Soil health— back to basics, part 2

Safeguarding soil for future must be key task for managers

Decline insoil physical properties takes considerable expense and manyyears to correct, and can increase the risk of soil erosion by water orwind.

So, safeguarding the soil for present and future generations is a key task of land managers.

Practices that damagesoil include over-cultivation, under or overfertilisation, decreased or increased water abstraction, indiscriminateuse of pesticides and other agrichemicals, clearing natural vegetation, intensive farming practices, and importantly, failure to maintain soil organic matter levels.

Average soil carbon stocks inNew Zealand’s agricultural soils estimated at about 100 tonnes ahectare in the top 30cm, any change in soil carbon couldmakea significant contribution to carbon footprints at national, industry and farm scales.

Farmers face anewenvironmental issue, with recent research showing somedairy soils are losingmore carbon andnitrogen thandry stock andhill country areas. Dairy farms on non-allophanic soils have lost an average of a tonne of soil carbon per hectare a year insomeareas.

Biologically active carbon is the most important part of the soil carbon andhowit is distributed through the soil profile is equally important.

Soil carbon is found primarily in organic forms, whichmakeupsoil organic matter.

Anumberof international agreements andconventions are likely to influence themanagement of soils in the near future.

If agricultural soils were to beused 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 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.

About40 to 50 per cent of soil organic matter is soil carbon by weight.

In order to achieve increases in soil carbon content, it would be necessary to achieve themaximum uptake of various landmanagement practices that contribute to soil sustainability.

The Waikato region has awide range of soils, includingsomeofNew Zealand’s most productive. However, even high-quality soils can be degraded through someland use practices. The Waikato Soil Quality monitoring in 2020/21 indicated only

The Waikato region has awide range of soils, including some of New Zealand’s most productive. However, even high-quality soils can be degraded through some land use practices.

19 per cent of monitored sites fully met all seven targets, while 25 per cent of productive land met all seven targets. Compaction and excessive fertility are themain soil quality issues in the intensively farmed areas.

The development of sustainable soilmanagementpractices clearly requires a multidisciplinary approach to find the best solutions. Aswelook for those answers, it will be thewise farmerwhokeeps an eye on these issues given their ability to influence the bottom line.

There are tools available to farmers and land managers to allow themto assess the physical/nutrient state of theirownsoils.

Atechnique called visual soil assessment (VSA) hasbecome popular. It involves soil structure in top soil being visually assessed and scored by comparing itwith a pictorial description of structural condition.

VSAhas been a good tool in assessing soil quality at farmer level and the results are easy to interpret.

VSAalso provides auseful educational andvocational training tool for those unfamiliar with soil science. It creates a better understanding of soil quality and its fundamental importance to sustainable resource and environmental management. In particular, VSAhas developed a greater awareness of the importance of soil physical properties (such as soil aeration) in governing soil quality and on-farm production.

TheVSApackage has been recently updated by addingsome moreimportant indicators. The second edition of theVSAis a significant improvement on the first edition, partly because it is better able to assess soil condition andplant performance as a result of amore balanced assessment of soil chemical, biological as well as physical properties. It ismorestrongly correlated to crop and pasture production and pasture quality, considers key aspects of the subsoil and better addresses the ecological footprint of organic carbon dynamics and environmental issues, including greenhouse gas emissions and nutrient loading (such as nitrogen and phosphorus) into waterways.

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VSA will be demonstrated at a field day to be held next Wednesday near Te Awamutu — go to waikatoregion.gov for the details and to RSVP.