Current nutrition issues in the cropping zone of Southern Australia

Current nutrition issues in the cropping zone of Southern Australia.

Dr Nigel Wilhelm, SARDI

Introduction
After it seems like forever, most cropping districts had a wet growing season last year with crop development finally above survival mode (no need to mention the overly long growing season !). While the generally high production levels were confirmation that many farming systems are in good shape and can result in heavy crops when the season allows, last year was also a season when many of my old “friends” returned. During the continued drought in many districts, nutritional disorders became far less common because even poorly fertile soils generally had sufficient reserves to supply the meagre crops. However, with increased demand as cereal crops developed towards 2-5 t/ha grain yields, some paddocks struggled to supply sufficient nutrients for these bulky crops. Nitrogen deficiency became common, especially in paddocks which have had long histories of continuous cereal. Manganese and zinc deficiencies returned with a vengeance as well, but just to reinforce the message that each nutrient must be assessed separately, copper deficiency which has been prominent in the recent dry springs of late, was not so evident in 2010.

In this paper, I will summarise what I see as many of the current issues which relate to balanced crop nutrition and also supply some information to refresh your memories.

Phosphorus management.

Substantial increases in the cost of P fertilisers over the last few years has certainly focussed the mind of all managers and advisers on ways to cut corners with fertiliser use. Unfortunately, it has also promoted a lot of interest in “silver bullet” solutions to management of phosphorus nutrition for our crops and pastures through the use of products other than the standard fertilisers for supplying phosphorus. The high analysis mineral fertilisers such as MAP or DAP are our standard fertilisers but there is now a lot of interest in alternatives such as crushed rock, organic mixtures or rock phosphates. I say unfortunately because although the high prices of fertilisers have focussed attention on their use, it has not changed their behaviour in the field. In other words, things that worked or did not work when standard fertilisers were cheap, still work or do not work now that standard fertilisers are more expensive. What may have changed is the relative cost of these alternative products, no more - no less.

However, before discussing the merits of alternative products for supplying phosphorus to our crops and pastures, I would like to revisit some old, but still relevant, principles of P management.

Strategy for P management in 2010
One of the few silver linings with the recent string of poor growing conditions is that many paddocks came into that series of droughts with good soil P reserves and these only tended to go further up with the poor production.. Previous applications of phosphorus do have useful residual benefits with about 80% of a wheat’s P requirements coming from soil reserves. These reserves have been exploited by many farmers, to good benefit over the last couple of years.

A replacement P strategy in paddocks with reasonable reserves is a very sound management approach, partly because it matches expenditure to income (eg after a good year, P export is high but so is income so it is easier to pay for the higher P rates in the following year). In paddocks with low P reserves, the strategy still works but there should be extra P applied to lift reserves to more adequate levels as a long term goal.

However, cutting back P fertiliser rates could only be done without production penalties in those situations with good reserves. Never has it been more important to undertake soil tests to determine current soil fertility levels. If good records of previous fertiliser use exist and prior soil tests have been taken, more soil tests in 2011 can be avoided. Otherwise, minimum fertiliser rates and choices can only be sensibly estimated with soil reserves as part of the background information. Production in paddocks with high reserves of fertility will not fall off a cliff if fertiliser rates are cut back severely, even to as low as none. Back in the 1970’s and 1980’s a huge number of phosphorus response trials were conducted on wheat throughout SA. The vast majority of these trials demonstrated grain yield responses of between 0 and only 20% where soil P reserves were moderate to high.

In all situations except the highly calcareous grey soils, the current Colwell P soil test will make a reasonable estimate of these reserves. For those unusual soils, previous fertiliser use and exports in commodities are the only guide to likely soil P reserves. As a fall back position, it is probably safe to assume that you will get reasonable responses to P fertiliser on these highly calcareous grey soils, no matter what their P history.

