Relationship between wheat yield and foliage temperature: theory and its application to infrared measurements

A theoretical basis is presented for the relationship between crop yield and one time-of-day measurements of the foliage-ambient temperature differential (T_f — T_a). The theory was used to analyse two contrasting relationships between wheat yield and T_f — T_a. The relationships resulted from a range of irrigation treatments and two times of sowing imposed on 26 plots. This caused yields to vary from 8.3 to 1.7 t ha^?1 when the crop was sown in June and from 5.5 to 2.2 t ha^?1 when sown in August. To explain these variations T_f — T_a and associated micrometeorological data were collected around solar noon during the period from jointing to maturity. From these data transpiration and the associated aerodynamic and canopy stomatal resistances to water vapour transport were predicted. The associated canopy conductances for diffusion of CO₂ were derived and used to predict the corresponding CO₂ assimilation rates.The predicted transpiration and CO₂ assimilation rates were closely related to yield within each year but not between years. However if the rates were normalised for the shorter growing season of the late sown crop the yields from the 26 plots formed a common relationship. The transpiration vs. yield relationship was further improved by normalising for differences in foliage vapour pressure deficit. The good agreement between field data and theory was probably due to the dominating effect of stomatal control on both T_f — T_a and CO₂ assimilation rate. If CO₂ assimilation rate is strongly influenced by factors other than soil water stress then the theory may not hold and a different relationship may exist. It was concluded that infrared thermometry is a useful technique for studying yield variations in agronomic experiments where these variations are due to stomatal control.     

PO和PVC薄膜温室的光温环境及其与薄膜流滴性的关系

本研究通过对ＰＯ薄膜和ＰＶＣ薄膜温室光温环境的连续测量，分析比较了两种温室光温环境，同时测量了薄膜内表面凝结水量的差异，推导出了计算温室内外气温差的简便计算式，在该计算式中包含了薄膜内表面凝结水量对透光率的影响     

High-Time Resolution Analysis of Diel Variation in Methane Emission from Flooded Rice Fields

Methane (CH₄) emission from flooded rice fields was measured hourly over 24 h for rice (Oryza sativa L.) seasons in 2008 and 2009. The objectives of this study were to identify typical diel variation in CH₄ emission and to estimate the best time of day for optimum extrapolation of daily CH₄ emission. Our results showed distinct diel variation in CH₄ emission, which exhibited a maximum at 14:00–15:00 and a minimum at midnight. About 5.2–5.6% of total CH₄ emitted per day (110–160 mg CH₄ m^?2 d^?1) was released at 14:00–15:00. The diel pattern of CH₄ emission resembled that of air temperature (T_a). The T_a coupled with solar radiation could cause a difference in partial pressure of CH₄ (DPPC) through the gas conduit of the plant. The best extrapolation of daily CH₄ emission was achieved with data observed at 10:00–11:00. We concluded that DPPC-induced CH₄ emission is an important mechanism causing diel variation.     

Light and temperature modulated expolinear growth model for potato (Solanum tuberosum L.)

Expolinear growth equations are robust and simple models for the early and middle stages of crop growth. Those proposed by Greenwood and by Monteith were compared for potato (Solanum tuberosum L.) crop biomass in well-managed fields in the Central Wisconsin Sand Plain, and the Monteith equation found preferable. A time-derivative form of the Monteith equation was coupled to daily solar radiation and air temperature. Solar radiation was linked to daily maximum absolute growth through light use efficiency, and daily maximum relative growth rate was made a function of temperature by assuming a doubling of biological processes with every 10 °C increase (Q₁₀=2). The modified model predicted dynamic dry matter accumulation variation from year to year, and showed improved prediction of potato growth until senescence.     

