from soil water saturation (0kPa) and field capacity (−10–30kPa) to the permanent wilting point (−1500kPa). We measured germinability (number of germinated seeds relative to total number of seeds per lot) and mean germination time (mean time required for maximum germination of a seed lot) to quantify germination. Further, we employed Hydrus-1D to simulate daily values of soil water potential and water content at 1mm depth of a Black Vertosol under the climatic conditions of Emerald in Central Queensland.While E. cambadgeana demonstrated the fastest and most prolific germination across the widest range of water conditions with germination being observed even at water potentials as low as −1500kPa, E. populnea and C. cristata required wetter conditions over longer periods to achieve maximum germination rates. For the 11 years of meteorological data examined in this study, soil water conditions were most favourable for germination of E. cambadgeana; this was primarily due to its high tolerance of water deficit in soils of lighter texture than that of the denser Black Vertosols. In contrast, for the seed-soil combination of C. cristata and Black Vertosol, modelled climatic conditions proved favourable to triggering germination only 25% of the time. The empirical data on seed germination can be used to parameterise and calibrate germination models.

Effect of soil water potential on methane and nitrous oxide emissions in upland soil during red pepper cultivation

Under intensive vegetable production, increased productivity is primarily considered for selecting better water management and irrigation intensity in upland soils. Soil water potential at −30 kPa (field capacity) for red pepper (Capsicum annum L.) production, which is the optimum moisture potential for plants, is recommended for Korean upland soils to maximize fruit yield; however its impact on greenhouse gas (GHG) emissions have not yet been considered. In this study, red pepper was cultivated under two soil water potentials at −30 and −50 kPa by drip irrigation control in two different textured soils (clay and sandy loams). Nitrous oxide (N2O) and methane (CH4) emissions were simultaneously investigated during the cultivation period. Results indicated N2O was the main GHG and contributed to approximate 97–9% of the total global warming potential (GWP), though the extent of its contribution varied depending on soil texture and soil moisture control with emitted CH4 being negligible throughout the investigation period. Between the treatments, soil moisture control at −50 kPa was effective in reducing the emissions of the two GHGs and also increased red pepper productivity in both clay loam and sandy loam soils. Comparing the gross GWP per unit pepper fruit yield between the treatments, maintaining soil water potential at −50 kPa by controlled irrigation led to a 50% reduction of GWP per unit pepper fruit yield. Therefore, drip irrigation control to lower soil water potential at −50 than −30 kPa is recommended to obtain high crop yield and reduce GWP per unit red pepper fruit yield for red pepper production in Korea.

Effect of Soil Water Potential on the Fruit Quality and Yield in Fertigation Cultivation of Paprika in Summer

Effect of Soil Water Potential on the Fruit Quality and Yield in Fertigation Cultivation of Paprika in Summer

Crescimento de plantas de cobertura sob déficit hídrico

One of the challenges to be overcome in no till deploying in tropical regions is the production of straw in the offseason, a period commonly with low water availability. To help in the choice of species to be used as cover crop in dry winter regions, the aim of this work was to evaluate the effect of soil water potential on growth of black oat (Avena strigosa Sckreb), pearl millet (Pennisetum glaucum (L.) R. Brown), grain sorghum (Sorghum bicolor L. Moench.) e guinea sorghum (Sorghum bicolor subespecie bicolor raca guinea). Pearl millet is a good option to be cropped during offseason by show high yield potencial, even been more sensitive to water deficit. Grain sorghum and guinea sorghum are also good options, particularly by showed abundant root system, which possibly gives them a certain tolerance to low water availability conditions. The black oat, even with high tolerance to water stress (tolerance conferred by highest percentage of fine roots), seems to be much affected by higher temperatures, common to these regions.

Stable Isotopes of Water Vapor in the Vadose Zone: A Review of Measurement and Modeling Techniques

The stable isotopes of soil water vapor are useful tracers of hydrologic processes occurring in the vadose zone. The measurement of soil water vapor isotopic composition (δ18O, δ2H) is challenging due to difficulties inherent in sampling the vadose zone airspace in situ . Historically, these parameters have therefore been modeled, as opposed to directly measured, and typically soil water vapor is treated as being in isotopic equilibrium with liquid soil water. We reviewed the measurement and modeling of soil water vapor isotopes, with implications for studies of the soil–plant–atmosphere continuum. We also investigated a case study with in situ measurements from a soil profile in a semiarid African savanna, which supports the assumption of liquid–vapor isotopic equilibrium. A contribution of this work is to introduce the effect of soil water potential (Ѱ) on kinetic fractionation during soil evaporation within the Craig–Gordon modeling framework. Including Ѱ in these calculations becomes important for relatively dry soils (Ѱ < −10 MPa). Additionally, we assert that the recent development of laser-based isotope analytical systems may allow regular in situ measurement of the vadose zone isotopic composition of water in the vapor phase. Wet soils pose particular sampling difficulties, and novel techniques are being developed to address these issues.

