Senior Soil Chemist, Agricultural Research Institute
NSW Department of Agriculture, Wagga Wagga
“They say you treat your soil as if it were dirt”
We all know that farming is no longer a cushy way of life, it is big business and the pressures to produce are increasing. This pressure had led to over-cultivation of our wheat lands,
We must be prepared for this challenge, for it threatens our very livelihood, it threatens the heart of our farming system, it threatens our soil
The soil is the “heart” of the farming system.
Is your “heart” in good condition?
Table 1. A selection of farmers’ costs and returns over the last two decades (1960/81 - from Julian Cribbs’ book “The Forgotten Country”)
All Farm Costs
All Farm Produce
Cost of Living
These figures must increase your blood pressure and put extra pressure on the heart/soil or should they? Sheep don't look too bad as compared with wheat, do they? In fact they have kept pace with the cost of living. What must we do to meet the challenge? What is our regional farming system? What is your farming system? Have we got a farming system, if so what makes it tick?
How many of you have said that: “This paddock has no heart”, or more likely “This paddock is gutless, nothing ever grows there, except weeds - it’s like farming a road.”
You don’t tell anybody else about it, you don’t have to, the neighbours already know, because they have seen the crops and the pastures. They have seen you out at night belting it with machinery, trying to ensure that you at least get the crop up. We are only fooling ourselves and getting ourselves into worse trouble.
Why can’t we admit that our management has failed? Why not admit that we have a problem? Once we admit to having a problem then we can start to do something about it.
How did your wheat and barley yields compare with the national and local yields in 1981? No, not your inflated yields for the pub, the real unabridged fair dinkum yields. Compare them in Figure 1.
Wheat yields National, State, Wagga 1981
Barley yields, Wagga, 1981
Figure 1. Comparative yields of wheat and barley - local, State, National
They should look pretty good when compared with the National and State figures, but how do they line up with the local results?
Some paddocks good, some poor. Why?
The question is, have you got a soil problem?
Once you have admitted to yourself that for the amount of money you spend on labour, fuel, machinery, herbicides, fertilisers, seed, etc, your yields leave a good deal to be desired, then you are ready to diagnose the problem.
When you are ill, what do you do? Wait a few days and if you get worse you go to the doctor for a diagnosis, but what about your soil? What consideration does it get? You don’t continue to place further stress on your own heart - not like the soil in poor heart which continues to be placed under stress with scarifiers, discs and rippers. For your soil, you must prepare a long term plan and, like a strategy to look after your own heart, it will look after you.
We are assuming here, of course, that you have a soil problem, that you sow the correct variety at the correct time, and you have good weed control, etc,
The problem can be either chemical (inadequate or toxic levels of elements in the blood) or physical (like clogged arteries and veins) or both.
Let’s look at symptoms of the problem.
What are your pastures like? Do they look like any of these sketches below?
Clover/ grass in balance
Grass/ weeds e.g. capeweed
- Ever checked to see how many clover plants you have in your pasture?
- Ever measured how much dry matter your pasture yields?
- Ever measured the residual seed level in your pasture?
- How much wool do you cut per hectare or per paddock?
- What is your overall return on your livestock enterprise (overall and per paddock)?
A good pasture, dominated by sub clover or lucerne, improves the organic matter content of the soil, by using the phosphorus and sulphur supplied by fertiliser, and nitrogen fixed by the rhizobium bacteria in the nodules on the roots of the clover plants. This pasture will also provide a high protein diet for your livestock.
This organic matter or humus consists of plant remains and those of bacteria, fungi and earthworms, etc. Under a good pasture this organic matter increases and the humus material and chemical exudates from roots and from dead organisms helps to bind the soil particles together. These particles, sand, silt and clay are “stuck together” by this organic matter and give us soil structure which we discuss in more detail later.
Now in the cropping phase, these organic materials decompose more quickly than they are produced and they release plant foods, such as nitrogen and to a lesser extent phosphorus and sulphur to plants. These essential plant foods are not available in the plants in the organic forms, so they must be converted to inorganic forms by microorganisms (“residue chompers”) before they can be taken up by the plant roots.
Sounds pretty simple; what can go wrong? Plenty!
We don’t pay enough attention to our pasture phase, We haven’t got the necessary commitment to a livestock enterprise.
Pastures improve our soil fertility and stabilise our soils. So where have we been going wrong?
- We do not establish pasture correctly!
- We don’t use the correct species and/or varieties!
- We don’t fertilise adequately!
- We don’t manage the pasture correctly!
All of these aspects will be discussed in greater detail by following speakers.
Let’s examine some of the underlying chemical problems of the soil. Acidity (low pH).
A very simple test will give you a good idea of the pH, some other indicators of an acid soil problem are:
- Lucerne doesn’t grow where it used to!
- Sub clover doesn’t grow and persist like it used to!
- Wheat crops not good enough!
- Barley crops fail!
