Making sense of fertilisers

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Better cereal yields and lower cost production



This is a practical guide to the use of shallow cultivation for seed bed
preparation and seeding. Shallow cultivation is essential for cereals after
medic in order to ensure regeneration. It is a low cost means of seeding
for cereal, grain legumes and vetches.

This chapter provides the economic justification for shallow cultivation.

Deep plough and cultivation is entrenched in the WANA region. The
technology is wasteful and costly.

This is an overview of deep ploughing and shallow cultivation.

Once the decision has been made to use shallow cultivation it is absolutely
essential to have the proper implements. These are simple and cheap. Their basic design principles are described.

Cultivation, hay production and rotations are the main methods of
controlling weeds in the WANA region. Herbicides have a role. Practical
problems are discussed.


The response of cereals to nitrogen fertiliser in the WANA region is erratic. This is explained and strategies developed to overcome the problem. Phosphate placement can also increase yield responses.

Mechanical harvesting is the main method of harvesting cereals in the
WANA region. The machines imported from Europe and North America
perform badly as they are designed for high yielding, damp crops.
Australian adaptations will improve efficiency in low to medium yielding
crops with short, brittle straw.

Even a modified harvester will not work efficiently on small farms, around
olive trees and with many types of cereal crops. The stripper is a genuine small scale machine suited to these conditions.

Using shallow cultivation will often require more weight on tractors. Why
and how?

Small farmers often employ contractors to carry out cultivation, seeding and
harvesting. This is expensive and various forms of group ownership provide
a low-cost alternative.






(Traditional rotation)




Cereal crop sown

Cereal crop sown

Cereal crop sown

Cereal crop sown


Cereal crop grows

Cereal crop grows

Cereal crop grows

Cereal crop grows


Cereal crop matures

Cereal crop matures

Cereal crop matures

Cereal crop matures


Cereal crop harvested
Stubble grazed by livestock

Cereal crop harvested
Stubble grazed by livestock

Cereal crop harvested
Stubble grazed by livestock

Cereal crop harvested
Stubble grazed by livestock


Weeds germinate naturally

Medic regenerates from seed
produced 18 months earlier.
No cultivation of the land

Land cultivated and sown to
vetch or similar forage

Land cultivated and sown to
grain legume such as lentils or
chick peas.


Weeds grazed. Low stocking rate.

Medic pasture grazed. High stocking rate.

Grazed or more often left for

Grain legumes grow.


Land cultivated for fallow

Medic grazed. Pods produced
for future regeneration.

Cut for hay.

Grain legumes mature.


Bare soil vulnerable to

Pods and stubble grazed.

Stubble grazed.


Stubble grazed.


Cereal cycle begins again.

Cereal cycle begins again

Cereal cycle begins again

Cereal cycle begins again



    Most soils in the WANA region are deficient in phosphorus or available phosphorus.

There are good responses from cereal crops and pasture to phosphorus fertiliser.

There are large resources of rock phosphate in many of the WANA countries - Morocco, Jordan, Tunisia and Algeria in particular.

In spite these factors the use of phosphorus fertiliser is low in the cereal zone.

Phosphorus is almost exclusively applied to cereal crops with nitrogen.

Virtually no phosphorus is applied to pastures in spite of the high returns from livestock and the good responses from pasture legumes to phosphorus application.

The use of phosphorus has been over shadowed by nitrogen in the WANA region yet phosphorus fertilisers provide a much lower risk means of improving yields.


     In this chapter application rates are given in kg of phosphorus (P).

The use of P, the element is consistent with other plant nutrients such as nitrogen.

Phosphorus was the first chemical fertiliser and was measured in the form of phosphate (phosphorus combined with oxygen). For many years P fertilisers were described in terms of their phosphate content (total phosphate, water soluble phosphate and citric acid soluble phosphate).

The phosphate was given the formula P O5 The following are conversions:-

Phosphate :  Phosphorus   =  1: 0.42

Phosphorus : Phosphate    =  1: 2.4

    I have to admit that I belong to the phosphate generation and you will find the term phosphate used most of the time on this site.

The need for phosphorus

        Phosphorus (P) is essential for healthy pastures and cereals.

An adequate level of P in the soil will produce:

Good seedling vigour.

Better root development by the seedling. This in turn will lead to a better uptake of moisture and other plant nutrients. The plants will grow faster.

Good levels of P will result in more cereal grains in each head and therefore a higher cereal yield.

P application also advances crop maturity by bringing forward flowering and filling of the grain. There can be as much as one week's difference. In areas of low rainfall early maturity will often mean higher yields.

    It is crucial to supply adequate P to plants in the first few weeks after germination.

P is quite mobile within the plant so P absorbed at this early stage will be redirected to filling the grains of cereals or seeds of medic pasture at a later stage. late application will produce a poor response.

Deficiency symptoms

    A lack of seedling vigour and poor root development is a good early sign of P deficiency in cereals and legumes.

Later a reddening of the leaves of cereals is an indication of P deficiency.

For legumes a pale colour and small nodules is often due to a lack of P.

Legume pastures go through a number of stages with P application.

At low levels the growth of the legumes is poor.

At medium levels there is a greatly improved level of production.

At higher levels of P pasture legume production is excellent but as the legumes also produce considerable quantities of nitrogen the pasture balance can change over a few years. The high nitrogen levels encourage the growth of grasses and other weeds.

A rotation with cereals will reduce the nitrogen levels periodically but on permanent legume pastures farmers should try to keep the legume content high by careful grazing management.

Response to P

    In the cereal zone of the WANA region soil moisture is critical to achieving a good response to P as with other fertilisers.

Application rates

    The theoretical framework for determining the optimum application rate is summed up by three questions.

    * How much P do you have?

    * How much P do you need?

    * How much P can you afford?

    The questions are simple but not the answers.

    How much P do you have?

Soil testing is one option for determining the level of P in the soil.

Tests can be expensive for small farmers and testing services are not always readily available.