Effect of combined water and salinity stress factors on evapotranspiration of Sedum kamtschaticum Fischer in relation to green roof irrigation

In dryland areas, secondarily treated municipal wastewater could be used in extensive green roof systems. In this study, the effects of water and salt stress on a crassulacean acid metabolism (CAM) plant, Sedum kamtschaticum Fischer, was evaluated under intermittent saline irrigation. The salinity of irrigation water varied from 6.0 to 18.0dSm−1. A reduction in soil water content and an increase in soil water electrical conductivity (EC) were observed during the irrigation interval (5–17d) as a result of evapotranspiration (ET). The effect of soil water potential (SWP) on reduction of the ET ratio (ETr) was successfully described with an equation that could be applicable to a wide range of soil salinities and water contents, to estimate ET. In this study, the stress factor was defined as the integration of solute potential, and matric potential less soil water content for optimum growth (less than −0.1MPa) with elapsed time. The stress factor rapidly reduced total ET in CAM plants but effectively increased water-use efficiency (WUE). Thus, by using CAM plants for green roofs under intermittent saline irrigation, the need for irrigation water is reduced without a considerable loss of plant biomass.

Stable Isotopes of Water Vapor in the Vadose Zone: A Review of Measurement and Modeling Techniques

The stable isotopes of soil water vapor are useful tracers of hydrologic processes occurring in the vadose zone. The measurement of soil water vapor isotopic composition (δ18O, δ2H) is challenging due to difficulties inherent in sampling the vadose zone airspace in situ . Historically, these parameters have therefore been modeled, as opposed to directly measured, and typically soil water vapor is treated as being in isotopic equilibrium with liquid soil water. We reviewed the measurement and modeling of soil water vapor isotopes, with implications for studies of the soil–plant–atmosphere continuum. We also investigated a case study with in situ measurements from a soil profile in a semiarid African savanna, which supports the assumption of liquid–vapor isotopic equilibrium. A contribution of this work is to introduce the effect of soil water potential (Ѱ) on kinetic fractionation during soil evaporation within the Craig–Gordon modeling framework. Including Ѱ in these calculations becomes important for relatively dry soils (Ѱ < −10 MPa). Additionally, we assert that the recent development of laser-based isotope analytical systems may allow regular in situ measurement of the vadose zone isotopic composition of water in the vapor phase. Wet soils pose particular sampling difficulties, and novel techniques are being developed to address these issues.

