Effects of size and amount and burial depth on early decomposition of maize straw and the links to microbial and nematode communities in the Mollisol of China

Abstract Crop straw is often incorporated into soil at different depths via agricultural practices like tillage, with regional variation in straw decomposition. However, the relative role of management practices on straw decomposition remains unclear. Here, a 5‐month field experiment using litterbags was conducted in three cold sites within China's Mollisol region, with two burial depths (15 and 30 cm) and four maize straw treatments (big straw and small straw at the amounts of 0.5% and 1.0%, respectively). The objectives were to determine the effects of the size and amount and burial depth of straw on its decomposition, microbial and nematode communities, and to identify the key factors regulating straw decomposition. Straw mass loss was affected by straw treatments rather than burial depths in all sites. Specifically, it was the lowest for 0.5% big straw among four straw treatments. Small straw lost more mass than big straw only at the amount of 0.5%, with the variations declining and even disappearing in the site experiencing relatively high temperatures. Microbial biomss and nematode abundance of specific groups were affected by the size and amount of straw in some cases, where the presence of 0.5% big straw corresponded with the lowest microbial biomass and the highest nematode abundance. All bacterial and fungal biomass and some nematode abundances were higher at 30 cm than at 15 cm in the sites with relatively low temperature. The abundance and Shannon index of nematodes were correlated with Gram‐positive bacterial biomass and microbial diversity and evenness index positively, and with other microbial biomass negatively. The straw decomposition explained 83.60% and 77.25% of variations in microbial and nematode community composition, respectively. These results suggest that the physical traits rather than burial depth dominate straw decomposition via changing microbial growth and their interaction with specific nematodes under similar climatic conditions, and the effects of straw physical traits are changed by climate on a large regional scale. Reducing the size and amount is a potential strategy stimulating straw decomposition, particularly in the cold regions.