Peak Growth Stage Research Articles

Crop Yield Estimation Using Time-Series MODIS Data and the Effects of Cropland Masks in Ontario, Canada

This study investigated the estimation of grain yields of three major annual crops in Ontario (corn, soybean, and winter wheat) using MODIS reflectance data extracted with a general cropland mask and crop-specific masks. Time-series two-band enhanced vegetation index (EVI2) was derived from the 8 day composite 250 m MODIS reflectance data from 2003 to 2016. Using a general cropland mask, the strongest positive linear correlation between crop yields and EVI2 was observed at the end of July to early August, whereas a negative correlation was observed in spring. Using crop-specific masks, the time of the strongest positive linear correlation for winter wheat was found between mid-May and early June, corresponding to peak growth stages of the crop. EVI2 derived at peak growth stages of a crop provided good predictive capability for grain yield estimation, with considerable inter-annual variation. A multiple linear regression model was established for county-level yield estimation using EVI2 at peak growth stages and the year as independent variables. The model accounted for the spatiotemporal variability of grain yields of about 30% and 47% for winter wheat, 63% and 65% for corn, and 59% and 64% for soybean using the general cropland mask and crop-specific masks, respectively. A negative correlation during the spring indicated that vegetation index extracted using a general cropland mask should be used with caution in regions with mixed crops, as factors other than the growth conditions of the targeted crops may also be captured by remote sensing data.

Using RapidEye imagery to identify within-field variability of crop growth and yield in Ontario, Canada

Remote sensing has been recognized as a cost-effective way to detect the spatial and temporal variability of crop growth and productivity. In this study, multispectral RapidEye images were used to delineate homogeneous zones of soil and crop development in two fields in Ontario, Canada, one planted with canola (Brassica napus L.) and the other with spring wheat (Triticum aestivum L.). The two fields received different levels of nitrogen (N) treatments during the pre-planting land preparation phase. Soil textures, mineral nitrogen content and crop yield were used to interpret the results of zone delineation. The analysis of variance (ANOVA) tests revealed that the high-resolution RapidEye data, particularly the imagery acquired at peak crop growth stages (i.e. when leaf area index (LAI) is high), provided valuable information for delineating within-field variability of crop growth and yield. Further analysis showed that for both crops, the spatial patterns of crop growth condition varied throughout the growth cycle, revealing different impacts of soil properties and N fertilization on the crops. In particular, during peak growth stage, the within-field variability was most strongly affected by the pre-planting N application and had the strongest correlation with crop yield. These results suggest that high-resolution satellite data (e.g., RapidEye) could assist in making decisions on optimal N fertilization for enhanced crop productivity.

Irrigation efficiency and shallow groundwater in anisotropic floodplain soils near Lake Tana, Ethiopia

AbstractField experiments were conducted (December 2014 to May 2015) in a small irrigation scheme (60 ha) to study the effect of flood irrigation on anisotropic soils with shallow groundwater in the Lake Tana floodplains of Ethiopia. Irrigation (470 ± 33 mm) was measured using V‐notches; rainfall did not occur, and the groundwater table was monitored daily using piezometers to estimate recharge from irrigated onion fields using the groundwater table fluctuation method. Recharge was influenced by applied irrigation amount, groundwater table depth, seasonal temperature variations, irrigation application efficiency and crop growth stages. The decreased deep percolation during the hottest periods and peak growth stages negatively influenced the reduction in groundwater decline caused by irrigation. The soil anisotropy also played a major role in the recharge amount: despite clay dominance in the topsoils, rapid groundwater table rises (0.02–0.56 m) were due to the presence of granular and blocky structures. Recharge was also influenced by irrigation efficiency, indicating higher recharge during periods of lower efficiency. The seasonal recharge was 34–46% of applied irrigation and there is much room for improving irrigation efficiency which is only 46 (±12) to 51 (±17)%. © 2019 John Wiley & Sons, Ltd.

