A mid-Canterbury farmer describes himself as a cropping farmer – the crop being grass.

Mike Salvesen, a former arable farmer, is concentrating on growing different varieties of grass and tailoring its management to suit the hill-country farm. Like a crop, it is a matter of harvesting it at the right quality, using mouths.

Mike, who comes from Britain, bought Wakare, a 1460ha Mt Somers farm, two years ago. He has spent a lot of time and money subdividing paddocks, installing troughs and renewing pastures and has still not finished.

He has also implemented a stock rotation policy with the aim of keeping fresh feed ahead of stock. The only exception is when the ewes and cows are set-stocked for a short-time at lambing and calving.

When Mike and his wife, Nicky, took over the farm, many of the paddocks on the lower part of the property were between eight and 20ha. Subdivision gave them the opportunity to better manage and use pasture to finish all the stock bred on the farm.

The farm has a good balance of land with two-thirds steep hill country and one-third cultivatable. It is upon this easier country that stock will be grown out and finished. Already the subdivision and rotation policy has made a huge difference to pasture quality and stock management, Mike says. The stock, including ewes and lambs, get used to being moved all the time and this makes them easier to handle and the lambs become familiar with gateways before weaning, which makes life a lot easier after weaning.

Based on previous experience, he is designing paddocks that are long and narrow making them easy to manage and break-fence in winter. There was a good lane system in place when Mike took over the farm and he has gone about extending it to make stock movement easier. The hill is also well-fenced with good-quality fences that don’t need touching. Half the hill has been deer fenced.

The farm winters 12000su which include 1800 ewes, 550 cows and 400 breeding hinds.

Mike is building cattle numbers but the limiting factor is the farm’s winter carrying capacity. He believes the only way to make money out of breeding cows and hinds is to winter them on the hill at zero cost.

“If you are feeding crop then the wintering costs are too high as unlike ewes they only have one calf.” The ewes are break-fed grass over much of the winter and are therefore a cost centre, Mike says. Young stock, including steer and heifer calves and some 18-month-old cattle, winter on the 50ha of winter feed crops (mainly Sovereign kale) grown every year.

Stock on feed crops also receive a supplement in the form of home-grown silage, bought-in ryegrass or wheat straw Because pasture growth is slow to come away in spring, stock need to stay on the crops until the equinox or the beginning of October.

An altitude of 500m to 850m is a challenge and winters can be long, so Mike has only a small window of opportunity to get stock grown out or finished. This is why the provision of quality pasture over summer is so important.

Lambing doesn’t begin until October 1 and the lambs are weaned in the first or second week of January. The lambs are shorn as soon as possible after weaning.

After weaning, the ewes are rotated around the hill blocks to tidy pasture while the lambs get first pick of the new grass paddocks. Cattle are used to open up pastures for the lambs, so by the time the lambs go on to the paddocks the pastures are clover dominant. Cattle then come in behind the lambs to tidy-up the pasture.

Over summer, Mike has different mobs of cattle each on its own rotation around a series of paddocks on the lower parts of the farm.

A small amount of summer feed crop is grown as an insurance against dry summers and any lambs not finished by autumn are carried through winter on swedes and sold in early spring.

Good pasture means no short-cuts

Angus steers are sold by Mike Salvesen on contract to Five Star beef and most have gone, weighing over 400kg, before their second winter.

Soils on the Mt Somers farm are silt clay loams over clay. The farm can get very wet in winter, but it is relatively summer safe, receiving around 1000mm of rainfall annually. Mike says the wet soils in winter are the biggest challenge; it is a matter of allowing soils to dry out enough in spring before pastures and feed crops can be established. He double-sprays the paddocks earmarked for renewal with Roundup, leaving four to five weeks between each spray.

The establishment of good feed crops is critical so he will not take any short-cuts. Depending on soil tests, crops are typically drilled with 200kg/ha of Cropzeal 16P along with selenium and boron.

