scholarly journals Environmental influences on carbon dioxide fluxes over three grassland ecosystems in China

2009 ◽  
Vol 6 (12) ◽  
pp. 2879-2893 ◽  
Author(s):  
Y. Fu ◽  
Z. Zheng ◽  
G. Yu ◽  
Z. Hu ◽  
X. Sun ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Soil Moisture ◽  
Alpine Meadow ◽  
Growing Season ◽  
Co2 Fluxes ◽  
Meadow Steppe ◽  
Temperate Steppe ◽  
Area Index ◽  
Grassland Ecosystems ◽  
Alpine Shrub

Abstract. This study compared carbon dioxide (CO2) fluxes over three grassland ecosystems in China, including a temperate semiarid steppe in Inner Mongolia (NMG), an alpine shrub-meadow in Qinghai (HB), and an alpine meadow-steppe in Tibet (DX). Measurements were made in 2004 and 2005 using the eddy covariance technique. Objectives were to document the seasonality of the net ecosystem exchange of CO2 (NEE) and its components, gross ecosystem photosynthesis (GEP), and ecosystem respiration (Reco), and to examine how environmental factors affect the CO2 exchange in these grassland ecosystems. The 2005 growing season (from May to September) was warmer than that of 2004 across the three sites, and precipitation in 2005 was less than that in 2004 at NMG and DX. The magnitude of CO2 fluxes (daily and annual sums) was largest at HB, which also showed the highest temperature sensitivity of Reco among the three sites. A stepwise multiple regression analysis showed that the seasonal variation of GEP, Reco, and NEE of the alpine shrub-meadow was mainly controlled by air temperature, whereas leaf area index can likely explain the seasonal variation in GEP, Reco, and NEE of the temperate steppe. The CO2 fluxes of the alpine meadow-steppe were jointly affected by soil moisture and air temperature. The alpine shrub-meadow acted as a net carbon sink over the two study years, whereas the temperate steppe and alpine meadow-steppe acted as net carbon sources. Both GEP and Reco were reduced by the summer and spring drought in 2005 at NMG and DX, respectively. The accumulated leaf area index during the growing season (LAIsum) played a key role in the interannual and intersite variation of annual GEP and Reco across the study sites and years, whereas soil moisture contributed most significantly to the variation in annual NEE. Because LAIsum was significantly correlated with soil moisture at a depth of 20 cm, we concluded that the available soil moisture other than annual precipitation was the most important factor controlling the variation in the CO2 budgets of different grassland ecosystems in China.

scholarly journals Environmental controls on carbon fluxes over three grassland ecosystems in China

2009 ◽  
Vol 6 (4) ◽  
pp. 8007-8040 ◽  
Author(s):  
Y. Fu ◽  
Z. Zheng ◽  
G. Yu ◽  
Z. Hu ◽  
X. Sun ◽  
...  
Keyword(s):  
Air Temperature ◽  
Alpine Meadow ◽  
Growing Season ◽  
Annual Precipitation ◽  
Co2 Fluxes ◽  
Meadow Steppe ◽  
Temperate Steppe ◽  
Growing Season Length ◽  
Grassland Ecosystems ◽  
Alpine Shrub

Abstract. This study compared the CO2 fluxes over three grassland ecosystems in China, including a temperate steppe (TS) in Inner Mongolia, an alpine shrub-meadow (ASM) in Qinghai and an alpine meadow-steppe (AMS) in Tibet. The measurements were made in 2004 and 2005 using the eddy covariance technique. Objectives were to document the different seasonality of net ecosystem exchange of CO2 (NEE) and its components, gross ecosystem photosynthesis (GEP) and ecosystem respiration (Reco), and to examine how environmental factors affect carbon exchange in the three grassland ecosystems. It was warmer in 2005 than in 2004, especially during the growing season (from May to September), across the three sites. The annual precipitation at TS in 2004 (364.4 mm) was close the annual average (350 mm), whereas the precipitation at TS in 2005 (153.3 mm) was significantly below the average. Both GEP and Reco of the temperate steppe in 2005 were significantly reduced by the extreme drought stress, resulting in net carbon release during almost the whole growing season. The magnitude of CO2 fluxes (daily and annual sums) was largest for the alpine shrub-meadow and smallest for the alpine meadow-steppe. The seasonal trends of GEP, Reco and NEE of the alpine shrub-meadow tracked closely with the variation in air temperature, while the seasonality of GEP, Reco and NEE of the temperate steppe and the alpine meadow-steppe was more related to the variation in soil moisture. The alpine shrub-meadow was a local carbon sink over the two years. The temperate steppe and alpine meadow-steppe were acting as net carbon source, with more carbon loss to the atmosphere in warmer and drier year of 2005. Annual precipitation was the primary climate driver for the difference in annual GEP and NEE among the three sites and between the two years. We also found the annual GEP and NEE depended significantly on the growing season length, which was mainly a result of the timing and amount of precipitation for the temperate steppe and the alpine meadow-steppe, but was more linked to the variation in air temperature for the alpine shrub-meadow.

