Influence of alternative fertilizers on pasture production, soil properties and soil microbial community structure

Abstract

Alternative fertilizers are commonly promoted for use on pastures to improve productivity and support a more ‘healthy’ soil microbial environment. However, minimal field research has been conducted to validate such claims. A 6-year study (2009–14) was conducted on phosphorus (P) deficient soils at three sites near Yass, NSW, to investigate the effect of top-dressing native perennial grass-based pastures with a range of alternative fertilizers and with single superphosphate (SSP). The alternative fertilizers included manures, composts, concentrated ash, crushed rock, rock phosphate-derived and microbial products. Annual measurements were made of soil chemical properties, pasture yield and botanical composition as well as relative effectiveness of products per unit of pasture grown. Soil microbial community structure was also analysed in the sixth year. Fertilizers with large quantities of P resulted in higher pasture production and clover content compared to the unfertilized control. Their cost-effectiveness in relation to pasture growth varied considerably and was a function of rate and frequency of application as well as amount and solubility of P applied. Despite large differences in pasture growth across the fertilizer treatments, there was no effect on microbial community structure compared with either the SSP or unfertilized controls. The observed variation in bacterial, fungal and archaeal community structures across all treatments was best explained by soil pH or aluminium concentration, which was influenced differentially by the fertilizer products. Fungal community structure was also correlated to pasture productivity parameters (i.e. pasture yield, clover percent and soil available P). These findings reveal a highly resilient soil microbial community influenced minimally by use of the alternative fertilizers, highlighting that on-farm management decisions regarding fertilizer product choice should primarily focus on pasture response and cost-effectiveness.