Predicting bare soil temperature. I. Theory and models for the multi-day mean diurnal variation

The energy balance equation for the soil-air interface is expressed, by suitable approximations, in a form linear in the surface temperature T₀. This forms the basis of two predictive models for the diurnal variation of T₀, averaged over a many-day interval, for potentially evaporating bare soil. Input data include total solar radiation, air temperature and vapour pressure, windspeed u_a, cloud cover c, and soil radiative, aerodynamic and thermal properties (the latter assumed uniform). In the simpler model, based on harmonic analysis, u_a and c are assumed constant. For N_t observations per day, an algebraic solution is found as a set of equations for the parameters of up to the first N_t/2 harmonics. In the second model, dynamic wind-speed is introduced, and a more complicated linear algebraic method of solution is required. The models have agroclimatic value, since by averaging they predict the thermal ‘climate’ of soil, in contrast to instantaneous models which describe the time-specific thermal ‘weather’.     

Total reflected solar radiation calculated from multi-band sensor data

Reflected solar radiation is a significant term in the net radiation equation and is the one most strongly affected by surface conditions. The evaluation of net radiation over a heterogeneous area requires a detailed knowledge of the areal distribution of the reflected solar radiation. Remote sensing offers a means to obtain this areal distribution, provided that the total reflected solar spectrum can be estimated from discrete band multispectral radiometric data. A radiative transfer model was used to calculate the irradiance at the earth's surface for a number of atmospheric scattering and adsorption conditions. Response functions of two multiband radiometers were used to obtain the partial spectrum/total spectrum (P/T) ratio for each radiometer at each atmospheric condition. It was found that the P/T ratio was essentially independent of atmospheric scattering and only mildly dependent on water vapor absorption. Reflectance spectral distributions for 14 different surface conditions (bare soil to full green canopy) were used along with the irradiance data to determine the P/T ratio for reflected solar radiation. Multispectral data, with the appropriate P/T ratio, were used to calculate the total incoming radiation and the total reflected radiation from a wheat canopy. The calculated data differed from wide band pyranometer data by about 5%. It was concluded that both total incoming and reflected solar radiation can be evaluated from multispectral radiometric data. This development is a step towards regional net radiation maps, and possibly regional evapotranspiration maps.     

Predicting bare soil temperature. II. Experimental testing of multi-day models

Two agroclimatic models described earlier are tested against measurements of temperature at the soil surface, T₀, and in bulk soil, T(z,t), at an experimental site near Aberdeen during spring, summer and autumn. Soil temperature is predicted most accurately in spring and autumn, when the constant-windspeed model ENBL1 predicts the mean within 0.3 K of measurement. Thedynamic-windspeed model ENBL2 predicts within 0.1 K in all intervals, and with error<0.3 K to depth z=32 cm in spring and autumn. A sensitivity analysis of the output diurnal wave, T₀(t), shows that maximum input economy requires only time-dependent shortwave radiation, R_s(t), and air temperature, T_a(t), other inputs being constant. Two or three harmonics in ENBL1 should suffice, requiring four or six measurements per day, depending mainly on the time-structure of the primary driving function R_s.     

Adjustment of radiation use efficiency of winter wheat by air temperature at different irrigation regimes and nitrogen rates

In this research, radiation use efficiency (RUE) of winter wheat was determined under different irrigation regimes and nitrogen application rates in experimental field at southwest Iran (semi-arid region) in 2009–2010 and 2010–2011. The experiment was laid out as a split plot design, with irrigation treatments as main plots and N fertilization as sub-plots with three replications. Irrigation treatments were 1.2 (I4), 1.0 (I3), 0.8 (I2), and 0.5 (I1) times of the full irrigation requirements and N treatments were 0 (N1), 46 (N2), 92 (N3), and 136 (N4) kg ha^?1. Air temperature had significant effects on RUE that was adjusted by multiplication of hourly temperature factor to the hourly values of solar radiation (RUE _a ). The values of RUE _a were significantly different from the values of RUE in both growing seasons. The values of RUE _a ranged from 1.44 to 1.83 g MJ^?1 and 1.45 to 1.81 g MJ^?1 in 2009–2010 and 2010–2011, respectively. In both growing seasons, minimum and maximum values of RUE were at I1N1 and I4N4 treatments, respectively. The methods of daily maximum and minimum air temperature were modified for considering the effects of air temperature on RUE at locations where hourly air temperature and radiation were not available.     

