Studies on chinampa soils have revealed that they have disease-suppressing capabilities. Lumsden et al’s 1987 study, cited by Zuckerman et al. (1989), revealed that chinampa soils, as compared to soils collected from experimental fields in Chapingo, Mexico, suppressed damping-off disease. Zuckerman et al. provide Lumsden et al.’s analysis of the chemical and physical characters of chinampa and Chapingo: “They found that the chinampa soil was a silty, clay loam, pH 5.8, and was significantly higher in organic matter and phosphorus, potassium, calcium, magnesium, nitrate, and ammonia content, as well as soluble salts. Chapingo soil, in addition to being lower in organic matter, was sandy and had a pH of 6.8.”
Zuckerman et al. find that chinampa soil also suppresses damage to tomatoes and beans by false root-knot nematode (Nacobbus aberrans) and damage to tomatoes by root knot nematode (Meloidogyne incognita). They conducted their study in greenhouse and growth chamber trials. Upon sterilizing the chinampa soil and introducing the plant-parasitic nematodes however, the suppressive effect was lost, “thereby indicating that one or more biotic factors were responsible for the low incidence of nematode damage.” In all instances, nematodes caused significantly less root galling to the plants in non-sterilized chinampa soil as compared to all other treatments (sterilized chinampa, non-sterilized Chapingo, sterilized Chapingo).
The scientists isolated nine organisms from chinampa soil which exhibited antinematodal properties in culture. Moreover, upon sampling chinampa and Chapingo soils and counting the populations of soil nematodes, it was found that the naturally occurring populations of plant-parasitic nematodes were of lower incidence in chinampa soil (130 vs. 156 per 100 cubed centimeters). In terms of the economically most important plant parasitic nematodes (Pratylenchus spp. and Nacobbus aberrans), the difference was quite significant: three (chinampa) vs. nineteen (Chapingo) individuals per 100 cubed centimeters. Overall, nematode suppression is estimated to be at 80% for chinampa soil.