Reduced Carbon Dioxide Sink and Methane Source under Extreme Drought Condition in an Alpine Peatland

Potential changes in both the intensity and frequency of extreme drought events are vital aspects of regional climate change that can alter the distribution and dynamics of water availability and subsequently affect carbon cycles at the ecosystem level. The effects of extreme drought events on the carbon budget of peatland in the Zoige plateau and its response mechanisms were studied using an in-field controlled experimental method. The results indicated that the peatland ecosystem of the Zoige plateau functioned as a carbon sink while under the control (CK) or extreme drought (D) treatment throughout the entire growing season. Maximum fluxes of methane (CH4) emissions and the weakest carbon sink activity from this ecosystem were in the early growth stage, the most powerful carbon sink activity was during the peak growth stage, while the absorption sink activity of carbon dioxide (CO2) and CH4 was present during the senescence stage. Extreme drought reduced the gross primary productivity (GPP) and ecosystem respiration (Re) of the peatland ecosystem by 14.5% and 12.6%, respectively (p < 0.05) and the net ability to store carbon was reduced by 11.3%. Overall, the GPP was highly sensitive to extreme drought. Moreover, extreme drought significantly reduced the CH4 fluxes of the ecosystem and even changed the peatland from a CH4 emission source to a CH4 sink. Subsequent to drought treatment, extreme drought was also shown to have a carry-over effect on the carbon budget of this ecosystem. Soil water content and soil temperature were the main driving factors of carbon budget change in the peatland of the Zoige plateau, but with the increase in soil depth, these driving forces were decreased. The findings indicated that frequent extreme drought events in the future might reduce the net carbon sink function of peatland areas, with an especially strong influence on CO2.

Using remote sensing to estimate forage biomass and nutrient contents at different growth stages

Lignocellulosic biomass is an important feedstock for the second generation bioenergy production. A sustainable supply of biomass feedstock having consistent composition is critical for a biorefinery. This requires a timely monitoring and estimation of the biomass yield and composition in the field. It is not clear if one can use the near infrared (NIR) vegetation canopy reflectance measured in the field and build a calibrate model to estimate biomass yield and nutrient contents (compositions) for the vegetation from vegetative growth through dormancy stages. In this study, the NIR canopy reflectance of a grass/legume mixture was measured in a field with a spectroradiometer with wavelength ranging from 400-2500 nm. The plants were then clipped, dried, and ground to measure the biomass yield, neutral detergent fiber (NDF), acid detergent fiber (ADF), and crude protein (CP). The measurements were conducted at the boot, peak growth, and at dormancy stages. Partial least significant regression (PLSR) models were built using data from each individual growth stage as well as all stages combined. Except for the yield model at peak growth stage and the NDF and ADF models at dormancy stage, models developed from each of the individual stages generally estimated the yield, CP, NDF, and ADF poorly, with R2CV ranging between -0.31 and 0.42. When data from all three growth stages were included, the accuracy of all models was greatly improved, with R2CV ranging between 0.77 and 0.80. Furthermore, multiple linear regression (MLR) models developed with 7–9 most significant wavelengths selected from 400-2500 nm estimated the yield, ADF, NDF, and CP equally well compared with the PLSR models. The estimates from MLR model showed strong correlations between the measured and estimated values, with R2 of 0.72, 0.67, 0.78, and 0.66 for the yield, ADF, NDF, and CP, respectively. These results indicate that biomass feedstock yield and composition can be estimated by the in-situ NIR canopy reflectance using a multiple linear regression model with 7–9 wavelengths. Further calibration is needed to use the model to other geological locations.

Exhumation of eclogite and blueschist (Cyclades, Greece): Pressure–temperature evolution determined by thermobarometry and garnet equilibrium modelling

