Guideline Index

Chapter 5: Understanding and Managing Soil Biology

5.7 Managing soils to improve biology

Opportunities to improve microbial biomass and biological function require management – in so far as possible – of the primary and secondary regulators.

5.7.1 Managing primary regulators

Primary regulators such as air and habitat can be managed through protection and enhancement of soil structure. Habitat will be protected if soils remain as undisturbed as possible, if air and water movement into and out of soils is optimised, and if the soil environment is free from toxicities such as salt from primary salinity or application of high salt-index fertilisers. Other primary regulators such as soil type, water and temperature may be more difficult to influence although access to irrigation may provide some flexibility.

Management practices that support habitat protection (good soil structure) include good wet weather management to avoid pugging by livestock in grazing operations, and no-till, stubble retention and direct drilling under cropping. Some work from New Zealand reported low abundances of earthworms, collembola (springtails), and oribatid mites on dairy farms possibly due to both direct and indirect effects on the decomposer community of livestock treading. The loss of decomposer habitat is proposed as a primary factor limiting the incorporation of organic matter from the soil surface into the profile to sustain soil carbon (Schon et al., 2011).

5.7.2 Managing secondary regulators

Improved management practices can influence the secondary regulators of soil biology including organic matter quality and quantity, the amount and frequency of soil disturbance, and the inputs used to manage production (fertilisers, herbicides, lime etc.). For example, heavy metals in biosolids or build-up of harmful chemical residues from repeated use of biocides should be avoided.

5.7.2.1 Managing soil organic matter

Organic matter in the form of plant residues (roots or surface litter), animal manures or composts is the substrate that provides energy to soil organisms. A diversity of inputs from diverse pastures and animal manures will promote below-ground diversity and support a range of soil functions. Diversity of plant species or rotations will also reduce pest and disease pressure through improved stability of the biological community. It is important to note that organic matter input must be maintained so that soil biology have regular and continued access to food stocks. A one-off application of animal manures will see a response from soil biology and a short term increase in soil carbon, but failure to follow up with repeat applications will see the system quickly return to previous levels of soil carbon and biological activity.

5.7.2.2 Managing chemical inputs

Although more data on the impact of fertilisers, pesticides or herbicides on soil organisms is required, available data shows that repeated use of the same biocide is likely to impact on different organisms by reducing their ability to ‘bounce back’ from the impact. Minimising the use of pesticides and herbicides is recommended through strategic spraying and promotion of improved soil condition and grazing management.