Soil fauna are an important component of farmland ecosystems. They play a very significant role in the decomposition of biological remains, affect soil properties and enhance material recycling and energy conversion in the soil. Conversely, soil factors determine the existence and activity of soil fauna.
The aim of this research was to examine the effects of long-term fertilization on the soil macrofaunal community structure. It was conducted in a wheat field at the Fengqiu (35°00' N, 114°24' E) Agro-Ecological Experimental Station of the Chinese Academy of Sciences in the spring of 2007 and 2008. A long-term located fertilization experiment was established in 1989. There were 7 treatments, and each treatment had four replicates : a control with no fertilizer (CK), chemical fertilizer NPK, chemical fertilizer without K (NP), chemical fertilizer without P (NK), chemical fertilizer without N (PK), organic manure (OM), and half organic manure and half chemical fertilizer (1/2OM + 1/2NPK). N, P and K chemical fertilizers were applied to wheat as follows: 150 kg/ hm² N fertilizer, 75 kg/ hm² P₂O₅ fertilizer, 150 kg/ hm² K₂O fertilizer. All P, K and OM fertilizers were applied as basal fertilizers, whereas N fertilizer was added in two applications as both the basal and supplementary fertilizer. A total of 3068 soil macrofaunal individuals belonging to eight classes, 19 orders and 28 families were collected. The highest number of total species was found in the OM treatment and the lowest number in the NK and CK treatments. Both groups (F = 2.51, P < 0.05, df = 55) and individuals (F=8.99, P < 0.01, df=55) of the soil macrofauna differed significantly under the different fertilization treatments with greatest numbers of groups of macrofauna in the OM and NPK treatments and lowest numbers in the NK treatment. The species similarity index of soil fauna (S₁) was highest in the NK and CK treatments (S₁=0.80), and the species similarity index between groups (S₂) was highest in the OM and NPK treatments, being > 0.70. The highest diversity indices of soil macrofauna (H') were observed in the OM and NPK treatments and decreased in the order: H' _NPK (1.91) > H' _OM (1.83) > H' _1/2OM+1/2NPK (1.80) > H' _NP (1.74) > H' _NK (1.64) > H' _PK (1.56) > H' _CK (1.02).
Principal component analysis (PCA) revealed the contribution of the first (PC1) and the second (PC2) principal components as 47.14% and 30.10%, respectively. PC1 was significantly positively correlated with the number of groups (R = 0.82, P < 0.05) and individual numbers of soil fauna (R = 0.85, P < 0.05). PC1 was linearly correlated with soil macrofaunal individuals (y = 0.335x-2.163, R² = 0.51) and soil macrofaunal groups (y = 0.042x-1.25, R²=0.67).
The soil macrofaunal community structure was similar in the wheat field following organic manure addition and balanced NPK fertilization. Numbers of earthworm numbers and its natural enemies were enhanced by the addition of OM. Soil organic matter and available P content were the key factors affecting the composition of the soil macrofaunal community.