AbstractHigh‐P rocks such as eclogite and blueschist are metamorphic markers of palaeo‐subduction zones, and their formation at high‐P and low‐T (HP–LT) conditions is relatively well understood since it has been the focus of numerous petrological investigations in the past 40 years. The tectonic mechanisms controlling their exhumation back to the surface are, however, diverse, complex and still actively debated. Although the Cycladic Blueschist Unit (CBU, Greece) is among the best worldwide examples for the preservation of eclogite and blueschist, the proposed P–T evolution followed by this unit within the Hellenic subduction zone is quite different from one study to another, hindering the comprehension of exhumation processes. In this study, we present an extensive petrological data set that permits refinement of the shape of the P–T trajectory for different subunits of the CBU on Syros. High‐resolution quantitative compositional mapping has been applied to support the thermobarometric investigations, which involve semi‐empirical thermobarometry, garnet equilibrium modelling and P–T isochemical phase diagrams. The thermodynamic models highlight the powerful use of reactive bulk compositions approximated from local bulk compositions. The results are also combined with Raman spectrometry of carbonaceous material (RSCM) to retrieve the metamorphic peak temperature distribution at the scale of the island. A major result of this study is the good agreement between all the independent thermobarometric methods, permitting reconstruction of the prograde and retrograde P–T trajectories. Garnet compositional zoning was used to retrieve prograde, peak and retrograde growth stages in line with the results of the P–T isochemical phase diagrams, RSCM temperature and peak‐pressure crystallization of the garnet–omphacite–phengite assemblage. Our results are consistent with previous thermobarometric estimates from other occurrences of CBU rocks (Tinos, Andros), suggesting a multistage exhumation process with (1) early syn‐orogenic exhumation within the subduction channel, (2) isobaric heating at mid‐crustal depths (~10–12 kbar) following thermal re‐equilibration of the lithosphere from a cold syn‐orogenic regime in the subduction zone to a warmer post‐orogenic regime in the back‐arc domain and (3) exhumation and cooling related to a post‐orogenic phase of extension following slab retreat. Expanding to the general aspects of subduction zones, we suggest that such metamorphic evolution of HP–LT units should be regarded as a characteristic feature of exhumation driven by slab rollback.

Determining root water uptake of two alpine crops in a rainfed cropland in the Qinghai Lake watershed: First assessment using stable isotopes analysis

Knowledge of crop root water uptake (RWU) is critical for understanding agricultural water management. However, the mechanisms underlying the RWU of alpine crops in rainfed cropland remain poorly understood. This study investigated seasonal variations in water uptake of oilseed rape (Brassica napus L.) and highland barley (Hordeum vulgare L.) coupled with dual stable isotope tracers at different growth stages. The method of direct inference showed that the soil depth layer from which water was predominantly taken up by roots was 0–30cm. More specifically, oilseed rape and highland barley exhibited different RWU patterns: oilseed rape had the high flexible performance and could revert to deep soil layers (30–60cm) as the main water source according to soil water availability due to short-term droughts at the peak growth stage. In contrast, water uptake by highland barley was primarily derived from both shallow and middle soil layers (<30cm) throughout all growth stages. These findings indicated that the appropriate irrigation wetting depth should be above 30cm for the different growth stages.

An Investigation of the Major Wheat Weeds in Different Zones of Dera Ismail Khan

On account of huge yield losses, weed infestation is a serious threat in wheat crops throughout the country. A comprehensive survey to find out the major weeds in wheat in Dera Ismail Khan was carried out during the crop season of 2012-13. Wheat fields at seed farms of Rakhmanghan, RakhZandani, Rata Kulachi and adjacent farmer’s fields to each seed farm were investigated. Data was collected at the peak growth stage of weeds and the quadratic method was used to record relative density (RD), relative frequency (RF), relative crowding coefficient (RCC) and importance value index (IVI). The results revealed that the major and most problematic weed of wheat at all the locations was Avena fatua (wild oat) on account of having maximum IVI at Rakh Manghan (78.51 & 77.44), Rata Kulachi (77.82 & 77.54) and Rakh Zandani (77.51 & 77.53) seed Farms and Farmer’s fields respectively. Rumex dentatus (dock) and Convolvulus arvensis (Lehli) were the second and third abundantly occurring weeds at almost all the seed farms and farmer fields on account of having the second and third highest IVI values at all the locations. Therefore Avena fatua (wildoat), Rumex dentatus (dock) and Convolvulus arvensis (lehli) seed were collected to find out the yield losses through further experimentation.

