MODIFYING FERTILISER APPLICATION RATES | When Low Rainfall and Tough Economic Conditions Prevail
This article examines the position often faced by farmers and growers when they manage difficult periods of productivity because of adverse climatic and economic conditions. Th

We revisit parts of an INSIGHT written by Richard Stone, RLF’s Field Operations Manager in NSW Australia, and published in 2015. It contains pertinent and important information about the role of phosphorus in setting the crop for optimal yield, and discusses scenarios around managing the phosphorus fertiliser budget in stressful times. It should be noted that monetary prices quoted at the time would no longer be current, but the formula for determining these costs remains the same. It is always good to look back at some of our previous articles and reports and to remind our customers of some of the published science around products and practices.


This article examines the position often faced by farmers and growers when they manage difficult periods of productivity because of adverse climatic and economic conditions. There are always difficult years imposed by low rainfall, extreme heat and other seasonal conditions that place stress on farm budgets. Can input costs such as expenditure on fertiliser be reduced by modifying application rates to help out at these times?

This article seeks to answer this question.

Following a run of abnormally dry seasons and/or economic downturns, many dryland broadacre farmers find it increasingly difficult to grow an economically viable crop.

The vagaries of climate have always been an integral part of broadacre cropping – but with rising costs, accompanied by little (if any) rise in commodity prices – the margin for growing a successful crop shrinks, and new methods of farming and fertilising need to be considered in order that financial viability is maintained.

In response to this dilemma, farmers and growers often ask if it is possible to reduce fertiliser rates, (or even do without fertiliser altogether in some situations), and still be able to grow a successful crop? The answer to this is not a simple yes or no, however what may be called for, and can prove useful, is a different approach to traditional methods. Most farmers, with a lifetime of growing experience of always planting with phosphorus, react cautiously to fertiliser routine modification, and continue to apply phosphorus with the seed.

However in tough economic times, or with below average seasonal conditions, there may be a case for fertiliser reduction – and in some cases even exclusion of applied phosphorus from cropping systems.

By providing both scientific and anecdotal evidence from practical broadacre situations, this article seeks to promote the discussion for modifying phosphorus application to varying degrees in cases of financial and climatic deficiencies.

Generally, Australian soil in its native state is low in phosphorus. But with the advent of super-phosphate, and today’s compound fertilisers such as MAP and DAP (and the relative ease of their application), in many cases phosphorus levels have risen – and especially so following a run of low yielding years caused by below average rainfall with its consequence of less loss, or leaching of
the fertiliser.

Stored phosphorus in the soil is good news for farmers, providing it can be extracted from the soil and utilised by the plant.

It should be remembered however, that there is always a range of individual factors involved in planting a crop, so considered review of all evidence, questioning and perhaps even trialling, is encouraged before embarking upon wholesale changes.

Questions to Ask before Modifying Phosphorus Application

In appraising individual circumstances, it would be beneficial to know the answer to the following questions:

1. What is the level of phosphorus in my soil?
2. What is the availability of phosphorus in my soil (PBI)?
3. What physical restraints are there to phosphorus uptake in my soil?
4. What chemical restrictions are there to phosphorus uptake in my soil?
5. How much fertiliser can I afford?
6. What is my target yield, in relation to the financial return I require in order for the bills to be paid?

All are very sensible, basic and common-sense questions, and together they are the important building blocks to embracing the changes needed to bring about potentially better financial outcomes.

Individually, the questions are expanded upon as follows:

1. What is the Level of Phosphorus in my Soil?

Phosphorus levels vary with different soil types, farming practices and varying phosphorus application rates.

The soils around Nyngan for instance (in mid NSW), are in the most part red clay loams that are quite stable in physical character and suited to large-scale broadacre farming. We know that the limiting factors for growing high yielding crops are moisture and temperature, and with this in mind some caution has to be exercised when spending funds on fertiliser.

Generally the red soils are low in nitrogen, high in potassium and low in trace elements, so there is a case for restricting soil testing to simply undertaking an audit of phosphorus, and looking after the trace minerals with seed priming and foliar applications which include nitrogen as well.

