Approximately 40 per cent of the soils in the Coonabarabran district (Coonabarabran and Coolah Shires with an agricultural area of 900,000 hectares) is of acid nature. Large parts of adjoining districts such as Mudgee, Dubbo, Tomingley and Pilliga are also acid. The total area of acid soils in this part of the world runs into hundreds of thousands of hectares. Some of this is owned by Forestry Department, National Parks and Wildlife, and Crown Land. However, much of it comprises private land with several hundred landholders having between 5 and 100 per cent of their land in this category.

Soil Description

The areas of acid soils in the Coonabarabran and surrounding districts are naturally occurring and not as a result of farming or other practices. Our soils may have experienced some further decline in soil acidity because of pasture improvement and other practices, however this is a relatively unresearched field. It is common to have similar highly acidic soil test results from adjoining underdeveloped and developed country.

Acid soils in the Coonabarabran and surrounding districts are extremely variable in profile and degree of acidity. Generally they are sandstone derived (granite in some areas), sandy to sandy loam texture, low to medium in clay content and variable in depth. Some soils are sandy right through the profile, often to one or more metres (sandy solodized), while others have a sandy surface of variable depths and a clay sub-soil (sandy solodic). Basically the soils are acid all the way down the profile although in northern areas neutral sub-soils are more commonly experienced (solodized solonetz).

Typical soil test results are indicated from Table 4.1. Total cations are low, pH 4.0 to 5.5 and aluminium toxicity often medium to high.

All the acid soil areas prior to development are or were very low in natural nitrogen and phosphorus.

Table 4.1 Typical soil test results - acid soils - Coonabarabran district

Sample No.	pH*	Elec. Cond.	Cation concentration (meg %)							Phosphate Bray-1	NO3N
			Ca	Mg	K	Na	Al		Total
1	4.5	0.03	0.65	0.37	0.17	0.02	0.3	(20%)	1.5	51	3
2	5.2	0.02	0.62	0.27	0.19	0.02	-		1.1	18	2
3	4.3	0.03	0.44	0.40	0.23	0.02	0.4	(27%)	1.5	7	2
4	4.8	0.03	0.67	0.61	0.17	0.03	0.2	(12%)	1.7	5	2
5	4.4	0.07	1.0	0.83	0.54	0.08	0.5	(17%)	3.0	25	8
6	4.3	0.03	1.2	0.61	0.44	0.02	0.8	(26%)	3.1	11
7	4.3	0.02	0.3	0.1	0.11	0.02	0.2	(28%)	0.71	34

* 1:5 w/v soil suspension in 0.01 M CaCl₂ at 25⁰C

Other Environmental Details

Average annual rainfall varies from 500 to 700 mm with winter months averaging around 40 to 50 mm and summer months 60 to 80 mm. Winter rainfall is much more erratic than southern NSW environments but summer rain much heaver although again extremely variable.

Temperatures are generally a few degrees Celsius higher than southern NSW districts.

Topography is variable although the majority of the acid soil country is arable to semi-arable.

Prior to clearing (much of which occurred in the 1950s and 1960s with sporadic clearing since) most of the acid country was heavily timbered ironbark, bloodwood, pine, gum, apple box and a large variety of under growth. Regrowth can be a problem for several years after clearing depending on techniques used and practices followed.

Agriculture prior to the 1970s

Little was known at grower level about acid soils and few solutions were forthcoming from sources such as the Department of Agriculture prior to the 1970s. Sub-clover was largely a failure on the acid country as was lucerne and other introduced legumes. Barley and wheat performed poorly even in trials with exorbitant rates of fertiliser, let alone more commercially viable rates. Oats also generally performed indifferently, even after higher rates of nitrogen fertiliser. Cowpeas, a summer legume crop, was used to some extent and was the only tool landholders had available to raise soil nitrogen fertility other than from expensive fertiliser.