When making decisions about P fertiliser use next year, keep your brain focussed on the right issues. Despite the publicity and pub talk about the high prices for P fertilisers, the profitability of using P fertilisers is still very strong. That is not the issue – it is the risk of not realising budgeted yield targets which is the issue. Poor yields at the end of 2011 will mean that the initial investment in fertiliser will not be covered at the end of the season, even though the rates used were “correct” when calculated in early 2011. For those farming businesses which can carry the risk, then strategies for determining P fertiliser rates are the same as they have been for the last 20 years or so.

Reducing P application rates is one important avenue for reducing these upfront costs BUT be very aware that this is only a short term option because this strategy will mine soil reserves of P. In general, these reserves will have to be replaced one day - and it is a lot harder to build them up again than to run them down !! For those farming businesses which can still afford to maintain soil reserves of P in 2011, I believe this is still a very sound strategy.

Efficient application strategies
In situations where phosphorus fertiliser is deemed to be necessary (and this is still going to be the majority of paddocks in 2011), ie will return a good profit and financing will stretch that far, this fertiliser should be placed with or near the seed at sowing. This is the most efficient way of applying P fertiliser to broadacre crops. P fertiliser should not be broadcast prior to seeding in 2011 because this approach is only justified in situations where soil P reserves are high and dressings are designed to maintain those reserves.
.
One new option for managing P nutrition which is doing the rounds at the moment is the use of foliar applied P. The attraction with this approach is that lower rates may be sufficient and timing may be delayed until mid season (when there may be more indications of how crop performance is likely to end up). However, it is my belief that this technique is not yet sufficiently understood to be recommended. It is my understanding that for every case where foliar P has been effective, there have been about ten cases when it has not. Until we can improve this ratio substantially, I think farmers should steer clear of this approach.

I have a similar position for the current role of microbial agents to enhance P nutrition. While this approach has some very attractive long term merits (ie potentially releasing some of the fixed P locked away in our paddocks now) our experience so far is that the microbes are really struggling to make their presence felt. A lot of work is continuing with this approach to improve P nutrition with less applied fertiliser but in combination with microbial products to help supplement P supply, but so far, their performances have been too unreliable to recommend this strategy for commercial use.

However, I do believe that we need to develop farming systems which cycle P more efficiently. This essentially means that these farming systems will reduce the amount of P which goes into the strongly fixed pools in the soil (only very very slowly released back into the available pools) and will also help release P from these fixed pools at the same time. While these improvements in P cycling will become increasingly important if the costs of P fertilisers continue to rise, they are unlikely to replace more than a few kg of P/ha in applied fertiliser. And remember that farming in many ways is a mining operation. Every tonne or kilogram of commodity taken to market is an export of nutrients. While new farming systems may cycle P more efficiently, those exported nutrients must still be replaced, if not tomorrow then certainly at some time in the future, if we hope to retain productive and sustainable systems.

Be very wary of new sources of P for crops and pastures being marketed as a cheaper option than our standard mineral P fertilisers. There are mountains of evidence and experience collected over the hundred years of superphosphate use in Australia that the most effective fertilisers for supplying P to crops and pastures are those which contain reasonable levels of water soluble P (DAP and MAP contain around 20% soluble P). There is very little evidence that anything which purports to enhance or promote P uptake or utilisation (to make up for low levels of actual P in the product) is a cost effective strategy for broadacre crops and pastures in southern Australia. The simple message is to work out how much soluble P you are buying in every tonne of your alternative product. If that is a higher cost per kg of P than in DAP or MAP then really question whether you are making a sound investment. I am not saying that some of these alternatives do not have a place, but review your strategy rigorously if the cost per unit of water soluble P is higher than in DAP or MAP.

A new soil test for P reserves
An additional soil test is now being offered commercially to assist interpretation of the Colwell P test. This is the phosphorus buffering index which estimates the P fixation capacity of soils or the capacity of the soil to convert applied P into forms which crops and pastures can not use. Values of PBI less than 100 are considered low (low fixation capacity) while values over 200 are considered high. Soils with a high PBI will require up to 5 kg P/ha more to raise Colwell P reserves more than one unit than soils with a very low PBI and desirable levels of Colwell P may be up to 10 units higher for these soils than for the low PBI soils. This additional test is a very useful addition to your monitoring programme but probably does not need to be done on every 0-10 cm soil test that you take – it is not likely to change much with time.

