Effects of root medium and watering on transpiration, growth and development of glasshouse crops

Abstract

The effect of adding clay, moisture and the compaction on the physical properties of peat as well as the effect on transpiration and growth of tomato plants were investigated during short term laboratory experiments. The effect of 6, 12, and 20 cm peat height in beds with constand water level were investigated in a 5 months tomato crop. Admixture of clay reduced the porosity of the peat. Adding the clay at moderate pressure (10, 100 g cm-2) decreased the amount of large pores (equivalent to pores emptied at pF 2.0) and to an increase of smaller pores (equivalent to pores emptied in the pF intervals 2.0–4.2). The reduction in the amount of large pores was greater with admixture of montmorillonite than with a soil clay. An increase of the soil clay content from 50 to 70 per cent had an insignificant effect on the amount of large pores. Increasing the moisture content of the peat resulted in that fewer pores were emptied at pF 1.3. At a pressure of 1000 g cm-2 the decrease of large pores was more marked for pure peat than for mixtures of peat and soil clay. Increasing the pressures from 10 to 100 g cm-2 had only a slight effect. For a mixture of peat and montmorillonite a linear relationship was found between the clay content and bulk density, while a curvilinear relationship existed for a mixture of peat and soil clay. In short term laboratory experiments with tomato seedlings transpiration and growth rate were at a maximum at a pF equivalent to 20–30 per cent airfilled pores. In a glasshouse experiment with tomatoes an increase was recorded in yield, size of fruit, leaf area and total dry matter production with increasing peat heights above a constant water level. The experimental results showed that porous root media, such as peat, should be treated to counteract the existence of zones having sub-optimal air content by use of sub-irrigation. re]19730227