Effects of warming on the decomposition rates of the straw of different crops in soils and modelling

Objectives This study aimed to investigate the effects of warming on the decomposition rates of different crop straws in soils.

Methods A field embedding experiment was performed during the two growing seasons from November 2019 to October 2020. The decomposition percentages of the straw of maize, sweet potato and soybean during the summer crops growing season and the straw of winter wheat, garlic and rape during the autumn crops growing season were measured. The coefficients of decomposition rates were simulated with a function including the initial C, N, lignin content and C/N ratio of different crop straws. The modelled decomposition coefficient k value was further used to predict the residual straw mass of different crops after the different embedding days. The predicted and observed residual straw mass was analyzed using a linear regression to evaluate the modelling efficiency.

Results Compared with control, warming significantly (P < 0.05) increased the decomposition percentage of the straw of maize, sweet potato and winter wheat during the early decomposition period, but had no significant (P > 0.05) effects on the decomposition percentage during other decomposition periods. Warming induced a significant (P < 0.05) increase in the decomposition percentage of the straw of rape during the whole growing season. Warming had no significant (P > 0.05) effects on the decomposition percentage of the straw of soybean and garlic during the whole growing season. Warming had no significant (P > 0.05) effects on the coefficients of decomposition rates of the straw of the six crops. However, there were significant (P < 0.05) differences in the coefficients of decomposition rates of the straw among the six crops. The decomposition coefficient was highest for the garlic straw and lowest for the soybean straw under both control and warming treatments. The decomposition coefficient of the garlic straw was twice times higher than that of soybean straw. Multiple regression (k=−1.073C+7.315N+0.223C/N−0.004L+33.900) including the variables of the carbon content (C), nitrogen content (N), the ratio of carbon to nitrogen (C/N) and lignin content (L) could be used to model the variations in the coefficients of decomposition rates of the straw of the six crops under the different treatments. The model simulated 92.1% (R² = 0.921, P < 0.001) of the variation in the decomposition rates of the straw. The slope for the linear regression function fitting the relationship between the modelled and the observed decomposition rates of the straw was very close the 1:1 line. The validation analysis based on the residual straw mass after the different embedding days and the modelled decomposition coefficients of straw showed that the modelled and observed values of residual straw mass of different crops fitted well (R² = 0.922, P < 0.001), indicating that this model effectively simulated the straw decomposition dynamics.

Conclusions Compared with control, warming significantly increased the decomposition rates of the straw of maize, sweet potato and winter wheat during the initial decomposition period and the decomposition rates of rape straw during the whole growing season, but warming did not impact the decomposition rates of the straw of soybean, garlic. The coefficients of decomposition rates of crop straws could be modelled by the C, N, lignin content and C/N of crop straws. This model could also well estimate the remained straw mass of different crops after different embedding days.