The relatively new Diffusive Gradients in Thin-Films (DGT) technology has been recently modified for the assessment of available phosphorus and micro-nutrients in Australian agricultural soils. Initial testing of the technology for prediction of wheat response to P in the glasshouse and in the field has clearly demonstrated the greater accuracy of DGT compared to other soil tests for assessing available P (Colwell P, Olsen P and resin). It is hoped that this test will be available in at least a limited commercial capacity for the next soil testing season, with several major soil testing services already conducting preliminary tests with the approach.

Liquid P
My take on the value of liquid P to cropping in southern Australia can be summarised under three headings :

The Good:
Delivering phosphorus to broad-acre crops as a continuous liquid stream in or near the seed row is a more efficient method of supplying this important nutrient to crops in many soil types of South Australia. These soil types are those which reduce P availability in the soil rapidly (mostly calcareous or ironstone soils). In our more “benign” soils, liquid delivery is just as good as granular.

More efficient means that the P requirements for a crop can be met with a lower rate of P per hectare as a liquid product compared to a granular one. For example, on highly calcareous soils of the upper Eyre Peninsula, P requirements for a wheat crop can be met with 3 kg P/ha as a liquid whereas 10 kg P/ha as a granular product will struggle to achieve the same result.

Liquid delivery of nutrients is also a more flexible method of application because different brews of nutrients (eg P, N or trace elements) can be easily made on farm. This means that nutrient rates can be easily adjusted for particular soil types, paddocks or crops.

Trace elements are also more efficiently delivered as liquid streams into or near the seed row compared to granulated products.

The Bad:
The complication with liquid forms of nutrients is that they require a separate delivery system to granular products. In order to use liquid nutrients, a farmer will need to invest in a storage system for the bulk liquid products, a transport system to get the mixed product from the bulk storage to the paddock and a delivery system on the seeder which will supply metered rates of the liquid product equally to all seed rows. The good news is that the cost for all of these three components does not have to be large.

The Ugly:
The major issue with liquid P fertilisers is that the products currently available for commercial use are substantially more expensive than granular P products. This means that for most cropping districts in South Australia, the extra cost of the liquid products is greater than the benefits realised from more efficient crop production. The highly calcareous soils are an exception to this rule in that the benefits often outweigh the extra costs of the liquid products. However, these soils only occur in parts of the cropping zone of South Australia (mostly on Upper Eyre Peninsula and in small areas on the Yorke Peninsula).

Five Tips to help you assess the value of liquid P on your client’s property:
1. You need to know the soil types on your farm and whether they are likely to be ones where liquid P will be more efficient.
2. Liquid P options for broad-acre farming are more difficult to source and supply than granular products so you need to be organised early to ensure timely deliveries.
3. Check the www.fluidfertilisers.com.au web site for a lot of valuable information on compatible liquid mixes and other practical issues for broad-acre farming.
4. Banding liquid fertilisers at seeding is safer if the stream is placed near the seed row rather than directly with the seed. Below the seed row is the most desirable.
5. Ensuring a continuous stream of liquid P which is robust to the challenges of broad-acre delivery is the key to success with liquid fertiliser approaches.

Trace Element Deficiencies in Crops and Pastures

Many soils in the cropping zones are deficient in trace elements in their native condition and crops can still be deficient in one or more trace elements despite many decades of research into their management. Just because these deficiencies have not been around much in recent years, do not assume they will not return (as we saw for Mn deficiency in 2010).