Effect of sources and levels of potassium in cotton as influenced fractions of soil potassium under vertisols in Vidarbha region of Maharashtra

The present investigation was carried out in vertisols of Akola district of Maharashtra to ascertain the effect of potassium application on yield and quality of Bt cotton. This was carried out by conducting field experiments on research farm of Department of Soil Science and Agricultural Chemistry, Dr. Panjabrao Deshmukh Krishi Vidyapeeth, Akola and similarly on five farmer’s fields in intensive cotton growing area of vertisols in Akola district during 2012-13 and 2013-14. The treatments comprised of various levels of potassium (0, 25, 50 kg K2O ha-1) applied through either MOP or SOP and additional foliar sprays of SOP @1.5 per cent at critical growth stages of cotton alongwith addition of equivalent quantity of sulphur through bensulf and control without potassium. The fractions of soil potassium were found to be increased alongwith increasing levels of potassium. The reduction in fractions of soil potassium during peak growth stages suggests that there was highest uptake of potassium during this stage and supplemental foliar application of potassium (SOP) had significant response at critical growth stages. The vertisols of present investigation categorized as low to medium in sulphur. Application of sulphur @ 18 kg ha-1 through bensulf was also found equally beneficial as that of SOP for increasing yield. From the present investigation it can be concluded that the fractions of potassium in soil decreased at critical growth stages of cotton viz., flowering and boll development due to increasing uptake by cotton. The application of potassium @ 50 kg K2O ha-1 either through MOP or SOP irrespective of sources showed increase in soil potassium fractions and improvement in soil fertility.

Representação de ciclos harmônicos de séries temporais Modis para análise do cultivo da cana-de-açúcar

Resumo O objetivo deste trabalho foi avaliar o cultivo da cana-de-açúcar, em análise harmônica aplicada a uma série temporal de índices de vegetação Modis, com a representação dos termos harmônicos. Os dados diários de precipitação pluvial para o Estado de São Paulo foram obtidos do Agritempo, acumulados para o período de 16 dias das composições Modis, ao longo das safras de 2004/2005 a 2011/2012. Utilizaram-se o índice de vegetação por diferença normalizada (NDVI) e o índice de realce da vegetação (EVI) em séries temporais decompostas em termos harmônicos pela análise harmônica. Para visualizar a condição de crescimento da vegetação de áreas agrícolas, em especial a informação de fase, aplicou-se a transformação HLS aos termos harmônicos obtidos com o algoritmo Hants, por meio do programa Envi. O cultivo da cana-de-açúcar no Estado de São Paulo apresenta padrões espaciais coerentes com o ciclo de desenvolvimento da cultura e consistentes com a variabilidade das precipitações sazonais que afetam diretamente o momento de máximo dos índices de vegetação. O pico vegetativo da cana-de-açúcar ocorre durante a fase de crescimento, em anos com chuvas normais; porém, em anos de pouca chuva, a fase de maturação da cultura é antecipada e, em anos de muita chuva, a fase de crescimento é antecipada, o que causa o atraso da maturação.

Response of carbon dioxide exchange to grazing intensity over typical steppes in a semi-arid area of Inner Mongolia

The eddy covariance technique was used to measure the CO2 flux over four differently grazed Leymus chinensis steppe ecosystems (ungrazed since 1979 (UG79), winter grazed (WG), continuously grazed (CG), and heavily grazed (HG) sites) during four growing seasons (May to September) from 2005 to 2008, to investigate the response of the net ecosystem exchange (NEE) over grassland ecosystems to meteorological factors and grazing intensity. At UG79, the optimal air temperature for the half-hourly NEE occurred between 17 and 20 °C, which was relatively low for semi-arid grasslands. The saturated NEE (NEEsat) and temperature sensitivity coefficient (Q 10) of ecosystem respiration (RE) exhibited clear seasonal and interannual variations, which increased with canopy development and the soil water content (SWC, at 5 cm). The total NEE values for the growing seasons from 2005 to 2008 were −32.0, −41.5, −66.1, and −89.8 g C m−2, respectively. Both the amounts and distribution of precipitation during the growing season affected the NEE. The effects of grazing on the CO2 flux increased with the grazing intensity. During the peak growth stage, heavy grazing and winter grazing decreased NEEsat and gross primary production (45 % for HG and 34 % for WG) due to leaf area removal. Both RE and Q 10 were clearly reduced by heavy grazing. Heavy grazing changed the ecosystem from a CO2 sink into a CO2 source, and winter grazing reduced the total CO2 uptake by 79 %. In the early growing season, there was no difference in the NEE between CG and UG79. In addition to the grazing intensity, the effects of grazing on the CO2 flux also varied with the vegetation growth stages and SWC.

