Sustainable soil management

Managing our soils sustainably is crucial for our regional economy and ecosystems.

Meeting the needs of the present without compromising the ability to meet the needs of future generations is a good definition of sustainable resource management.

So soil management is sustainable when it lets us get what we need today without compromising the capacity of the soil to provide for future needs.

The recently released Environment Waikato report on the condition of rural water and soil in the Waikato revealed only 34 per cent of sites sampled in the region fully met national soil quality targets.

Numerous management practices can threaten soil sustainability.

These include over-cultivation, under or over-fertilisation, decreased or increased water abstraction, indiscriminate use of pesticides and other agri-chemicals, clearing natural vegetation, intensive farming practices, and, very importantly, failure to maintain soil organic matter levels. Practices which contribute to erosion can naturally also cause soil problems.

The impacts of poor soil management have sometimes become so severe in many parts of the country that the adoption of sustainable soil management practices is of crucial importance for future generations.

Also farmers, particularly dairy farmers, face a new environmental issue with recent research showing some dairy soils are losing more carbon and nitrogen than dry stock and hill country areas. Dairy farms on certain soils (non-allophanic) have lost an average of one tonne of soil carbon per hectare a year in some parts of the country.

Biologically active carbon is the most important part of the soil carbon and how it is distributed through the soil profile is equally important. Soil carbon is found primarily in organic forms, which make up soil organic matter.

A number of international agreements and conventions are likely to influence the management of soils in the near future. Management practices that increase in soil organic carbon, such as reduced tillage, use of more organic amendments, and greater use of mixed farming may help to improve soil bio-diversity as well as soil sustainability.

The Kyoto protocol might also influence soil sustainability in the near future. Under Kyoto, agricultural soils are highlighted for possible future inclusion as a biospheric sink for carbon. If agricultural soils were to be used as carbon sinks, there would be a greater need and responsibility by farmers and land managers to increase the soil organic carbon content of their soils.

Soil organic matter (SOM) helps to maintain soil structure, retain soil moisture, prevent erosion, and can act as a reservoir for nutrients and as a source or sink for carbon. Increasing levels of SOM is likely to enhance soil biological processes and soil sustainability.

Soil carbon is mostly found in the decomposed remains of plant and animal matter and in soil microbes. Soil carbon shouldn’t be confused with soil organic matter. About 40-50 per cent of soil organic matter is soil carbon by weight.

Land uses that could enhance carbon sequestration and improve soil sustainability include best agricultural management practices which have potential to restore soil carbon. In order to achieve increases in soil carbon content, it would be necessary to achieve the maximum uptake of various land management practices that contribute to soil sustainability.

The further development of sustainable soil management practices in this country clearly requires a multidisciplinary approach to find the best solutions. As we look for those answers, it will be the wise farmer who keeps an eye on these issues given their ability to influence the bottom line.

Bala Tikkisetty is a sustainable agriculture coordinator for Environment Waikato, phone 0800 800 401.