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NIRS analysis for manure management

The use of NIRS analysis for manure management – background, benefits and vision

Interview with Dr. Phil Williams, PDK Projects, Inc.


In this in-depth interview for Nirperformance.com, Dr. Phil Williams shares his extensive experience with the use of NIRS analysis in the increasingly important discipline of manure management. Continuous measurement of liquid manure combined with modern GPS mapping can greatly improve the application of the phosphorus and nitrogen-rich ‘black stuff’ with significant financial benefits for farmers and applicators alike. In addition, a more intelligent use of liquid manure will mitigate the environmental impact.

Can you start by giving an overview of how manure is being used today in North America?

There are several kinds of manure. These include manure from dairy cattle, pigs (hogs), poultry (mainly chickens) beef cattle, and manure from other domestic animals, including horses, sheep, goats, and grazing cattle. Manure from horses, sheep, goats and grazing cattle is spread on the land by the animals as they graze, and otherwise move around, and is rarely analyzed.

A large proportion of beef cattle are raised in feed lots and the manure is composted and analyzed periodically in solid form. This analysis is usually done by traditional chemical methods, although NIRS calibrations have been developed for the analysis of composted manure. Manures from dairy cattle, chickens, and particularly hogs are stored in liquid form, in lagoons (small lakes), or in pits below the barns. The lagoons or pits have to be pumped empty from time to time and the manure is spread on land near the barns.

It is mainly these liquid manures that I will cover in this interview.

Who is analysing manure?


Manure applicator

A manure applicator


Liquid manure is spread by applicators using spreading equipment of up to 14 metres in width. In North America most applicators cultivate the manure into the land. In Europe some applicators cultivate the manure into the land, others simply spread it. In Manitoba the lagoons or pits are manually sampled a few times during pump-out and these are considered to represent the entire volume (sometimes as high as 13 million litres). The samples are sent for testing to a certified laboratory. Manure composition changes during pump-out and the changes in composition are more marked in lagoon storage because of the influence of rain. Because of the generally lower volume, and resultant more efficient agitation during pump-out, pit-stored manure is rather more consistent in composition than is lagoon-stored hog manure.

Some dairy cattle slurries are applied by the farmer using a tanker, but most hog and dairy cattle slurries are applied by commercial applicators, using tankers or drag-hose. Provinces in Canada, and States in the USA have their own strategies and regulations. For example, in British Columbia the emphasis is on dairy cattle manure, whereas in Manitoba hog-manure is foremost. In Manitoba the drag-hose system is used for 95% of the hog manure. Farmers work with manure managers to develop plans for pump-out and application. In Canada, practically all liquid manures are handled by manure applicators who organize and operate their own businesses. Their clients are hog (pig) producers. In Manitoba hog-farmers contact manure managers when they need pump-out of lagoons or pits, and contracts are developed in accordance with government regulations. Agreements are then developed between the hog-farmers, and the applicators of their choice to spread the manures on fields as instructed by the farmers.

What can be analysed in manure?

Liquid manure varies in composition from as low as 0.5% to over 12% in dry matter (DM). The most important constituents of the manure are nitrogen (N) phosphorus (P) and potassium (K). The total nitrogen contains ammonia that varies from about 50 to over 75% of the total. Ammonia is very soluble in water. This makes it readily available to growing plants, but ammonia can be lost to the atmosphere during storage and transportation. The contents of N, and P are correlated with the DM content, with r2 values of 0.79 to 0.86. The manures contain other constituents in lesser amounts. Composition is affected by the diet of different types of animal. For instance, weaning pigs are fed a diet richer in protein content than are pregnant sows, so the manure is higher in nitrogen. Some farmers supplement the diets of their animals with phytase, which is an enzyme that assists in breakdown of phytate during digestion. This reduces excretion of P in the manure.

What methods are being used to test manure?

The biggest difficulty with manure analysis lies with the sampling.

Today, lagoons or pits are mostly sampled manually and intermittently from valves attached to the pumps. The samples are assumed to represent the composition of the entire volume as far as possible. The analytical work is by classical “wet-chemistry” methods. The disadvantages with this intermittent sampling is that it gives only approximate information of the entire pump-out and it does not give sufficient data to enable mapping of nutrients over the field. For example, even if 10 samples of 1 litre are taken during the pump-out of a lagoon containing 3 million litres, that is a ratio of about 1:3-6 of the total volume of manure.

In recent years, the introduction of industrial-level calibrations for continuous on-line analysis by NIRS have offered new possibilities to manage manure application more precisely. Continuous analysis eliminates the need for taking samples because all of the manure is analyzed as it is being pumped. Analysis by NIRS is generally regarded as being equally precise to analysis by wet chemistry. The need for sampling and the associated sampling error is virtually eliminated and the entire volume of the lagoon or pit is analyzed. This gives a reliable estimate of nutrients, and fields can be more accurately mapped with regard to the nutrients applied over different parts of the field.