A Novel Approach for Sugarcane Yield Prediction Using Landsat Time Series Imagery: A Case Study on Bundaberg Region

Quantifying sugarcane production is critical for a wide range of applications, including crop management and decision making processes such as harvesting, storage, and forward selling. This study explored a novel model for predicting sugarcane yield in Bundaberg region from time series Landsat data. From the freely available Landsat archive, 98 cloud free (<40%) Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) images, acquired between November 15th to July 31st (2001-2015) were sourced for this study. The images were masked using the field boundary layer vector files of each year and the GNDVI was calculated. An analysis of average green normalized difference vegetation index (GNDVI) values from all sugarcane crops grown within the Bundaberg region over the 15 year period identified the beginning of April as the peak growth stage and, therefore, the optimum time for satellite image based yield forecasting. As the GNDVI is an indicator of crop vigor, the model derived maximum GNDVI was regressed against historical sugarcane yield data, which showed a significant correlation with R2 = 0.69 and RMSE = 4.2 t/ha. Results showed that the model derived maximum GNDVI from Landsat imagery would be a feasible and a modest technique to predict sugarcane yield in Bundaberg region.

Characteristics of soil evaporation, plant transpiration and water budget of Nitraria dune in the arid Northwest China

Nitraria, a widely growing shrub plant in the dry desert area of China, can fix moving sand along its canopy and form a large number of sand dunes. The Nitraria dune is one of the most effective ways to fix moving sand and protect oasis in Northwest China. However, after dune formation, Nitraria plants gradually die and then release the fixed sand which causes damage to the oasis again. A decrease in the ratio of transpiration (T) to evapotranspiration (ET) was assumed to be the main reason for Nitraria dune degradation because more water was used for soil evaporation, however, this assumption has remained untested because of the difficulty in measuring the Nitraria dune transpiration rate. To overcome this challenge, an intensive field experiment was carried out in 2008–2012 in the Minqin, a typical desert-oasis region in Northwest China. Four measurement sites (early growth stage, rapid growth stage, peak growth stage, and senescence stage) represent the different succession stages of a Nitraria dune. Meteorological parameters were measured by Bowen ratio system, vegetation features and soil physical properties were measured by conventional methods, soil evaporation and transpiration by thermal remote sensing and three-temperature model (3T model), soil moisture by gravimetric and neutron probe method, and evapotranspiration (ET) by Bowen ratio energy balance and water balance methods. Results showed that in a wet year (2008), annual ET was 121, 108, 114, and 126mm, for the four stages, respectively. The ratio of ET to precipitation (P) was 103, 92, 97, and 107%, respectively. In a dry year (2010), ET was 75, 89, 79, and 79mm, respectively, while the ET/P was 106, 126, 112, and 112%, respectively. ET accounted for 92–107% of the precipitation in the wet years and 106–126% in the dry years. ET was nearly equal to precipitation in the wet years and greater than precipitation in the dry years, indicating almost all water from precipitation evaporated in all sites. Our results also showed that vegetation coverage in the four stages was 0.15, 0.35, 0.74, and 0.23, respectively. Instantaneous value of T was 0.021, 0.014, 0.033, and 0.003mmh−1, respectively for the four stages. Instantaneous value of soil evaporation (E) was 0.054, 0.013, 0.004, and 0.009mmh−1, respectively. The corresponding ET was 0.075, 0.027, 0.037, and 0.012mmh−1 for the four stages, respectively. The ratio of T/ET was 0.28, 0.52, 0.89, and 0.25, respectively for the four stages. The ratio reached to its maximum value of 0.89 and then began to decrease, which clearly proved our hypothesis. It concluded that the Nitraria plant not only consumes all the rainfall in the growing season, but also some of the water stored in the soil, which gradually consumes all the soil water storage and finally causes the Nitraria plant death. It also concluded that increasing T, decreasing E and keeping a high T/ET ratio is crucial for desert plants to survive. These results show that the above hypothesis is true and it will be useful for vegetation rehabilitation in the desert area.