Testing is most accurate for soils with a pH between 5 and 7.

It is not easy to interpret the results from soils which are alkaline that is a pH above 7. Most of the soils in the cereal zone of the WANA region have a pH of 7 or more. In spite of these difficulties soil testing can be a useful tool in determining P levels in the soil.

The history of the field is a useful means of estimating the amount of P.

Records should be kept of the amount and type of fertiliser applied to cereals and pasture and the grain yield for cereals. From these it is possible to estimate a build up or depletion of P in the soil.

    It is important to understand the pathways taken by the P fertiliser as a means of interpreting the field history.

    The most important component of the P fertiliser is that which is water soluble.

This can be readily used by plants.

Usually less than 25% of P in the fertiliser is used in the year of application.

Over time a large proportion of the remaining water soluble P is converted to other P compounds that have a low solubility and thus a low availability to plants (this is particularly important source of P loss in the neutral to alkaline soils of the WANA region).

The leaching of P from the soil is not an important source of loss. Leaching can occur on sandy soils but on most medium to heavier textured soils it is not an important factor.

Soil erosion can lead to P loss. P is not very mobile in the soil. It remains near the surface (top 5 cm or perhaps as deep as 10 cm) where it has been applied.

Sheet erosion by water or wind erosion can remove fertile surface soil containing P and other important nutrients.

If erosion occurs after P fertiliser has been broadcast most of it will be lost.

    How much P do you need?

    Crops and pastures need to have access to 2 or 3 times as much water soluble P than they actually need or is contained in the crop or pasture.

The average P content of some agricultural products.



Cereal grain

0.3 kg per qx.

Grain legume (lentils, chick peas etc.)

0.45 kg per qx.

Rape oil seed 

0.7 kg per qx.

Medic seed 

0.84 per qx.

Medic hay

0.3 kg per qx of dry hay.

From these figures it is possible to calculate that a 10 qx crop of cereals will contain 3 kg of P, a 20 qx crop 6 kg of P and so on.

The crop will require access to more than this amount. Working on the basis of three times a 10 qx crop would need 9 kg of P to be available from that already in the soil and the applied fertiliser. 

Soil P level

P requirement in kg of P per ha of fertiliser for 10 qx crop of cereal


6 kg


4.5 kg


3 kg


A  cereal crop is expected to yield 25 qx of grain per ha.

The soil P level is considered to be low because of the history of low applications on the field.

15 kg of P is required as fertiliser (6 kg per 10 qx see above).

If a single super phosphate with a P level of 9% is used 166 kg per ha should be applied.


A medic pasture is expected to produce 50 qx of dry matter.

The soil P level is considered to be low.

30 kg of P is required which would be supplied by about 150 kg of triple phosphate at 20% P.

How much can you afford?

    The application of P to a crop or pasture will almost always result in a yield response.

That response will be considerable for the first kg of P applied.

As each additional kg is applied there will be a further response but less than the response from the kg before.

This is the famous law of diminishing returns.

Finally there will be no further response at all from the addition of a further kg of P. At this stage you have reach the maximum yield.

There is no absolute amount of P needed by the crop or pasture only the amount that is profitable to apply.

Theoretically that profitable amount is slightly less than the point where the cost of the last kg of P is equal to the value of the additional yield response from that kg of P.

In fact most farmers will keep below this theoretical point.

Firstly the point of maximum profit cannot be measured with such precision. There are too many other variables such a rainfall and crop management to confuse the response to P.

Secondly even if the it was possible to produce an exact step by step picture for each additional kg of P the farmer will want to obtain a good margin over his cost of P fertiliser in order to allow for risk.

In practical terms farmers will usually apply enough P fertiliser to obtain 80 to 85% of the maximum yield response from P.

This will usually be about half the P required to produce the maximum yield.

Put another way the first half (of the maximum) of the P fertiliser applied will produce 80% of the maximum yield response and the second half will produce a further 20% of the maximum yield response.

This is of course only an indication and there is considerable variation from place to place.

The response of cereal crops to P is generally good.

In a large number of trials the yield response to the first 10 to 12 kg of P fertiliser applied per ha was 4.5 qx.

Depending on the price of the P fertiliser and the cereal grain this represents a return of perhaps 200% on the investment in fertiliser.

This is obviously an excellent return but the yield response per kg of P will diminish as more fertiliser is applied. Farmers need to determine the optimum rate.

    Typical responses for P fertiliser are as follows:-

Medium rainfall zone. Medium level of P in the soil.

P fertiliser applied in kg of P per ha.

Yield response for cereals in qx per ha.

First 5 kg of P

1.3 to 5.0

Second 5 kg of P (10 kg of P in total)

0.7 to 3.4

Third 5 kg of P (15 kg of P in total)

0 to 3.4

Fourth 5 kg of P (20 kg of P in total) 

0 to 0.7 

    The first stage is to calculate the cost of a kilo of P as follows:

    Cost per qx of fertiliser delivered onto the farm
            per cent of P in the fertiliser

For example a P fertiliser that cost $22.50 per qx and contained 15% P would cost $1.50 per kg of P.

    This formula is simple and can be used for straight P fertiliser but many fertilisers are compounds with nitrogen in which case you will need to assume a cost per kg for the N using the price of another simple N fertiliser such as urea.

From the balance it is possible to calculate the cost per kg of P.

The table below gives some indicative figures for the common P fertilisers.





Super phosphate (SUPER)


Double super phosphate


Triple super phosphate


Di Ammonium  Phosphate (DAP)


Mon Ammonium Phosphate


* Sulphur can be an important fertiliser on some sandy soils. Particularly important for annual legume pastures.

    The cost of the P, the yield response and the price of the additional yield can be fed into a calculator to provide a optimum application rate.

Break-even Yield

    Many farmers find it more useful to work out a Break-even Yield response. That means the addition yield required to break even or pay back the cost. Obviously farmers will want to obtain more than a repayment of the cost but the break-even yield response provides the zero risk position.

Below is an example of a break-even chart.