Mike then sprays with postemergence herbicides and insecticides and keeps a close eye on the crops through to autumn. Kale crops are followed by rape crops then by short-term pastures such as Taboo mixed with clover. When these run out, permanent pasture is established.

This first grass allows Mike to get on top of weeds so the ground is clean before the permanent pasture goes in and stops Browntop from re-seeding.

Because of the relatively high number of cattle, he is mainly using the tetrapolid Bealey NAE2 endophyte ryegrass as a basis for his permanent pasture, but also has paddocks in later flowering ryegrasses including Arrow and Alto.

Mike says Bealey benefits from being rotationally grazed, but it is not an ideal sheep pasture because it does not like being eaten to low levels. It is a highly palatable grass and if it is overgrazed the root reserves will run out allowing other grasses and weeds such as nodding thistle to take over.

He believes each variety of grass has to be managed differently and because he tries to seek independent advice on the varieties, he buys his seed from the noncommercially biased RD1. He says it is often the person he is dealing with that makes the difference – not the company.

The short-term pastures are used to make silage which is used on priority mobs over winter-the weaner deer and R2 cattle. These are stock he aims to finish as early as possible to try to capture spring premiums.

To boost silage crop yields Mike applies Cropzeal 16P at 300kg/ha to the paddocks and, if needed, will apply extra nitrogen(N).

The paddocks earmarked for silage are grazed in early winter and then left alone.

He points out that he is growing silage as a crop rather than just harvesting surpluses and will therefore graze these paddocks only as a last resort.

To help drive pasture growth on the permanent pasture about 30kg/ ha of N is applied early in spring – when the paddocks are dry enough to travel on. He admits the temperatures are usually marginal but the N is then available for when soil temperatures rise. Mike works with his Ballance representative to work out the fertiliser requirements of the farm. Soil samples are taken and Mike aims to keep Olsen P levels at about 18.

“Capital fertiliser doesn’t increase the value of the farm,” he says. The pH on the hill was, at 4.9, too low and last year Mike flew on Optimise lime pellets at 250kg/ ha along with 6kg/ha of elemental sulphur.

He says the response to the lime has been “massive”, over and above what would have been expected given the very good season they have just had.

One hill block was deliberately left without lime in order to make a comparison, and Mike says the difference has been extraordinary. The hill blocks have also responded well to being rotationally grazed instead of overgrazed. With a relatively large number of cattle compared with sheep, Mike says the blocks are benefiting from higher residuals.

The sheep and cattle are rotated around the same blocks, as are the deer and cattle, but sheep are kept out of the deer blocks as they would compete for feed with the hinds.

Mike is aiming to lift deer weaning weights and autumn growth rates so he can sell the finished weaners earlier in spring. Because the altitude slows grass growth in spring, he has not been selling the weaners – finished to a minimum 100kg LW – until November when the chilled market premiums have come off.

To try to get the weight on the weaners earlier, Mike is using a mixture of feeding and genetics. He has bought Eastern sires to try to lift the size and quality of the farm’s Red hinds and this should have a flow-on effect in the size and quality of their progeny. Mike also uses Wapiti terminal sires.

The weaned deer are grown out on grass in autumn and kale in winter.

Having invested so much in stags, Mike also intends running a velvet herd alongside the breeding hinds. The cows are a mixture of Hereford, Angus and Hereford Angus-cross, the latter put to a Charolais terminal sire. The Herefords came with the farm and Mike bought in the Angus and Angus Hereford-cross cows.

Hereford bulls are bought off Mike’s neighbour, David Morrow, while the Angus bulls come from Kakahu.

The Angus steers are sold to Five Star before their second winter and any small yearling cattle that will obviously not be finished at 18 months are treated as store stock over summer and used to tidy up blocks. Mike tries to finish any cattle not sold to Five Star to a minimum 250kg CW, depending on markets and season. In future Mike is hoping to finish the Hereford steers for the Hereford Prime brand.

Yearling heifers are mated and as Mike is trying to build cattle numbers, this year he selected the replacement heifers on size – they needed to be 300-350kg before going to the bull. Last year 156 heifers went to the bull.