白刺沙堆退化与土壤水分的关系研究

PDF HTML阅读 XML下载 导出引用 引用提醒 白刺沙堆退化与土壤水分的关系 DOI: 10.5846/stxb201310242571 作者: 作者单位: 北京大学环境与能源学院,北京大学环境与能源学院,甘肃民勤荒漠草地生态系统国家野外科学观测研究站 甘肃省治沙研究所,甘肃民勤荒漠草地生态系统国家野外科学观测研究站 甘肃省治沙研究所,北京大学环境与能源学院,北京大学环境与能源学院,北京大学 作者简介: 通讯作者: 中图分类号: 基金项目: 国家林业公益性行业科研专项项目(201304305);国家自然科学基金面上项目(20972421); 深圳市人民环境重点实验室专项. The degradation of Nitraria dunes and soil water in Minqin oasis Author: Affiliation: Energy and environment school, Peking University,,,,,,Peking University Fund Project: 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:近几十年来,我国西北干旱区白刺沙堆退化严重,导致固定沙丘活化,流沙掩埋绿洲,造成了严重危害。如何尽可能长期保持白刺沙堆的稳定、防止白刺沙堆活化成为绿洲保护和沙漠化防治急需解决的问题。在多年野外观察的基础上,提出了"土壤水分收支不平衡所导致的土壤水分减少是白刺沙堆退化的主要原因"的研究假设。但是,由于缺少长期的野外观测试验,这个假设一直未被很好地证明。为了证明这个假设,在甘肃民勤的绿洲外围选择了雏形、发育、稳定和死亡四个退化阶段的白刺沙堆,于2008年1月至2012年6月利用中子水分仪和土壤烘干称重法对土壤水分进行了长期观测。结果表明:各样地的土壤含水量均呈现出2008年最大,2009年和2011年次之,2010年最小的趋势。年内变化是春季土壤含水量最低,夏季逐渐增加,随后逐渐减小。在不同发育阶段,雏形阶段的土壤含水量最大,且降水容易下渗。稳定和死亡阶段的白刺沙堆土壤含水量很低,降水难以下渗,只有大的降水事件发生时,水分才可以下渗。因此,稳定和死亡阶段白刺沙堆的土壤水分经常在植物的凋萎点之下,是造成白刺沙堆退化重要原因。证明了"土壤水分减少是白刺沙堆退化的原因"的研究假设。研究结果对今后的植物固沙实践活动会有积极的参考意义。 Abstract:Nitraria dunes can fix a huge amount of moving sand and are one of the most effective ways to protect oasis from moving sand in Northwest China. In recent decades, Nitraria dunes in Northwest China have seriously degraded. As a result, the fixed sand is released, and the oasis is damaged again and again. How to sustain Nitraria dunes long term and prevent the Nitraria plant from dying is an important issue. Based on observation over time, we hypothesized that declining soil water content resulted from an imbalanced soil water budget leading to Nitraria dunes degradation. However this hypothesis hasn't been proved satisfactorily for the lack of long-time field experiments. To prove this hypothesis, we observed soil water content from January 2008 to June 2012 in different degradation stages of Nitraria dunes in the marginal oasis of Minqin, Gansu Province. The methods we used to observe soil water content were the neutron moisture gauge method and weighting method after dried. Results showed that average volumetric soil water content was the highest in 2008 and the lowest in 2010.The variation of volumetric soil water content was the most obvious at the depth of 0-50 cm.The vertical variation pattern of volumetric soil water content was different in different degradation stages. At the depth of 0-90 cm, volumetric soil water content varied the greatest in the early growth stage and rapid growth stage for low water-holding capacity, high seepage power and high air permeability of soil. Three kinds of soil layers divided by soil water variation features occurred in these stages of the Nitraria dunes. These were sudden-change layer, stable layer and increasing layer. However, in the peak growth stage and senescence of Nitraria dunes, volumetric soil water content varied slightly because of crust on the Nitraria dunes surface. Average volumetric soil water content was lower in the early spring, gradually rising in the summer and declining in the autumn.The maximum soil water content occurred in July and September. Moreover, the variation of volumetric soil water content in different seasons was the most obvious at the depth of 0-30 cm. With increasing depth, the volumetric soil water content variation became less. During different degradation stages, the volumetric soil water content in the early growth stage was the highest because precipitation was easy to infiltrate. However, the soil water content was the lowest in the peak growth stage and senescence because precipitation cannot infiltrate without a significant precipitation event. And soil water content in the peak growth stage and senescence of Nitraria dunes was lower than their wilting coefficient. As a result, soil water content cannot satisfy the basic water demand for plant growth which was the principle reason why Nitraria dunes degraded. Through this study, it can be concluded that declining soil water content is the main reason why Nitraria dunes degraded. To take advantage of precipitation efficiently and prevent evapotranspiration on the surface of Nitraria dunes is the key to protecting Nitraria dunes and sand stabilization. This result will provide a positive influence on subsequent vegetation sand-control activities. 参考文献 相似文献 引证文献

