SOME growers are increasingly turning to compost to fertilise their crops.
But what sort and what quality is best?
Composts are simply decayed organic material, which is used as a fertiliser and soil amendment for growing plants.
The recycled organic materials have been processed by natural organisms, breaking down the original ingredients into a form that plants can use readily as food.
What’s more, composts can stimulate beneficial microbes, improve soil structure and help soil retain nutrients, water and warmth.
They can also be a cheaper alternative to artificial fertilisers. Whereas poultry manure has issues such as odour, quality composts do not.
So composts can be a win-win. But, as not all composts on the market are the same.
MRA, in conjunction with the NSW EPA and the compost industry has produced specifications that will help fruit and vegetable growers decide which composts to use.
The specifications describe the characteristics of composts that can provide benefits in fruit and vegetable production.
They can be used as guidelines for growers interested in using composts to improve productivity and ask the right questions of manufacturers.
Composts perform many functions once applied to soil.
Primarily composts add organic matter to soil. Soil organic matter (SOM) influences the chemical status of the soil, the physical nature of the soil and the biological activity of the soil.
Each of these interact to influence soil fertility and therefore productivity (See Figure 1 below).
Several conditions indicate that a soil could benefit from the application of composts.
These include:
- Surface crusting;
- Low water infiltration rates;
- Compaction;
- Erosion;
- Low soil organic carbon (SOC) levels (< 1.5 per cent);
- Reduced fertiliser responsiveness; and
- Low biological activity.
Application of composts can increase SOM and influence a wide range of functional soil properties and have a direct influence on crop performance.
These specifications provide guidance on the characteristics of specific recycled organics products, composted products and composted mulches for horticultural applications, primarily vegetable production and orchard production.
These specifications use AS4454 (the Australian Standard for composts) as the basis and recommend additional criteria where it is directly relevant to optimising horticultural performance. It includes information on:
- General characteristics for composts to be used in horticulture;
- Performance characteristics;
- Acceptable contamination levels;
- Food safety standards; and
- Appropriate use and application recommendations.
These do not include specifications or details for other recycled organics products such as manures, biosolids or food wastes.
These specifications do not bypass nor supersede local environmental or waste regulations and should be used along with other production advice.
Where there is a discrepancy, the legislation always takes precedence. Every grower must first comply with environmental and waste regulations in any case.
This includes not accepting or applying any material to their land that does not meet the criteria for acceptable land application.
These specifications can be used to assess the suitability of any compost for use in horticulture.
They provide a checklist that can be used to select suitable composts and to request relevant information about products from the manufacturer.
For more information on composts, and to download a copy of the specifications go to the Compost for Soils website or your particular industry website.
This work was supported by the NSW Environment Protection Authority as part of Waste Less Recycle More, funded from the waste levy.
- Virgina Brunton is the principal consultant for organics with MRA Consulting Group. Contact her at: virginia@mraconsulting.com.au.
