The experimental site is located at the Eco-farming Research Station of Shandong Agricultural University, based in Jiang Jiazhuang Village, Pingyi County, Shandong Province, Eastern China (35° 26′ 21″ N, 117° 50′ 11″ E). The area experiences a typical temperate and monsoonal climate, with a mean annual rainfall of 770.2 mm and average annual temperature of 13.2 °C. The soil type is brown. Before the application of fertilizer, the experimental soil (0–20 cm) contained organic matter, 1.22 %; total nitrogen, 0.08 %; available P, 14.93 mg kg−1; and available K, 144.96 mg kg−1.
Collection of cattle manure and earthworms
Both cattle manure and earthworms (Eisenia fetida) were obtained from Hongyi Organic Farm in Jiang Jiazhuang Village. Before composting, the experimental cattle manure contained organic matter, 54.14 %; total nitrogen, 1.87 %; available P, 0.24 %; and available K, 0.52 %, and had a pH of 8.63.
This study was conducted in two different systems, cattle manure-vermicompost-maize system (VC system) and cattle manure-traditional compost-maize system (TC system).
In the VC system, cattle manure (30 t, dry weight) was shaped into cuboids with width 1.5 m and height 0.2 m. A total of 309 kg earthworms was added into the cattle manure (Guo 2012). Water was sprinkled daily onto the manure using a sprayer to maintain a moisture level of 55–65 %. After 60 days, the earthworms were separated from the cattle manure, the remainder cattle manure vermicompost was applied into the field 1 (1 ha) before tillage.
In the TC system, cattle manure (30 t, dry weight) was shaped into cuboids with width 1.5 m, height 0.5 m, and moisture 60–70 % and then covered with plastic film, stirred, and mixed every 20 days. After 60 days, the remainder cattle manure traditional compost was applied into the field 2 (1 ha) before tillage.
Three completely randomized experimental plots were selected in each field; each plot was 2.4 × 5 m. The experimental crop was the ordinary high-yield maize Zhengdan 958. The maize was sown on June 21, 2011 and harvested on September 30, 2011. The distance between rows was 0.6 m, and the distance between plants was 0.27 m.
Sampling and chemical analysis
After 60-day composting, cattle manure vermicompost and traditional compost samples were drawn by using an auger with the bore of 6 cm. Five random sites in the same compost plot were selected and the samples were taken from top to bottom; the five random subsamples were pooled together and air-dried for nutrients analysis. Determination of pH was done by a digital pH meter (PB-10, Sartorius, Germany). Nutrient estimations involved Walkle and Black (1934) method for organic matter, macro-kjeldahl method for total N, sodium bicarbonate extractable method (Olsen et al. 1954) for available P, and ammonium acetate extractable method (Simard 1993) for available K. All the determinations were carried out in triplicate.
Dry matter of total aboveground biomass was measured two times during the growing season, at flowering and at harvest stage. The aboveground biomass included corn stem, leaves, corncob, and kernels. The whole maize plant was cut on the bottom close to the ground and was transported to the laboratory to segment and then dried at 105 °C for 30 min and at 75 °C until reaching a constant weight.
At maize harvest, three replicates of 10 consecutive plants in the same row were selected. The grain and fresh straw yields were measured for each replicate.
Data regarding economic benefits were scaled to 1 ha based on historic data collected from Hongyi Organic Farm and the present experiment. Input refers to the costs for purchasing seeds, fertilizers, plastic films, sprayers, and earthworms; cultivating, irrigation seeding, and crop harvesting; and applying fertilizer and controlling pests and weeds. Output includes the sales of earthworms, maize grain, and fresh straw.
All data were analyzed using one-way analysis of variance (ANOVA) and nonparametric tests with SPSS 17.0 at the 0.05 level. Differences between treatments were considered significant if P ≤ 0.05. Analyses were performed in Sigma Plot 10.0 (Aspire Software Intl. Ashburn, VA, USA).