Yellow Tomatos

[rutineli]

I have raised 24 tomato plants from seed in a well scrubbed and sanitised greenhouse.  All was well untill the plants were set into the soil when the leaves started to turn a lemon yellow colour from the outside edge inwards.  Only some of the plants have acted thus and they are otherwise vigorous, in flower and setting the first trusses.  The leaves are starting to look stripey with dark green lines on yellow leaves.

Can anyone tell me what it is and why and of course what ai should do next???        

I change the greenhouse soil every year down to a depth of one metre.  I have grown tomatos for 15 years with great success so what is going on???          rut.

[Clanad]

This from a University site:

Yellowing leaves can be caused by several situations. The following are the most common: 1) Early Blight (fungus) - If this is the cause, you should see small circular brown lesions on the leaves as well. The spots become larger. Eventually bottom leaves fall off. 2) Shading - As the plants mature, the bottom leaves get heavily shaded and naturally turn yellow as they senesce (age). This is not a problem. Any yellowing leaves are no longer productive and should be removed to improve air circulation. 3) Low nitrogen or potassium - If the nitrogen or potassium level is too low, yellowing will occur. Nitrogen deficiency shows up as a general yellowing of the entire plant. Potassium deficiency will appear as bright yellow leaf margins (edges) on otherwise green leaves. 4) Low Magnesium - Interveinal yellowing on older leaves is from low magnesium. It this is suspected, spray 2 TBL per gallon of magnesium sulfate (epsom salt) on the plants and see if they "green up" in a few days. For all suspected nutrient problems, a tissue analysis is recommended.

Good Luck!