An analysis of the environment inside a plastic tunnel with and without 30 per cent. shadecloth, and in shadehouses with 15 and 40 per cent shadecloth was made at Pietermaritzburg, South Africa (30°S), and their affect on tomatoes and cucumbers was measured.
The total radiant density, the radiant flux density and radiation spectra were typically reduced by the plastic, and different density shadecloths.
In April (autumn) outside radiant flux densities reached 750 W m-2, being reduced to 450 W m-2 under plastic and 300 W m-2 under 30 per cent. shade cloth.
Air temperatures under shade inside plastic were not different to those under plastic alone due to the free air movement between these two environments inside one tunnel, but under shadehouses air temperatures were always lower depending on the amount of shading.
On average, shaded plants adapted to their environment by producing a greater leaf area, but smaller root system, associated with which was an increased resistance to leaf water movement.
Shaded cucumbers produced less total dry matter and proportionately put more dry matter into leaves and stems, and less into roots and fruits.
Net assimilation rates were higher in unshaded plants.
Tomato yields were best under 15 per cent. shade in comparison to under plastic, 40 per cent. shade and in the open.