SOIL PHYSICAL CONDITIONS IN GREENHOUSE CROPS IN SWEDEN

Normal chemical analyses have been much used for fertilization control in Sweden. These analyses will always be valuable but in addition analyses of soil physical conditions will have a certain interest, as these conditions will also markedly influence the growth and development of the plants.

In 1965 a team of four Swedish workers began a survey to find out the soil physical conditions in different cultivations. Ten cucumber-, 16 tomato- and 14 carnation beds were investigated. Analyses were made on soil samples taken by metal-cylinders, 10 cm deep, and the beds were studied down to 40 cm in steps of 10 cm. The metal-cylinders were pressed down in the soil to give a sample of exact volume and with the soil not disturbed.

Following analyses were made:

• soil texture (size of the mineral particles), distribution of clay, silt, fine sand etc.
• humus content
• space (volume) of material
• space (volume) of pores
• distribution of water and air in the pores at field capacity and under tensions of
• 25 cm, 50 cm and 100 cm of water
• specific weight
• volume weight
• permeability

The texture analyses show that the content of clay increases at deeper levels. Very large differences were registrated in texture oof soil from one bbbe dto another. 23% was the highest percentage of clay in the top 10 cms of a tomato bed and at lower levels 30% was recorded. But there was also beds in which there was no clay content at all. These large differences in the texture are due to the fact that the greenhouse are on soils of very different types.

The humus content depends mainly on the amount of organic matter added to the soils. It is quite obvious that the humus content well decrease with depth as it will be more difficult to mix in organic matter at lower levels. Of special interest are texture and humus content in some selected beds of carnations, as among these there are some beds of peat only. From these, the large difference between soil and peatbeds can be studied. The highest content of humus was found in a peat-bed with 82,7% of organic matter.

The volume in the beds is divided between solid matter, water and air. That part occupied by water and air is called pore volume. Large differences in volume- relations were recorded between different beds. In cucumber-beds, a mean, 26,1% of solid matter was noted, but the most compact bed had 40% and the most porous one 17,1% of solid matter in the top 10 cm. At lower levels the beds are more compact and the material-volume will increase considerably. In cucumber beds the material volume will increase from 29,8 to 33,2 43,3 and 49,4% at different levels down to 40 cm. The peat beds have extremely low material-volume, often around 10% or less. At the same time there will be a very high pore volume that around 10% or less. At the same time will be a very high pore volume that at field capacity will be nearly filled with water.