John L. Monteith

Bio: John L. Monteith is an academic researcher from International Crops Research Institute for the Semi-Arid Tropics. The author has contributed to research in topics: Atmosphere & Transpiration. The author has an hindex of 58, co-authored 138 publications receiving 30024 citations. Previous affiliations of John L. Monteith include Goddard Space Flight Center & University of Nottingham.

The reflection of short‐wave radiation by vegetation

Abstract: The fraction of short-wave radiation reflected from agricultural crops was measured from May till September 1958 using two portable solarimetric thermopiles. Maximum reflection coefficients for grass, lucerne, potatoes, sugar beet, and spring wheat were between 0·25 and 0·27. Lower values found in the early stages of crop development, and for spring wheat even at maturity, can be correlated with low leaf areas and mutual shading of the leaves, also reduced reflection. Data by Billings and Morris (1951) have been used to compute total reflection coefficients for different types of vegetation including two desert species and to explain why these do not normally differ as much as the coefficients for the visible component.

Time, Temperature and Germination of Pearl Millet (Pennisetum typhoides S. & H.): III. INHIBITION OF GERMINATION BY SHORT EXPOSURE TO HIGH TEMPERATURE

Abstract: Seeds of pearl millet were germinated on wet filter paper at temperatures up to 50 °C. In one experiment, the temperature was held at 50 °C during imbibition and was then lowered to 32 °C or 25 °C. Germination rate and the maximum fraction of seeds germinating (Gm) both decreased as the time of exposure to 50 °C increased. In contrast, exposure to 50 °C after imbibition for 8 h slowed germination but did not significantly reduce Gm. When the 'high' temperature imposed after imbibition was reduced from 50 °C to 45 °C, there was a small reduction in the rate of germination but not in Gm. The responses have implications for the optimum time of sowing in the tropics when maximum daytime soil temperature at the depth of sowing is in the range of 45-50 °C.

Radiation and Crops

Abstract: The analysis of radiation climate is a central problem of agricultural meteorology because rates of photosynthesis depend on the receipt of visible light and rates of transpiration depend on the net exchange of radiation by a crop canopy. Both short-wave (solar) and long-wave (terrestrial) radiation are correlated with cloud amount, and in south-east England the income of net radiation in summer is proportional to the income of solar radiation.In principle, the fraction of total radiation in the visible waveband depends on cloud cover and on the amount of absorption and scattering in the atmosphere, but in practice the fraction is often between 0·40 and 0·45. The calculation of photosynthetic efficiency needs a figure for the number of quanta (or Einsteins) per unit energy, and this figure can be calculated from the mean wavelength of the radiation weighted by energy, about 0·55μ for direct sunlight.The reflection of radiation by vegetation changes with solar elevation, and at angles between 40° and 60° it ranges between 0·15 for a rough crop (e.g. pineapple) to 0·26 for smoother crops (e.g. sugar beet, kale). The transmission of radiation through the canopy can be expressed as a function of the leaf area index and a parameter that depends on the distribution and orientation of leaves.

An empirical method for estimating long-wave radiation exchanges in the British Isles

Abstract: From radiation measurements at Kew Observatory (tabulated by Lonnqvist), the effective emissivity of the atmosphere e, defined as the ratio of incoming long-wave radiation to black-body radiation at screen temperature, can be related to optical path m (cm) by With standard deviation ± 0·018. The relation between m and surface vapour pressure e (mb) found from Belasco's (1952) air mass analysis is giving almost the same as Brunt's equation from Benson data. Net long-wave radiation L over short grass can be calculated from where c is fractional cloudiness; σTA is black-body radiation at screen temperature; ΔL1 is a correction for the difference between TA and cloud-base temperature; and ΔL2 for the difference between TA and surface radiative temperature. From Roach's Kew data, ΔL1 = – 18 cal cm−2 day−1 and ΔL2 varies with season from – 12 cal cm−2 day−1 (December) to + 20 cal cm−2 day−1 (June). Throughout the British Isles, annual mean L with c = 0 is close to – 200 cal cm−2 day−1, and for real values of c Estimated annual net (total) radiation is 29 k cal cm−2 with little variation over the British Isles.

Crop evapotranspiration : guidelines for computing crop water requirements

Abstract: (First edition: 1998, this reprint: 2004). This publication presents an updated procedure for calculating reference and crop evapotranspiration from meteorological data and crop coefficients. The procedure, first presented in FAO Irrigation and Drainage Paper No. 24, Crop water requirements, in 1977, allows estimation of the amount of water used by a crop, taking into account the effect of the climate and the crop characteristics. The publication incorporates advances in research and more accurate procedures for determining crop water use as recommended by a panel of high-level experts organised by FAO in May 1990. The first part of the guidelines includes procedures for determining reference crop evapotranspiration according to the FAO Penman-Monteith method. These are followed by updated procedures for estimating the evapotranspiration of different crops for different growth stages and ecological conditions.

Large Area Hydrologic Modeling and Assessment Part i: Model Development

Abstract: A conceptual, continuous time model called SWAT (Soil and Water Assessment Tool) was developed to assist water resource managers in assessing the impact of management on water supplies and nonpoint source pollution in watersheds and large river basins. The model is currently being utilized in several large area projects by EPA, NOAA, NRCS and others to estimate the off-site impacts of climate and management on water use, nonpoint source loadings, and pesticide contamination. Model development, operation, limitations, and assumptions are discussed and components of the model are described. In Part II, a GIS input/output interface is presented along with model validation on three basins within the Upper Trinity basin in Texas.

Primary Production of the Biosphere: Integrating Terrestrial and Oceanic Components

Abstract: Integrating conceptually similar models of the growth of marine and terrestrial primary producers yielded an estimated global net primary production (NPP) of 104.9 petagrams of carbon per year, with roughly equal contributions from land and oceans. Approaches based on satellite indices of absorbed solar radiation indicate marked heterogeneity in NPP for both land and oceans, reflecting the influence of physical and ecological processes. The spatial and temporal distributions of ocean NPP are consistent with primary limitation by light, nutrients, and temperature. On land, water limitation imposes additional constraints. On land and ocean, progressive changes in NPP can result in altered carbon storage, although contrasts in mechanisms of carbon storage and rates of organic matter turnover result in a range of relations between carbon storage and changes in NPP.

Correction of flux measurements for density effects due to heat and water vapour transfer

Abstract: When the atmospheric turbulent flux of a minor constituent such as CO2 (or of water vapour as a special case) is measured by either the eddy covariance or the mean gradient technique, account may need to be taken of variations of the constituent's density due to the presence of a flux of heat and/or water vapour. In this paper the basic relationships are discussed in the context of vertical transfer in the lower atmosphere, and the required corrections to the measured flux are derived. If the measurement involves sensing of the fluctuations or mean gradient of the constituent's mixing ratio relative to the dry air component, then no correction is required; while with sensing of the constituent's specific mass content relative to the total moist air, a correction arising from the water vapour flux only is required. Correspondingly, if in mean gradient measurements the constituent's density is measured in air from different heights which has been pre-dried and brought to a common temperature, then again no correction is required; while if the original (moist) air itself is brought to a common temperature, then only a correction arising from the water vapour flux is required. If the constituent's density fluctuations or mean gradients are measured directly in the air in situ, then corrections arising from both heat and water vapour fluxes are required. These corrections will often be very important. That due to the heat flux is about five times as great as that due to an equal latent heat (water vapour) flux. In CO2 flux measurements the magnitude of the correction will commonly exceed that of the flux itself. The correction to measurements of water vapour flux will often be only a few per cent but will sometimes exceed 10 per cent.