Nitrogen content and enzyme activity in rhizosphere and non-rhizosphere soils of paddy field under maize−rice rotation and rice continuous mono-cropping

Objectives We investigated the effect of maize−rice rotation on soil nitrogen content and enzyme activity in rhizosphere and non-rhizosphere using rice−rice as a control, to provide the scientific understanding of maize−rice rotation on the transformation of soil nitrogen and soil quality.

Methods Rice−rice and maize−rice were performed using the root pocket pouch test. Soil samples were taken from the soil rhizosphere and non-rhizosphere at maize stages of trumpet, heading and maturity, and rice stages of tillering, booting and maturity to quantify ammonium, nitrate, total nitrogen, and urease, and nitrate reductase activities in the two rotations.

Results The two different rotations and crop growth periods had significant effects on soil nitrogen content and enzyme activities. The changes in the enzyme activity under the two rotations were basically similar. Compared with the rice continuous mono-cropping, the ammonium nitrogen in the maize−rice rotation decreased by 24.7% and the soil nitrate nitrogen content increased by 153.4%, which mainly happened in the first season. The total nitrogen content was lower at the end of the rotation. Soil urease activity in the maize−rice rotation was 24.3% higher while soil nitrate reductase activity was 34.6% lower than those of the rice-rice rotation. In addition, the impacts of maize−rice rotation on other indicators could sustain to the next crop. Ammonium nitrogen content and urease activity in the rhizosphere soil were lower than those in the non-rhizosphere. Nitrate content in the maize rhizosphere was lower than that in the non-rhizosphere. In contrast, nitrate nitrogen content in the rice rhizosphere was higher than that in the non-rhizosphere. Nitrate reductase in the rhizosphere was higher than that in the non-rhizosphere.

Conclusions The impacts of maize−rice rotation on soil nitrogen content and enzyme activities in the first season could sustain to the second season. Compared with the rice continuous mono-cropping, the nitrate nitrogen content and soil urease activity were higher in the maize−rice rotation, which could improve nitrogen availability.