Fertiliser programs should be objectively based (based on facts; unbiased). Based on a need for nutrients confirmed by reliable soil tests. When nutrient requirements are known, a range of products which will supply the required nutrients (in a plant available form) can be compared on cost.
These were among strong points spelt out in a paper presented to the recent conference of the NSW Grassland Society of NSW “Alternatives and fundamentals – considerations when using fertilisers and ameliorants”. Author of the paper is noted pasture specialist Neil Griffiths, NSW Department of Primary Industries (DPI), based at Tocal, and involved with crop and pasture research for over 30 years.
Mr Griffiths quoted considerable independent research he and colleagues have been involved in comparing various organic and conventional fertilisers, including composts, animal manures and litters, liquids and solids, mineral blends and various preparations.
There is a place for alternative fertilisers to substitute for products like urea (for nitrogen deficiency) and superphosphate (sulphur and phosphorus) but alternative products will only work if they can supply equivalent amounts of missing nutrients.
Neil Griffiths documents several independent research studies to support such claims and these commonly also refute claims of products with little or no content of available elements to correct soil deficiencies.
A study, involving experiments at Tocal, Taree and Berry, involving Neil Griffiths and other DPI staff, compared a range of products in a nitrogen deficient situation but where other nutrients levels were adequate.
Products included in the research included those promoted to be cheaper, more productive, better for the environment and soil quality including soil biology and the like.
Over two years of assessment the Tocal results typify the findings. Urea proved by far the most cost-effective nitrogen fertiliser. Responses were related closely to a products nitrogen content and nitrogen applied at various advocated rates.
Poultry litter has been assessed in several experiments by Mr Griffiths and colleagues. While a product containing multiple elements, he feels its most valuable role is as a phosphorus fertiliser.
Where freight is not insurmountable poultry litter has proved cost effective in this role. It is important to have reliable nutrient analysis of organic fertilisers like litter as levels of nutrients vary greatly. Typical analysis of poultry litter, on a dry matter basis, is 1.1 percent phosphorus (0.5 percent water soluble 0.5 percent citrate soluble).
Neil Griffiths cites six years of results from a detailed fertiliser comparison research study in the Binalong Bookham areas of south west slopes under leadership of Fiona Leech, agronomist with Local Land Service and previously NSW DPI. This extremely detailed research is not only looking at production but also product effect on soil quality.
Six years of analysis shows pasture responses are in line with a products ability to supply available phosphorus and sulphur to natural grass with annual legume. Soil types are typically acidic and natural fertility is especially low in phosphorus and sulphur. No soil quality gains have yet been measured by any of the products tested in the research.
A concluding comment by Mr Griffiths is that fertiliser programs should be “objectively based”.
That is based on a need for nutrients confirmed by reliable soil testing and/or nutrient budgeting. When nutrient requirements are known, a range of products which can supply the required nutrients can be compared for cost”. For more information contact Neil Griffiths neil.griffiths@dpi.nsw.gov.au
- Bob Freebairn is an agricultural consultant based at Coonabarabran. Email robert.freebairn@bigpond.com or contact (0428) 752 149.