Fertility options for organic and transitional growers

The benefits of organic growing methods, long known and advocated by agricultural scientists and organic farmers, have received a lot more acknowledgement over the past decade, and particularly over the last five or six years. It is interesting that the booming market for organic produce is only a small part of this sea-change. While the certified organic industry is growing very rapidly, it started from such a small base, that the total number of certified organic growers remains small (less than 2% of Australian farmers).

In some ways even more surprising than the rush of new growers to certified organic production, is the rate at which conventional growers are adopting organic practices, especially the use of compost, organic fertilisers and soil fertility products.

Almost all fertility problems can now be confidently solved with organic methods. The one remaining serious issue is phosphorus fertility in alkaline soils. Furthermore, as some of the more unsustainable growing areas progress down the path of declining organic matter, compaction and accumulation of salt, herbicide and pesticide residues, conventional products have ceased to deliver economic returns. Without enough organic matter in soils to support the vital soil ecosystem, conventional growers are forced to confront the failure of the conventional NPK fertilisers. In horticulture production areas such as Virginia and Two Wells, in the previously highly productive northern Adelaide Plains, all the better growers are now spending more money on organic inputs than they spend on conventional fertilisers. They have adequate N, P and K in their soils but still can’t produce the yields they need to remain viable. This trend is also observable in intensive horticulture areas in the other states.

The prevalence of organic products in broadacre cropping and dairy farming regions is even more indicative of change. Even a decade ago, the conventional wisdom was that organic fertility solutions might work in high value horticulture, but could not be economically delivered to broadacre crops. Now there are many manufacturers and purveyors of certified (and ‘certifiable’) inputs in all farming regions. So much so, that the old problem of “how can I obtain organic fertilisers at a reasonable cost” has been replaced with the dilemma of “which one”?

So what are the options available to organic producers, or to anyone else in the transitional area between fully conventional and fully organic, and, faced with so many new products, how do or should producers chose between these products?

Soil analysis

Any commercial grower starting out on new land or contemplating conversion to organic should attempt to understand as much as possible about the particular soil characteristics where they will farm. It is fundamental to organic management to identify, as soon as possible, the ‘limiting factors’. This is best done with an Albrecht style analysis and report; that includes all the major, minor and trace elements, pH and CEC. It may be worth seeking out an independent laboratory, so that the recommendations are free of direct commercial interest. If you do choose to use a fertiliser supplier’s analysis, you may still be able to get a comment on the recommendations from an independent consultant.

It is very important that growers understand how to take soil samples. The following recommendations will help, but also heed advice from the laboratory.

· Sample very different soil types (or history of use) independently

· If possible, sample at the time of year when crop nutrition is most critical, this will vary depending on the crop

· Walk an “S” pattern path, from corner to corner of the paddock or portion to be sampled

· Take an even core down to about 15cm in depth (i.e. if not using a soil probe, which makes correct sampling easy, try not to bias the sample in favour of surface or subsurface layers

· Use a clean spade or sampling tool and bucket

· Take at least 10 sub-samples. 20 is better. Mix them thoroughly at the end and send off the required amount as a sample of the batch

· ALWAYS test in roughly the same location and at the same time of year – otherwise your results will not be directly comparable

Some organic growers sample different paddocks frequently and use the information obtained to constantly tweak their soil fertility. Many of these growers find this fascinating and it can become as significant to them as other basic farming operation such as machinery maintenance or routine stock management. For most growers, it is only necessary to test soils annually for a few years. Based on the first report, major soil deficiencies and imbalances are corrected. For the next few years growers can test soil to confirm that the initial adjustments and maintenance fertility-replacement is delivering the required results. Thereafter, testing can be much more infrequent, to check up on nutrient and soil-balance conditions. The frequency of on-going testing will probably be determined by the economic return of the crop, but three to five years may well be appropriate.

The recommendations

Independent laboratories make generic recommendations, but they may also report on acceptable products to fulfil the requirement. The qualifications, skills and experience of the person making the recommendations is critical. Like any professionals, soil consultants should be prepared to reveal their background and commercial affiliations and provide details of previous satisfied clients. Knowledge of your particular region and enterprise is also important. The consultant should be able to give a good account of why each material is required and why the particular product recommended is the best for the job.

Soil organic matter: start with the basics

This author firmly believes in the importance of re-creating a diverse and healthy soil ecosystem as the first requirement of organic growing. It is not just necessary to satisfy certification conditions, but is fundamental to getting the best possible sustainable return from a property. The best way to establish this organic soil profile, for almost all Australian soils, except perhaps some peat soils, is to add organic matter.