This chart can be constructed with different prices for the P fertiliser and different prices for the yield of wheat, barley, grain legume or other output.

Amount of P applied per ha. Cost of P = $1.50 per kilo

Break-even yield response needed to cover cost of P with wheat at $10 per qx.

Break-even yield response needed to cover cost of P with wheat at $15 per qx.

Break-even yield response needed to cover cost of P with wheat at $20 per qx.

5 kg of P per ha = $7.5

75 kg of wheat = $7.5

50 kg of wheat = $7.5

37.5 kg of wheat = $7.5

10 kg of P per ha = $15

1.5 qx of wheat = $15

1 qx of wheat = $15

75 kg of wheat = $15

15 kg of P per ha = $22.50

2.25 qx of wheat = $22.50

1.5 qx of wheat = $22.50

1.22 qx of wheat = $22.50

20 kg of P per ha = $30

3 qx of wheat = $30

2 qx of wheat = $30

1.5 qx of wheat =$30

25 kg of P per ha = $37.50

3.75 qx of wheat = $37.50

2.5 qx of wheat = $37.50

1.87 qx of wheat = $37.50

30 kg of P per ha = $45

4.5 qx of wheat = $45

3 qx of wheat = $45

2.25 qx of wheat = $45

Some examples of variations to application rates.

    * Following an exceptionally high yielding cereal crop in the previous year.

    High yielding crops will extract more and application rates need to be increased to compensate.

Usually applies to cereal crops but also high yielding pastures.

The farmer is in a good financial position to apply more phosphorus.

    * Following a poor crop in an average or good season.

    If the crop is poor due to weeds, disease or some other management factors such as late sowing there should in theory be a lower uptake of phosphorus and a surplus for the following year.

Unfortunately part of this phosphorus will become unavailable and it is unwise to reduce application rates if there is a reasonable expectation of a good crop (that is the weed or disease problem has been overcome).

    * Re-sowing a crop in the same season.

    If for any reason a crop has to be re-sown in the same season it is still necessary to apply a small amount (say 5 kg/ha of P) with the seed.

As the crop is growing it will take up the previous P but the small amount placed near the seed is still required.

    * Late sowing.

    No amount of additional P will compensate for the lower yield expected from late sowing.

Application rates should be adjusted down to match the lower expected yield.

    * After a drought.

    There will be a considerable carryover of available P and application rates can be reduced by one third.

Grain Legumes

    The above discussion of P fertiliser relates mainly to cereal crops.

Grain legumes crops are rich in P and application rates are different from those used for cereals.

Chick peas secrete malic and other organic acids from their roots and are capable of utilising P compounds that are insoluble as far as other crops such as cereals are concerned.

P fertiliser is not normally needed unless the soil P levels are very low.

For lentils the yield response and application rates are similar to cereals but need to be adjusted for the economic value of the output.

Annual legume pastures (medic and sub clover)

    Annual legume pastures respond well to P fertiliser.

The growth of the pasture is increased and more seed is produced.

A vigourous legume pasture with adequate P will fix abundant N from the air for the following cereal crop.

When the pasture is deficient in P the growth is poor.

The cotyledons of P deficient seedlings turn yellow and die earlier. The stem below the cotyledons becomes a bright red colour.

The decision on application rates follows the same principles as that for cereals but the output is more difficult to measure as it has to be converted into animal products.

There is no point is applying high rates of P unless the livestock system is capable of converting the extra pasture growth into profitable returns.

P is usually applied to legume pastures in late summer.

The P washes in with the first rain. There is no need to cultivate the soil.

        On a few highly deficient soils the response curve for P is anomalous.

The usual response curve is that each additional application of phosphorus produces a diminishing return until a maximum response is produced. After this further applications will produce no additional yield.

The actual (or optimal) application rate will be below the maximum yield point.

It will be determined by the response to the last kg of P, the price of the P (including the cost of application) and the value of the response (extra cereal yield or more pasture).

On these anomalous soils the level of P is so low that small amounts produce no response. The farmer needs to apply 200 to 300 kg of triple phosphate in the first application before there is a response.

Once the base has been established normal responses apply. This high rate only needs to be applied once.
         This anomalous situation is unlikely to occur on arable land because P has been applied in the past to cereal crop.

It can occur on the parcour or rangeland where P fertiliser has never been applied in any form what so ever. 

    As a starting point I have recommended throughout this site that farmers in the WANA region apply 100 kg of triple super phosphate (20 kg of P) to their medic and other legume pastures.

    This recommendation is based on the following assumptions:

    * P has not been applied to pastures in the past or only in very small quantities.

    * In medic rotations P has been applied to cereals but the amount has not been great and P levels are not high in the soil.

    * Returns from livestock fed on pasture are high. Early growth in autumn and winter which replaces hay and grain is particularly valuable.

Leaf analysis

    Leaf analysis is a useful means of determining the P status of crops and pastures.

Unfortunately the results come too late to provide an indication of the application rate.

As stated above P must be applied early with the germinating seed. Late applications have little or no value. For this reason leaf analysis is unlikely to be used by most farmers.

The most valuable role for leaf analysis is for the Ministry of Agriculture extension service.

Application rates for pasture are always going to be general rules. If the extension service carries out some sample analysis on farms that have followed their recommendations they can check how effective they are and fine tune them for the future.

Placement of fertiliser near the cereal seed.

    The placement of the P fertiliser is relevant to the application rate.

    P is used by the cereal plant during the early stages of germination and growth.

P fertiliser placed near the seed is much more effective than P fertiliser broadcast over the crop. 

There have been many hundreds of experiment that have consistently demonstrated the beneficial effects of placement.

On soils that are low in P the response to P placed close to the seed can be as much as six times greater than P broadcast.

Soils that have a higher P level do not show such a dramatic effect but on average twice as much P fertiliser is needed if it is broadcast rather than placed close to the seed. 

P fertiliser broadcast after seeding has an even lower response and that applied more than ten days after seeding will not produce any response at all.