Effect of Simulated Acid Rain on Chlorophyll and Carotenoid Content of Sunflower (Helianthus annuusL.) Leaves

The effects of simulated acid rain (SAR) of different pH [distilled water – 7.0 (control), 5.7, 4.5 and 3.0] were studied on chlorophyll and carotenoid content using sunflower (Helianthus annuus L.) cv. ‘Morden’ as the test system. Test plants were sprayed with 30 ml acid rain solution/plant at weekly intervals starting from two leaved stage till initiation of flowering in the early morning under natural environment. In case of control, the total chlorophyll content at the peak growth stage was recorded 1.947 mg g−1 FW. The SAR application showed a decreasing trend in the total chlorophyll content of leaves with increasing acidity of SAR. Chlorophyll a and b contents followed a similar trend in change as was observed in the case of total chlorophyll. Carotenoids at a peak growth stage were recorded maximum in control (0.683 mg g−1 FW) and declined gradually in SAR-treated plants reaching minimum (0.496 mg g−1) at pH 3.0. Chl a: b ratio at peak growth was recorded 4.02 in control. The chlorophyll a: b ratio showed reduction to 3.79 at pH 5.7; however at pH 4.5 and 3.0, the chlorophyll a: b ratio slightly increased to 3.89 and 3.99, respectively. Simulated acid rain application did not affect total chlorophyll: carotenoid ratio.

Estimating biomass on CRP pastureland: A comparison of remote sensing techniques

Biomass from land enrolled in the Conservation Reserve Program (CRP) is being considered as a biofuel feedstock source. A quick, accurate and nondestructive method to estimate biomass yield would be valuable for land managers to ensure sustainable production. The purpose of this study was to compare the ability of regression models to estimate biomass yields using data from satellite and ground based remote sensing platforms. Biomass yields and plant spectral responses were obtained at different phenological stages over two growing seasons (2011–2012) on an 8.1 ha CRP pasture in central Montana. Regression models were constructed using the normalized difference vegetation index (NDVI) and various band combinations from a hand held Crop Circle sensor and from Landsat satellite images. All models showed reasonable accuracy in estimating biomass, with a difference of <276 kg ha−1 or 8% of measured values. None of the models showed statistically significant differences (p > 0.05) between actual and estimated biomass. Results suggest that the usefulness of the spectral regions is a function of phenological growth stage. Red, red edge, and the near-infrared bands are more responsive at boot and peak growth stages while bands in the short-wave infrared increased the accuracy for the dormant stage biomass estimations. Land managers may construct spectral models to more effectively manage biomass resources.

Influence of Drip Irrigation and Plastic Mulch on Yield of Sapota (Achraszapota) and Soil Nutrients

The experiment was carried out to study the response of Sapota (Achraszapota) crop under drip irrigation and plastic mulch. Three levels of irrigation water applied through drip, ring basin irrigation method in combination with plastic mulch were experimented with five replications on Sapota plants. Reference evapotranspiration was estimated using FAO-56 Penman Monteith approach. The Sapota crop water requirement was estimated using reference evapotranspiration data and crop co-efficient for different crop growth stages. The irrigation water was applied at 60%, 80% and 100% of the crop water requirement. Irrigation intervals were at 2 and 5 days respectively in drip and ring basin irrigation treatments. The water requirement of Sapota crop varies between 2.14 mm (10.71 L) per day per plant in winter season and 6.89 mm (34.44 L) per day per plant in summer season for 100% water requirement treatment at peak growth stage. To investigate the effect of plastic mulch on soil, the physico-chemical analysis of soil was performed for the soil samples collected from three different depths (0-30, 30-60, 60-90 cm). The soil chemical analysis indicated increase in organic carbon, organic matter, humic acid, microbial count, available potassium, available phosphorus, total nitrogen content and C:N ratio for the soil covered with the plastic mulch treatment. The pH and available nitrogen was found to decrease in the soil covered with plastic mulch. The biometric observations (canopy, height, girth, no. of branches) of Sapota plants showed positive influence of the irrigation and plastic mulch treatments on growth of Sapota crop. Due to mulch alone the increase in Sapota yield varied from 7.62% to 41% in different treatments. Yield of Sapota crop was found to increase by 21.05% due to drip in comparison to ring basin irrigation.