Is there a need for trace elements ?
Essential trace elements are nutrients which are required by plants and animals to survive, grow and reproduce but are needed in only minute amounts. There are three trace elements which are most common in southern farming systems because there can be too little of them in your cropping soils; - these are copper (Cu), zinc (Zn) and manganese (Mn). Of these three, Zn deficiency is probably the most important because it occurs over the widest area, although it has not been seen to cause the total crop failures that Cu deficiency is capable of. However, Zn deficiency can still severely limit annual pasture legume production and reduce cereal grain yields by up to 30%. If these trace elements are not managed well, the productivity of your crops and pastures can suffer valuable losses and you can also lose further productivity through secondary effects such as increased disease damage and susceptibility to frost.
Note: Mature lucerne stands tend to experience trace element deficiencies infrequently because their deep and extensive root systems are very good at scavenging resources from the soil profile. Establishing stands however, can be just as susceptible as annual crops and pastures.

Adequate trace element nutrition is just as important for vigorous and profitable crops and pastures as adequate major element (such nitrogen or phosphorus) nutrition.

Both Zn and Cu will remain available to crops and pastures for long periods (up to 10 years for Zn and up to 40 years for Cu) following a recommended rate of application to soil.

For those paddocks which have not previously received soil applications of Zn or Cu and are suspected to be trace element deficient in any element, then the best strategy for 2011 would be to plan for a foliar spray mid-season. For Cu, this in-crop spray could be delayed until the crop is running up but for all others early is best. The advantage of a foliar spray approach is that it avoids up-front costs for the cropping programme and allows a more prolonged assessment of how the season is unfolding, including the opportunity to do a plant test prior to application to check whether the crop is actually deficient.
The next best option for managing trace element deficiencies in 2011 would be to consider a trace element seed dressing. This approach is cheaper than a soil application but, like foliar sprays, has the disadvantage of having no residual benefits for subsequent years.

The next best option for managing these two trace element deficiencies in the longer term is to band them as a fluid in or near the seed row at seeding. This technique is proving very effective at delivering these trace elements to the crop and allows you to use the cheaper sources of trace elements (eg the sulphates). However, it does require that you have the capability of delivering fluids with your seeding unit – something to consider for the future !

Now some notes about each of the three trace element deficiencies.

Zinc deficiency
Zn deficiency was first identified in Australia in the 1930’s but it assumed increased importance in the 1980s and early 90s because of a resurgence in extent and severity. This resurgence appears to have been linked to the widespread use of high analysis fertilisers in our broad-acre cereal crops and also, perhaps, to the introduction of some herbicides. Single super contains higher levels of Zn than high analysis fertilisers, possibly enough to mask severe Zn deficiency (but not sufficient to correct it fully) and has allowed the low Zn status of many of our agricultural soils to go unnoticed. With the widespread use of high analysis fertilisers Zn deficiency has re-appeared as an obvious and major problem. Some herbicides (especially the sulfonylureas and some of the group As) can make a Zn deficiency more severe and these herbicides have also been responsible for more frequent appearance of Zn deficiencies.

Zn deficiency has been identified on many soil types; acid sandy soils, sandy duplex soils, red-brown earths, “mallee” soils, and calcareous grey and red heavy soils have all had either Zn responses confirmed or crops have been identified with Zn deficiency symptoms. Zn deficiency appears to be equally severe in both high and low rainfall areas.

Symptoms
It is very difficult to diagnose Zn deficiency in pasture or grain legumes because characteristic leaf markings are rarely produced in the field. Zn deficiency causes shortening of stems and leaves fail to expand fully. This results in plants which appear healthy but are stunted and have small leaves.

In cereals, symptoms are usually seen on seedlings early in the growing season. An early symptom of Zn deficiency is a longitudinal pale green stripe on one or both sides of the mid-vein of young leaves. The leaf tissue in this stripe soon dies and the necrotic area turns a pale brown colour. Severely affected plants have a “diesel-soaked” appearance due to the necrotic areas on leaves, which generally start mid-way down the leaf, causing the leaf to bend or break in the middle.

Plant symptoms appear to be worst early in the season when conditions are cold, wet and light intensity is low. In spring, symptoms often do not appear on new leaves but grain yields will usually be reduced.