- You grow more oats than you used to:
- Horror of horrors You have large areas of Triticale
If you think one or some of these symptoms apply to any of the paddocks on your farm, then it s time to consider the use of lime.
Lime is not “Murk and Mystery”, it is an established fertiliser practice in developed agricultural countries. It has been used for decades on dairy farms etc on the East Coast of Australia.
We have to get it into our thinking, and we have to get used to using it. We have to try it out, it is no miracle, but it will become an essential ingredient if we are to maintain flexibility in our new and successful farming system. That is, the system that we are going to develop after this conference. We will need this system to meet the challenge of increasing productivity, whilst we protect our soil.
Let us now examine a few questions in regard to liming:
Why are infertile acid soils a problem?
What does liming do? How much do I apply? how do I apply it?
Q. Why are infertile acid soils a problem?
A. Because the essential plant foods, such as Calcium, Magnesium, Potassium, etc, are displaced from the reservoirs in the soil by non-essential elements such as Aluminium. This effectively reduces the amounts of the good and essential elements in the soil for plant growth.
Q. What does liming do?
A (i) Addition of lime in any form, calcium oxide (CaO - neutralising value 180), calcium hydroxide (CaOH2 neutralising value 140) or the more common calcium carbonate (CaCO3 neutralising value 100), converts Aluminium to non-toxic material. Soils with a pH of 5.5 contain no toxic Aluminium.
(ii) Liming increases the soil's capacity to hold plant nutrients. It increases the calcium levels in the soil and reduces the amount of manganese found when a soil is waterlogged. Manganese is an essential plant food, but can be present in toxic amounts in some soils. Have you a paddock which has a manganese problem?
(iii) Liming and increased calcium levels in plants may reduce the incidence and the effects of root rots on plants. The organisms responsible for many of these diseases are fungi, which prefer acidic conditions. Lime can also improve the survival and the fixation of nitrogen by the Rhizobium bacteria in the soil or inoculated onto your clover or lucerne seed.
(iv) Liming may increase the availability of soil nitrogen, phosphorus and sulphur by making conditions more favourable for the “residue chompers” which convert the organic (humus) material to plant available food. It may make molybdenum more available (if there is any left in the soil). Have you applied "Moly" lately?
(v) Liming acid soils which have a high level of sodium in the surface (sodic) can improve the surface stability of the soil and enhance water entry into soil.
Q. How much do I apply?
A. (i) If your pH is less than 5.0, get a soil test done. Soils at the same pH can have different requirements for lime. We have found lime requirement tests to be useful in estimating how much lime to apply.
a simple pH test can tell you if lime is required,
but it cannot tell you how much to apply!!
Rates can vary from 0.1 to 4.5 tonnes/hectare. Our general approach in the Department of Agriculture Is to encourage farmers with pH’s less than 5.0 (0.01M CaCl2 ) to start to experience the use of lime as soon as possible. Put out strips of lime, mix some lime and super (50:50) and use it on one round in your paddock. Dribble it in to your pasture in the spring. Always leave strips untreated and carefully observe and even measure differences over a number of years.
Remember also that livestock have to eat this pasture/crop that you grow and you need a good balance of nutrients for them and their health.
Q. (ii) Can I overlime?
A. Yes, in this year’s research carried out by the Research Institute workers on subterranean clover pastures, we have three positive responses in early pasture growth (increases of around 25%) and one negative response in pasture growth to liming. Have we put on too much lime? Our research will tell us this and these results will help us to give you the correct advice.
But we cannot cover all soils and farms and this is why you must start to experiment yourselves.
Remember, if we do nothing things can only get worse and we will all be growing Triticale or oats and using massive amounts of acid-forming nitrogen fertilisers.
Q. How do I apply it?
A. It must be incorporated into the soil, so either drop it out onto the surface and then mix it in thoroughly. It can be drilled in directly as a lime super mix. If you cannot get it to run, modify your machinery to make it run~
Q. When should I apply it?
A. As soon as possible!!
But remember what I have said about a soil test and the fact that it takes six (6) weeks in the soil for you to get the major benefits on your soil and then plants.
Q. What should I apply?
A. Check the neutralising value and the moisture content of the material. Ask for a written value if you have any doubts because that is what you pay for! You also pay for fineness, the finer the lime the faster it acts in the soil BUT the more difficult it is to apply. I am sure that you can sort that small engineering problem out.
Q, What about other essential plant foods?
A. We must not neglect our superphosphate and molybdenum - we know that they contribute towards increasing yields, so long as our other soil problems are in order.
What other problems can I have with my “heart”?
Now let’s examine the physical problems.
Clogged “arteries” and “veins”, no transmission pores to carry the “blood” of our farming system, i.e. water and air in the soil!
Our main interests here are:
To diagnose and treat the problems related to soil structure and soil water, e.g. surface crusting, waterlogging, pans or, if you like, poor movement of water into and through the soil.