Calibration of the Ångström–Prescott coefficients (a,b) under different time scales and their impacts in estimating global solar radiation in the Yellow River basin

The Ångström–Prescott (A–P) equation relating in its current form the incident top-of-atmosphere solar radiation to the solar radiation received at the surface, is one of the most accurate and widely used sunshine-based methods estimating global solar radiation (R_s). The key in its application is the calibration of the locally specific coefficients. Although the coefficients have been extensively studied and calibrated in many places over the world, their relations with time scale are much less investigated. This paper addressed the variation in these coefficients caused by time scale and how this variation results on the accuracy of R_s predictions. This was done using long-term data at 31 sites from the Yellow River basin in China by parallel calibration at three time scales: daily, monthly mean daily and yearly mean daily. We found that the A–P coefficients obtained using monthly data generally had higher a and lower b and larger variations over those using daily data. At yearly time scale, the sunshine–radiation relationship can no longer be described by the linear A–P formula. The difference in coefficients between daily and monthly calibration was rather large accounting for 71% of the differences in a and 61% in b that in turn were greater than 0.03, corresponding to 81% for a and 49% for b being greater than 10%. Time scale had a larger effect on a than on b, and it caused a maximum variation of 82% in a and 43% in b in the basin, equaling half of the variation caused by geographical location. However, the large effect of time scales on a and b produced no significant impact on the estimation accuracy of R_s because of the conservative response of the sum a + b to time scale. In this sense, the coefficients calibrated at daily scale are interchangeable with those calibrated at monthly scale, indicating the high flexibility of the A–P formula. Nevertheless, calibration made at daily scale has two important advantages over monthly scale in that it requires fewer years’ data to obtain stabilized coefficients, and that it is easily predicted more accurately with common site information. Our findings have two implications. Firstly, they provide an additional guidance on the explanation of the large variability of the coefficients found in the literature for the same geographical location. Secondly, they facilitate the choice of the coefficients in practical applications by proving their interchangeability in the estimation of R_s.     

贵阳市及其郊区土壤大气界面间汞交换通量的初步研究

利用动力学通量箱与高时间分辨率测汞仪联用技术对贵阳市市区及其郊区4个点的土壤大气界面间的汞交换通量进行了测定,用小型多功能气象仪记录了采样期间的气象参数。结果显示:4个采样点的大气汞含量都明显高于全球背景值(1.5~2.0 ng m-3),显示出贵阳市市区及郊区都遭受了不同程度的大气汞污染。土壤大气界面间的汞交换通量与光照强度具有显著的相关关系,与土壤温度也有很好的相关性。     

Application of Response Surface Methodology and Machine Learning Combined with Data Simulation to Metal Determination of Freshwater Sediment

A comparative study between conventional methods (EPA 3050B and ISO 11466.3) of metal extraction and a simple low-cost method, using aqua regia, was carried out in this work. Six elements (Mn, Cu, Zn, Pb, Ni, and Cd) were determined by flame atomic absorption spectrometry (FAAS) in a certified sample of sediment (CNS 392). Central composite design (CCD) and response surface methodology (RSM), as well as machine learning, were used to find the optimal conditions for metal extraction. The influence of the parameters—volume of nitric acid in aqua regia (v), time of extraction (t), and temperature (T)—on Mn, Cu, Zn, and Pb recoveries was investigated. The best condition for the recovery of all the metals was v = 2.5 mL of HNO₃, t = 2 h, and T = 90 °C. In comparison with the conventional methods, the aqua regia method was found to present better recovery values and lower standard deviations for all the metals studied.     