The heifers’ calves are tagged at birth and Mike checks the calving heifers twice a day, shedding off any that have calved.

Replacement selection 

In the future he will be taking a more scientific approach to selecting replacements and will use data gathered through an electronic identification system to select on summer weight gains and efficiency. He will also use the system for things such as sire selection for individual cows. Mike welcomes NAIT and sees it as an opportunity for him to gather a lot of data which will be analysed and used in management decisions.

He has installed a Gallagher system and already has 9000 records from the weigh station. This information will be used for pasture management because weight gains on different paddocks and different grasses will be visible, highlighting pastures needing renewing.

Before mating the heifers are vaccinated for BVD and all the cows are given a rotovirus vaccine before calving.

The ewes are predominately Perendale, but there are a few odds and sods which will be put to a terminal sire and gradually culled. Mike is happy with the fecundity of the ewe flock as they have been lambing 140-150% on the hill. He buys Perendale rams from his neighbour Blair Gallagher and uses Suftex and Dorset Down terminal sires.

Last year the hoggets were mated to a Southdown ram. To stimulate ovulation a teaser ram was run with the ewe lambs for one month before the ram went out.

Despite this only 75% of the hoggets weaned a lamb, due to appalling weather at lambing. Mike aims to finish the lambs to 18-19kg CW and these are sold to either Alliance or Silver Fern Farms. Mike employs one full-time and one part-time staff member and uses contractors only for making silage, for shearing and for spreading fertiliser and lime. Everything else they do themselves.

Kellogg programme project

Mt Somers farmer Mike Salvesen is making the transfer of agronomic information to farmers the subject of his Kellogg Rural Leadership Programme project.

Since arriving in New Zealand from the UK, Mike has struggled to find independent information on different pasture varieties and their specific management requirements. He says that while he is swamped by advertisements, independent, scientifically-based information is much more difficult to find.

Mike would welcome feedback from farmers on this subject and can be contacted on (03) 303-9173.

Published courtesy of Country-Wide March 2010
http://www.pasturerenewal.org.nz/cgi-bin/article.cgi?cmd=show&article_id=100&view=view_printable&border=none

Glenfoyle Station, in the upper Clutha, is typical of many South Island high country farms with large areas of over-sown tussock country. Glenfoyle has had a good history of superphosphate application, but despite this, in recent years feed production and quality appears to be deteriorating. This problem is common to many high country properties.

A Merino Benchmark Group study by P Espie & R Dolby in 2004 identified high aluminium levels on Glenfoyle’s Blackstone Hill soils as being a key factor limiting pasture production. High aluminium levels occur when soil pH is low with the effect of restricting root development, particularly in clovers. This limits the plant’s ability to take up nutrients and hence the potential benefit of fertiliser applications. Poor root development reduces the plant’s ability to take up water, increasing stress during dry periods. Aluminium toxicity also inhibits nodulation of legumes. Lifting the low pH levels will address the aluminium toxicity. 

Steep terrain (requiring aerial application) and proximity mean that transport and application costs are a significant issue for this type of hill country operation. Optimise is being trialled at relatively low application rates as a means of minimising the cost of addressing these key soil fertility issues. 

Trial Environment & Treatments

The trial area is on steep terrain at an elevation of 790m with an average rainfall of 675mm annually. Vegetation includes native grasses that has been previously over-sown with improved species. The trial consists of replicated control plots and treatments as follows: 

• Control: Nil application 
  
• Treatment 1: Optimise pelletised ultra-fine lime at 250kg/ha 
  
• Treatment 2: Optimise pelletised ultra-fine lime at 500kg/ha 
  

24-Month Results

Soil tests have been taken every three months following application. These results are charted below. A sustained response has been measured in both increased soil pH and reduced exchangeable aluminium levels.

Regular monitoring will continue with results available online at www.optimise.net.nz

Introduction

High aluminum levels on Glenfoyle’s Blackstone Hill soils have been identified as being a key factor limiting pasture production (P Espie & R Dolby 2004). High aluminum levels occur when soil pH is low with the effect of restricting root development. Lifting the low pH levels will address the aluminum toxicity. 