In 2008, eighty-five (85) soil test sites were mapped and the results reviewed from the Nyngan District. The graph that follows gives insight to the levels and potential yields at that time.

As can be seen from the graph, there is ample opportunity to modify phosphorus strategies when phosphorus levels are above the median 20mg/kg.

Values below 20 mg/kg do not have the same potential for yield, but in times of soil moisture deficit and financial pressure, are capable of producing a target yield for the moisture and funds available without additional phosphorus.

Fertiliser management is rather like the share market, it is a risky business but becomes less risky the more information that can be brought to bear before a decision is made.

Soil sampling and analysis of results is generally undertaken by accredited soil testing laboratories. Soil samples are taken from each paddock and mixed together to form one sample, which is then sent to the laboratory. Samples are best taken after harvest, so that results can be analysed and decisions made on how much fertiliser needs to be applied to the soil in readiness for the next crop. However, soil tests don’t have to be done every year, as an allowance for nutrient removal of the crop can serve just as well to establish phosphorus and nitrogen amounts taken from the harvested crop, (i.e. 1-tonne of wheat removes 3kg of phosphorus and 20kg of nitrogen per tonne of grain).

2. What is the Availability of Phosphorus in my Soil (PBI)?

The availability of phosphorus is a complex issue.

Most soils have reserves of phosphorus, but vary in their ability to supply phosphorus to the plant for some of the following reasons:

  • lack of root growth restricting interception of phosphorus
  • compaction of soils restricting root growth
  • climatic soil conditions, either too wet or too dry
  • chemical imbalances in the soil
    (e.g. high iron, high calcium, high sulphur, high aluminium)
  • low pH acid soils
“It is not so much about how much phosphorus is in the soil, it is more about how much of it is available to the plant.”

A complete soil test in the hands of a trained experienced soil consultant will greatly assist in understanding how much phosphorus is available to the growing plant. This quotation sums up the essence of this question: “It is not so much about how much phosphorus is in the soil, it is more about how much of it is available to the plant.”

3. What Physical Restraints are there to Phosphorus uptake in my Soil?

Compaction of the soil caused by machinery, water-logging and livestock are some of the major physical restraints to the uptake
of phosphorus.

4. What Chemical Restrictions are there to Phosphorus uptake in my Soil?

Chemical restrictions are very much tied to the question of the soil availability of phosphorus, but excesses of iron, aluminium and
calcium are indicative, along with low pH acid soils.

5. How Much can I Afford to Spend on Fertiliser?

Data gathered from many sources including the NSW Department of Agriculture suggests that on average Australian broadacre farmers are spending between 12% -15% of their gross revenue from crop proceeds on fertiliser.

NOTE: these prices were current in 2015 so adjustment will need to be made for today’s prices.

(A generalised explanation of this averaged fertiliser spend would be : fertiliser cost of $75 per hectare, gross return of $500 per hectare, representative application rate of 50kg MAP and 30kg Urea = $75 per hectare, and target yield 2 tonne wheat per hectare at $250 per tonne = $500 per hectare x 15% = $75 per hectare spent on fertiliser).

Simple calculation:

Area Sown Seed Yield Gross Income
Hectare Seed kg/ha Seed per tonne t/ha Total tonnes $/t $ Total
2,000 35 70 1.5 3,000 220 660,000

Using 15% of this example equates to a total fertiliser spend of $99,000.

By using gross income from crop as a yardstick to establish your fertiliser spend, the variance in seasons is automatically catered for as the funds for fertiliser spend are regulated by available income. In addition to this, when yield/gross income is down, the need for as much fertiliser is less, as nutrient removal is less.

6. What is my Target Yield in Relation to the Financial Return I Require in order to Pay the Bills?

Realistically, each farming enterprise will need to use their own figures and pricing structures in estimating gross margins. There are many considerations in determining the projected financial return on crops. Some of these factors – with most of them involving actual costs – are the sowing time, weed control, fertiliser choices, machinery used, labour incurred and other farm overheads. In terms of crops benefiting from the availability of phosphorus and other nutrients from past cropping activity, where it sits within the crop rotation cycle is a significant factor. Obviously, rotation following pulses will attract higher target yield and financial returns over a rotation following a cereal crop.

