Abstract
<strong class="journal-contentHeaderColor">Abstract.</strong> The straw return practice is essential to soil organic matter (SOM) accumulation in the black soil area with high carbon sequestration potential. However, due to lacking accurate spatial distribution of straw return, few studies took straw return as a variable to carry out rigorous research on the impact of straw return on SOM variation on a regional scale. Based on soil samples and 16 environmental covariates including a 10-meter-resolution straw return amount, the study mapped the spatial distributions of SOM in 2006 and 2018 by random forest (RF) and evaluated the effects of the interaction of soil properties, land use and straw return on SOM spatial-temporal variation. The results show that in the context of the straw returning, the mean SOM content increased from 18.93 g kg<sup>−1</sup> to 20.84 g kg<sup>−1</sup> during 2006–2018. And 74.49 % of the region had a significant increase (maximum: 24.41 g kg<sup>−1</sup>) of SOM. The severest SOM loss occurred in the northwest due to the light texture and the transition from paddy fields to dryland. Nevertheless, for areas from paddy fields to dryland, the SOM loss decreased with the increased amount of straw return. The SOM even increased by 1.84 g kg<sup>−1</sup> when the straw return amount reached 60–100 %. In addition, soil with higher initial SOM and sand content had a lower response to straw return. The study revealed that straw return is beneficial to carbon sink in farmland and is a better way to prevent a carbon source caused by the change of paddy field to dryland.
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