Steep terrain (requiring aerial application) and proximity mean that transport and application costs are a significant issue for this type of hill country operation. Optimise is being trailed at relatively low application rates as a means of minimising the cost of addressing these key soil fertility issues. 

Treatments

The trial area is on the Zig-Zag site at an elevation of 790m. The trial consists of control plots and treatments as follows: 

• Control: Nil application 
  
• Treatment 1: Optimise pelletised ultra-fine lime at 250kg/ha 
  
• Treatment 2: Optimise pelletised ultra-fine lime at 500kg/ha 
  

Trial plots are replicated 4 times. Plots measure 5m x 2m ie 10m2 and are spaced 1m apart. 

24-Month Results

Soon after application soil test results show a significant and sustained increase in soil pH and reduction in aluminium levels.

Lime is primarily applied to raise soil pH, but lime has many other significant but less-considered benefits. By applying small amounts of Optimise pelletised ultra-fine lime regularly (or as regularly as practical in your farming scenario), you can maintain both optimal pH levels and stimulate soil biology.





Increasing Biological Activity

The advantages to soil biology are not so easily measured and often overlooked. Biological activity is fundamental to soil fertility. Earthworms and microbiology respond positively to lime — both to optimal pH levels and to readily available calcium. As biological activity increases, so does the cycling of organic matter. It will also improve soil structure breaking down thatch, making soil more friable, and improving aeration and water holding capacity. Increased biological activity is probably the most significant means by which liming increases nutrient availability and pasture growth. Application of small volumes of fine lime can boost biological activity, even in higher-pH soils.

Reducing Soil Acidity — pH

Soil acidification is a natural soil process that is accelerated by legume-based pastoral farming, common throughout New Zealand. If left unchecked, over time, soils become increasingly acid (ie lower pH), making for a less favourable growing environment.

When lime (calcium carbonate) is applied, it gradually dissolves, providing both calcium and carbonate to the soil. The neutralising effect is caused by the calcium carbonate dissolving with water in the soil to produce an alkaline solution that removes Hydrogen (H+) ions and thus raises soil pH. Optimal soil pH for pastoral farming in New Zealand is generally considered to be around pH 6. At this level there is good availability of most macro and micronutrients. In soils with extremely low pH levels, priority should be to lift pH levels above 5.4 to avoid aluminium toxicity.

Optimising Your Liming Effect

Lime is essentially a rock that breaks down very slowly, and hence must be ground extremely fine to be effective. Optimise is ultra-fine lime in an easily applied pellet that breaks down rapidly in contact with water.

Optimise has the added benefit that it can be custom blended to incorporate other nutrients such as elemental sulphur, RPR, and trace elements.  All the additives are micronised to ensure the benefit of ultra-fine particle size in a form that can be distributed evenly. Incorporating trace elements in the pellets also means you can get excellent coverage even with light rates. Optimise can be made to order with any combination of minerals and trace elements included with your fine lime.

Take a look at the average lime outcrop or man-made limestone structure and you'll see that it is not breaking down in a hurry. A large block has only a small proportion of its mass exposed to the weather at any one time. Over the millennia the rock will gradually weather, taking very small amounts of calcium carbonate at a time and depositing it in the surrounding earth.

This is the very same rock that we apply to our soil. By grinding it to a finer particle we expose a greater proportion of lime, putting it into contact with soil water. This in turn allows the natural weathering process to occur at a much faster rate.

Each time the average particle diameter is halved the exposed surface area doubles – hence significant improvements in availability can be achieved by micronising limestone.

There is a school of thought that says that larger particles will last for longer. This is very true; the issue is that a small piece of rock remaining in the soil for a long period is of little agronomic benefit. More important than longevity is the benefit that the liming product will have over its life, be it long or short. If longevity is all we require, then we would not take the trouble to process rock phosphate into superphosphate.