scholarly journals The growing season greenhouse gas balance of a continental tundra site in the Indigirka lowlands, NE Siberia

2007 ◽  
Vol 4 (6) ◽  
pp. 985-1003 ◽  
Author(s):  
M. K. van der Molen ◽  
J. van Huissteden ◽  
F. J. W. Parmentier ◽  
A. M. R. Petrescu ◽  
A. J. Dolman ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Soil Temperature ◽  
Greenhouse Gas ◽  
Growing Season ◽  
Light Limitation ◽  
Greenhouse Gas Balance ◽  
Area Index ◽  
North East ◽  
Methane Fluxes ◽  
Gas Balance

Abstract. Carbon dioxide and methane fluxes were measured at a tundra site near Chokurdakh, in the lowlands of the Indigirka river in north-east Siberia. This site is one of the few stations on Russian tundra and it is different from most other tundra flux stations in its continentality. A suite of methods was applied to determine the fluxes of NEE, GPP, Reco and methane, including eddy covariance, chambers and leaf cuvettes. Net carbon dioxide fluxes were high compared with other tundra sites, with NEE=−92 g C m−2 yr−1, which is composed of an Reco=+141 g C m−2 yr−1 and GPP=−232 g C m−2 yr−1. This large carbon dioxide sink may be explained by the continental climate, that is reflected in low winter soil temperatures (−14°C), reducing the respiration rates, and short, relatively warm summers, stimulating high photosynthesis rates. Interannual variability in GPP was dominated by the frequency of light limitation (Rg<200 W m−2), whereas Reco depends most directly on soil temperature and time in the growing season, which serves as a proxy of the combined effects of active layer depth, leaf area index, soil moisture and substrate availability. The methane flux, in units of global warming potential, was +28 g C-CO2e m−2 yr−1, so that the greenhouse gas balance was −64 g C-CO2e m−2 yr−1. Methane fluxes depended only slightly on soil temperature and were highly sensitive to hydrological conditions and vegetation composition.

scholarly journals Carbon Dioxide Fluxes and Carbon Stocks under Conservation Agricultural Practices in South Africa

Agriculture ◽  
2020 ◽  
Vol 10 (9) ◽  
pp. 374 ◽  
Author(s):  
Patrick Nyambo ◽  
Chiduza Cornelius ◽  
Tesfay Araya
Keyword(s):  
South Africa ◽  
Carbon Dioxide ◽  
Soil Moisture ◽  
Carbon Stock ◽  
Crop Residue ◽  
Agricultural Practices ◽  
Carbon Stocks ◽  
Residue Management ◽  
Co2 Fluxes ◽  
Carbon Dioxide Fluxes

Understanding the impacts of agricultural practices on carbon stocks and CO2 emission is imperative in order to recommend low emission strategies. The objective of this study was to investigate the effects of tillage, crop rotation, and residue management on soil CO2 fluxes, carbon stock, soil temperature, and moisture in the semi-arid conditions in the Eastern Cape of South Africa. The field trial was laid out as a split-split-plot design replicated three times. The main plots were tillage viz conventional tillage (CT) and no-till (NT). The sub-plots were allocated to crop rotations viz maize–fallow–maize (MFM), maize–oat–maize (MOM), and maize–vetch–maize (MVM). Crop residue management was in the sub-sub plots, viz retention (R+), removal (R−), and biochar (B). There were no significant interactions (p > 0.05) with respect to the cumulative CO2 fluxes, soil moisture, and soil temperature. Crop residue retention significantly increased the soil moisture content relative to residue removal, but was not different to biochar application. Soil tilling increased the CO2 fluxes by approximately 26.3% relative to the NT. The carbon dioxide fluxes were significantly lower in R− (2.04 µmoL m−2 s−1) relative to the R+ (2.32 µmoL m−2 s−1) and B treatments (2.36 µmoL m−2 s−1). The carbon dioxide fluxes were higher in the summer (October–February) months compared to the winter period (May–July), irrespective of treatment factors. No tillage had a significantly higher carbon stock at the 0-5 cm depth relative to CT. Amending the soils with biochar resulted in significantly lower total carbon stock relative to both R+ and R−. The results of the study show that NT can potentially reduce CO2 fluxes. In the short term, amending soils with biochar did not reduce the CO2 fluxes compared to R+, however the soil moisture increases were comparable.