地下滴灌下土壤水势对毛白杨纸浆林生长及生理特性的影响

在6、7年生三倍体毛白杨(triploid <em>Populus tomentosa)</em>纸浆林中研究了地下滴灌(SDI)下不同土壤水势(-25、-50、-75 kPa,即灌溉起始阈值)对林木生长及生理特征的影响。结果表明:与不灌溉(CK)相比,SDI使6、7年生林分的生产力分别平均提高24%和28%;其中,-25 kPa使6年生林分的生产力达到39.90 m³ hm^-2a^-1,较CK极显著提高43.5%(<em>P</em><0.01)。各水势处理间,-25 kPa的生产力在林分6年生时分别较-50和-75 kPa极显著提高20%和31%(<em>P</em><0.01),在7年生时分别提高13%和14%(<em>P</em>>0.05)。能在毛白杨速生期内(4-7月)大幅提高土壤含水率(20和50 cm处分别平均提高35%和27%)、树干日平均液流速率(46%,SF_mean)、黎明前叶水势(41%,<em>ψ</em>_pd)是SDI促进林木生长的重要机制。灌溉起始水势阈值的差异对毛白杨SF_mean和<em>ψ</em>_pd无显著影响(<em>P</em>>0.05)。3个水势处理中,-25 kPa的平均SF_mean和<em>ψ</em>_pd均最高,且其能使根系活动剧烈的表土层(0-20 cm)的水分有效性有最大幅的提高,这可能是其对林木生长有最大促进作用的主要原因。综上,应在毛白杨纸浆林培育中大力推广SDI,并在应用时可将距滴头10cm、地下20 cm处的土壤水势达到-25 kPa作为灌溉起始阈值。另外,在与试验地环境相似地区栽植毛白杨时,应于4-7月灌溉,8-10月一般可不灌溉。;Subsurface drip irrigation (SDI) is an intensive silvicultural practice which has the potential to increase productivity of triploid <em>Populus tomentosa</em> pulpwood plantations. In order to efficiently apply SDI in the cultivation of <em>P. tomentosa</em> pulpwood plantations, it is necessary to determine irrigation timing. A field experiment was conducted to investigate the effect of soil water potential (<em>ψ</em>_soil) on the growth and physiological characteristics of 6-7 year old trees under SDI in a <em>P. tomentosa</em> pulpwood plantation. The experiment included three <em>ψ</em>_soil treatments, which initiated irrigation when the <em>ψ</em>_soil at 20 cm soil depth and 10 cm distance from a drip emitter reached -25, -50, and -75 kPa, respectively. A control non-irrigation treatment (CK) was also included. Meteorological factors, <em>ψ</em>_soil, groundwater level, and tree growth were monitored hourly, daily, every 1-10 days, and monthly for two years, respectively. Soil water content at 20 and 50 cm depth, pre-dawn leaf water potential (<em>ψ</em>_pd), and trunk sap flow rate were measured in selected periods. Results showed that relative to CK, SDI could improve diameter, height, and individual volume increment of <em>P. tomentosa</em>. Irrespective of SDI treatment, SDI on average increased annual volume growth of the 6- and 7-year-old plantations by 24% and 28%, respectively over the CK treatment. Annual volume growth of the 6-year-old plantation following the -25 kPa treatment reached 39.90 m³ hm^-2a^-1, which was 43.5% higher than the CK treatment (<em>P</em><0.01). Relative to the -50 and -75 kPa treatments, annual volume growth in the -25 kPa treatment was 20% and 31% higher (<em>P</em><0.01) in the 6-year-old plantation, respectively, and 13% and 14% higher (<em>P</em>>0.05) in the 7-year-old plantation, respectively. Relative to CK during the fast growing period (April-July) of <em>P. tomentosa</em>, SDI increased the soil water content at 20 and 50 cm depth by 35% and 27%, respectively; increased average daily trunk sap flow rate (SF_mean) by 46%; and increased <em>ψ</em>_pd by 41%. The <em>ψ</em>_soil threshold for initiating irrigation had no significant effect (<em>P</em>>0.05) on the SF_mean and <em>ψ</em>_pd of <em>P. tomentosa</em>. However, among the three <em>ψ</em>_soil treatments, the average SF_mean and <em>ψ</em>_pd values were highest following the -25 kPa treatment. The increase of soil water availability in the 0-20 cm soil layer (i.e., active rooting zone) was also greatest in the -25 kPa treatment. These results may explain why the -25 kPa treatment had the highest tree growth rate among the three <em>ψ</em>_soil treatments. Overall, the observed increase in soil water content, SF_mean, and <em>ψ</em>_pd indicate that these are the mechanisms by which SDI significantly improves <em>P. tomentosa</em> tree growth. In conclusion, our findings suggest that SDI should be promoted in the cultivation of <em>P. tomentosa</em> pulpwood plantations. To realize optimum tree growth, irrigation should be initiated when the <em>ψ</em>_soil at 20 cm depth and 10 cm distance from a drip emitter reaches -25 kPa. Furthermore, it is recommended that irrigation should be applied between April and July, and terminated between August and October when planting <em>P. tomentosa</em> in regions similar to our experimental plantation.

Modelling the effects of soil water potential on growth and quality of cut chrysanthemum ( Chrysanthemum morifolium)