For most growers this is best done with well-matured compost, but in the initial stages of conversion, many forms of organic matter may be appropriate. Soil organic matter can also be produced by green manure crops, which may take longer, but may also come cheaper (depending on the time out of production). Another alternative is to return the land to pasture cover for a period of three to six years.

Compost was once considered to be suitable for horticulture application only. Although the nutrient value of compost is well below the values of bagged fertiliser products, compost is used in much larger applications, is much cheaper by weight, and provides many different functions, as well as nutrition. Depending on the raw ingredients of the compost, commonly used doses can significantly contribute to plant nutrition.

Some soils with nutrient oversupply problems need special care, as the broad nutrition of compost, usually an advantage, can become a disadvantage. In this case weathered coal and humates have a special purpose, to lift soil carbon without adding un-wanted minerals. These products are also useful in intensively farmed soils, where shorter-term humus is continuously burnt up and destroyed but cultivation and exposure.

In broadacre farming situations, compost is used at a lesser rate, and possibly banded rather than broadcast, Bob Long of Jefferies reports responses from applications as low as five tonne per hectare (around $30 per tonne). Bob also believes that “spending the money at the outset to get things right is very important. Until that is done a lot of other money can be miss-spent, and the mineral fertiliser products will very likely not produce maximum returns.”

Phil Barnett, of the Australian Perry Agricultural Laboratory (APAL), says “that might be true of some producers, but in intensive horticulture, there are also producers who overload the system with fertilisers, especially with Phosporous (P).” He continues “we have some clients who we have advised not to use P and they have farmed for six years without phosphates, while their soil levels remain high”. He concludes “it is easy to spend too much on fertiliser, if all the organic matter is gone. Inputs have to be economic and produce returns. Growers need good soil information, including salinity factors. Then they have to establish a budget and sopend it as wisely as possible.”

There has been a lot of research into compost tea products, for nutrition and disease control. These products can now be made more specific for particular soil and crop combinations. Although the science of compost tea is becoming much more high-tech and precise, there is still a role for simple old-fashioned compost tea, as a way to make limited compost spread better over a large area.

soil nutrient balance
soil nutrient balance
The basics 2: soil nutrient balance

In the Albrecht system, it is important to balance soil nutrients. In order to determine fertility requirements, we first establish the cation exchange capacity (CEC) of soils. In soils with a high CEC, we can accept a lower percentage of cations, as the volume of each is greater. In a low CEC soil, we require a greater percentage in order to provide the minimum requirement for plants.

Cations are positively charged minerals, and include calcium++, magnesium++, potassium+, sodium+, hydrogen+ and aluminium+++. Negatively charged minerals are called anions and include nitrate-, phosphate-, sulphate- and chloride-.

Low CEC soils will also require more frequent applications of fertiliser. In other words the storage is less, so we need to recharge the well more often.

Good balance is considered to be approximately the following values:

Calcium 60 – 70%

Hydrogen around 12%

Magnesium around 12%

Potassium 4%

Sodium 1%

Other base minerals about 3 - 4%

Fertiliser options

There is now a huge range of products available in all parts of the country. These products may be divided into the following categories for convenience, although there are many combinations as well:

· Mineral fertilisers mined mineral products such as soft rock phosphates, and Langbeinite (or K-mag), but also including trace elements.

· Some ‘naturally chelated’ trace elements (non-EDTA chelates).

· Manure based products including pelletised chicken manure and guano.

· Seaweed products, particularly kelp based liquids or powder.

· Fish-based products, often utilising fermented shark or fish processing waste.

· Coal and humates derived from coal deposits.

The minerals contained in these fertilisers will be more available, and will remain available longer, if we are able to adjust the soil towards the ideal described by Albrecht.

Exactly which products to use, is exceptionally controversial. The answer has to be derived for each property, depending upon the soil CEC, total mineral levels and balances, the crop requirement, availability of funds and other environmental factors (soil moisture availability and other factors can also affect nutrient availability).