Changing sensitivity of global vegetation productivity to hydro-climate drivers

2021 ◽  
Author(s):  
Wantong Li ◽  
Matthias Forkel ◽  
Mirco Migliavacca ◽  
Markus Reichstein ◽  
Sophia Walther ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Land Surface ◽  
Root Zone ◽  
Growing Season ◽  
Climatic Conditions ◽  
Terrestrial Vegetation ◽  
Spatial And Temporal Patterns ◽  
Vegetation Productivity ◽  
Area Index ◽  
Global Vegetation

&lt;p&gt;Terrestrial vegetation couples&amp;#160;the global water, energy and carbon exchange between the atmosphere and the land surface. Thereby, vegetation productivity is determined by a multitude of energy- and water-related variables. While the emergent sensitivity of productivity to these variables has been inferred from Earth observations, its temporal evolution&amp;#160;during the last decades is unclear, as well as potential changes in response to trends in hydro-climatic conditions.&amp;#160;In this study, we analyze the changing sensitivity of global vegetation productivity to hydro-climate&amp;#160;conditions by using satellite-observed vegetation indices&amp;#160;(i.e. NDVI)&amp;#160;at the monthly timescale from 1982&amp;#8211;2015. Further, we&amp;#160;repeat the analysis&amp;#160;with simulated leaf area index and gross primary productivity from the TRENDY vegetation models, and contrast the findings with the observation-based results. We train a&amp;#160;random forest model to predict anomalies of productivity from&amp;#160;a comprehensive set of hydro-meteorological variables&amp;#160;(temperature, solar radiation, vapor pressure deficit, surface and root-zone soil moisture and precipitation), and to infer the sensitivity to each of these variables. By&amp;#160;training models from&amp;#160;temporal independent subsets of the data we detect the evolution of sensitivity&amp;#160;across time. Results based on observations&amp;#160;show that vegetation sensitivity to energy- and water-related variables has significantly changed&amp;#160;in many regions across the globe. In particular we find decreased (increased) sensitivity to temperature in very warm (cold) regions. Thereby, the magnitude of the sensitivity tends to differ between the early and late growing seasons. Likewise, we find changing sensitivity&amp;#160;to root-zone soil moisture with increases predominantly in the early growing season and decreases in the late growing season.&amp;#160;For better understanding the mechanisms behind the sensitivity changes, we analyse land-cover changes, hydro-climatic trends, and abrupt disturbances&amp;#160;(e.g. drought, heatwave events or fires could result in breaking points of sensitivity evolution in the local interpretation). In summary, this study sheds light on how and where vegetation productivity changes&amp;#160;its response to&amp;#160;the drivers under&amp;#160;climate change, which can help to understand possibly resulting&amp;#160;changes in spatial and temporal patterns of land carbon uptake.&lt;/p&gt;

scholarly journals Nitrogen fertilizer regulates soil respiration by altering the organic carbon storage in root and topsoil in alpine meadow of the north-eastern Qinghai-Tibet Plateau

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
Wen Li ◽  
Jinlan Wang ◽  
Xiaolong Li ◽  
Shilin Wang ◽  
Wenhui Liu ◽  
...  
Keyword(s):  
Soil Moisture ◽  
Tibetan Plateau ◽  
Soil Respiration ◽  
Alpine Meadow ◽  
Growing Season ◽  
N Storage ◽  
The North ◽  
C Storage ◽  
North Eastern ◽  
C And N