利用MODIS数据计算地表蒸散

地表蒸散影响着地表水分和能量的输送,在水文、气象、地理等诸多领域占有重要地位。该文首先基于大气辐射传输原理,利用MODIS大气产品提供的臭氧、水汽以及550 nm气溶胶含量,运用大气透过率计算模型,进行了太阳总辐射的计算,均方根误差（RMSE）为61.4 W/m2,相比FAO-56透过率模式112.1 W/m2的误差有了明显改进。在此基础上结合MODIS的地表温度、植被指数产品进行了地表蒸散的计算。瞬时显热通量与郑州市大孔径闪烁仪（LAS）观测相比,有较好的一致性,RMSE为29.9 W/m2。应用本文的透过率模型计算得到的日蒸散与观测值相比,RMSE为0.69 mm,应用FAO-56透过率计算式得到的日蒸散RMSE为1.42 mm。从验证结果来看,透过率的准确计算能够比较明显的提高地表蒸散计算精度。     

An analysis of solar beam penetration through circular gaps in canopies of uniform thickness

A model for direct solar beam penetration through a canopy gap is presented. A canopy gap is assumed to be a circular opening in a canopy of uniform thickness. Distinct seasonal patterns of T_ps (daily duration of possible sunshine) under a model gap were revealed: long T_ps was found during seasons with high solar altitudes at noon, and short T_ps during those with low solar altitudes. Latitude showed profound effects on both the seasonal pattern of T_ps and gap-size dependency of T_ps; with increasing latitude, the seasonal variation of T_ps was enhanced and the beam penetration through a small gap decreased.The aspect of the slope of the ground influenced the seasonal pattern of T_ps, especially at higher latitudes. In the earth's northern hemisphere, solar beam penetration was enhanced on a south-aspect slope, but reduced on a north-aspect slope during the seasons of lower solar altitudes.On the ground below the model gap, the area where T_ps0 was an oblique ellipse extending east-west. The area moved in the north-south direction during the year. In regions of the northern hemisphere out of the tropics, the northern part of the gap projection on the ground showed much higher T_ps than the southern part. These results suggest that the direction to, not only the distance from, the gap center greatly affects the light regime on forest floors.     

The temperature dependence of dicyandiamide (DCD) degradation in soils: A data synthesis

Dicyandiamide (DCD, C₂H₄N₄) is a nitrification inhibitor that has been studied for more than 80 years. However, there are few papers that have examined the use of DCD on dairy farms where cattle graze pasture and where urine is the primary form of nitrogen (N) deposited onto soils. After DCD was applied (10 kg DCD ha^?1) with bovine urine (700–1200 kg N ha^?1) to five soils throughout New Zealand, the reduction in direct nitrous oxide (N₂O) emissions was significant and remarkably consistent (71 ± 8%, average ± standard error). The application of DCD to these soils occurred in autumn and winter; daily average soil temperature (T) was reported but these data were not further analysed. Perusal of the literature suggested no consensus on the temperature dependence of DCD degradation in soils. Based on published data from controlled-environment studies of soils sampled in four countries, we quantified the relation between T and the time for DCD concentration in soils to decline to half its application value (t_½) as t_½ (T) = 168e^?0.084T with parameter standard errors of ±16 d and ±0.011 d^?1, respectively (n = 16). For example, at 5 °C a 1 °C increase in T reduced t_½ from 110 to 101 d whereas at 25 °C the reduction was 20–19 d. Analysing T data from the New Zealand trials using our t_½ (T) function, over 43–89 d when direct N₂O emissions from treated plots became indistinguishable from the controls, the estimated percentage of applied DCD remaining in the soil averaged 43 ± 10%. These calculations suggested the apparently remaining DCD was ineffective with respect to direct N₂O emissions. In the absence of measurements, explanations for this interpretation included vertical displacement of the DCD and sorption onto organic matter in soils. The consistent DCD efficacy from these trials corresponded with T generally <10 °C, so it is suggested as an application criteria for the reduction of direct N₂O emissions from pastoral soils subjected to urine excretion by grazing cattle.     