(Reference : The NSW Department of Primary Industries keeps statistical data on dryland wheat growing outcomes that can give more insight and analysis of the costs and returns of wheat grown in the districts similar to the ones discussed in this article).

What Scientific Trials and Research Projects Show

Excerpts from three different studies and trial data outcomes – all relating to the question of phosphorus and the potential for modifying its application – are given in support of the proposition.

1. The Mixotrophic Nature of Photosynthetic Plants
From CSIRO Publishing, Functional Plant Biology, 2013, 40, 425-438

Length and surface area of root hairs were significantly correlated with the depletion of phoshorus-compounds in the rhizosphere in low phosphorus growth condition. (Bates and Lynch 1996; Gahoonia and Nielsen 1996; Gahoonia et al. 1997; Ma et al. 2001).

Long root hairs are considered a beneficial trait for sustaining crop yields in low phosphorus soil. (Gahoonia and Nielsen 2004).

RLF Comment
Increasing root growth and root hair development dramatically increases phosphorus uptake and is a direct result of sowing good quality seed with high phosphorus reserve. BSN Superstrike (BSNSS) enhances nutrient reserves within the seed.

2. The Increase in Nutrient Levels generated through Seed Priming
From Adelaide University, Y-G. Zhu and S.E. Smith, Plant and Soil 231 : 105-112

Increased seed phosphorus serves improved plant growth at rates of phosphorus supply up to and over 100mg/kg in the soil. Plants grown from seeds with high phosphorus reserves tended to accumulate more phosphorus from the soil which was mainly attributable to better root system development.

3. The Increase in Nutrient Levels generated through Seed Priming
From Waite Analytical Services Adelaide University 2010, Coordinator Michael Taylor Vanguard AG, Griffith NSW
Actual nutrient level increases from applying at 5-litres per tonne of seed prior to sowing.
4. The Nyngan Fertiliser Trial (2008)

In 2008 a group of Nyngan farmers requested a trial to look at varying fertiliser rates to establish whether rates of phosphorus could be cut back, or omitted entirely. BSN Superstrike was applied at 5-litres per tonne to three plots. The other plot received just DAP. As can be seen from the images that follow, root growth and microbial activity was improved dramatically when Seed Priming (BSNSS)
was applied.

The BSN only sample on the leftt of the image visually shows greater activity in the rhizosphere, and increased greener top growth. Current research supports that increased sugar transport from greener, larger top growth will transport to the root, which in turn support
active rhizosphere.

Recent scientific evidence (excerpt: Functional Plant Biology, 2013, 40, 425 – 438) implies that:
“Microbes occur in much higher density in the rhizosphere than bulk soil and are attracted by root – derived compounds and debris, and it is conceivable that plants acquire and digest microbes as sources of nutrients. As microbes compete with plants for soil nutrients, uptake and digestion of microbes could be an adaptation for securing nutrients”.

What we know about Phosphorous

The importance of the role of phosphorus cannot be over emphasised – it’s role is crucial.

Equally, the importance of the role of Seed Priming cannot be overstated – as it also brings many advantages.

All added phosphorus delivered by BSN Superstrike (BSNSS) is as inorganic (i.e. available phosphorus) and it is known that the seed and plant can only use and metabolise inorganic phosphorous.

Research tells us that the typical availability of phosphorus in each seed is only about 10% of the total phosphorus, which means that the phosphorus available for seed germination and early growth is often too low. But with the action of priming the seed with BSNSS, the seed is provided with inorganic available phosphorus that both the seed embryo and the developing plant can access immediately. The amount of available phosphorus that BSNSS renders can provide up to a 350% increase to the embryo.

This early development then goes on to support greater phosphorus conversion, further providing available phosphorus to the plant for its continued growth.

If phosphorus is too low then the opportunity to set high yield potential is lost. Seed Priming with BSNSS overrides these uncertainties, and gives certainty to the level of phosphorous required to set the maximum yield potential for the plant.