In a nutshell, the acid light soil areas were considered “poverty country” and contributed little towards farm productivity. This meant many farms were non- or semi-viable and other farms with predominantly heavier soil types disregarded their acid soil portions.

A Dramatic Change Occurs

The spin-off from the acid soils research effort of the 1970s and 1980s has been nothing short of dramatic in areas such as the Coonabarabran district. This is perhaps in contrast to districts where acid soils problems have evolved over the past 40 to 60 years as a result of agricultural practice.

An account of what has occurred in the past 20 years is worth summarising.

(1) Lupins: The first alkaloid free (non-bitter), white flowered Lupinus augustifolius variety (Uniwhite) was developed and released in Western Australia in 1967. An improved non-shattering variety (Uniharvest) was released in 1971. Both these varieties were late maturing. The release of Unicrop followed in 1973 (non-shattering, early maturing); then Marri in 1976; Illyarrie 1979; Yandee 1981; Chittick 1982 and Wandoo and Danja 1985.

For the first time a crop that excelled on the acid sandy soils was available which could produce a payable cash return while also contributing enormously to soil nitrogen fertility.

(2) Triticale: The first variety, Groquick,became available in 1976 and since has followed many lines including Coorong, Ningadhu, Dua, Satu, Venus, Towan, Tyalla, Currency and Samson.

Triticales have proven eminently tolerant of acid soils and able to exploit the soil nitrogen build-up from previous legume crops and pastures.

Cereal rye is very tolerant of acid soils but has a restricted market (not being particularly suitable in large quantities to the stock feed trade). Triticale by contrast has a large stockfeed market.

A greater awareness of the difference in acid soil tolerance of many cereals developed with the release of triticale varieties. Information provided by the laboratory screening work at Wagga Agricultural Research Institute combined with breeding programmes has assisted in this direction.

Acid-tolerant wheats and barleys are now a real possibility in the near future. Carbeen (released in 1981) and Saia oats were found superior acid-tolerant lines suitable for dual purpose grazing and grain production.

(3) Serradella Pastures: Landholders, supported by trial results, found it impossible to successfully establish lucerne and sub-clover pastures on much of the acid soil areas. The development of widespread soil testing to determine aluminium toxicity levels confirmed the reasons for the failures. In general soils with aluminium levels above 20 per cent (20% of bases) would not support sub-clover pastures and levels above 3 to S per cent would not support lucerne.

During the early 1970s,Serradella (Pitman and Uniserra varieties) was included in variety trials and after several years proved to be persistent and productive. Commercial sowings began in 1976.

Three new varieties, CR1 47250, GM065-2 and G50461, are likely to be released this year and will extend the role of Serradella.

(4) Lime: A major research programme that commenced in 1981 has confirmed the advantages of lime on our acid soils even when using acid-tolerant cereals. Over a three year trial period, on two sites, grain yields were 0.5 tonne/hectare greater per year where 1.5 tonne lime/hectare was initially applied. Lime at this rate reduced aluminium levels of 35 per cent to zero in the surface 10 cm and has shown little sign yet of receding to previous levels.

Because soils are generally also acid in the sub-soil, and because lime is relatively immobile, acid-tolerant cereals remain by far the superior performers after lime application.

No evidence is available as to the advantages of lime application to lupin performance. It is probably not great.

Despite two trials of three years duration, no clear evidence has emerged as to the advantage of lime to pasture production. One feels there is a significant advantage, however variable pasture establishment and trial design (in the case of one trial) has prevented any scientifically significant findings in this area.

Soil Nitrogen Build-up from Lupins and Serradella

Trials conducted in the Coonabarabran district by staff from Tamworth Research Centre have regularly measured high nitrogen fixation levels from lupins on the acid soils. In good years net nitrogen contribution from lupin crops has reached 200 kg/hectare. Cereal yields following lupins have shown responses equivalent to applying between 40 and 80 kg nitrogen/hectare in the first crop but only around 20 kg/hectare in the second crop and even less in the third.