 The placement story has been ignored in the WANA region because of the high rates of nitrogen fertiliser recommended.

Many of the nitrogen fertilisers have an adverse effect on germination and cannot be placed near the seed or only in small quantities.

Phosphate fertilisers are safe to place with the seed at any of the application rates that are likely to be used.

The use of P placement had a dramatic effect on fertiliser use in South Australia at the end of the 19th century. High rates recommended by research centres were not economic for farmers. When farmers developed placement techniques they found that a half or a third or the P fertiliser was needed to obtain the same response.

    Most of the machinery used for the application of fertiliser and the sowing of cereal seed in the WANA comes from the USA, Canada or Europe or is manufactured to similar designs.

In the northern temperate zones fertilisers have been used at high rates for a long period.

The additional response from the placement of the fertiliser close to the seed has been forgotten. It is a distant folk memory of the period of low soil phosphorus levels and low application rates.

 In the WANA region fertilisers are still not used on many small farms.

Elsewhere (except on research centres) high levels have not built up in the soil.

The high climatic risk will mean that application rates will always be lower than those used elsewhere.

    Machinery for placement.

    In the 1890s when South Australian farmers began to use super phosphate for cereals on a large scale they placed the fertiliser close to the seed.

At first this was done by mixing the fertiliser with the seed and drilling the two together. This was a time consuming operation and farmers would not have done it if it had not been so profitable.

Soon a combine seeder was developed which combined the seeder with a scarifier and combined the seeding of the cereal and the fertiliser placement.

The seeder had two boxes. One for cereal seed and one for fertiliser. The seed and the fertiliser feed into a tube that in turn feeds into a boot. The boot is attached to the back of the sowing tines and feeds the seed - fertiliser mixture into the ground behind the tine.

Other tines then close the soil over the seed and fertiliser.

Over one hundred years later this machine has been improved with new materials (such as plastic coated parts that come in contact with the fertiliser) and modifications ( such as the spring release tines rather than the spring tines). It is however still the same basic machine and is robust and effective.

    The combined seeder is more expensive than the existing seeders used in the WANA region but carries out many tasks and is more efficient.

It is more expensive because it is a trailed implement rather than one mounted on the linkage.

Linkage mounting is not possible because of the weight of the machine, the seed and the fertiliser.

The combine seeder can be used as a scarifier with the seeding and fertiliser mechanisms disengaged. It carries out the seeding more accurately than the existing seeders.

It is possible to reduce the seeding rate to achieve a similar plant density.

It places the fertiliser with the seed. A separate fertiliser spreader is not required.

The placement of the P fertiliser produces a large saving in fertiliser costs.

    Advantages of combine seeder:

    * It combines three implements the scarifier, seeder and fertiliser spreader. This off-sets most of the higher cost.

    * More efficient seeding means cereal seeding rates can be reduced.

    * Placement of P fertiliser means less can be used for same yield response.


    * Extra weight means trailed not linkage.

    * Placing fertiliser in the box slows down filling.

Not a big problem with application rates of about 100 to 150 kg per ha.

If higher rates used box has to be filled more frequently than the seed box and rate of working is reduced.

Higher P application rates may be achieved without more fertiliser if a more concentrated fertiliser is used.

Other machinery for placement

    A combine seeder  can be used for placement of simple P fertiliser and NP compounds.

Super phosphate, triple phosphate and Di Ammonium Phosphate (DAP) can all be placed near to the seed provided the application rates are not too high for the N fertiliser.

With nitrogen fertilisers particularly urea there is a danger that germination will be reduced.

No more than 25 kg of N should be placed with the seed.

Placement has to be modified to a banding system where the fertiliser is placed in a band under the seed and is separated by a few centimetre of soil. These machines are more expensive than the simple combine seeder.

Other application methods.

    Placement is the preferred option for crops.

For pasture the phosphorus is broadcast on the surface by hand or using a machine.

The farmer can use the combine seeder without putting the tines in the ground.

Alternatively a spinner type spreader can be used.

There is no need to cultivate the soil.

The phosphorus can applied in late summer and left on the surface. It will wash in with the autumn and winter rains.

Super phosphate or triple phosphate are robust compounds that do not break down or evaporate. They are washed into the soil with the rain.

 Soil inoculation.

    Research work in Australia and Canada has shown that inoculation of the soil with Penicillium radicum or P. bilaiae can increase yields by a small but significant extent.

In any one season the crop or pasture will take up 10% to 30% (on average 25%) of the phosphorus applied. The remainder will become unavailable over time as it is chemically bound to the soil.

It has been shown that these fungus can mobilise some of the phosphorus reserves in the soil.

They can also extend the roots of the crop plants so they can access more nutrient in general. 

More is available to the crop and yields are increased.

Most of the soils of the WANA region have an alkaline pH and the immobilisation of phosphate is greater in these soils than in acid soils.

There are some fungus strains that are effective in alkaline soils also.

A package for small farmers.

    A package that includes:-

    + A small amount of phosphorus fertiliser applied through the combine seeder so it is placed near the seed.

    + A reduced amount of cereal seed sown with greater accuracy to achieve a similar crop density. (Combine seeder)

    + A seeder that carries out a final cultivation for weed control.

Provides a most attractive package for small farmers.

It has achieved a high level of acceptance in Libya, Jordan and Iraq.

Over time the package can be fined tuned using soil and leaf analysis to provide the optimum application rate for phosphorus but at the initial stages a low rate of less than 100 kg/ha of triple super phosphate can be used to get farmers started.


    The same three questions form the base for determining nitrogen (N) application rates.

    How much nitrogen do you have?

    How much nitrogen do you need?

    How much nitrogen can you afford?

Nitrogen from a bag

 Low soil nitrogen.

     Low soil nitrogen or low soil fertility is the greatest single problem for cereal production in the WANA region.

The cereal-fallow rotation has had a devastating impact on the soil fertility and soil structure of the arable land in the region.

