Response of soil nutrient concentrations and stoichiometry, and greenhouse gas carbon emissions linked to change in land-use of paddy fields in China

The conversion of paddy cropping to vegetable production and other crops is a common agricultural practice, driven by economic benefits. However, soil carbon emissions and nutrient stoichiometric responses to this type of land-use change remain unclear. In this study, carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) emissions, Soil Organic Carbon (SOC), total nitrogen (TN), and total phosphorus (TP) concentrations and their stoichiometric relationships were measured over one year, following conversion of paddy fields to vegetable and jasmine crops 10 years ago. Soil CO2 emissions increased by 1.16 and 2.35 times after conversion to vegetable and jasmine production, respectively, and soil CH4 and N2O emissions decreased by 52 and 66%, and 12.3 and 42.5%, respectively. Global warming potential increased by 0.81 and 1.67 times, respectively; the increases in total C emissions were associated with decreases in SOC concentrations. TN decreased by 27% in jasmine soils following conversion from paddy cropping, and TP concentrations increased by 11% in vegetable soils. Carbon soil stocks increased by 19% in vegetable soils and decreased by 11% in jasmine soils, due to changes in SOC concentration and bulk density. Soil CO2 and total C emissions were negatively correlated with soil TN concentration and C:P ratio (p < 0.05), and CH4 emissions were positively correlated with SOC concentrations (p < 0.05) and soil N:P and C:P ratios (p < 0.01). Thus soil elemental stoichiometry was a good indicator of soil nutrient cycling and greenhouse gases emissions. Our findings suggest that the conversion of paddy cropping to vegetable and jasmine production increased C emissions and conversion to jasmine cropping does not lead to retention of soil nutrients, whereas TP concentration and SOC stocks increased following conversion to vegetable cropping. This study highlights that future conversion of paddy soils to vegetable or tree crops will have implications on carbon balances and global warming.