Aglime, worms and microbes
Soils are alive with a wide range of organisms that can add to farm productivity by improving soil structure and nutrient recycling.
It is widely known that soil acidity limits the growth of many soil organisms. Recent research in NSW has shown liming can substantially improve earthworm and microbe populations.
The trial was established by Agriculture NSW and cooperating organisations at Book Book, in southern NSW (Helyar et al, 1994; 1997, White et al, 1997).
The trial site is a sandy loam over clay loam around 60cm deep. The initial pH levels (CaCl2) were 4.1 (0-10cm), 4.2 (10-20cm), 4.6 (20-30cm) and 6.2 (100-120cm).
In 1992, the limed plots received 3.7 t/ha of local agricultural lime that was incorporated to 10cm with a disc harrow. Topsoil pH increased from 4.1 to 5.5.
The trial plots were sown to either perennial or annual pastures, and these were managed either with or without cropping rotations. In the study reported here, only the permanent pasture treatments (both annual and perennial) were measured.
Earthworms were measured in soil samples taken late August to early September (1994-1997). During these months soil moisture is high and earthworms are close to the surface.
Both native earthworm species (predominately Spenceriella spp) and introduced species (mostly Aporrectodea trapezoides) were identified. The results show that liming increased both types but the most dramatic effect was on the introduced species, rising from 16 to 137 per m2 over the 4 year study period (Figure 1).
These results substantiate the positive effect of liming on earthworm numbers, especially introduced species.
It is thought that the increased numbers, especially of the introduced A trapezoides, were associated with improvement in soil properties (infiltration rate, aggregate stability and aeration) and nutrient recycling measured after liming. A. trapezoides is able to physically move lime from the surface throughout the soil to 10 or 20cm depth. This could be important for liming under no till farming methods.
It has long been known that most soil microbes are sensitive to acid soils. Soil microbes are responsible for fixing nitrogen from the air, breaking down organic matter and recycling nutrients (particularly legume nitrogen) back to growing crops and pastures.
In this study the effect of lime on microbes was measured by identifying the carbon component in the soil that came from microbes. Measurements were made in the 0-5cm and 5-10cm layers in both the autumn/winter and spring in 1994, 1995 and 1996.
The microbial biomass carbon in the limed soil was significantly greater than in the unlimed soil for 3 sampling dates in the 0-5cm layer and for all 6 sampling dates in the 5-10cm layer (Figure 2).
The variability in the 0-5cm layer made it more difficult to achieve significant effects at that level and, although the readings for all sampling dates were much higher with liming, only 3 of the 6 sampling dates were significant.
The boost to earthworm and microbial activity achieved by liming improves numerous soil properties including soil structure and nutrients recycling. These beneficial changes can lead to increased productivity in crops and pastures.
The improved numbers and productivity of soil organisms and plants continued to increase for several years after liming. It may be concluded that maximum benefit from liming is achieved in the long rather than short term.
Helyar, KR; Conyers, MK and Cullis BR, 1994, Managing Acid Soils Through Efficient Rotations. Final Report to Australian Wool Research and Promotion Organisation , 1991-1994
Helyar, KR; Conyers, MK, Cullis BR and Li GD, 1997, Managing Acid Soils Through Efficient Rotations. Final Report to IWS (International Wool Secretariat), 1994-1997
White, RE et al, 1997. Soil water and nitrogen dunamics under perennial and annual pastures. Final Report to Temperature Pastures Sustainability Key Program Southern Site (SGS140/417) 1993-1997
Australian Wool Research Promotion Organisation/IWS 1991-1997. MRC/IWS/LWRRDC, 1994-1997. GRDC, 1997-2002.
Omya Southern Pty Ltd, Incitec Pty Ltd
Research team from NSW Agriculture
Helyar, KR; Conyers, MK; Li, GD; Cullis BR; Risher, RP; Poile, G and Castleman, LJ.
Cregan, PD, Charles Sturt University Wagga Wagga