Soil sickness problem

In areas where particular crops are grown continuously, decreases in production with time have been noted. The condition is usually species speciAc, and the disorders which result are frequently referred to as soil-sickness or replant problems. Fruit trees are especially sensitive and the problem has been encountered with apples, peaches, grapes, cherries, plums, and citrus. In most situations, phytotoxicity has been related to the formation of toxic materials as a consequence of the microbial decomposition of plant remains. 

Soil microorganisms produce many compounds that are potentially toxic to higher plants. Examples include members of the following antibiotics (1-6), fatty and phenolic acids (7-12), amino compounds (13-15), and trichothecenes (16, 17). "Soil sickness" and "replant problems" have been reported where certain crops or their residues interfere with establishment of a subsequent crop (18, 19). Toxins resulting from microbial activity sometimes are involved, but it is often unclear whether these are synthesized de novo in microbial metabolism or are breakdown products of the litter itself (20). 

This has been referred to as soil sickness, or a sod-bound condition for grasses. Often, the cause is unknown, but the problem for several legumes may be due to allelopathy. In soil sickness of red clover pfiatzyiiz L.), isoflavonoid and phenolic acid... 

Borner (1960) states that soil sickness in fruit culture is a problem of economic importance in Germany. This is a replant problem that involves micro-element depletion and nematodes, but also root residues. As little as 1 g of air-dry root bark of an old apple tree per half liter of nutrient solution reduced root and stem growth of apple seedlings up to 50% within 30 days. Phlorizin, a natural constituent of apple root bark, and its breakdown products, are at least partially responsible for this apple soil sickness. 

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