Effect of nitrogen and phosphate fertilisers on microbial and nematode diversity in pasture soils

• Published in: Soil biology & biochemistry 2001-06, Vol.33 (7-8), p.953-964
• Main Authors: SARATHCHANDRA, S. U, GHANI, A, YEATES, G. W, BURCH, G, COX, N. R
• Format: Article
• Language: English
• Subjects: Agronomy. Soil science and plant productions; Biochemistry and biology; Biological and medical sciences; Chemical, physicochemical, biochemical and biological properties; Fundamental and applied biological sciences. Psychology; Fusarium culmorum; Generalities; Gliocladium; Physics, chemistry, biochemistry and biology of agricultural and forest soils; Soil science
• ISSN: 0038-0717; 1879-3428
• DOI: 10.1016/S0038-0717(00)00245-5

Soil microbial and nematode populations, soil microbial community structure, and microbial and nematode functional diversity were studied in two fertiliser trials on perennial pasture at three sampling times. The N trial involved the application of 0, 200 and 400 kg N ha super(-1) y super(-1) in the form of urea. The P trial involved the application of 0, 30, 50 and 100 kg P ha super(-1) y super(-1) as superphosphate. The purpose of this study was to determine biological characteristics that may be used as indicators of soil quality as affected by fertiliser inputs. The N or P treatments had no effect on total bacteria, cellulolytic microbes, or the fluorescein diacetate hydrolysis. The fungus Fusarium culmorum was found only in the 200 kg N treatment (P < 0.01). Gliocladium roseum declined in isolation frequency with increasing N (P < 0.05,) while other Gliocladium spp. increased (P < 0.01). The microbial community structure, ecophysiological index (EP), and colony-development index (CD) were determined using: colony development rates in 1/10 tryptose soy agar (TSA), a Pseudomonas medium, and a nutrient poor medium. These parameters were not affected by the addition of the N or P fertilisers. In the N trial, the functional diversity of soil microbes, as determined by Shannon Diversity Index (H) and average well colour development (AWCD) (using Biolog gram negative microplates) was higher in the unfertilised than fertilised treatments. The values for H and AWCD were 4.2 and 0.78 in the unfertilised compared to 4.0 and 0.53 in fertilised treatment (P < 0.01, 48 h, mean for both N treatments), respectively. There were no significant differences in these values in the P trial. Populations of the plant feeding nematodes Pratylenchus and Paratylenchus were greater (P < 0.05) whereas those of Meloidogyne were lower (P < 0.001), in soils fertilsed with N than in unfertilised soils. The genera Aporcelaimus, Dorylaimellus, and Tylencholaimellus were found only in control plots and their loss paralleled faunal changes resulting from pasture improvement reported elsewhere. Nematode Maturity Index (MI) values were 1.78, 1.85, and 1.53 for the N fertiliser treatments (P < 0.05) suggesting a reduction at 400 kg N. The MI was not affected by the application of P (mean, 2.01), however, but all values in the P trial were greater than in the N trial. In the N and P trials an average of 29 and 35 nematode taxa were discriminated. The ratio of bacterial-feeding nematodes to b