The cultivated fallow will in the initial years mobilise nitrogen from the break-down of soil organic matter.

After a period of time almost all the nitrogen contained in organic matter has been mobilised.

The decline and fall of the fallow is well documented in the long-term rotational experiment carried out at the Waite Institute in Adelaide since the early 1920s Returns.

The soil fertility after some years of fallow is low.

Cereal crops grown after fallow are poor.

The fallow phase of the rotation consists of a growth of weeds followed by cultivation in the spring.

The weeds and animal manure from the livestock grazing the weeds produces little organic matter. The mobilisation of nitrogen from the soil is greater than the return of nitrogen from the weed phase.

Soil organic matter declines under a fallow rotation. 

In the WANA region soil nitrogen levels are very low as the fallow rotation has been used for fifty years and virtually all the nitrogen in the soil has been mobilised.

Emphasis on nitrogen fertiliser.

     It is not surprising in these circumstances that research and development organisations in the WANA region should emphasise the use of nitrogen fertiliser as a solution to the chronic low fertility of arable soils and the low yield of cereal crops.

The use of nitrogen fertiliser has had an enormous impact on the yield of cereals in the temperate regions of northern Europe and America.

It has also helped to produce some of the highest yields of wheat in the world in the Punjab region of northern India.

Everywhere nitrogen fertiliser seemed to be producing spectacular results.

Even if the results in the WANA region were not as spectacular it was thought that the low cost of nitrogen (due to the low cost of energy from oil over most of the last 50 years) would still make it a sound investment.

How much nitrogen do you have?

    For farming systems based on nitrogen fertiliser the simple answer is that very little is carried over from the previous year.

Nitrogen fertiliser provides a mineralised source of nitrogen that is readily available to plants.

N is taken up and utilised and there is little residual nitrogen available for the following crops.

A rotations such as the fallow - cereal rotation or continuous cereal farming provides little or no additional organic nitrogen.

All the nitrogen comes from the bag. The full amount will be needed each year.

Nitrogen supplied by legumes is discussed separately in the section below.

How much nitrogen do you need?

    A cereal crop will require 4 to 5.5 kg of N in a mineralised form to produce a qx of grain.

A crop yielding 20 qx will need 80 to 110 kg of mineralised N as provided by N fertilisers.

About half of this N is removed with the grain.

How much can you afford?

    The same method can be used for nitrogen as with phosphorus for determining the application rate that is profitable.

The same law of diminishing returns applies.

Farmers will need to take into account the risk of applying nitrogen fertiliser at higher rates because of the possibility of yield reduction


 Yield reduction

    The difficulty in the WANA region is that nitrogen fertiliser can cause a yield reduction.

Australian farmers were extremely lucky as early experimental work carried out at the Roseworthy Agricultural College in South Australia in the 1880s showed that the application of nitrogen could cause the yield of cereals to fall.

After those experiments both farmers and scientists approached the use of nitrogen fertiliser with great caution.

Scientists in the WANA region did not have this historic tradition to guide them and found it difficult to accept the anomalous response of nitrogen in the region.

    + Uptake of nitrogen.

    Yield reduction for cereal crops is now well understood and no longer considered anomalous.

The addition of nitrogen fertiliser in the usual soluble mineralised forms is readily taken up by the cereal seedling in the autumn.

The cereal plant produces more shoots or tillers.

    + Lower carbohydrate levels.

    The additional number of tillers results in lower carbohydrate levels in each of the stems.

If the cereal plant suffers from water stress in the spring after flowering the grain is filled from these reserves of carbohydrate in the stem.

The leaves of the cereal plant are too stressed by drought to produce more carbohydrate through photosynthesis.

As there are fewer reserves to fall back on the grains fail to fill and the yield declines.

This scenario is only the scientific explanation of what farmers have observed.

Nitrogen fertiliser increases the number of heads. In a good year the extra heads produce a higher yield.

In a dry year the heads fail to fill.

Without nitrogen fertiliser one has fewer heads but those that exist produce some grain.

The more abundant heads from the nitrogen fertilised crop contain nothing.

    + Old and New varieties of cereals.

    The old tall cereal varieties are more severely affected by the nitrogen - water stress syndrome than modern semi dwarf varieties but the yield reduction can occur with all varieties.

     Avoiding the risk of yield reduction.

     Avoiding the risk of yield reduction is a high priority for small farmers.

To say, for example, that nitrogen fertiliser will produce a profitable return over a five year period is not acceptable to a small farmer if that five year period includes two years of yield reduction.

If the first two years produce a lower yield the farmer will be totally convinced of the futility of using nitrogen fertiliser.

The risk is obviously climatic.

It is one aspect of the great difficulties facing the WANA region and the cereal zone.

There has been a tendency to regard the WANA cereal zone as a continuation of the northern Mediterranean cereal zone. The rainfall is lower but otherwise it is more of the same.

In fact that is not the case. Somewhere around 500 mm there is a major tipping point and techniques that are perfectly acceptable in a higher rainfall zone (if expensive) suddenly no longer work in lower rainfall zones.

Nitrogen fertiliser is one.

Breaking down clods is another.

Early sowing as a high priority is a third.

 Less nitrogen fertiliser should be used in areas with lower rainfall where the risk of moisture stress after flowering is greater.

Less nitrogen fertiliser should be used with late sown crops.

The placement of the fertiliser near the seed will also reduce the risk to the farmer.

Smaller quantities can be used to produce the same yield response. If the crop fails the farmers' loss is less.


Taking advantage of good years.

    Risk reduction through low inputs is a well recognised strategy for small farmers in areas with low rainfall.

It certainly has its attraction but it can mean that farmers fail to take advantage of the good season.

There needs to be a balance that allows farmers to gain from good seasons.

Farmers in the WANA region find it unbelievable that low rainfall regions can produce crops of over 30 qx. per ha. in a good year if they have sufficient nitrogen and are free from weeds.

Soil testing

     Soil testing can be used for nitrogen as well as for phosphate.