Abstract Soil respiration (Rs) plays a critical role in the global carbon (C) balance, especially in the context of globally increasing nitrogen (N) deposition. However, how N-addition influences C cycle remains unclear. Here, we applied seven levels of N application (0 (N0), 54 (N1), 90 (N2), 126 (N3), 144 (N4), 180 (N5) and 216 kg N ha−1 yr−1 (N6)) to quantify their impacts on Rs and its components (autotrophic respiration (Ra) and heterotrophic respiration (Rh)) and C and N storage in vegetation and soil in alpine meadow on the northeast margin of the Qinghai-Tibetan Plateau. We used a structural equation model (SEM) to explore the relative contributions of C and N storage, soil temperature and soil moisture and their direct and indirect pathways in regulating soil respiration. Our results revealed that the Rs, Ra and Rh, C and N storage in plant, root and soil (0–10 cm and 10–20 cm) all showed initial increases and then tended to decrease at the threshold level of 180 kg N ha−1 yr−1. The SEM results indicated that soil temperature had a greater impact on Rs than did volumetric soil moisture. Moreover, SEM also showed that C storage (in root, 0–10 and 10–20 cm soil layers) was the most important factor driving Rs. Furthermore, multiple linear regression model showed that the combined root C storage, 0–10 cm and 10–20 cm soil layer C storage explained 97.4–97.6% variations in Rs; explained 94.5–96% variations in Ra; and explained 96.3–98.1% in Rh. Therefore, the growing season soil respiration and its components can be well predicted by the organic C storage in root and topsoil in alpine meadow of the north-eastern Qinghai-Tibetan Plateau. Our study reveals the importance of topsoil and root C storage in driving growing season Rs in alpine meadow on the northeast margin of Qinghai-Tibetan Plateau.

scholarly journals Seasonal variations in carbon dioxide exchange in an alpine wetland meadow on the Qinghai-Tibetan Plateau

2009 ◽  
Vol 6 (5) ◽  
pp. 9005-9044 ◽  
Author(s):  
L. Zhao ◽  
J. Li ◽  
S. Xu ◽  
H. Zhou ◽  
Y. Li ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Tibetan Plateau ◽  
Soil Temperature ◽  
Ecosystem Respiration ◽  
Growing Season ◽  
Research Station ◽  
Rain Event ◽  
Area Index ◽  
Alpine Wetland ◽  
Yearly Average

Abstract. The unique climate of the alpine wetland meadow is characterized by long cold winters and short cool summers with relatively high precipitation. These factors shorten the growing season for vegetation to approximately 150 to 165 days and prolong the dormant period to almost 7 months. Understanding how environmental variables affect the processes that regulate carbon flux in alpine wetland meadow on the Qinghai-Tibetan plateau is critical important because alpine wetland meadow plays a key role in the carbon cycle of the entire plateau. To address this issue, Gross Primary Production (GPP), Ecosystem Respiration (Reco), and Net Ecosystem CO2 Exchange (NEE) were examined for an alpine wetland meadow at the Haibei Research Station of the Chinese Academy of Sciences. The measurements covered three years and were made using the eddy covariance method. Seasonal trends of both GPP and Reco, followed closely changes in Leaf Area Index (LAI). Reco, exhibited the same exponential variation as soil temperature with seasonally-dependent R10 (the ecosystem respiration rate (μmol CO2 m−2 s−1) at the soil temperature reach 283.16 K (10°C)). Yearly average GPP, Reco, and NEE (which were 575.7, 676.8 and 101.1 gCm−2, respectively, for 2004 year, and 682.9, 726.4 and 44.0 gCm−2 for 2005 year, and 630.97, 808.2 and 173.2 gCm−2 for 2006 year) values indicated that the alpine wetland meadow was a moderately important source of CO2. The observed carbon dioxide fluxes in this alpine wetland meadow plateau are high in comparison with other alpine meadow environments such as Kobresia humilis meadow and shrubland meadow located in similar areas. And the cumulative NEE data indicated that the alpine wetland meadow is a source of atmospheric CO2 during the study years. CO2 emissions are large on elevated microclimatology areas on the meadow floor regardless of temperature. Furthermore, relatively low Reco, levels occurred during the non-growing season after a late rain event. This result is contradicted observations in alpine shrubland meadow. The timing of rain events had more impact on ecosystem GPP and NEE.

