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.

Solarimeter for field use

Abstract: Using simple materials a thermopile solarimeter has been constructed with output 5.5 mV cal-1 cm-2 min-1; resistance 13 Ω; response time 20 s; weight 35 g; dimensions 4 × 4 × 4 cm. It can therefore be used with a portable millivoltmeter for measuring reflexion coefficients, radiation within crops, etc. General equations for solarimeter performance and a simplified theory for the present design give a non-linearity of -0.8% cal-1 cm-2 min-1 and a temperature coefficient of -0.12% per deg C. Outdoor comparison with a Kipp solarimeter gave ±0.03 cal cm-2 min-1 as the maximum deviation from the mean response with radiation up to 1.1 cal cm-2 min-1. The standard deviation for thirty observations in bright sunshine and with overcast skies was ±0.002 cal cm-2 min-1. Cosine and azimuth response were improved using a larger instrument of the same design and comparisons of this with a Kipp solarimeter gave maximum deviation of ±0.02 cal cm-2 min-1.

Transfer Processes in Animal Coats. III. Water Vapour Diffusion

Abstract: The diffusion of water vapour through samples of cured and uncured fleece and fibreglass wool was measured. The diffusion resistance of the fibreglass was close to the value expected for still air, i.e. 4.2 s cm$^{-1}$ per centimetre for samples ranging in depth from 1 to 7 cm. The resistance for natural fleece was similar to the resistance for still air up to a depth of 4 cm but at 7 cm deep was only 2.5 s cm$^{-1}$ per centimetre. The difference in behaviour of the three materials was interpreted in terms of liquid movement. By appeal to principles of similarity, an equation for sensible heat transfer by free convection from an isolated sample of fleece is used to estimate corresponding rates of latent heat transfer when the skin is wetted by sweat. When a sheep is exposed to air at a temperature close to deep body temperature the exchange of sensible heat between the skin and the air may be a trivial component of the heat balance but provided the skin is wet, the evaporative heat flux from the skin may reach 200-300 W m$^{-2}$.

Consistency and Convenience in the Choice of Units for Agricultural Science

Abstract: The Systeme International d'Unites (SI) provides a consistent and coherent set of units for specifying the magnitude of physical quantities. Use of SI is recommended by most scientific journals and in many, including Experimental Agriculture, it is now mandatory. Multiples and sub-multiples of units should be chosen to minimize the repetition of zeros before or after the decimal point. Several units related to SI (e.g. tonne and hectare) are convenient in speech as well as in writing but should be avoided in analysis to minimize the risk of numerical errors. Units common in agricultural science are discussed with special reference to the need for compromise between consistency and convenience.

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.