**3.6 Employment or avoidance of effects of secondary metabolites in cotton stubble on soil health and cotton crop next season as another field of application of cotton secondary metabolites in cotton production**

As a cumulative stress index, cotton root gossypol concentration increases with age and size. At harvesting stage, cotton root gossypol concentration is high and around 1% (Yue unpublished data) fresh weight, each cotton stubble is estimated as 10 grams, and cotton plant density is estimated as 40,000 plants/acre [106]. The phytoalexin gossypol dose is estimated as 4000 g/acre, this dose is significantly heavier comparing to other herbicides and insecticides. For example, glyphosate burndown dose is 1 lb./ acre [107]. Despite constrained in the dead cotton stubbles, the root gossypol and its glands are expected to have significant impact on soil health and possibly cotton crop next season. Employment of their effects on soil health and cotton plants next season and avoidance of the effects are another field of application of secondary metabolites in cotton production.
