Denitrification in a chinampa soil of Mexico City as affected by methylparathion: A laboratory study

Abstract

Chinampas are raised garden beds used for agriculture in the valley of Mexico since pre-Hispanic times. Large amounts of methylparathion, i.e. approximately 0.5 kg ha −1 per crop cycle, are used to control pests with an unknown effect on soil processes, such as the denitrification process. Soil was amended with nitrate ( NO 3 − ) with or without chloramphenicol known to inhibit de novo synthesis of enzymes, with or without acetylene (C 2H 2) known to inhibit the reduction of nitrous oxide (N 2O) to dinitrogen (N 2) and spiked with or without methylparathion. Methylparathion increased the N 2O and N 2 emissions, the NO 2 − concentration and removal of NO 3 − from soil. The NO 2 − concentration in the anaerobic incubation was larger when soil was conditioned aerobically <7 days compared to soil conditioned for >7 days, but no such pattern was observed for the removal of NO 3 − . C 2H 2 and/or chloramphenicol had no significant effect on NO 3 − removal and the NO 2 − concentration in the methylparathion-amended soil, but increased the NO 2 − concentration in unamended soil with C 2H 2 plus chloramphenicol compared to the other treatments. C 2H 2 increased the N 2O emission in soil amended with or without methylparathion and with or without chloramphenicol.