Diagnosis
Plant tests for diagnosing Zn deficiency are reliable and have been calibrated in the field under Australian conditions for wheat, barley, medic, beans and peas. In tillering plants of wheat and barley, YEB (youngest fully emerged blades) levels above 20-24 mg kg-1 are considered adequate. The minimum value in YOL’s (youngest fully open leaves) of medic is 15 mg kg-1 and in beans and peas the figure is approximately 23 mg kg-1 (although our information on peas is very limited). For lucerne, levels above about 20 mg kg-1 in young shoots appear to be adequate.

Correction
Correction of Zn deficiency in a way which provides benefits after the year of treatment is possible through the use of Zn-enriched fertilisers or a pre-sowing spray of Zn onto the soil (incorporated with subsequent cultivations). There is also the option of a Zn-coated urea product which can be used to supply Zn to the crop, and is most useful when you are pre-drilling urea before the crop.

Another option which will also provide long term benefits but has become available only recently is the application of fluid zinc at seeding. As part of the research programme investigating the benefits of applying phosphorus to crops as a fluid at seeding, trace elements were applied in the same way. This technique appears to be very efficient at supplying trace elements to crops and offers the prospect of reducing rates of zinc/ha but still fully correcting a problem. The advantage of this approach is that it will provide residual benefits for subsequent crops and pastures but at a low up-front application cost (providing you ignore the capital investment in a fluid delivery system !). At current prices, a typical application may cost about $3.00/ha.

Only Zn-enriched fertilisers of the homogenous type (the fertiliser is manufactured such that all granules contain some Zn) are effective at correcting Zn deficiency in the first year of application. A rate of 2 kg of elemental Zn per hectare applied to the soil is necessary to overcome a severe Zn deficiency and should persist for 3-10 years (depending on soil type). Short intervals between repeat applications of Zn will be necessary on heavy and calcareous soils in the higher rainfall areas, while 7-10 year intervals will be acceptable in the low rainfall areas. Following an initial soil application of Zn of 2 kg ha-1 repeat applications of 1 kg ha-1 will probably be sufficient to avoid the re-appearance of Zn deficiency in crops and pastures. Most zinc-enriched fertilisers are currently not sold as pure homogeneous types but, providing a homogeneous fertiliser is used as part of the mix then the final product is still satisfactory for correcting zinc deficiency. For example, the company may produce a DAP Zn 5% “parent” product which has zinc on every granule which they will then blend with straight DAP to give 1 and 2.5% products for the retail market. This option will currently cost approximately $17.00/ha.

Zn deficiency can be corrected in the year that it is recognised with a foliar spray of 250-350 g Zn ha-1 but it has no residual benefits and is thus not the best approach for a long-term solution. This option will currently cost approximately $1.00/ha (plus the cost of the operation). Zinc can be mixed with many herbicides and pesticides but not all so check with your supplier for compatible tank mixes before you make the brew.

Seed dressings of zinc are yet another option for managing Zn deficiency. These products are effective and will supply Zn to the young crop but they will not completely overcome a severe deficiency, nor increase soil reserves of Zn. Seed with high internal levels of Zn can also be used in a similar way. However, both approaches should be used in conjunction with soil applications to correct and manage Zn deficiency in the long term. This option will currently cost approximately $3.00/ha.

Copper deficiency
Symptoms
Apart from shrunken heads in cereals, heads with gaps in them or “frosted” heads, Cu deficiency rarely produces symptoms in plants in the field. The symptoms produced by Cu deficiency in the maturing cereal plant are due to poor seed set from sterile pollen and delayed maturity However, under conditions of severe Cu deficiency cereal plants may have leaves which die back from the tip and twist into curls. Cereal stubble from Cu-deficient plants has a dull grey hue and is prone to lodging due to weak stems.

Cu-deficient pasture legumes are pale, have an erect growth habit and the leaves tend to remain cupped (as if the plant were suffering from moisture stress).