STUDI FLUKS KARBON DIOKSIDA PADA BERBAGAI TIPE PENGGUNAAN DI LAHAN GAMBUT PASANG SURUT DAN PEDALAMAN (Study of Carbon dioxide Fluxes (CO2 fluxes) on Various Land Use in Low Tide and Ombrotrophic Peatland)

AgriPeat ◽  
2019 ◽  
Vol 18 (02) ◽  
pp. 68-81
Author(s):  
Journal Journal
Keyword(s):  
Carbon Dioxide ◽  
Soil Moisture ◽  
Soil Temperature ◽  
Rubber Plantation ◽  
Co2 Fluxes ◽  
Forest Land ◽  
Carbon Dioxide Fluxes ◽  
Ombrotrophic Peatland ◽  
A Value ◽  
Burnt Areas

ABSTRACT The aim of this study to known Co2 fluxes in low tide and ombrotrophic peatland on forest land, ex- burns land, rubber tree land, and maize land and to known amount of microbial populations there. Observation method was carried out at the village Kalampangan (ombrotrophic peatland) , Sebangau, Palangka Raya, and at the village Purwodadi (low tide peatland), Maliku, Pulang Pisau, from May to July 2014. Observation variables consist of CO2 fluxes, fluctuations of groundwater levels, soil temperature, soil humidity and microbial populations. The results show that overall carbon dioxide fluxes higher in low tide peatland, with the highest fluxes in burnt areas, 430.24 mg C m-2 h-1, whereas in Ombrotrophic peatland, the highest on 292 forested land, 92 mg C m-2h-1. In Ombrotrophic peatland, relation between fluxes of carbon dioxide and the soil temperature is significant in the burnt areas with a value of R = 0.856 with a quadratic pattern, with the average temperature of 28.89 ° C. Fluxes of carbon dioxide significantly effected by soil moisture that is at a rubber plantation with a value of R = 0.640 with quadraticpatterned, average soil moisture of 0.61 m3/m-3. Fluxes of carbon dioxide to the groundwater depth is significant on a rubber plantation with a value of R = 0.872 with a quadratic pattern, and depth of groundwater on average of 83.74 cm. The populatuin of microorganisms, in forest land 137 sel/ml, rubber plantations 154 sel/ml, cornfields 157 sel/ml and ex-burnt is 80 sel/ml. In Low Tide peatland, fluxes of carbon dioxide to the soil temperature is significant in forest land with the value of R = 0.545 with cubic pattern, and the average temperature of 27,39 oC. Soil moisture has the siginificant effect to fluxes of carbon dioxide that is in the burnt areas with a value of R = 0.617 with patterned quadratic, and average soil moisture of 0.50 m3/m-3. The ground water depth has a siginificant effect to fluxes of carbon dioxide in a cornfield with a value of R = 0.743 with a quadratic pattern, and the depth of soil water on average of 68.98 cm. Population of soil microorganisms, in forest land 73 sel/ml, rubber plantations 36 sel/ml, cornfields 51 sel/ml and ex-burnt 18 sel/ml. Soil temperature, soil moisture, groundwater depth and microoganisms effect on carbon dioxide fluxes. Key words : carbondioxide, fluxes, microorganisms, peatland ABSTRAK Tujuan Penelitian adalah untuk mengetahui pengaruh tipe penggunaan lahan gambut pasang surut dan lahan gambut pedalaman, baik pada hutan alami, eks kebakaran, lahan pertanian (jagung) dan perkebunan karet terhadap fluks karbon dioksida dan mengetahui pengaruh jumlah mikroorganisme terhadap fluks karbon dioksida pada hutan alami, eks kebakaran, lahan pertanian (jagung) dan perkebunan karet pada kedua tipe lahan gambut tersebut. Penelitian dilaksanakan dari tanggal 23 Mei sampai dengan 19 Juli 2014 (2 bulan) di Kalampangan dan Purwodadi (Kanamit). Hasil Penelitian menunjukkan, fluks karbon dioksida secara keseluruhan lebih tinggi di Gambut Pasang Surut dibandingkan dengan di Pedalaman. Rata-rata fluks karbon dioksida di Gambut Pasang Surut, Jurnal AGRI PEAT, Vol. 18 No. 2 , September 2017 : 68 - 81 ISSN :1411 - 6782 69 pada lahan berhutan 285, 22 mg C m-2h-1, pada kebun karet 264,69 mg C m-2h-1, pada kebun jagung 232,08 mg C m-2h-1, pada lahan bekas kebakaran 430,24 mg C m-2h-1. Meskipun demikian, di Gambut Pedalaman, pada lahan berhutan lebih tinggi dibanding di Pasang Surut yaitu 292, 92 mg C m-2h-1, pada kebun karet 224,93 mg C m-2h-1, pada kebun jagung 211,30 mg C m-2h-1, pada lahan bekas kebakaran 228,07 mg C m-2h-1. Di Gambut Pedalaman, hubungan fluks karbon dioksida terhadap suhu tanah yang berpengaruh nyata yaitu pada areal bekas kebakaran dengan nilai R = 0,856 dengan berpola kuadratik, suhu rata-rata 28,89 oC. Fluks karbon dioksida terhadap kelembaban tanah yang berpengaruh nyata yaitu pada kebun karet dengan nilai R = 0,640 dengan berpola kuadratik, kelembaban tanah rata-rata 0,61 m3/m-3. Hubunganfluks karbon dioksida terhadap kedalaman air tanah yang berpengaruh nyata yaitu pada kebun karet dengan nilai R = 0,872 berpola kuadratik dengan kedalaman air tanah rata-rata 83,74 cm. Mikroorganisme, di lahan hutan 137 sel/ml, kebun karet 154 sel/ml, kebun jagung 157 sel/ml dan dilahan bekas kebakaran 80 sel/ml. Di Gambut Pasang Surut, hubungan fluks karbon dioksida terhadap suhu tanah yang berpengaruh nyata yaitu pada lahan hutan dengan nilai R = 0,545 dengan berpola kubik, suhu rata- rata 27,39 oC. Hubungan fluks karbon dioksida terhadap kelembaban tanah yang berpengaruh nyata yaitu pada lahan bekas kebakaran dengan nilai R = 0,617 dengan berpola kuadratik, kelembaban tanah rata-rata 0,50 m3/m-3. Hubungan fluks karbon dioksida terhadap kedalaman air tanah yang berpengaruh nyata yaitu pada kebun jagung dengan nilai R = 0,743 berpola kuadratik dengan kedalaman air tanah rata-rata 68,98 cm. Mikroorganisme, di lahan hutan 73 sel/ml, kebun karet 36 sel/ml, kebun jagung 51 sel/ml dan dilahan bekas kebakaran 18 sel/ml. Suhu tanah, kelembaban tanah, kedalaman air tanah berpengaruh terhadap fluks karbon dioksida dan mikroorganisme pengaruhnya kecil. Kata kunci : carbondioxide, fluxes, microorganisms, peatland