Jute Crop Discrimination and Biophysical Parameter Monitoring Using Multi-Parametric SAR Data in West Bengal, India

The article highlights the results of a study carried out to understand the Synthetic Aperture Radar (SAR) response to the second most important fibre crop of India i.e. Jute at C and L band frequency and at multiple polarizations. Methodology has been well established to classify jute crop using 3-date multitemporal HH SAR data and is being used for national level forecast in India. Performance comparison of single polarization (HH) multi-date versus dual-polarization 2-date data from Radarsat (both dual-pol HH/HV and quad-pol) was evaluated. Three-date HH polariza-tion (May, 05, May 29 and June 22) data had results comparable to two-date HH/HV data with around 90% accuracy. Correlation between backscattered signals and crop height shows that L-band signal has high correlation with crop height particularly in the peak or advanced crop growth stage as compared to C-band. Also backscatter variation with percent area cover has been investigated. Both plant height and area cover show stronger dependence to cross-polarization backscatter. Biophysical parameters viz. crop height and vigour map has been generated which will aid in monitoring growth and yield potentials.

A Comparative Study on Hourly Real Evapotranspiration and Potential Evapotranspiration during Different Vegetation Growth Stages in the Zoige Wetland

Abstract The Zoige wetland, located in the eastern edge of Qinghai-Tibet Plateau, is highly sensitive to global climate change for its high elevation and cold environment. As one of the major components in the hydrological cycle, evapotranspiration (ET) affects regional water balance and ecosystems in alpine wetlands. To identify the impact of the changes of wetland eco-environment on ET, and to indicate the relation between the real ET and the potential ET, a comparative study on the hourly real ET measured by weighting lysimeters and the hourly potential ET, calculated by the FAO Penman-Monteith equation, has been carried out at three blocks with different surface water levels during three vegetation growth stages in the Zoige wetland. Results show that the hourly potential ET is generally higher than the real ET during the studied period. The hourly ET changed with the variation of the vegetation growth stage, the water level and vegetation characteristics. The hourly potential ET is the largest in the peak growth stage, and the least during the last growth stage for each water level. The real ET is the least at the highest water level for all growth stages. The results suggest that future wetlands management strategies should emphasize the protection of a reasonable vegetation pattern and the basic water demands of ecosystems for improving the wetland ecosystem health in the Zoige wetland.

Hysteresis response of daytime net ecosystem exchange during drought

Abstract. Continuous measurements of net ecosystem CO2 exchange (NEE) using the eddy-covariance method were made over an agricultural ecosystem in the southeastern US. During optimum environmental conditions, photosynthetically active radiation (PAR) was the primary driver controlling daytime NEE, accounting for as much as 67 to 89% of the variation in NEE. However, soil water content became the dominant factor limiting the NEE-PAR response during the peak growth stage. NEE was significantly depressed when high PAR values coincided with very low soil water content. The presence of a counter-clockwise hysteresis of daytime NEE with PAR was observed during periods of water stress. This is a result of the stomatal closure control of photosynthesis at high vapor pressure deficit and enhanced respiration at high temperature. This result is significant since this hysteresis effect limits the range of applicability of the Michaelis-Menten equation and other related expressions in the determination of daytime NEE as a function of PAR. The systematic presence of hysteresis in the response of NEE to PAR suggests that the gap-filling technique based on a non-linear regression approach should take into account the presence of water-limited field conditions. Including this step is therefore likely to improve current evaluation of ecosystem response to increased precipitation variability arising from climatic changes.