A complete dynamic model was developed to describe the effects of soil water potential ( WP) on the growth and external quality of standard cut chrysanthemum ( Chrysanthemum morifolium) in order to optimise water management of greenhouse crops. Experiments using chrysanthemum cv. ‘Jinba’ with different planting dates and levels of water treatment were conducted in a lean-to type greenhouse from 2006 to 2008. The dynamics of leaf area index (LAI), dry matter partitioning, and external quality traits (plant height, number of leaves per plant, flower-head diameter and peduncle length) were first determined as functions of accumulated photothermal index ( PTI). Impacts of WP on leaf photosynthetic rate, LAI, dry matter partitioning, and the external quality traits were quantified via introducing the experimentally identified effects of WP on the parameters in the light response curve of leaf photosynthetic rate and the PTI-based functions. These quantitative relationships were incorporated into a generic crop growth model SUCROS. Using independent experimental data, the model was found to give good predictions for biomass production, dry weight of organs, and the external quality traits of the chrysanthemum cultivar grown under different levels of water supply. The coefficient of determination ( r 2) between the predicted and measured results was 0.91 for LAI, 0.88 for biomass production, and varied between 0.83 and 0.93 for organ dry weight and the external quality traits. Further evaluation is needed when applying this model to a wider range.

Effect of soil water potential on grain quality at different spike positions during grain filling in rice

为探讨结实期土壤水分对水稻籽粒品质的影响, 以中熟籼稻“扬稻6 号”和中熟粳稻“扬粳9538”为材料, 在盆栽条件下, 研究了不同土壤水势(0 kPa、-15 kPa、-30 kPa、-45 kPa)对水稻籽粒品质的影响, 并进一步探讨了不同粒位间的差异。结果表明, 结实期土壤水分对稻米籽粒品质有较大影响, 且影响程度因品种、粒位不同而异。与对照(0 kPa)相比, 土壤轻度胁迫(土壤水势在-15~-30 kPa 之间)籽粒的精米率、整精米率和崩解值增加, 垩白度和消碱值降低; 不同粒位间比较, 土壤轻度胁迫对水稻穗上二次枝梗或同一枝梗上较迟开花籽粒的影响较大。随土壤水势进一步降低稻米品质变劣。在0 ~ -45 kPa 范围内, 随土壤水势的降低,粗蛋白含量和胶稠度增加。灌浆期土壤轻度落干(土壤水势在-15 ~-30 kPa)有利于稻米品质的改善。

Effects of Soil Water Potential and Moisture Content on Sound Speed

To monitor and understand the temporal variations of sound speed due to the changes of soil physical properties such as soil water potential, moisture content, and soil temperature under natural conditions, a long‐term field soil survey has been conducted. In this study, transmitter and receiver acoustic probes, consisting of ten (five pairs) and five transducers respectively, were inserted into a prepared trench containing a soil‐sand mixture in an outdoor test site. Five time domain reflectometers, five tensiometers, and five thermocouples were buried during the trench‐filling at the same depths as the acoustic transducers. Measurements of sound speed, soil temperature, soil moisture content, and water potential were performed continuously, along with the measurements of surface temperature and precipitation over a period of 2 yr. Analysis of the data shows that there is a power law relationship between the sound speed and water potential. It is also found that the water potential is the dominant influence on the sound speed whereas the moisture content and temperature have relatively minor impacts. Brutsaert and Luthin's theory was employed to calculate the sound speed as a function of the effective stress. The theoretical predictions were compared with the experimental data and they are in good agreement. The study suggests that sound speed measurement could be used as a new and effective tool for water potential measurement.

Effects of soil water potential and moisture content on sound speed.

In order to monitor and understand the temporal variations of sound speed due to the changes of soil physical properties under natural conditions, a long‐term field soil survey has been conducted. Measurements of sound speed, soil temperature, soil moisture content, and water potential were performed continuously, along with the measurements of surface temperature and precipitation over a period of 2 years. The effects of water potential, moisture content, soil temperature, and depth on sound speed were assessed. Analysis of the data shows that there is a power law relationship between the sound speed and water potential. It is also found that the water potential is the dominant influence on the sound speed, whereas the moisture content and temperature have relatively minor impacts. Brutsaert and Luthin’s theory was employed to calculate the sound speed as a function of the effective stress. The theoretical predictions were compared with the experimental data and they are in good agreement. The study suggests that sound speed measurement could be used as a new and effective tool for water potential measurement.