scholarly journals EFFECT OF WATER GRADIENT ON SORGHUM GROWTH, WATER RELATIONS AND YIELD

1982 ◽  
Vol 62 (3) ◽  
pp. 599-607 ◽  
Author(s):  
U. N. CHAUDHURI ◽  
E. T. KANEMASU
Keyword(s):  
Soil Moisture ◽  
Plant Height ◽  
Water Use ◽  
Dry Matter ◽  
Canopy Temperature ◽  
Water Source ◽  
Growing Season ◽  
Moisture Gradient ◽  
Growth And Yield ◽  
Area Index

A field study was conducted during the 1980 growing season to determine the effects of soil moisture gradient on sorghum water relationships, growth, and yield of four hybrids: Sorghum bicolor L. ’G-623 GBR,’ ’RS 626,’ ’RS 671’ and ’A 28+’. June to September was warmer than normal (2.3–4.8 °C), with precipitation of only 16.2 cm during the cropping season. Sprinklers provided a continuously decreasing moisture gradient away from the water source. Plant height, dry matter, and leaf area index (LAI) decreased as watering level decreased. Higher leaf diffusive resistance and lower water potentials were associated with decreasing plant height and decreasing LAI. Canopy temperature (Tc) of the water-stressed sorghum was generally 3.2–3.7 °C warmer than canopy temperatures of well-watered plants. Canopy temperature also correlated well with water use by all hybrids. The average canopy minus air temperature [Formula: see text] was positive for all hybrids receiving less than 25 cm of irrigation and precipitation during the growing season, which corresponds to soil moisture values of 0.32 maximum available. Increasing the watering levels increased the water use efficiency (WUE) for total dry matter and grain yield.

