Multi-point temperature measuring equipment for crop environment, with some results on horizontal homogeneity in a maize crop. 1. Field results.

Abstract

The use of temperature measurements above, below and within plant stands in physiological and ecological studies is briefly reviewed and the choice of sensor and protection from radiation effects in measuring temperatures within a maize crop are discussed. The horizontal homogeneity of temperature was investigated. Measurements in 1973 and 1974 showed the greatest horizontal temperature difference at 1.8 m above ground level due to an increase in leaf area density just above the height where the crop became closed and air flow was reduced; at lower levels temperature differences increased as turbulence was reduced, and differences in soil surface conditions influenced temperature measurement. The need for a large number of measuring points in the lower parts of the canopy is emphasized. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Multi-point temperature measuring equipment for crop environment, with some results on horizontal homogeneity in a maize crop. 2. Equipment used.

“…In a section on thermometers used (Stigter et al, 1976a) we explained our choice of platinum resistance Degussa P4 thermometers in a waterproof protection and also protected from radiation but freely accessible to horizontal air movements at the height concerned. This protection against humidity and moisture together with a prevention of mechanical dammage of the glass holding the resistance wires, but without introducing large thermal contact resistances, was obtained by using a copper tube with silicon heat sink compound (Dow Corning 340) as embedding material.…”

“…To ensure a constant long-wave emissivity during experiments regarding radiation errors, the copper tube got an opaque plastic sleeve. The sleeve was white to give a good protection against solar radiation (including reflected solar radiation from outside the partly open radiation protection during actual measurements (Stigter et al, 1976a)). After a few years of use some of these resistances became unstable due to large thermoelectric effects within the sensor.…”

“…In an earlier paper (Stigter et al, 1976a) we have explained the choice of the sensor in our case of multi-point temperature measurements within a crop. The accuracy we needed, in view of the use of the data concerned (Stigter et al, 1976a(Stigter et al, , 1977Stigter, 1977) and in relation to other sources of error (Stigter et al, 1976b), forced us to pay more than routine attention to data collection problems. In this second paper we discuss separately some details regarding errors and calibration of the sensors and regarding modification and field performance of the datalogger.…”

Horizontal and vertical distribution of air temperature in a vegetation [maize] canopy.

“…For example, Shaw et al (1974) and Mulhearn & Finnigan (1978) made observations of turbulence and turbu lent transport of momentum and heat above a rough surface rather close to the roughness elements. Stigter et al (1976) studied the horizontal homogeneity of the temperature and moisture within a maize canopy. Graser et al (1987) studied tem perature patterns within sorghum canopies with different row spacing.…”