Effects of partial substitution of chemical fertilizer with manure and/or straw on soil nematode community in greenhouse vegetable production

Objectives A fixed-site greenhouse vegetable field fertilization experiment was carried out in Xiqing District, Tianjin to investigate the effects of partial substitution of chemical fertilizer with manure and/or straw on the total number of soil nematode, nematode community structure and nematode ecological indices for providing a scientific basis for the construction of healthy soil fauna.

Methods Six treatments were included based on substitution of chemical fertilizer nitrogen (N) with different exogenous organic resources: 1) complete chemical N (4/4CN); 2) 3/4 chemical N plus 1/4 manure N (3/4CN + 1/4MN); 3) 2/4 chemical N plus 2/4 manure N(2/4CN + 2/4MN); 4) 1/4 chemical N plus 3/4 manure N (1/4CN + 3/4MN); 5) 2/4 chemical N plus 1/4 manure N plus 1/4 straw N (2/4CN + 1/4MN + 1/4SN), and 6) 2/4 chemical N plus 2/4 straw N (2/4CN + 2/4SN). All treatments had the same amounts of N, P₂O₅, and K₂O inputs. After the uprooting stage of the 16^th-season vegetable (after soil disinfection) and the 18^th-season vegetable (one year after soil disinfection), surface soil (0‒5, 5‒10, and 10‒20 cm depth) samples were collected for the determination of the nematode-associated indices.

Results 1) The total number of nematode were increased in organic-amended soils by 16.8%, 31.8%, and 11.2%, respectively, compared with those in 4/4CN-treated soils in the 0‒5, 5‒10, and 10‒20 cm soil layers. Moreover, the total number of nematode in the 1/4CN + 3/4MN, 2/4CN + 1/4MN + 1/4SN, and 2/4CN + 2/4SN treatments were relatively higher than other organic-amended treatments, which were increased by 12.1%‒26.4%, 34.3%‒42.8%, and 13.2%‒18.3%, respectively, compared with those in the 4/4CN treatment in different layers. 2) The number of beneficial nematodes, i.e., bacterivore, fungivore, and omnivore-predator, were higher in organic-amended soils than those in 4/4CN-treated soil by respective average of 13.0%, 7.4%, and 26.7% in the 0‒5 cm soil layer, and 35.5%, 20.2%, and 56.5% in the 5‒10 cm soil layer. In comparison with the 4/4CN treatment, organic amendments increased the number of harmful herbivore, but decreased the relative abundances of harmful herbivore by average of 6.3% and 13.1%, respectively, in the 0‒5 cm and 5‒10 cm layers. 3) The organic amendments, especially the 1/4CN + 3/4MN, 2/4CN + 1/4MN + 1/4SN and 2/4CN + 2/4SN treatments had higher MI, WI, EI and SI values than the 4/4CN treatment, which were increased by 3.9%, 11.5%, 6.2%, and 130.4%, respectively, in the 0‒5 cm soil layer, and by 1.8%, 19.1%, 2.4%, and 138.7%, respectively, in the 5‒10 cm soil layer.

Conclusions Under the same N, P₂O₅, and K₂O rates, organic amendments could promote the growth of nematodes and relative abundances of beneficial nematodes (i.e., bacterivore, fungivore, and omnivore-predator). Conversely, organic amendments could decrease the relative abundances of harmful herbivores, and thus inhibite harmful herbivores growth. Overall, organic amendments could optimize soil nematode community structure, decrease soil environmental interference, and improve soil quality conditions, which is beneficial for soil ecosystems healthy development in the greenhouse vegetable production. Combined with the 9-year yield of this experiment (the yield is highest in the 2/4CN + 1/4MN + 1/4SN treatment), soil nematode data and practical operability, chemical fertilizer plus organic manure plus corn straw (2/4CN + 1/4MN + 1/4SN) is a continuous high-yield fertilization treatment for greenhouse vegetables.