Table 1.
General properties of the soils tested.
Table 2.
Soil particulate organic matters contents in the different rotation systems.
Fig 1.
Soil potentially mineralizable N (PMN) contents under the different rotation systems.
Note: RR corresponds to the rice-rapeseed rotation and CR corresponds to the cotton-rapeseed rotation. Sites A, B, C, and D represent the 4 paired soils from which particulate organic matter (POM) was removed to study the effects of POM removal on soil N mineralization.
Fig 2.
The relationships between the content of POM-N and PMN.
Note: RR corresponds to the rice-rapeseed rotation, and CR corresponds to the cotton-rapeseed rotation. Bars indicate the standard error of the mean (n = 31).
Fig 3.
The effects of POM removal on the soil PMN contents under the different rotation systems.
Note: RR corresponds to the rice-rapeseed rotation, and CR corresponds to the cotton-rapeseed rotation. Bars indicate the standard error of the mean (n = 2).
Table 3.
Generalized linear model analysis of sources of variation of soil potentially mineralizable N (PMN) contents under two different rotations and particulate organic matter removal treatment.
Fig 4.
The relationships between the ratio of POM-N to TN and the reduction rate of PMN after POM-removal.
Note: the hollow open represent the soils from the rice-rapeseed rotation and the solid symbols represent the soils from the cotton-rapeseed rotation. Reduction rate of PMN = (PMNoriginal soil—PMNPOM-removal soil) / PMNoriginal soil × 100.
Table 4.
Effect of POM removal on soil microbial biomass C, N and C/N ratio under the different rotation systems.
Fig 5.
The relationships between the reduction rates of microbial biomass N (MBN) and PMN after POM-removal.
Note: the open symbols represent the soils from the rice-rapeseed rotation and the solid symbols represent the soils from the cotton-rapeseed rotation. Reduction rate of MBN = (MBNoriginal soil—MBNPOM-removal soil)/MBNoriginal soil × 100; reduction rate of PMN = (PMNoriginal soil—PMNPOM-removal soil) / PMNoriginal soil × 100.
Table 5.
Effect of POM removal on the contribution of soil microbial biomass N to soil potential mineralizable N under the different rotation systems.
Fig 6.
The relationships between the reduction rate of the contribution of MBN to PMN and the reduction rate of PMN content after POM-removal.
Note: the open symbols represent the soils from the rice-rapeseed rotation and the solid symbols represent the soils from the cotton-rapeseed rotation. The contribution of soil MBN to PMN = MBN / PMN; decrease in the rate of contribution of MBN to PMN = (Contribution original soil—Contribution POM-removal soil) / Contribution original soil × 100; Reduction rate of PMN = (PMNoriginal soil—PMNPOM-removal soil) / PMNoriginal soil × 100.
Fig 7.
Infrared spectroscopy of soil POM under the different rotation systems.
Note: RR corresponds to the rice-rapeseed rotation, and CR corresponds to the cotton-rapeseed rotation.