Problems with porometry: measuring stomatal conductances of potentially transpiring plants

Porometer measurements of the stomatal conductances (C_s) of potentially transpiring water hyacinth plants at Phoenix, Arizona in October of 1984, May–June of 1985, and September of 1986 indicate that C_s steadily drops as the vapor pressure deficit (VPD) of the air in the measuring system's cuvette or leaf chamber rises. Utilizing this relationship to calculate the foliage-air temperature differential (T_F−T_A) response of these leaves to leaf-chamber air VPD, as per the basic equations of standard heat and water vapor transport theory; we obtain a leaf-chamber “non-water-stressed baseline” that is consistent with leaf-chamber measurements of T_F−T_A vs. air VPD. Free-air T_F−T_A vs. air VPD data, on the other hand, produce a relationship that is similarly consistent with a plant stomatal conductance which is invariant with respect to the air VPD. Hence, we conclude that the very act of stomatal conductance measurement alters a potentially transpiring plant's evaporative water loss rate in such a way that, for very high air VPD conditions, the directly measured C_s value (although correct for the leaf in the cuvette or leaf chamber) may be much reduced from that characteristic of comparable non-chamber-encumbered plants in the free air. We then demonstrate that this instrument-induced reduction in directly measured C_s values is a unique function of the leaf-chamber IJ index, evaluated with respect to the plant's free-air non-water-stressed baseline. Similar results obtained by others for cotton suggest that this phenomenon may be quite general, and that the C_s vs. air VPD interaction, believed by many to be widely operative throughout the plant kingdom, may not really exist in actual field situations.     

Ratio of PAR to broadband solar radiation measured in Cyprus

The relationship between the two radiant fluxes is studied from almost a 3-year data archive of hourly photosynthetically active photon flux (Q_P) and global solar irradiance (R_S) performed at Athalassa, Cyprus. These data are used to determine temporal variability of the ratio (Q_P/R_S) and its dependence on sky conditions. The seasonal variation of the ratio obtained from daily data ranges from 1.942 E MJ⁻¹ (summer) to 1.892 E MJ⁻¹ (winter) with an annual mean value of 1.919 E MJ⁻¹. The ratio increased from 1.865 to 2.01 E MJ⁻¹ (daily values) or from 1.878 to 2.197 μE J⁻¹ (hourly values), as sky conditions changed from clear to overcast. Effective atmospheric parameters such as sky clearness, brightness and path length were found to cause substantial changes to the PAR fraction.     

Estimating stomatal diffusion resistance for Douglas-fir,lodgepole pine and white oak under light saturated conditions

Stomatal diffusion (leaf) resistance (r_s) of Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco), lodgepole pine (Pinus contorta Dougl. ex Loud.) and white oak (Quercus alba L.) in a variety of natural environments is described during conditions of light saturation as a function of the product of the predawn (base) xylem pressure potential of twigs (ψ_xb) or the soil water potential (ψ_s), and the saturation deficit of the atmosphere (δ_e). This general functional form was derived from an analysis based on an Ohm's law analog for water flow in the soil—plant—atmosphere system. The specific form used in each case was determined using regression analysis, where dependent variables considered were xylem pressure potential of the twigs or leaves (ψ_x) and air temperature (T) as well as δe and ψ_xb (or ψ_s). For three independent sets of Douglas-fir data, it is shown qualitatively that a single function describes the combined data as well as the functions derived for each of three data sets individually. The results imply that it may be possible to describe stomatal response of Douglas-fir, and perhaps other species, over a range of environmental conditions using the same model.     