What are the financial benefits of NIRS analysis for farmers and applicators?

Farmers need to apply fertilizers to growing crops, including pastures, to obtain maximum yield, crop quality and revenue. They make decisions about how much N, P or K to apply to their crops. Some of these are supplied by the manure, so if farmers know the composition of the manure that is being applied they only need to supplement the manure with commercial fertilizer, which is much more expensive than manure.

Analysis of the manure as it is being applied, allows the applicator to map the nutrients that have been applied to a field. Control of the application by GPS means that fields can be accurately mapped with regard to the amounts of nutrients that are being applied. This information can be passed on to the farmers who can then apply supplementary fertilizer more effectively. Commercial fertilizers, such as urea and ammonium sulphate cost an estimated $ 4-500.00 per ton, so farmers can save a great deal of money and use the fertilizers more efficiently if they know with reasonable accuracy how many Kg of nutrients have been spread on different areas of their fields. This process comes under the heading ‘Precision Farming’ and is receiving increased attention.

Applicators can also benefit, for example, the value of nutrients applied to the land in southern Manitoba in the form of liquid pig manure has been estimated at $11 million. At present, only a small proportion of this is recovered by the applicators in terms of invoicing farmers for the value of the nutrients that they receive. Using the data revealed by continuous on-line analysis of the manure, a system could be developed whereby applicators could charge a reasonable fee for the nutrients.

Figure 2

Figure 2

Figure 2 illustrates how the distribution of the amounts of nutrients applied over a field is affected by the dry matter content of the manure. Applicators usually divide fields into roughly four sections, using a GPS system. They spread the early manure on the first section, then move accordingly, so the last quarter of the field receives the richest manure. The next time that they spread manure on that field they reverse the process, so that a degree of balance is achieved.

What about the environmental aspects?

Governments are becoming increasingly concerned about the effects of residual nitrogen (N) and phosphorus (P) in agricultural soils. Seepage can contaminate subterranean water sources; run-off can contaminate aquifers, creeks, streams, rivers and eventually lakes. Restrictions are imposed by governments and are monitored by periodical sampling of farmers’ fields. For instance, farmers in southern Manitoba are limited to 60 ppm of phosphorus in the soil. Similar examples can be found all over the world.

What does it take to analyze manure with NIRS?

For reference analysis, samples have to be taken, tested for moisture content, dried and ground to pass through a screen with apertures of no more than 2.00 mm. The manure can also be tested as received, but hog manure sediments very quickly which affects sub-sampling for analysis.

For NIRS analysis, the original samples can be scanned, but for calibration development the reference data should be converted to the original moisture basis. This becomes particularly important with high moisture materials such as fresh forages or manure. Liquid manures can be tested directly on-line by NIRS by mounting the instrument in a flow-through system. The instrument should use diode-array technology which is capable of very rapid scanning. Samples must be taken for calibration development, but when the calibrations have been developed and evaluated, the manure can be analyzed continuously. This eliminates the need for further sampling and avoids the associated risk of sampling error.

So is it worth it – what are the considerations for businesses wanting to start using NIRS?

An important question to ask is what is the cost for all of the analytical work required to run the operation, and how much can be saved by using NIRS.

To give an example, when the Canadian Grain Commission switched from Kjeldahl to NIRS testing for wheat protein content for their annual workload of about 500,000 samples they saved an estimated $350,000.00 in the first year. That was back in 1976, so by now salary, and chemical purchase and disposal cost increases would have ballooned those savings to $3-4 million. Also, for example, I have just finished working with a big laboratory which wanted to a) reduce staff engaged in “wet chemistry” analysis, and b) achieve a 750-per-day workload. They were able to achieve their aims very well, because by installing the appropriate NIR calibrations they were able to process the required volume for all of the parameters that they were testing simultaneously. They were able to reduce the costs/per/test that they were previously charging their clients, and substantially improved their income at the same time – a win/win situation.

In addition, there is the question of how can NIRS be used to generate revenue (e.g. by putting a price on nutrients dispensed during manure application), as already discussed.

And finally, there is the question of convenience. It is far better for analytical data for quality assurance be available instantaneously, or to to arrive in minutes, rather than after time-lag of hours or even days.

Dr. Phil Williams (First Class B.Sc. Honours, Chemistry, 1954; Ph.D., 1958, University of Wales at Aberystwyth) has had one of the longest careers in the world of continuous experience with NIRS. In 1972, he aquired the second instrument ever manufactured, and introduced NIRS as the primary method of analysis for protein throughout Canada’s wheat terminals in 1975-6. His persistence in working with the engineers in companies designing and manufacturing NIR instruments is credited with the ability of the early NIRS industry to grow into the multi-million dollar industry it is today. He introduced NIRS not only to Canada, but also to England, Australia, Russia and the Middle East.

Dr. Williams is the noted author of over 200 technical articles and two editions of a classic NIRS reference book. Read more about his work.

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