It is more difficult to test for N than soil phosphate as the level varies more rapidly after a crop or during a medic pasture.

It is at present too costly and too complex for small farmers in the WANA region. Given that legume nitrogen (see below) exists as a low cost and low risk alternative it is doubtful whether soil testing for nitrogen is a practical and economic idea.

Leaf analysis is an easier method of determining nitrogen status in a crop.

The difficulties are practical. Locally base Crop Monitoring Groups may include leaf analysis as part of their service to farmers but analysis needs to result in immediate action if the application of further nitrogen to a cereal crop is to be profitable.

A centrally organised system with long turn round times for results would be of little practical use to farmers.

Placement of nitrogen fertiliser

    There are considerable advantages in placing the fertiliser close to the seed.

This encourages early grow of the cereals and gives them an advantage over the weeds.

The placement of nitrogen with the seed through a combine seeder is possible with rates of up to 25 kg of N.

Above that level the N can reduce the germination of the cereal.

The N can be placed in a band under the seed with a different and more expensive machine.

With systems based totally on N fertiliser much of the N will be broadcast as the quantities are so great that sowing with the seed will slow down the seeding operation.

Form of nitrogen

    Nitrogen fertilisers come in many different compounds of nitrogen.

Probably the most common is Urea but ammonium and nitrate forms are also available.

In the soil the various compounds of nitrogen are broken down to nitrate which is then taken up by the plants.

In the temperate regions or the tropics the urea or ammonia initially applied is rapidly dissolved in the soil water and then converted to nitrate.

In the WANA region winter rainfall is not reliable. Urea applied on the surface can dissolve in light rain or dew. It is converted to ammonia which evaporates if there is not a good rain soon after.

Losses of nitrogen can be high - as much as 20% of the urea can be lost.

Placement of the fertiliser in the soil is the best option but the equipment is not always available.

One cannot place large amounts of nitrogen near the seed (see Combine seeder and placement of phosphate fertiliser) so a seeder which can band the fertiliser below the seed is needed.

For a second application of fertiliser surface broadcasting is the only option.

Nitrogen from legumes

 Eliminating the risk of yield reduction altogether

    The considerable experimental evidence from the region over the last 50 years and farmer experience has shown that "slow release" nitrogen from the breakdown of organic matter does not carry any risk at all of yield reduction.

Nitrogen from previous legume crops or pastures will increase soil fertility and provide adequate amounts of nitrogen for the following cereal crop.

This will not only save money on nitrogen fertilisers but be more effective.

How effective are legumes?

  Needs of the cereal crop

A cereal crop requires about 4 to 5.5 kg of mineral nitrogen (N) for each 1 qx. of yield.

About half is taken off with the grain and half remains with the straw and other residues.

That is about 100 kg of urea (46 kg of N) is required for each 10 qx. of grain yield.

If we say in a rainfall zone of 400 mm that we expect a crop of 25 qx. we will need 100 to 125 kg of N.

If nitrogen from a bag is used 200 to 250 kg of urea would need to be applied. The risk of loss if such a high rate of urea were to be applied would be considerable. There is also a considerable risk that the yield will be reduced in a year when the spring is dry. (see above for details)

Supplies of N from medic

    High levels of nitrogen are returned to the soil from grazed medic provided there is a good density of medic plants.

If the density of medic is lower and that of weeds (including grass) is higher the production of nitrogen will be less.

A legume pasture will produce the equivalent of about 12 kg of mineral N for each 10 qx. of growth.

See Photo Guide for exact amount of N produced by medic.

The pathway is that the medic pasture produces high protein organic matter that is returned to the soil directly or through animal manure.

The organic matter in the soil breaks down and releases mineral nitrogen as nitrates.

A yield of 50 to 60 qx. of dry matter from a well fertilised medic pasture will produce the equivalent of 60 to 72 kg of mineral N.

This alone will supply the N needed by a 15 to 18 qx. cereal crop.

This is higher than average yields in the WANA region for this rainfall zone at present but well below the potential yield.

If the medic-cereal rotation is used there will be a need to top up the nitrogen for a 25 qx. crop provided weed control and other management factors are good. 

Initially farmers can expect a considerable yield increase without any additional nitrogen from a bag. Later as farmers improve their weed and disease management they can apply 100 kg of DAP which contains 18 kg of N with the seed at sowing.

This is near the maximum (about 25 kg per ha of N) that can be placed near the seed without reducing germination and brings the total up to 90 kg of N.

Supplies of N from longer medic pastures

Farmers who use the Zaghouan 4 rotation will have higher levels of nitrogen (in the form of organic matter) in the soil from the longer medic phase and the fallow is an excellent means of mineralising the soil organic matter into a form of nitrogen that can be used by the cereal crop.

Vetch and grain legumes

For vetch and grain legumes the same applies.

However grain legumes provide less nitrogen to the soil because they are harvested rather than grazed.

A grain legume crop will usually supply 30 to 40 kg of N to the following cereal crop.

Similar figures apply to vetch cut for hay as a large part of the nitrogen is removed and mostly lost.

If the vetch is fed back to livestock in the form of hay and the manure used on the field some is returned but frequently the manure is used elsewhere or the hay is sold.

It spite of this all legumes will improve the soil to some degree and will provide more nitrogen than the cereal-fallow rotation.

Vetch green manure

    In the 1950s green manures were heavily promoted. They are vetch or other legumes grown only as a fertiliser.

They are ploughed in and not grazed.

They are extremely effective and produce about 16 kg (rather than the 12 kg above for grazed medic) of mineral N per 10 qx. but with current high livestock prices and low cereal prices the idea of growing a green manure crop of legume pasture is totally uneconomic.

 One of the difficulties with the classic medic rotation as practised in Australia (medic-cereal alternate years) is that the abundant organic nitrogen produced by the medic pasture is not always mineralised and mobilised quickly in the following autumn for the cereal crop.

 Zaghouan 4 rotation

    This is the most effective means of providing nitrogen to cereal crops as the fallow begins the break down process early.