To be of benefit the liming material must breakdown and release calcium and carbonate into soil solution. It is important to understand the difference between altering soil solution as opposed to having product in the soil at large - after all, plants and microorganisms source their nutrients from soil solution. Larger particles can influence the bulk soil pH when tested in the lab, but on a paddock lime is of little benefit until it is broken down and available in soil solution.

By increasing the pH in soil solution we can improve the availability of key nutrients (including phosphorus & sulphur), enhance biological activity (including earthworm, bacteria & mycorrhizal fungi) and advance legume performance (and hence N-fixation). In very low pH soils (below 5.4) aluminum toxicity can restrict root development, especially in legumes. At these levels it is crucial to lift pH to take aluminum out of solution.

The same principles with respect to particle size apply to RPR and elemental sulphur. Both P & S can be applied as a soluble salt (ie superphosphate) but when applied in mineral forms (ie RPR & elemental-S) they must undergo a similar process whereby they gradually become available in solution over time. Reduction of particle size increases surface area and significantly improves availability.

The importance of particle size has been well established but application of finely-ground minerals has always been a problem. Optimise provides a solution to this issue by forming ultra-fine lime into a pellet that is both convenient to apply and breaks down easily. Optimise can also be made-to-order to incorporate finely ground elemental sulphur, RPR and trace elements.

 

Correcting soil pH is one of the key reasons that we apply lime, but there are other factors that should be considered. A basic understanding of these will help to determine your soils lime requirements and what to expect from lime applications.

Soil pH measures the concentration of hydrogen ions in the soil, the greater the concentration the more acidic. On the pH scale, a pH of 5.0 is ten times more acidic than a pH of 6.0. This is why a small change in pH can make such a difference to soil biology and nutrient availability.  A measurement of soil pH can indicate that lime is required, but it does not by itself govern how much is required to correct a given pH. Factors that will influence lime’s effectiveness include the soil characteristics (especially CEC), environment (rainfall etc), application and the lime itself (particle size, hardness and CaC03 content). 

Cation exchange capacity (CEC) measures the soil’s ability to hold cations, including hydrogen (which drives pH), calcium, magnesium, potassium and sodium. 

One of the key reasons that soils require differing amounts of lime to change the soil pH relates to the soil CEC and the "reserve" acidity that is contained by the soil. At a given soil pH, a soil with a higher CEC will normally require more lime to reach a given target pH than a soil with a lower CEC.  High-CEC soils typically have more organic material and clay content, with a greater capacity to hold nutrients and better water-holding capacity than low CEC-soils. 

pH buffering, put simply, is a soil’s ability to resist change in pH. When applying larger particles of lime to a high-CEC soil, change can be resisted to the extent that there is little effect on soil pH. This happens because the release of carbonate is slower than the soil’s buffering capacity can counter it. In these situations particle size and availability are very important. 

Particle size is a key determinant of a lime’s effectiveness. The surface area and hence availability of lime is directly related to particle size. This explains why Optimise pelletised ultra-fine lime can be observed to have dramatic effects relative to heavier applications of aglime on some soils. Although a lower quantity of fine lime will be more rapidly ultilised than a heavy application of aglime, it can be much more effective. Improved availability means a significant change can be bought about in soil solution, lifting pH and calcium availability, and reducing soluble aluminium levels in low-pH soils. This change in soil solution leads to improved nutrient availability (including phosphorus & sulphur), biological activity (including earthworm, bacteria & mycorrhizal fungi) and legume performance (including N-fixation). 

Significant long-term changes in pH are easier to bring about in low-CEC soils. The cost of a heavy liming program can be cost prohibitive, particularly for high-CEC soils, but regular applications of fine lime can be ultilised to great benefit. Rapid availability can overcome pH buffering in the short term to bring about improved biological activity and legume establishment. This will have longer-term benefits over and above any pH change that are ultimately more important for the future potential of your pastures.

The importance of lime has come to the forefront recently, due in-part to the increased costs of imported fertilisers. Liming has many benefits, the most well known being to counter soil acidification, and in turn improve nutrient availability. Liming is also extremely beneficial to soil biology. Earth worms, fungi and bacteria respond positively to lime which leads to improved nutrient cycling.