The general purpose of these products may be described as follows:

· Mineral fertilisers are generally the best and cheapest way to apply nutrients, if other factors are not limiting (eg soil pH is very high)

· Manure products are recommended if there is a high requirement for nitrogen

· Trace elements may be added in mineral form or as chelates. They may be present as contaminants (good or bad) in many sources of lime, dolomite, gypsum and other mineral products, The trace element content of these products should be declared by the manufacturer

· Fish and seaweed products are often used as a tonic or at major times of stress such as just after germination (when the root system is not established to scavenge for nutrients), flowering and fruit production

· Coal and humates are excellent where soil organic matter is seriously depleted and where soils are cultivated frequently

The latest range of new fertility products

In the last few years, a variety of new, ‘high tech’ products have become available. These products generally combine mineral fertility with clever micro-organisms. In these products, the micro-organisms are specifically selected for their scavenging ability and their ability to make insoluble nutrients available. They may appear as selections of organisms, such as the ‘EM’ or ‘BM’ type products, or as combinations of organisms and a food source. An example of such a product is ‘Nutrismart’. It contains a selection of fungi, bacteria and yeasts, with some minerals, all wrapped into a protective coal-based pellet. The nutrition of the fertiliser itself is much less important than the ability of these highly-selected organisms to quickly multiply and assist the plant to scavenge otherwise unavailable nutrients from the soil. When used in close proximity to the feeding roots, only small quantities are required.

Problem solving

Does your soil analysis indicate that you should be getting a better response from the crop? In this situation, always suspect nutrient imbalance. An Albrecht style analsis should help to correct this problem. For many Australian soils, the solution is calcium or calcium and magnesium (supplied by lime or dolomite). It may also be necessary to take leaf samples for testing. Comparison of soil and leaf test results through the growing period should reveal what is happening to soil nutrients and if the problem is availability, rather than gross nutrient levels. Whereas foliar fertilisers should not be the basis of an organic nutrition program, they may be needed to get nutrients into plants while soil imbalances are corrected. They are also useful at other times of stress, such as this year in southern Australia, when soil temperatures in spring remain too cold for roots to be fully operational (we just had the coldest October in 57 years).

Keep it simple, and plan for conversion

Generally the solution to fertility problems does not rely on using dozens of different products. Start with a soil test. Improve organic matter and adjust soil mineral balance as a priority. Apply NPK and trace elements as permitted by the budget after correcting soil balance, otherwise these products may well not work effectively.

Soil management and development does cost money, and therefore it should be considered as (an important) part of the conversion plan.

Alkaline soils

Very alkaline soils do present a significant problem in broadacre organic production. There is a tendency for researchers in this field to imply that this indicates a failure of certification systems to address Australian conditions, to claim that organic agriculture in broadacre situations is unsustainable and to press for ‘exceptions’ to the internationally accepted rules. While not wanting to close debate on these issues, I perceive this response to be short on understanding of and commitment to organic production. It is true that alkaline soils are a significant challenge but there may yet be ways around the issue.

Firstly, there are undoubtedly areas under agricultural production that are so marginal they would be best taken out of farming and dedicated to conservation uses, or shifted to some form of tree-based agriculture. Large areas of the Eyre Peninsula (SA) and some parts of the WA wheatbelt are in this category.

There are also other avenues for experimentation. Phil Barnett from APAL says “there has been very little work done on organic production in alkaline soils. Most of the Albrecht work, for instance, is done overseas in acid soils, and a lot of rock phosphates have up to 30% calcium, which is rather throwing fuel onto the fire. Biological farmers [he means transitional farmers] who do not have to conform to certification rules may use MAP, which is quite acidic. Sulphur is also important, so they could use sulphur-coated MAP. They also cannot obtain trace elements, so these are used as foliar fertilisers. Most also use seed dressings, to get the nutrition into the plant early.”

Phil continues “organic growers may use sulphur blends, but it is very difficult indeed to change pH in a broadacre context. They also try to increase organic matter in every available way, especially P-scavenging plants as green manure. They can use foliar fertilisers for trace el;ements and seed dressings, if these are acceptable to the certifiers. Some compost products available, such as those from Laurie and Co or Nutri-Tech Solutions, combine humates, crushed-rock fertilisers, trace elements and inoculations of soil organisms, in an attempt to chelate these products before adding them to soil, and make them more available’.

Other interesting areas of research are the permanent bed systems more common in the USA, or adaptations of these systems, such as the one being developed by Gavin Dunn at Tarlee (SA). These systems either concentrate on soil improvement only in the planting zone (i.e. they do not attempt to apply to the traffic area between the raised beds) or they try to maximise the effect of organic matter breakdown from the residue of the previous crop. In one such system, a series of swales and ridges are established. Seed is planted Inter-row cultivations in the standing crop may throw soil further up onto the ridges. The residue is then rolled into the gully to compost. Next years ridge is built on top of last years swale (which contains the decomposing residues).

Use of compost and fertiliser combinations and the placement of these products with respect to the seed are also interesting areas for experimental work. The banding of high rates of compost (for broadacre situations) and bio-phosphate products under or alongside the seed is of special interest, particularly for crops such as wheat where phosphorus nutrition is establish early in the life of the plant.

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