Temporal variability of available P, microbial P and some phosphomonoesterase activities in a sewage sludge treated soil: The effect of soil water potential

Available P and enzyme activities strongly depend on the soil water potential. The objective of this study was to test the effects of water potential on soil available P, microbial biomass P(MBP) and some phosphomonoesterase activities. A semiarid soil classified as Calcic Haploxerept was treated with raw sewage sludge at a rate of 20 g kg-1. Four levels of irrigation (deionized water) were established for 90 days of incubation. Constant water potentials used for soil incubation were: saturation (SA, 0 bar), field capacity (FC, -0.3 bar), and permanent wilting point (PWP, -15 bar) in three treatments. An irrigation treatment was also drying-rewetting cycle (DWC) between -0.3 to -15 bars. After 0, 20, 60 and 90 days of incubation, soils were sampled for analysis. The addition of sewage sludge decreased soil pH and increased soil EC, organic C, total N, organic P, available P, MBP contents and phytase, alkaline and acid phosphatases activities significantly. The effects of soil moisture, incubation time and their interaction on soil available P, MBP and phosphomonoesterase activities were significant at different levels. During 20 days of incubation, available P and phosphatase activities decreased, whereas microbial P and phytase activity increased significantly. Thereafter, only available P increased and phytase activities decreased continuously, but microbial P, alkaline and acid phosphatase activities fluctuated during incubation. Soils incubated in DWC and FC compared to soils incubated in SA and PWP had higher available P contents. Microbial P and phosphomonoesterase activities increased with increasing soil water potentials significantly. The highest (38.7 mg kg-1) and lowest (28.9 mg kg-1) microbial P was measured in soil incubated in SA and PWP respectively. Correlation coefficient between available and microbial P was negative and significant. The activities of alkaline phosphatase, acid phosphatase and phytase were higher and lower in soils incubated in SA and PWP, respectively.

Modelling stomatal ozone flux and deposition to grassland communities across Europe

Regional scale modelling of both ozone deposition and the risk of ozone impacts is poorly developed for grassland communities. This paper presents new predictions of stomatal ozone flux to grasslands at five different locations in Europe, using a mechanistic model of canopy development for productive grasslands to generate time series of leaf area index and soil water potential as inputs to the stomatal component of the DO 3SE ozone deposition model. The parameterisation of both models was based on Lolium perenne, a dominant species of productive pasture in Europe. The modelled seasonal time course of stomatal ozone flux to both the whole canopy and to upper leaves showed large differences between climatic zones, which depended on the timing of the start of the growing season, the effect of soil water potential, and the frequency of hay cuts. Values of modelled accumulated flux indices and the AOT40 index showed a five-fold difference between locations, but the locations with the highest flux differed depending on the index used; the period contributing to the accumulation of AOT40 did not always coincide with the modelled period of active ozone canopy uptake. Use of a fixed seasonal profile of leaf area index in the flux model produced very different estimates of annual accumulated total canopy and leaf ozone flux when compared with the flux model linked to a simulation of canopy growth. Regional scale model estimates of both the risks of ozone impacts and of total ozone deposition will be inaccurate unless the effects of climate and management in modifying grass canopy growth are incorporated.

Modelling the effect of soil moisture on germination and emergence of wheat and sugar beet with the minimum number of parameters

AbstractSoil moisture and temperature, sowing depth and penetration resistance affect the time and percentage of seedling emergence, which are crucial for the simulation of drought‐limited crop production. The aim of this research was to measure the effect of soil water potential on germination and emergence, shoot and root elongation rates (SER and RER) of two different seed/crop types. Sugar beet and durum wheat seeds were sown into two soils (clay and loam), submitted to five matric potentials (−0.01, −0.1, −0.2, −0.4 and −0.8 MPa) and incubated at constant temperature (25°C) and humidity. Cumulative count analysis was used to estimate parameters of the distribution of germination or emergence times for each box of beet or wheat seeds and to derive estimates for base potentials (ψb), hydrothermal times (H) and numbers of viable units. In a second experiment, NaCl solution was used to mimic the soil matric potentials to estimate potential RER and SER. Germination of sugar beet was slightly more sensitive to matric potential than durum wheat (ψb of −1.13 and −1.23 MPa, respectively). H(g) was longer for sugar beet than for durum wheat (67 vs 47 MPa °Cd). For emergence ψb was similar for both seed types and soils but hydrothermal times (H(e)) were 40 MPa °Cd higher for sugar beet than for wheat. Emergence was about 20 MPa °Cd earlier in loam than in clay. SER measured in soils were similar for both crops and for durum wheat it agreed with those determined in NaCl solution. RER and SER fell with decreasing osmotic potential to approximately 20% of their maximum values (1.03 mm h−1 and 0.57 mm h−1, respectively). Seedling viability decreased with decreasing matric potential and more in clay than in loam soil and more for sugar beet than durum wheat. Seed and soil aggregate size are discussed with respect to the effects of water diffusion and soil–seed contact on germination and emergence modelling.