Glenbrook, Canowindra, NSW 2804
“Acid soils revisited” - I believe a lot of farmers have not yet addressed the problem of acid soils for the first time, so it is of utmost importance that conferences such as this continue to make farmers aware of the economic importance associated with this widespread soil problem.
in these modern times of rising costs and falling commodity prices, farmers can well do without a third major factor limiting the profitability of their farming enterprises.
I run an 800 hectare, all arable, mixed farm about 20 km north of Canowindra, NSW. It is gently undulating country, with the soil being a light sandy loam of granite origin. It was originally timbered with white box, yellow box, some pine and kurrajong, first cleared about the turn of the century.
Currently, we are running first cross ewes for prime lamb production, plus Merino wethers, with about 400 hectares of crop sown annually. Crops include rapeseed, oats, wheat, lupins, field peas, together with improved pastures.
The normal rotation, depending on seasonal variation, consists of one crop of rapeseed followed by wheat, then lupins or field peas and then wheat. In the fifth year we sow subclover and lucerne pasture to give a legume-dominant pasture. This provides a greater volume of higher quality feed and also increases the nitrogen level in the soil ready for the next cropping phase.
We are currently looking at ways to suppress annual grass weeds in the pasture, so that we have a weed free situation to commence the cropping cycle. Basically this consists of sub-lethal applications of knock-down herbicides followed by crash grazing, with timing of application of paramount importance; hence the need for Merino wethers.
Until about 10-12 years ago, I was of the opinion that our soil was indestructable. Trifluralin was the answer to a severe ryegrass problem. By adding varying amounts of nitrogen in the form of anhydrous ammonia (NH3) we found we could not only lift our level of production by 60-80%, but we could maintain production at this high level for an indefinite period.
As a consequence of this wonderful discovery, a large proportion of the district was converted over to continuous cultivation, which in turn led to a rapidly decreasing soil pH, and other associated soil problems such as aluminium toxicity, manganese toxicity, destroyed soil structure, waterlogging and soil erosion.
In the mid 1970s,during a succession of years with a high incidence of abnormally wet winters, we noticed large, irregular-shaped yellow patches appearing in the crop paddocks. After consultation with the District Agronomist, we suspected subsoil compaction and hard panning, or possibly soil acidity. We commenced experimenting with deep ripping using a chisel plough and we even ran some trial strips using bulldozer rippers. It soon became apparent that this was going to be a very costly operation and, at this stage, the benefits were unknown. We therefore restricted the experiment to a 32 ha paddock where the yellow patches were the most severe. Much to our disappointment, a following wheat crop showed little, if any, effect for the work we had done. The yellow patches appearing in the same location as before.
Thinking that maybe the soil was farmed out, we decided to abandon growing crops and establish the area back to improved pasture and give it a spell. I prefer to sow pasture by itself without competition from the cover crop. The pasture establishes better and is far more productive in the first year. You do not have to wait 1-2 years for it to thicken up. I also find it an advantage to sow as early as possible, April to early May, as this gives the seedlings a chance to develop a strong root system before the onset of winter. This gives them a better chance of survival through the following summer.
Bearing this in mind, we sowed the problem paddock under favourable moisture conditions and obtained a good strike. On the better areas of the paddock the lucerne appeared to be growing reasonably well. On the areas where the wheat had been very yellow, however, the lucerne and clover were doing very poorly, so much so that the lucerne had almost completely disappeared before the weather started to warm up in spring. By mid-summer there were only a very few plants to be found anywhere. The clover had survived but was very stunted and did not set much seed.
It was at this stage we realised we had a serious problem more than just soil structure. Prior to now we could always find some excuse for poor pasture establishment - i.e. too wet, too dry, sown too late, too much competition from weeds. There was always something.
So in 1979, we took some soil samples and had them analysed. The results showed a pH of 4.1 and an Al level of 26.3% of exchangeable cation (i.e. % of the sum of Ca, Mg, K, Na and Al) in poor patches, which confirmed our suspicion of soil acidity to be correct. In conjunction with the District Agronomist, we proceeded to sample several other problem areas on the farm and, on checking the results of these samples against the results of samples taken from similar location about 10 years previously, we noticed that on average the pH level had dropped from 5.1 to 4.5 for the 10 year period. These figures convinced me that we would have to change our farming practice if our level of profitability were to be maintained.
We had the choice of either changing the species we grow, or changing the environment to suit the species we want to grow.
We already have enough limitations and restrictions placed on us, that we can do nothing about, and I did not particularly want the soil telling me what I could, or could not, grow. Consequently the decision was made to apply lime and the questions were raised:
• how much lime?
• how to apply it?
• when to apply it?
• where to get it?
• how to incorporate it into the soil?
• what will it cost?
• how long will it last?
All of these questions had to be considered. A whole new ball game had been introduced into agriculture but no one had written the rule book.
Progressively, by attending discussion groups and meetings, visiting sites where experimental work was being carried out, reading reports of experimental work done by specialists in the field of soil acidity, our knowledge of the subject began to grow and our conviction that this was the right way to go became more apparent.
In January 1982, we bought 150 tonnes of lime from the newly opened plant of Omya Minerals at Bathurst. A recommended application rate of 2.5 t/ha (1 ton/acre) proved to be very hard to achieve, as any equipment available at the time was not designed for spreading lime at all, and certainly not at these rates. After trying several different types of machines, we found a truck-mounted, direct drop method, to be the most satisfactory. It carries 7-8 tonnes and has a working width of 9.0 m (30 ft).
Not knowing quite what to expect, it was decided to leave a control strip, with no lime applied, and a strip with 1.25 t/ha (0.5 ton/acre) so that we could monitor the effect lime was having on subsequent crop production. The lime was applied to bare soil prior to any cultivation, as it was felt that the normal process of cultivation would be sufficient to completely mix the lime with the soil.
Half the treated area was sown to wheat, the other half to lucerne and clover. The untreated strip in each crop was visible throughout the year, and a harvest comparison showed an increase in wheat yield of 50% from the areareceiving-2.5 t/ha of lime and approximately the same from the strip which received 1.25 t/ha. In the pasture, no lucerne survived at all on the untreated area, and there was no visible difference between the 2.5 t/ha and 1.25 t/ha rates.
Soil samples taken 12 months after the application of lime are showing on average one pH unit higher than samples taken prior to the addition of lime, e.g. 4.2 up to 5.2.
In spite of there being no visible difference between 1.25 t/ha and 2.5 t/ha, we have been advised to continue to apply the 2.5 t/ha rate, as it is generally felt that lower rates will not last as long. We did not want to have to reapply lime for a very long time.
I am convinced that applying lime to our soil is the right thing to do. We are growing better crops and pastures than we did 10 years ago. In these troubled times in agriculture we need 100% from every resource available to us.