Allelopathy and acidic soil

• Allelopathy:

Previous crops involving certain plants may prove to be stimulants or, on the contrary, inhibitors for the growth of lettuce. These effects are due to the production of chemicals, exuded from the roots or from the decomposition of crop debris, which are released into the soil. These can be responsible:
- inhibition of seed germination;
- reduced growth of lettuce, dwarfism and yellowing of leaves;
- various root damage (poor installation, reduction in the number and length of roots, necrosis located at the apices and portions of roots in contact with plant residues, etc.).

Previous crops likely to generate such a phenomenon involve: asparagus, broad beans, broccoli cabbage, celery, lettuce, vetch, barley, wheat and rice. The quantity of toxic residues produced and therefore the extent of the damage also depend on the type of soil, its humidity and the quantity of oxygen present, on the duration of decomposition of plant debris before planting salads.

In many situations, a sufficient period of decomposition of plant debris makes it possible to avoid the manifestation of this phenomenon. 

• Acidic soil:

It should be noted that in some soils that are too acidic, salads, and more particularly lettuce, may have more limited growth and roots showing a dull gray tint.