Evapotranspirasie‐studies op themeda triandra forsk. Onder veldtoestande

Uittreksel

Relatief eenvoudige hidrouliese lisimeters is gebruik om die verliese as gevolg van evapotranspirasie (Et) van Themeda triandra onder veldtoestande te bepaal vir die periode Desember 1972 tot Julie 1975.

Die hoogste Et‐verliese het gedurende die reproduktiewe stadium van die plante (Desember en Januarie) voorgekom en soveel as 10,22 mm water per dag het, as gevolg van evapotranspirasie, verlore gegaan. Die verliese as gevolg van verdamping (Eo) vanaf die onbedekte grondlisimeters was ongeveer 67% van die Et‐verliese vanaf die graslisimeters. Die gemiddelde weeklikse Et/Eo‐verhouding vir die 1972/73, 1973/74 en 1974/75 groeiseisoene was in dieselfde orde, 0,341, 0,389 en 0,334 onderskeidelik. Die reenval vir die drie seisoene was onderskeidelik 252,2 mm, 986,6 mm en 524,2 mm.

Die maandelikse Et/Eo‐verhouding soos bereken vir die 1973/74 groeiseisoen, kan as die potensiële Et/Eo‐verhouding van ‘n T. triandra‐veld op die Shorrock‐grondserie beskou word.

‘n Harmoniese kromme is op die gegewens gepas. Die waterverbruik van ‘n T. triandra‐veld sowel as die voginhoud van die grond is bepaal met behulp van die Et/Eo‐verhouding, weerkundige en grondkundige gegewens. ‘n Rekenaar‐program is vir hierdie doel geskryf en gebruik.

Abstract

Hydraulic non‐floating lysimeters were used to determine the evapotranspiration (Et) of a Themeda triandra grass cover under field conditions.

The highest evapotranspiration losses were recorded during December and January when the plants were in the reproductive phase, provided the soil moisture was not limiting. As much as 10,22 mm water per day was lost during this period from grass‐covered lysimeters. The evaporation (Eo) losses from the bare soil lysimeters were approximately 67% of those from the grass covered lysimeters. The average weekly Et/Eo relationship was 0,341, 0,389 and 0,334 for the 1972/73, 1973/74 and 1974/75 seasons respectively. The rainfall for the three seasons was 252,2 mm, 986,6 mm and 524,2 mm respectively.

The monthly Et/Eo relationship values for the 1973/1974 season can be considered to be the potential Et/Eo relationship of a T. triandra grass cover under non‐limiting soil moisture conditions. A harmonic curve was fitted to the data with a computer programme. The water use of a T. triandra veld and the soil moisture content were determined with the aid of the harmonic curve, weather, soil data and a computer programme.

Notes

Gebaseer op ‘n proefskrif deur die senior outeru voorgelê ter gedeeltelike vervulling van die vereistes vir die graad D.Sc. Agric. aan die Universiteit van die Oranje‐Vrystaat.