Diagnosis
Leaf analysis to detect Cu deficiency in plants is a very important management tool because Cu deficiency can produce devastating losses in grain yield of crops and pastures with little evidence of characteristic symptoms.

Cu concentrations in YEB’s of cereals above 3 mg kg-1 are considered adequate and below 1.5 mg kg-1 deficient. Pasture legumes including lucerne have higher requirements for Cu and plants are considered deficient if YOL values are below 4.5 mg kg-1. Lupins are tolerant of Cu deficiency and levels above 1.2 mg kg-1 are adequate.

Correction
Traditionally, Cu deficiency has been corrected by applying Cu-enriched fertilisers and incorporating them into the soil. Most soils require 2 kg Cu ha-1 to fully correct a deficiency, which may be effective for many years. Due to the excellent residual benefits of soil-applied Cu, Cu deficiency in crops and pastures has been largely overcome in most areas from “blue stone” mixes used in the 1950s and 1960s. However, it may be re-surfacing as a problem again for several reasons. Firstly, the applications of Cu made 20-40 years ago may be running out. Secondly, the use of nitrogen fertilisers is increasing and they will increase the severity of Cu deficiency and thirdly, Cu deficiency is affected by seasonal conditions and farming practices, eg. lupins in a lupin/wheat rotation make Cu deficiency worse in succeeding wheat crops. This option will currently cost approximately $19.00/ha.

Cu deficiency in crops can also be corrected by fluid application at seeding for an application cost as low as $4.60/ha.

Cu deficiency in livestock (steely wool in sheep; sway-back in lambs; rough, pale coats and ill-thrift in young cattle) is a continuing problem in some areas because livestock have higher requirements for Cu than pasture plants and low availability of Cu in the diet can be induced by high Mo intake, which can be further exacerbated by high sulphur levels. The introduction of Cu bullets which provide 12 months protection has made treatment of the problem simple and cost-effective.

Although Cu deficiency is best corrected with soil applications, the performance of which will improve with increased soil disturbance, foliar sprays will also overcome the problem in the short term. A foliar spray of Cu (75-100 g Cu ha-1) is very cheap (approximately 90c/ha for the ingredient) but a second spray immediately prior to pollen formation may be necessary in severe situations.

Manganese deficiency
The availability of Mn in soil is strongly related to soil pH; the higher the pH, the lower the availability. Hence, Mn deficiency is most frequently a problem on alkaline soils although responses to Mn have also been recorded on impoverished, acid to neutral sandy soils. The availability of Mn is also strongly affected by seasonal conditions and is lowest during dry spring weather. Transient Mn deficiency may also appear during cold, wet conditions but affected plants are often seen to recover following rains in spring when soil temperatures are high.

Symptoms
Mn is poorly translocated within the plant so symptoms first appear in young leaves. Old leaves on plants severely affected by Mn deficiency can still be dark green and healthy because they acquired Mn from the seed and once Mn enters a leaf it cannot be shifted out.

Mn deficiency results in plants which are weak and floppy and pale green/yellow in appearance. Mn-deficient crops can appear to be water-stressed due to their sagging appearance. Close examination of affected plants can reveal slight interveinal chlorosis; the distinction between green veins and “yellow” interveinal areas is poor.

In oats, Mn deficiency produces a condition known as “grey speck”. Mn-deficient oats are pale green and young leaves have spots or lesions of grey/brown necrotic tissue with orange margins (this contrasts with Septoria lesions which have purple/red margins). These lesions will coalesce under severely Mn-deficient conditions.

Mn deficiency delays plant maturity, which is a condition most marked in lupins. Mn-deficient patches in lupins will continue to remain green months after the rest of the paddock is ready for harvest. Delayed maturity in patches of the crop is frequently the only visual symptom of Mn deficiency in lupins. Mn deficiency will also cause seed deformities in grain legumes. Lupins suffer from “split-seed” which is caused by the embryo breaking through a very weak seed coat. “Split-seed” will reduce yields and also viability of the harvested grain. A similar condition in peas is known as “marsh spot” due to a diffuse dark grey area within the seed.