scholarly journals Vegetation Optical Depth and Soil Moisture Retrieved from L-Band Radiometry over the Growth Cycle of a Winter Wheat

2018 ◽  
Vol 10 (10) ◽  
pp. 1637 ◽  
Author(s):  
Thomas Meyer ◽  
Lutz Weihermüller ◽  
Harry Vereecken ◽  
François Jonard
Keyword(s):  
Soil Moisture ◽  
Winter Wheat ◽  
Optical Depth ◽  
Incidence Angle ◽  
Soil Surface ◽  
Growing Season ◽  
Area Index ◽  
Vegetation Height ◽  
L Band

L-band radiometer measurements were performed at the Selhausen remote sensing field laboratory (Germany) over the entire growing season of a winter wheat stand. L-band microwave observations were collected over two different footprints within a homogenous winter wheat stand in order to disentangle the emissions originating from the soil and from the vegetation. Based on brightness temperature (TB) measurements performed over an area consisting of a soil surface covered by a reflector (i.e., to block the radiation from the soil surface), vegetation optical depth (τ) information was retrieved using the tau-omega (τ-ω) radiative transfer model. The retrieved τ appeared to be clearly polarization dependent, with lower values for horizontal (H) and higher values for vertical (V) polarization. Additionally, a strong dependency of τ on incidence angle for the V polarization was observed. Furthermore, τ indicated a bell-shaped temporal evolution, with lowest values during the tillering and senescence stages, and highest values during flowering of the wheat plants. The latter corresponded to the highest amounts of vegetation water content (VWC) and largest leaf area index (LAI). To show that the time, polarization, and angle dependence is also highly dependent on the observed vegetation species, white mustard was grown during a short experiment, and radiometer measurements were performed using the same experimental setup. These results showed that the mustard canopy is more isotropic compared to the wheat vegetation (i.e., the τ parameter is less dependent on incidence angle and polarization). In a next step, the relationship between τ and in situ measured vegetation properties (VWC, LAI, total of aboveground vegetation biomass, and vegetation height) was investigated, showing a strong correlation between τ over the entire growing season and the VWC as well as between τ and LAI. Finally, the soil moisture was retrieved from TB observations over a second plot without a reflector on the ground. The retrievals were significantly improved compared to in situ measurements by using the time, polarization, and angle dependent τ as a priori information. This improvement can be explained by the better representation of the vegetation layer effect on the measured TB.

Application of Copernicus Global Land Service vegetation parameters and ESA soil moisture data to analyze changes in vegetation with respect to the CORINE database

2020 ◽  
Author(s):  
Hajnalka Breuer ◽  
Amanda Imola Szabó
Keyword(s):  
Soil Moisture ◽  
Land Cover ◽  
Land Surface ◽  
European Space Agency ◽  
Growing Season ◽  
Research Centre ◽  
Area Index ◽  
Soil Moisture Data ◽  
Global Land ◽  
Vegetation Parameters

&lt;p&gt;Vegetation and soil moisture monitoring are complicated and expensive with in-situ measurements thus remote sensing is a favorable tool to monitor changes in the land surface. Under the supervision of the European Environment Agency and the Joint Research Centre the Copernicus Global Land Service (GLS) became a prominent service providing satellite data for climatological purposes. In this study the Copernicus GLS provided leaf area index (LAI) and dry matter productivity (DMP) data are used at 1 km resolution over Europe. Based on the LAI, growing season start and length is also determined. Around 18 years of data (2000-2018) is analyzed to look for changes in vegetation. Using the CORINE land cover categories changes in vegetation parameters are also analyzed by differentiating between land cover categories. Furthermore, the ESA (European Space Agency) Climate Change Initiative soil moisture data is coupled with the changes in vegetation parameters. In the case of soil moisture, the data is available at a 0.25&amp;#176; resolution, therefore vegetation parameters are interpolated accordingly.&lt;/p&gt;&lt;p&gt;Initial results show, that the maximum value of LAI increases the most in North Europe, the increase is almost linear. Changes in LAI derived start of growing season shows an earlier start in Central Europe and a later start in North Europe. The connection between vegetation parameters and soil moisture varies based on land cover and location. The strongest correlation is found for summer soil moisture and autumn LAI for arable lands and a negative correlation is found for shrublands. &amp;#160;&amp;#160;&amp;#160;&lt;/p&gt;

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