Utilising the locked phosphorus in soil through Seed Priming has a much more practical implication than for other trace elements.

Whilst the element deficiencies such as those often seen with zinc and manganese, can be simply and effectively overcome with foliar spraying, the same is not true for phosphorous deficiency. If phosphate availability is not good, the crop yield potential would not be recovered by an in-season application of phosphorus. Again, research tells us that future agricultural practice should be structured along the lines of unlocking soil phosphorus and bringing about changes to the root structure and other physiological functions that unlock more of the soil nutrients.

This is the important role that phosphorous plays.

Phosphorus is however a finite resource, and it is estimated that current levels are expected to be halved within the next 20 to 40 years. Clearly, clever use and new technology options in support of phosphorus need serious consideration.

Seed Priming with BSNSS not only provides the seed with all the inorganic phosphorus it needs to establish strong plant development and growth, it also gives back to the soil through enhanced microbial activity and greater organic mass created by this same
strong growth.

How RLF Products Help

BSN Superstrike

Providing optimum levels of seed nutrient in a single application.
It is fast becoming the new world standard in modern farming practice where fertilising the seed is becoming as important as fertilising the plant.

By priming the seed, the level of essential elements is elevated to above optimum level. This ensures the maintenance of nutrient adequacy in the seed, because all nutrients are safely transported inside the seed to be within close proximity to the embryo. The broad spectrum nature of BSNSS means maximum yield potential is set, and that it does not miss out on establishing this response due to suboptimal grain nutrient levels.

Seed Priming has a direct effect on yield, since 100% of the nutrients contained within it are absorbed by the seed. It is very common in untreated seeds for nutrient levels to be at suboptimal levels, and BSNSS has been scientifically tested and demonstrated to improve the seed’s internal nutrient concentrations. In part, this is because BSNSS ensures ‘plant-available’ phosphorus which directly influences yield potential – regardless of fertiliser rates applied to the soil – hence a direct effect on yield achieved
through seed priming.


Growing crops can be a risky business when taking into account variable rainfall, high temperatures, rising input costs and fluctuating commodity prices. Some of these variables are well outside of the control of the farmer, but in this article we have sought to focus on fertiliser inputs and practices, and whether or not they can be modified to suit climatic and individual economic situations – just one of the variables that can be managed to a certain extent.

The short answer, based on research and anecdotal evidence, is YES.

However, much needs to be known and understood about each individual situation, and answers and adherence to the following
‘quick tips’ need first to be established and then implemented:

  • an estimate of the moisture available to establish the required target yield
  • a soil test to establish phosphorus levels and any physical and/or chemical restrictions in the soil
  • attention paid to the quality of the seed, as bigger seed has more reserves of nutrients
  • undertake seed priming with BSN Superstrike to increase nutrient reserves within the seed to ensure early supply of phosphorus and zinc, essential for increased root growth and phosphorus uptake

In western NSW, where many of the trials have taken place, the major limiting factors to successful crop growing are moisture
and heat.

Generally there is a history of applying granular phosphorus fertilisers around 40–50kg/ha MAP or DAP, (8–10kg phosphorus/ha). Taking into account the conditions and low crop yields over the past decade, in most cases there is enough phosphorus in the soil to grow 1.5 – 2.0 tonnes of wheat per hectare, and possibly more if the season is above average. With this in mind there is an option to reduce – or even exclude – granular fertilisers in adverse seasons, or when funds are low. However it must always be remembered that crops take nutrients out of the soil, and that they need replacing to sustain production.

As an economic option to soil applied granular fertiliser in tough times, it has been proven that Seed Priming with BSNSS enhances seed nutrient reserves and will create root hair development, and greater root system exploration to extract more nutrients from the soil. The result of this enhanced ability is healthier, greener seedlings, with more vigorous root systems that photosynthesise more efficiently and have the potential to yield more grain.

RLF acknowledges that crop nutrition and protection is a dynamic business and that new ideas are often met with scepticism, however sufficient scientific and anecdotal evidence now exists to provide real insight into modifying fertiliser strategies with some confidence that in turn may deliver even better returns.