Diagnosis
Plant analysis will accurately diagnose Mn deficiency in crops and pastures at the time of sampling but Mn availability in the soil can change dramatically with a change in weather conditions. This means that the Mn status of the sampled crop or pasture can also change dramatically after sampling - this must be allowed for when making recommendations on Mn deficiency.

Concentrations of Mn in YEB’s greater than 15 mg kg-1 are considered adequate for cereals at tillering. For legumes, the corresponding figure in YOL’s is 20 mg kg-1. The WA Dept. of Agriculture also advocates a main stem analysis of lupins for diagnosing Mn deficiency at flowering.

Correction
Due to the detrimental effect of high soil pH on Mn availability, correction of severe Mn deficiency on highly calcareous soils can require the use of Mn-enriched fertilisers banded with the seed (3-5 kg Mn ha-1) as well as 1-2 follow up foliar sprays (1.1 kg Mn ha-1). In the current economic climate, farmers on Mn-deficient country have tended not to use Mn-enriched fertilisers (due to their cost) but have relied solely on a foliar spray. This is probably not the best or most reliable strategy for long term management of the problem.

Neither soil nor foliar Mn applications have any residual benefits and must be re-applied every year. Another approach is the coating of seed with Mn. This technique is cheap and will probably be the most effective in conjunction with foliar sprays and/or Mn enriched fertilisers. Mn deficiency in lupins must be treated with a foliar spray at mid-flowering on the primary laterals. The use of acid fertilisers (eg. nitrogen in the ammonium form) may also partially correct Mn deficiency on highly alkaline soils but will not overcome a severe deficiency.

Mn deficiency in crops can also be corrected by fluid application at seeding.

Final note.
There are other trace element deficiencies which can occur in crops and pastures (eg boron, molybdenum, manganese) but they are likely to be so localised in southern NSW (or may not occur at all) that I did not want to confuse the situation any further. If you require any information on these, please contact me.

Due to the increased complexity of management in our current cropping systems and increased costs of fertilisers, there is a greater need for crop monitoring to help make informed nutritional decisions. There is a large array of crop monitoring tools available now to help manage this complexity, all of which have their own strengths and weaknesses. These tools include -

Accurate paddock records 0-10 cm soil fertility test
0-60 cm mineral nitrogen soil test sap nitrate plant test
NIR plant nitrogen test Plant test for nutritional status
Grain test for nutritional composition Fertiliser test strips
Fertiliser/nutrition extension material Crop inspection for deficiency/toxicity symptoms

Nitrogen management.

I have no intention of summarising everything we know about N physiology and managing N nutrition because it would fill volumes. Rather I would like to make a few points regarding some of the rural myths which seem to be building around commercial management of N in crops of southern Australia.

• N can only be used by the crop early in its development.
Only partly true. Annual cereals can take up and use N at any stage up until early grain fill, contributing to both yield and protein in grain. The later extra N is applied, the more it is partitioned into protein but yields can still be boosted by N at or around flowering. Timing of N applications is more about environmental conditions and logistics than crop physiology.

• N is difficult to diagnose in commercial crops.
Completely false. The plethora of new gizmos to detect N deficiency (actually yellowness) could easily create the impression that we have struggled to detect N deficiency in crops until recently. However, we have been able to reliably diagnose N deficiency for decades. These new toys may be faster, cheaper and portable with real time outputs but they have not discovered anything new.

• UAN is the only N product to use a foliar spray.
While UAN does have some advantages over urea as a foliar spray, in the vast majority of situations the two perform much the same. When there is a difference, it is UAN which will be ahead but as it is the more expensive product, this is the least you should expect.