No trials have been conducted to measure the residual nitrogen worth of Serradella. However, observations would suggest a similar effect as from lupins.

Rotations

Because of the choice of legume crops (lupins and cowpeas) and pasture (mainly Serradella on the acid areas), landholders have considerable flexibility in the choice of rotations. Some examples of commonly used rotations are indicated in Table 4.2.

TABLE 4.2. Commonly used Rotations on Acid Soils in the Coonabarabran District of NSW

	ROTATIONS
YEAR	1	2	3	4
1	Lupins	Oats/Triticale	Lupins	Lupins
2	Triticale*+	Lupins	Oats/Triticale*	Triticale**
3	Serradella	Triticale*+	Lupins	Serradella
4	Serradella	Serradella	Triticale+	Serradella
5	Serradella	Serradella	Serradella	Serradella
6	Serradella	Serradella	Serradella	Serradella
7	Triticale	Oats/Triticale	Triticale	Serradella

* Most appropriate period to apply lime

+ Generally undersown with pasture

Rotations are not often rigid and do not need to be. Some general guidelines, however, apply.

(a) The benefit of a lupin crop is at its best in the year immediately afterwards and appears to quickly recede if subsequent cereal crops follow unless high rates of nitrogen fertiliser are used.

(b) Two consecutive crops of lupins appear to have too much disease risk.

(c) Undersowing a lupin crop with Serradella is successful, but if a wet harvest occurs and lupinosis is a problem the area can be difficult to manage for a considerable time. It is generally safer to sow pasture under a triticale crop or direct drill (with minimum disturbance points) into the stubble in the autumn following the cereal crop.

(d) Serradella pastures have persisted successfully for 10 years. There appears no reason why continuous Serradella is not a viable option.

(e) Cowpeas are an option not included in the suggested rotations but often used by landholders. Cowpeas fix less nitrogen than lupins but nevertheless are very useful

(f) Lime at 1.2 to 1.5 tonnes/hectare is the recommended rate for sandy acid soils and generally reduces surface aluminium toxicity from around 30% to zero. After 5 years little deterioration in pH and aluminium has occurred and other research work suggests the one lime application should be beneficial for 15 to 20 years.

(g) On acid soils phosphate levels (Bray test) are often high (30 ppm) but generally still responsive. At very high levels (+40 ppm) they are often non-responsive.

Some Future Research Areas

The following areas of research are identified:

(1) the place of a perennial grass in the pasture phase. Perennial veldt grass is increasingly included in pasture mixes and, given good management, is quite persistent. Pioneer Rhodes Grass is also sometimes used to advantage.

Consul love grass looks very promising and could well prove more persistent and easier to manage.
A perennial grass (especially a summer grower) could well prevent or restrict further acid soil deterioration by recycling leached calcium nitrates and other cations;

(2) the benefit of lime to lupins and pasture is still poorly documented;

(3) the long term effect on lime;

(4) the long term effect on soil pH and aluminium level from lupins and Serradella pastures;

(5) a more effective strain of Rhizobium bacteria for Serradella may well further substantially increase the role of this most valuable pasture. There is evidence that some strains perform better in winter and therefore will ensure better growth and nitrogen build-up;

(6) oat, triticale, wheat and barley breeding programmes need to incorporate aluminium tolerance screening as routine at an early stage to ensure new varieties meet acid soil needs. The same should probably apply to lupins and Serradella;

(5) with all research programmes increasingly being critically examined, the value of the Wagga-based State lupin variety assessment programme must never be forgotten. Because of this programme the gains possible from new varieties such as Chittick (1982) and the more recently released Wandoo and Danja are well documented and widely understood.

Conclusion

The Coonabarabran story is naturally not directly applicable to the southern NSW one. However, much of our technology and expertise emanated from the Wagga-based southern NSW programme and still does. I’m only hopeful that in return our story can have some measure of interest and value to you.