Toxicants, sick soil

Root Exudates Leaf Leachates Volatile Inhibitors Sick Soil Toxicants... 

Sick soil" toxicants Accumulation of toxicants from previous inhabitants evidently results in growth inhibition of roots and interfere with seedling establishment (46). 

Hatsuda Y, Murao S, Terashima N, Yokota T 1960 Biochemical studies on soil sickness. 1. Toxic substance in fig roots. Nippon Nogei Kagaku Kaishi 34 484-486... 

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). 

For the last few decades, the people of the United States and their judicial system have placed a high priority on the protection of the environment. That protection includes special environments such as national forests, wilderness areas, or scenic rivers, and it also extends to such common place natural resources as the air we breathe, the water we drink, and the soil of our community. No country can allow the lakes and rivers that supply its drinking water to become contaminated with toxic chemicals, the air of its cities to become so unhealthy that its children become sickly, and its soil to become so polluted that crops grown on it cannot be consumed. 

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