When applying lime, the importance of particle size can not be overstated. Lime is a rock which must break down in the soil to become available in soil solution. The smaller the particle size, the greater the total surface area and the greater and faster the liming effect. Larger particles provide minimal benefit and can often be found in the soil many years after application.

Soil testing is useful in establishing if lime is required to correct soil pH. In addition to the longer-term effect on soil pH, we should also be considering the short-term availability to soil biology and the immediate effect on soil solution pH; ie how we can benefit the current crop.

High fertility soils with a high cation exchange capacity require significantly more lime than low CEC soils; this resistance to pH change is known as buffering. Fine lime is ideal for releasing carbonate faster than a soil's exchange capacity can buffer it and so a significant change can be brought about to soil solution pH and calcium availability. This improves earthworm potential, bacteria activity, mycorrhizal fungi activity and legume performance (including N-fixation).

The problem with fine lime has always been application - the finer lime particles being extremely prone to drifting. Optimise pelletised ultra-fine lime provides a practical and cost effective means to achieve accurate placement of effective ultra-fine particle lime. 

Optimise can also be custom blended with additives such as elemental sulphur, RPR and trace elements to suit your specific needs. This means you can address liming and other nutrient requirements in a simple combined application. All ingredients are fine-ground prior to pelletisation to maximise availability. This is especially beneficial for elemental sulphur; as with lime, the availability of elemental sulphur is strongly related to particle size. Incorporating trace elements into Optimise that are applied at relatively low application rates, such as boron, means that you can far better distribution than might otherwise be achieved.

As a solid lime-based fertiliser, Optimise can easily be used in aerial, ground-spread and drill applications.

Optimise is certified with AsureQuality as an input for organic production, and certified custom blends can be provided on request.

For more information see www.optimise.net.nz or talk to your local CRT TFO.

The importance of lime has come to the forefront recently, due in-part to the increased costs of imported fertilisers. Liming has many benefits, the most well known being to counter soil acidification, and in turn improve nutrient availability. Liming is also extremely beneficial to soil biology. Earth worms, fungi and bacteria respond positively to lime which leads to improved nutrient cycling.

When applying lime, the importance of particle size can not be overstated. Lime is a rock which must break down in the soil to become available in soil solution. The smaller the particle size, the greater the total surface area and the greater and faster the liming effect. Larger particles provide minimal benefit and can often be found in the soil many years after application.

Soil testing is useful in establishing if lime is required to correct soil pH. In addition to the longer-term effect on soil pH, we should also be considering the short-term availability to soil biology and the immediate effect on soil solution pH; ie how we can benefit the current crop.

High fertility soils with a high cation exchange capacity require significantly more lime than low CEC soils; this resistance to pH change is known as buffering. Fine lime is ideal for releasing carbonate faster than a soil's exchange capacity can buffer it and so a significant change can be brought about to soil solution pH and calcium availability. This improves earthworm potential, bacteria activity, mycorrhizal fungi activity and legume performance (including N-fixation).

The problem with fine lime has always been application - the finer lime particles being extremely prone to drifting. Optimise pelletised ultra-fine lime provides a practical and cost effective means to achieve accurate placement of effective ultra-fine particle lime. 

Optimise can also be custom blended with additives such as elemental sulphur, RPR and trace elements to suit your specific needs. This means you can address liming and other nutrient requirements in a simple combined application. All ingredients are fine-ground prior to pelletisation to maximise availability. This is especially beneficial for elemental sulphur; as with lime, the availability of elemental sulphur is strongly related to particle size. Incorporating trace elements into Optimise that are applied at relatively low application rates, such as boron, means that you can far better distribution than might otherwise be achieved.

As a solid lime-based fertiliser, Optimise can easily be used in aerial, ground-spread and drill applications.

Optimise is certified with AsureQuality as an input for organic production, and certified custom blends can be provided on request.

