Earthworm responses to cropping rotation with oilseed rape in no-tillage rice fields and the effects of earthworm casts on human-essential amino acid content in rice grains

The rice-oilseed rape rotation is a major rice-based cropping system in the Yangtze River basin in China, and no-tillage technology has been successfully adopted in this system. The main objectives of this study were to determine: (1) the response of earthworm density to rotation with oilseed rape in no-tillage rice fields; and (2) the effects of earthworm casts produced during the oilseed rape-growing season on the content of human-essential amino acids in resulting rice grains. An on-farm study was conducted from 2015 to 2017 to compare earthworm density in no-tillage fields where rice was rotated with oilseed rape and with a fallow period. A micro-plot experiment was also carried out to compare the grain content of human-essential amino acids in rice with and without the addition of earthworm casts (produced during the oilseed rape-growing season) under three nitrogen fertilizer rates. We observed that medians of earthworm number per m(2) were 68-154% higher in the fields rotated with oilseed rape than in the fallow fields. The contents of human-essential amino acids detected in rice grains were generally increased by the addition of earthworm casts, and there were significant increases (8-13%) for phenylalanine, threonine and valine. Our study suggests that earthworms can be increased by rotation with oilseed rape in no-tillage rice fields, and that their casts can increase the contents of human-essential amino acids in rice grains.