Effects of Rice Straw Mulching on Nematode Communities in Upland-Paddy Rice Systems in Salt-Affected Soils

Rice straw mulching is a soil management practice that influences soil microbial communities. However, its effects on nematode communities under upland rice systems in salt-affected soils remain unclear. This study examined nematode community responses to rice straw mulching at rates of 0, 3.5, 7.0, and 10.5 t ha−1 in paddy fields at two sites, Lieu Tu and Long Phu, in Soc Trang Province, Mekong Delta, Vietnam. A total of 37 and 35 nematode genera were identified in Lieu Tu and Long Phu, respectively. Bacterivores were the dominant group, followed by herbivores. Acrobeloides, Hirschmanniella, Chronogaster, Aporcelaimellus, and Prismatolaimus were prevalent in Long Phu, while Acrobeloides, Prismatolaimus, Hirschmanniella, and Alaimus dominated in Lieu Tu. The highest mulching rate (10.5 t ha−1) increased total nematode abundance, particularly cp1 and cp2 groups in Long Phu, while the application of 7.0 t ha−1 increased the proportion of omnivorous feeders in Lieu Tu. Mulching increased total nematode biomass and metabolic footprints, indicating improved soil fertility. At Long Phu, mulching also increased biodiversity, as reflected by the higher species richness and Shannon–Wiener indices. The highest mulching application rate (10.5 t ha−1) increased the relative abundance of cp2 functional guilds at both sites. Mulching reduced the relative abundance of plant-parasitic nematodes at both sites, and increased cowpea yield from 5.1 to 13.9 t ha−1 and 5.67 to 9.70 t ha−1 at Lieu Tu and Long Phu, respectively. These findings suggest that the rice straw mulching at 10.5 t ha−1 improves soil structure and nematode diversity, thereby supporting agricultural sustainability in salt-affected soils under climate change conditions.