For more information see www.optimise.net.nz or talk to your local CRT TFO.

As a general rule, the South Island's sedimentary soils tend to be deficient in sulphur. Areas closer to the coast benefit from a small amount of sulphur naturally present in rainfall, but for the most part we need to apply some form of sulphur.

We can apply sulphur as either sulphate (most commonly applied as super phosphate) or as elemental sulphur. Sulphate sulphur is readily plant available, but is also prone to leaching, especially in much of the South Islands sedimentary soils. High rainfall exasperates this problem, and this is why we should generally avoid applying sulphate sulphur over winter months.

Elemental sulphur, on the other hand, is not immediately soluble and can be retained in the soil in this form. Elemental sulphur must be converted to sulphate by soil micro organisms in order to be taken up by plants, providing a steady release of sulphate over time. The rate of elemental sulphur release is determined by particle size. The smaller the particle size, the more readily available it is to soil biology. When combined with Optimise fine lime soil biology is stimulated, further enhancing the effectiveness.

We have two soil tests that we can use to measure sulphur levels. Sulphate sulphur is standard on most soil tests, but results can vary seasonly. Organic sulphur makes up over 95% of the soil's sulphur pool. Hence we recommend also using the organic sulphur test for a better overall picture.

While superphosphate prices remain high, many farms may limit it's use. Sulphur by itself is still a very cost effective input and in many cases can be the limiting factor to production. While it may be possible to reduce or withhold P applications for a short term without substantially reducing production, withholding sulphur can have a more immediate and detrimental effect. Elemental sulphur has the added bonus that it has a high purity by weight, i.e. everything that you applying averages 95% effective.

Optimise Sulphur blends offer a cost effective alternative for application of elemental sulphur. In Optimise Sulphur, elemental sulphur and lime are micronised, increasing availability and effectiveness. Both are incorporated into a pellet form that is readily transported, and easily and accurately applied.

In hill country in particular we often see a reduced P-response where there has been no regular liming program. While there is no magic remedy by which we can avoid the long-term requirement for phosphorus in our farming systems, by better understanding how phosphorus exists in our soils, we can make more effective use of what we have and what we apply.

Typically 500-3000kg/ha of phosphorus is present in the soil as both organic and inorganic forms, in roughly equal proportions. Inorganic forms include P in soil solution through to much less readily available forms. Plants can only take up phosphate that is in soil solution (this is a very small part of total soil P). Organic forms exist in organic matter ranging from plant litter through to stable humus. There is a constant equilibrium between different inorganic forms and organic forms due to microbial activity and the mineralisation of organic matter. The P-cycle diagram depicts the various forms of P and how they interact.

Assessing Your P Profile
Our most common measure of phosphorus, the Olsen P test, is a measure of “available-P”. It is considered to comprise of the soil solution P plus a small proportion of the less-available inorganic P. This generally adds up to 1.5-3% of the total soil P. While the Olsen P gives an indication of the phosphorus status of the soil, it is important to understand its limitations. The idea of continually applying P in the hope of obtaining a desired Olsen P level has some serious shortcomings. For low-pH soils, Olsen P can overestimate plant available P. Olsen P can be influenced by soil pH and P-retention. For a more complete picture of soil P also consider testing for P retention, resin P, organic matter (especially for crops), soil pH and calcium levels, and exchangeable aluminum if pH is below 5.4.

Influencing P-Fixation
Phosphorus availability is affected by soil pH. In acid soils phosphorus reacts with minerals such as iron, aluminium and manganese, taking them out of solution to form insoluble ‘fixed’ compounds. Soils of pH 6.0-7.0 have a reduced potential to ‘fix’ P. Generally high-pH is not a problem in New Zealand. Low-pH soils can be improved with the application of available lime.

Ultilising Organic P
Organic matter may be mineralised by soil organisms to release nutrients such as nitrogen, sulphur and phosphorus into the soil solution in plant available forms. Application of a good fine-lime product such as Optimise is beneficial to soil biology and can influence available P by enhancing the cycling of organic matter.