Soil structure is simply the arrangement of sand, silt and clay in the soil to form aggregates. The size and the arrangement of the aggregates determines the porosity of the soil. These pores are sub-divided into macro or transmission pores through which water and air move and roots grow. The other pores are micro or storage pores. Water is stored in these pores. As we have already seen, the component of aggregates - sand, silt and clay are held together by organic matter - the plant and animal residues we talked about earlier, which are accumulated under a good pasture and which are lost with cropping.
Now, if your soil is a loam or a silt or a sand and you have had poor pastures and have cropped continuously and burnt your residues, then there is a good chance that your soil will crust on the surface. What happens is this - when water is applied to the soil surface it slakes (it falls apart), When it dries out a hard crust is seen.
Test your soil for yourself. Do the tin can test (described later) or simply collect some surface soil, air dry and drop into water; see how fast they fall apart (slake). Compare the speed of this process in old pasture soils and soils of the same type that have been continuously cropped. OK, if you haven’t got any old pasture paddocks that haven’t been hammered by machines, then try some of the wife’s garden soil. I am sure it will be considerably better physically than any of your paddocks:
As we can see from the diagram, surface crusting reduces water movement into the soil and likewise crusts reduce the movement of gases to and from the plant roots and soil microorganisms. Crusting can severely restrict crop emergence and give very patchy stands.
What can we do?
Get the organic matter level up and by the correct farming system keep it up:
Grow good pastures
Keep your residues
Direct Drill/Minimum Till
Don’t Hammer your “HEART”
Any other problems?
Yes, we can have the situation where we have too much sodium in our soils (soil is sodic). More usually these soils tend to have a higher clay content, and if they set hard in the surface, the use of gypsum at rates of 2-3 tonnes per hectare may assist.
If you believe that you have a soil of this type (sets hard in the surface rather than a simple crust millimetres in thickness), put some aggregates or “clods” in water and see if they both slake and disperse. This latter dispersion (formation of “halo” of milky clay material) is a good indicator of a sodic, gypsum-responsive soil, If you have any doubts about this then contact your local Department of Agriculture adviser.
So, we now have the recipe for surface soil recovery: PHASE 1
- GET ORGANIC MATTER INTO THE SOIL AND MAINTAIN IT
• Get a good productive pasture established
• Use reduced tillage
• Use stubble retention
• Lime and gypsum may be necessary
What about Pans? (Compaction zone)
Before we can put PHASE I into operation we must check to see if our previous farming methods, or if nature, or both, have created a problem below the surface of the soil!
How do we know if we have a pan?
Did your wheat crops look like 18 bags in 1981 and you ended up with 10-12 bags?
Does your sprayer sink into 10cm and sit on a hard layer?
DIG A HOLE
1. If you have an unusually dense layer in the soil, i,e. very few visible pores (compare with a household sponge) with few roots growing through it, then you probably have a pan of significance.
2. Do the tin can test: That is, push a can into the hard layer and pour some water into it and see how long it takes the water to disappear (infiltrate into the soil). Compare the time taken for the same amount of water to move into a soil which has good visible pores and plenty of roots growing through it, or again use the wife’s garden soil.
3, If you do have a denser pan area then take some aggregates from it and do the rapid slaking test and see if a “halo” develops. If the soil in the problem area both slakes and disperses, then you have a sodic layer in your soil which has formed partly from machinery damage or compaction but also naturally. This natural process occurs because when the soil gets wet, it tends to fall apart and the finer silt and clay material move down the soil profile and block the pores, in essence they block the "arteries and veins".
If you have a surface compaction problem because of crusting then we have already got the answer, organic matter, etc.
If you have a surface compaction problem due to livestock, don’t hammer with machines - just be careful about stocking in wet conditions and keep the organic matter level up and use less tillage
If your problem is deeper in the soil, it is a plough pan created by your previous cultivations or by the general movement of machines across the soil, then it must be removed.
Once this is removed by any of the ranges of machinery available, such as chisel ploughs, etc, make sure that your NEW FARMING SYSTEM doesn’t recreate the problem.
It has been estimated by a farmer in Western Australia that in his normal farming operations he covers 135 % of his soil surface with wheels in one season. How about you work out the figures for your farm?
If the problem compaction zone both slakes and disperses, then for a job that is going to last you should try to get gypsum into the soil in an effort to get a more lasting improvement. How do I do this? Well, it isn't easy, but some farmers and researchers are trying to push gypsum down behind the tynes of chisel ploughs with air seeders. This is another area for farmer ingenuity.
Once you have removed the physical problems in your soil make sure that your farming system does not allow them to recur. Get the roots of the plant growing deeply into the soil and, by the use of direct drilling and stubble retention systems in the cropping phase, maintain these large macro or transmission pores to ensure that water and air can get into the soil, so that the chemical fertility that you have provided from your legume pasture and from superphosphate fertiliser can be efficiently utilised by actively growing and healthy plant roots.
If we can achieve this, and I am sure that we can, our “heart” will remain healthy and our farming system and generations of Australians to come will live happily ever after in this great country of ours.
“They say you treat your soil as if it were your heart”