One of the difficulties is assessing the amount of nitrogen provided by legumes is that it is in the form of organic matter.

The organic matter must breakdown into a mineral form of N before it is available to the cereal crop. The cereal crop grows away strongly in the autumn with the N mineralised by the fallow. The Zaghouan rotation has 2.5 years of medic so there is plenty of organic nitrogen to break down.

The break down of soil organic matter releases about 5% of its weight in the form of mineralised N each year.

A soil with 1% of soil organic matter has more than 10 qx. of N per hectare but it is locked into organic structures and only 60 to 90 kg  are released in mineralised forms each year.

The medic pasture in the Zaghouan 4 rotation is usually grazed and large amounts of organic matter including organic nitrogen are returned to the soil.

Over the 2.5 years of medic pasture large amounts of organic matter at returned to the soil. The land is then fallowed. The fallow mobilises the soil nitrogen for the cereal crop sown in the autumn.

There is no need to top up with nitrogen from a bag.

The fallow also helps to control weeds. Without good weed control high soil nitrogen levels can be ineffective as weeds take up the nitrogen and choke the crop.

Experimental evidence shows that the Zaghouan rotation can double cereal yields compared to the fallow-cereal rotation. For a small farmer dependent on contractors it is more profitable to grow half the area of cereal with double the yield.

The usual Zaghouan rotation is 4 years. 2 full years of medic. 1/2 year of medic followed by fallow and 1 year of cereal.

This is based on average assumptions of reasonably good medic.

If however the standard of medic pasture (that is a high density of medic plants and a low density of other plants) is improved and maintained the amounts of organic nitrogen added to the soil are very considerable.

There will be sufficient nitrogen for two cereal crops.

It becomes the Zaghouan 5 rotation.

    Ingredients for success of Zaghouan 5:

    + Medic dominance of the pasture.

    + Good early fallow. Control grasses in particular.

    + Good cereal crop with low weeds and disease.

    + Second cereal crop should be successful. Perhaps some additional nitrogen from a bag say DAP

Nitrogen budget

Nitrogen INTO soil from legumes

 Soil organic matter

Nitrogen OUT  of soil for cereal crop 

1% soil organic matter releases 5% as N per year.
Reserve in soil more than 10 qx. of N.

60 to 90 kg released for cereal crop

Fallow will release more N from organic reserves.

25 qx. crop requires 100 to 120 kg of mineralised N. About half removed with grain.

Medic pasture will add organic matter to soil.

60 to 72 kg of N in organic form added to soil reserves each year.

Grain legume crop or vetch removed as hay.

30 to 40 kg of N added to reserves.

Vetch (or other forage legume) not grazed but grown as green manure and ploughed in.

80 to 96 kg of N added to reserves.

Zaghouan 4 rotation 2.5 years of medic.

150 to 200 kg of N added to reserves.

Zaghouan 5 rotation with two cereal crops.

Second cereal crop may need N fertiliser to top up N for optimum yield.


The author with his own wheat crop in Australia. This was grown after a few years of vigourous legume pasture. No nitrogen fertiliser was applied only phosphorus. The crop was sown after pasture without a fallow.

Second application of nitrogen fertiliser

    This is a regular practice in temperate regions north of the Mediterranean.

It is common to apply a second application of nitrogen fertiliser to the cereal crop 3 to 8 weeks after sowing.

Countries such as Algeria that have been more influenced by European technology regularly use a second application of nitrogen.

The same problems can occur with the second application as the first. Nitrogen can reduce yield as well as increase them.

A second application should only be applied in the higher rainfall parts of the cereal zone and even then with great care.

A useful guide is the number of shoots or tillers.

It is a simple task to count the tillers using the sampling disc for medic seed  Measuring medic seed pods . Using this method it is possible to determine the number of tillers per square metre.


+ If the number of tillers is less than 500 per square metre the application of nitrogen fertiliser will increase the number and can produce an increase in yield provide the rainfall is sufficient after flowering.


+ Above 500 tillers per square metre little response can be expected from the application of more N fertiliser.

+ Above 700 tillers per square metre the response from additional nitrogen fertiliser is likely to be negative. That is there could be a yield reduction.

    The yellow colour of the cereal crop is an excellent indicator of acute nitrogen deficiency but the decision to use nitrogen fertiliser should be taken well before such acute symptoms are apparent.

Sap nitrate testing can be used to at the two leaf stage to measure the nitrogen status.

The equipment is relatively simple but again we doubt whether the development of complex testing organisations is the best way to go when the use of legume nitrogen is so simple and low cost.

 Increased protein levels in the grain

    Nitrogen fertiliser or legume nitrogen will increase the level of protein in the grain.

In countries such as Australia grain protein levels are tested and a higher price paid for high protein grain. In some cases the use of nitrogen fertiliser can be justified by the increased price rather than an increase in yield.

In the WANA region protein levels do not have such an impact on price and for small farmers a large proportion is retain for family consumption not for sale.


    The text book theory on nitrogen application is that N from the mineralisation of organic matter or from the bag is all the same.

There may be some minor difference in availability but they do not make a large difference.

Below is a chart of the results of an experiment conducted in Erbil, northern Iraq and reported in the Annual Report July 1982 of the Agro-pastoral Development Project.

The experiment was conducted by the South Australian Department of Agriculture.

    It is worth looking at these experimental results in some detail as they are quite remarkable.

Amount of Urea applied.
Kg per ha

Yield of wheat after a year of wheat.

Qx per ha

Increase in yield from application of last 100 kg of urea. (46 kg of N)

Qx per ha

Yield of wheat after a year of medic pasture.

  Qx per ha

Increase in yield from application of last 100 kg of urea. (46 kg of N)

Qx per ha.

The medic advantage.

  Qx per ha

Zero urea


100 kg of urea = 46 kg of N


200 kg of urea = 92 kg of N


300 kg of urea = 138 kg of N


    * Law of diminishing returns.