长江三角洲地区麻栎和栓皮栎蒸腾规律及其对气候因子的响应

森林蒸腾在维系森林生态系统水量平衡上起着重要作用,研究麻栎和栓皮栎的蒸腾耗水规律,有助于了解栎林的水文过程和水量平衡。采用热扩散探针法,对江苏省句容市麻栎和栓皮栎林蒸腾速率进行连续观测,研究蒸腾速率在晴天、阴天和雨天的日变化特征,以及不同天气下气候因子对蒸腾速率的影响机制。结果表明,麻栎和栓皮栎蒸腾速率日变化在晴天、阴天均为单峰型,而雨天峰型波动较大。晴天峰值出现在11:30—12:30,阴天峰值出现在13:30—14:00。不同天气下,麻栎、栓皮栎日均蒸腾速率表现为麻栎>栓皮栎,晴天>阴天>雨天。总辐射、气温、饱和水汽压差与麻栎、栓皮栎蒸腾速率呈极显著正相关。总辐射对麻栎、栓皮栎蒸腾速率的贡献最大,在晴天其贡献度分别为91.7%和85.5%,而在阴天为71.0%和80.1%,在雨天为50.4%和57.9%。总辐射是影响麻栎和栓皮栎蒸腾速率最大的气候因子,其次是饱和水汽压差、气温和土壤含水量。     

Detection of water stress in an olive orchard with thermal remote sensing imagery

An investigation of the detection of water stress in non-homogeneous crop canopies such as orchards using high-spatial resolution remote sensing thermal imagery is presented. An airborne campaign was conducted with the Airborne Hyperspectral Scanner (AHS) acquiring imagery in 38 spectral bands in the 0.43–12.5 μm spectral range at 2.5 m spatial resolution. The AHS sensor was flown at 7:30, 9:30 and 12:30 GMT in 25 July 2004 over an olive orchard with three different water-deficit irrigation treatments to study the spatial and diurnal variability of temperature as a function of water stress. A total of 10 AHS bands located within the thermal-infrared region were assessed for the retrieval of the land surface temperature using the split-window algorithm, separating pure crowns from shadows and sunlit soil pixels using the reflectance bands. Ground truth validation was conducted with infrared thermal sensors placed on top of the trees for continuous thermal data acquisition. Crown temperature (T_c), crown minus air temperature (T_c − T_a), and relative temperature difference to well-irrigated trees (T_c − T_R, where T_R is the mean temperature of the well-irrigated trees) were calculated from the ground sensors and from the AHS imagery at the crown spatial resolution. Correlation coefficients for T_c − T_R between ground IRT sensors and airborne image-based AHS estimations were R² = 0.50 (7:30 GMT), R² = 0.45 (9:30 GMT) and R² = 0.57 (12:30 GMT). Relationships between leaf water potential and crown T_c − T_a measured with the airborne sensor obtained determination coefficients of R² = 0.62 (7:30 GMT), R² = 0.35 (9:30 GMT) and R² = 0.25 (12:30 GMT). Images of T_c − T_a and T_c − T_R for the entire field were obtained at the three times during the day of the overflight, showing the spatial and temporal distribution of the thermal variability as a function of the water deficit irrigation schemes.     

Relationships between single tree canopy and grass net radiations

It is reported a simple approach to transform daily values of grass net (all-wave) radiation (R_n, MJ m⁻² day⁻¹), as measured over standard grass surface at meteorological stations, into whole tree canopy net radiation (A, MJ tree⁻¹ day⁻¹). The revolving Whirligig device [McNaughton, K.G., Green, S.R., Black, T.A., Tynam, B.R., Edwards, W.R.N., 1992. Direct measurement of net radiation and photosynthetically active radiation absorbed by a single tree. Agric. For. Meteorol. 62, 87–107] describing a sphere about the tree measured A in five trees of different species (walnut, dwarf apple, normal apple, olives and citrus), with leaf area L_A varying from 8.65 to 40 m². For each tree, A and R_n were linearly related (A = bR_n), as previously reported elsewhere, but it was found that the slope of such regression was also a linear function of L_A or, b = 0.303 (±0.032) L_A. Consequently, the hypothesis that total daily tree canopy net radiation per unit leaf area is linearly related to grass net radiation could not be rejected after 86 days of measurements in five locations, and the empirical relationship is A = 0.303 (±0.032) R_nL_A (R² = 0.9306).