• N management is tricky because we do not know how much N a crop needs at the time.
Completely false. We have reliable tools for estimating soil reserves of available N, good models for simulating how much N will be released from the soil and a very good handle on how much N supply the crop needs at the time of application. HOWEVER, N demands are extremely sensitive to final crop performance – this is the missing piece of the jigsaw puzzle. So N management is tricky due not to lack of understanding of physiology in the crop or efficacy of N applications but due to our inability to predict the end of the season. Until seasonal forecasting becomes more accurate, there will always be uncertainty around N applications. No new N deficiency detection tool will alter this.

• The correct rate of N application is critical to success.
Refer to previous point. The only way you can get the N rate exactly right for every situation is to have a reliable seasonal forecast which eventuates every time. Otherwise you just have to be lucky. Do not waste sleep by trying to capture a shadow – make an informed decision at the time with all available information and remember that it is most unlikely that any N application decision has sent a farm business into bankruptcy !

• Excess applied N is a total waste.
Not true. The worst case scenario for N applications is onto shallow sandy soils in winter which are followed by heavy rainfall events. In this scenario, the very soluble N fertilisers will move with the wetting front and possibly out of the root zone and effectively lost to the paddock. In all other scenarios, at least some of the applied N which is not captured by the target crop will enter the soil cycle and be released to subsequent crops.

Better Fertiliser Decisions.

This GRDC funded project is working with the fertiliser industry to collate and provide critical levels for all cropping zones for a raft of important soil tests. Soil test calibration trials are common in Australia, but there is currently no central repository for the results of these trials. Making Better Fertiliser Decisions for Cropping Systems in Australia (BFDC) is aimed at building confidence in soil test–crop response calibrations nationally. This task involves the collation and assessment of 3500–4000 regional soil test calibration trials for Australian cereal, pulse and oil seed crops. BFDC will develop nationally and regionally agreed soil test–crop nutrient calibrations for nitrogen (N), phosphorus (P),potassium (K), and sulphur (S); A national web-based database of crop nutrient response trials and an interrogator interface for future users of the database; and Training resources and technical publications for communicating soil test–crop nutrient calibrations and scientific findings across the grains and fertiliser industries. BFDC will make accessible all available fertiliser trial data across all Australian cropping regions. This will include data gathered by the fertiliser industry; government agencies; universities; and private consultants. The fertiliser and grains industries will benefit from BFDC with the products of the project being available online for access by: agribusiness and consultants; the fertiliser industry; public advisors; and researchers.

Contacts for further information:
DR SIMON SPEIRS
Leader – Making Better Fertiliser Decisions for Cropping
Systems in Australia
Industry & Investment NSW
02 6938 1986 0428 647 787
simon.speirs@industry.nsw.gov.au
www.industry.nsw.gov.au/info/bfdc

DR KEN PEVERILL
K I P Consultancy Services
03 9574 8110 0408 748 110
ken.peverill@bigpond.com

DR DOUG REUTER
Reuter & Associates
08 8269 1494 0438 879 269
dreuter@bigpond.com


Sulphur and potassium deficiencies.

I have put S and K deficiencies together because they share some common attributes. In my experience both are not common in the cropping zones of southern Australia but are more frequent on the infertile sands of Western Australia where intensive cropping has a longer history.

Both will inevitably get more common if we continue to export appreciable amounts of both nutrients to the silo. Both are more likely on sandier soils which have inherently low reserves of both nutrients and little capacity to hold them in the profile.

Soil tests, especially for S are not proving particularly reliable for predicting deficiencies, esp for K on the heavier soils of south-eastern Australia. Hopefully the BFDC project (section above) will help improve matters there.

Canola is a good indicator crop for S deficiency. Comparing strips of urea versus ammonium sulphate is a good test for S deficiency.

Hay is a major exporter of K so look for deficiencies where cereal hay has been a frequent phase in the paddock.

Leaf testing for S and K in major crops is a reliable approach for detecting deficiencies of either nutrient and the N/S ratio in grain is particularly suitable for S deficiency.


Dr Nigel Wilhelm, Senior Research Scientist, SARDI, Waite Research Precinct
Ph: 0407 185 501
Email: nigel.wilhelm@sa.gov.au