    If we look at the increases in yield of wheat with the application of each additional 100 kg of urea (46 kg of N) we see that both the wheat after wheat and wheat after medic show the classic law of diminishing returns.

Each additional 100 kg increases the yield of wheat but by a lesser amount.

    * The medic advantage.

    The last column shows the medic advantage.

That is the higher yield obtained from wheat after medic compared to wheat after wheat but with the same amount of N applied.

The extraordinary fact is that the advantage actually increases with the additional N while in theory the yields from the two rotations should converge to a similar yield.

Both treatments are levelling off and would probably reach their maximum yields with the addition of another 50 kg of urea. If this is the case they would never converge.

The medic pasture must be having some additional effect.

Perhaps it is the improved soil structure or it could be a break in the disease cycle for cereals.

Perhaps it is the slow release of N from the organic matter.

Extrapolation of the above to a 10 ha farm

Low risk strategy - wheat after wheat with no urea


Land use - ha

Yield - qx. per ha.

Total output - qx.

Output less seed - qx.

Fertiliser and other costs

Wheat 10 ha




No N fertiliser. Cultivating and seeding 10 ha

Cereal stubble for livestock 10 ha

Low risk strategy - wheat after medic with no urea

Land use - ha

Yield - qx. per ha.

Total output

Output less seed

Fertiliser and other costs

Wheat 5 ha




No N fertiliser. Cultivating and seeding 5 ha.

Cereal stubble for livestock 5 ha

Medic pasture for livestock production 5 ha

High risk strategy - wheat after wheat with 300 kg of urea


Land use - ha

Yield - qx. per ha.

Total output

Output less seed

Fertiliser and other costs

Wheat 10 ha




30 qx of urea. Cultivating and seeding costs for 10 ha.

Cereal stubble 10 ha.

High risk strategy - wheat after medic with 300 kg of urea.


Land use - ha

Yield - qx. per ha.

Total output

Output less seed

Fertiliser and other costs

Wheat 5 ha




15 qx of urea and cultivating and seeding costs for 5 ha.

Cereal stubble 5 ha.

Medic pasture for livestock production -5 ha.


    * It is fairly obvious that with the low risk strategy the medic-wheat rotation will be more profitable under all circumstances.

There is 27.5 qx less wheat produced but this is more than compensated for by the livestock output from medic pasture and the lower cost of production. The cost of production is half because only half the area is sown.

    * With the high risk strategy the difference is 55 qx of additional grain produced with wheat after wheat.

The costs are lower with the medic-wheat rotation and there is the livestock production from the medic pasture but the profitability will depend on the relative price of grain and livestock.

If we assume that urea cost twice as much to purchase (a conservative estimate given high oil prices) as the farmer obtains for his wheat then:-


Output of wheat after seed - qx,

Amount of urea - qx.

Net output of wheat when urea deducted (2:1 wheat:urea)

Net output of wheat when urea deducted (3:1 wheat:urea













    Potassium is the third great fertiliser in the NPK trio used in the temperate regions. Potassium is not required for the vast majority of soils in the WANA region and in particular it is not required in the cereal zone.

Trace elements

    A few trace element deficiencies occur in the WANA region.

They are rarely so acute as those in Australia where cereals and pasture cannot be grown at all without correcting the deficiencies. In the WANA region trace element deficiencies only cause yield reduction.

As they are cheap and easy to correct this should be done.

    The application of trace element is usually done with the P fertiliser. The amounts of trace element vary from a few hundred gm. per ha to a few kg. These can be mixed with the fertiliser at the factory. Mixing on the farm is difficult.

    Alternatively some trace element can be applied to cereal seeds as a dressing with the usual application of fungicide.



By Michael Wurst, Nigel Wilhelm and Ross Brennan. Grains Research and Development Corporation (no date)

The following information is taken from the table of contents. In "Winter cereal nutrition: the ute guide," each cause is illustrated and explained in detail.





Nitrogen deficiency

Phosphorous deficiency

 Cereal cyst nematode

Potassium deficiency

Aluminium toxicity

Salt toxicity

Boron toxicity


Sulphur deficiency

Molybdenum deficiency


Iron deficiency

Barley yellow dwarf virus

Sulfonylurea herbicide damage

Manganese deficiency

Zinc deficiency

Rugby stripe


Calcium deficiency

Magnesium deficiency

Manganese deficiency

Grass and broad leafed herbicide damage

Phenoxy herbicide damage

Paraquat herbicide damage


Calcium deficiency

Copper deficiency

Boron deficiency

Molybdenum deficiency

Leaf crinkling


Salt toxicity

Phosphorus deficiency

Barley yellow dwarf virus


Copper deficiency


Drought stress

Phenoxy herbicide damage






Nitrogen deficiency

      Water logging

Potassium deficiency

Salt toxicity

Aluminium toxicity


Sulphur deficiency

Molybdenum deficiency


Manganese deficiency

Iron deficiency

Barley yellow dwarf virus

Sulfonylurea herbicide damage

Rugby stripe


Magnesium deficiency

Zinc deficiency

Barley scald

Grass control herbicide damage

Boron deficiency

Boron toxicity

Manganese toxicity


Calcium deficiency

Copper deficiency


Phosphorus deficiency

  Water logging


Copper deficiency

Barley yellow dwarf virus







Nitrogen deficiency

Cereal cyst nematode

Potassium deficiency

Salt toxicity


Sulphur deficiency

Boron toxicity


Magnesium deficiency

Iron deficiency

Barley yellow dwarf virus

Sulfonylurea herbicide damage

Manganese toxicity

Boron deficiency


Manganese deficiency

Red leather leaf

Diflufenican herbicide damage

Septoria blotch


Calcium deficiency

Copper deficiency


Nitrogen deficiency

      Water logging

Phosphorus deficiency

Barley yellow dwarf virus

Sulphur deficiency

Magnesium deficiency

Zinc deficiency


Copper deficiency


         Heat stress

        Drought stress




Sulphur deficiency in triticale