Not correcting soil deficiencies, for crops or pastures, is a way to ever decreasing soil fertility. Lower production, greater chances of poor groundcover, more over grazing (less available feed), more weeds and even further decreasing of healthy soil aspects like soil carbon are also outcomes of ignoring soil deficiencies.
It is important, as accurately as possible, to assess soil fertility.
Decades of research into soil testing, by bodies such as state departments of agriculture, universities, CSIRO and commercial companies, has established the most reliable soil tests for Australian conditions.
This is especially the case for common soil deficiencies like phosphorus, sulphur and nitrogen. Tests for many trace elements, and elements like potassium, are useful, but commonly requiring local trials for better interpretation.
No system of grazing management or cropping, can substitute for correcting soil deficiencies known and proven to exist in given environments. For example over 130 pasture trials conducted by NSW DPI through the 1980s, 1990s and into this century, identified widespread sulphur and phosphorus deficiencies in pastures for large areas of the Upper Hunter, central and northern slopes and plains. Other research has verified similar deficiencies in areas like the southern tablelands.
Correcting deficiencies with fertilisers that contain deficient elements in sufficient quantities is essential. A recent long term study conducted in the southern tablelands, on typical phosphorus and sulphur deficient native grass plus winter legume pasture, reinforces this reality. Pasture response was directly in relation to how much sulphur and available phosphorus a fertiliser supplied at product recommended rate.
This research, was conducted by Yass LLS Senior Agronomist Fiona Leech, Dr. Alan Richardson CSIRO, Michael Kertesz University of Sydney, Beverley Orchard, formerly NSW DPI, Dr. Samiran Banerjee North Dakota State University, and Phillip Graham, formerly NSW DPI. It was published (Comparative effect of alternative fertilisers on pasture production, soil properties and soil microbial community structure) in CSIRO journal, Crop and Pasture Science, Volume 70 (12) 2019.
This research confirms other studies, including ones in my DPI days. Products often promoted to improve soil and pasture or crop production but containing little of required elements have generally not been scientifically proven to achieve claimed outcomes. Some have been promoted for decades without scientific support. Products like superphosphate, on a cost effectiveness basis are commonly the economic choice. Animal manure, provide applied heavy enough, can for example be a viable choice, especially if close to source, can be cost effective. Some have estimated animal manure has the potential to supply 20 percent of the nation's crop fertiliser needs.
A multitude of other factors are also important for good crop and pasture production. For example variety suitability for a given soil and environment, for cropping conserved fallow moisture, grazing management for dual purpose crop and pastures, to name just a few. But none of these will be vital unless soil fertility is addressed.
Timing of fertiliser application for pastures tends to be less critical than for crops. For example I have been involved in pasture fertiliser studies where fertiliser was applied but drought conditions followed. While there was little response in the drought year, expected good responses occurred once the drought broke. Other studies have shown that phosphorus and sulphur added to soil via fertiliser can contribute to soil build-up of these elements and pasture and crop responses can still be measured years later.
So while autumn is commonly detailed as the best time to apply fertiliser to pastures, for my money apply it when circumstances allow.
For example if soil tests indicate low phosphorus and sulphur, application in the next couple of months can normally result in reasonably quick responses.
If little follow-up rain occurs, for many environments good responses are likely to occur next year.
Next week: Wet weather options. Self-sown crops can work.
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