By Brian Houlihan

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In a previous post I highlighted the hemp research undertaken by An Foras Taluntais (The Agricultural Institute) in the 1960's. An Foras Taluntais was a predecessor to Teagasc which was established in 1988. Since its inception Teagasc has researched and/or promoted hemp on a number of occasions.

This post looks at the three-year research Teagasc undertook over 20 years ago between 1997 and 1999. Experiments were undertaken looking at different varieties, seed rates, sowing times, harvesting methods and other aspects.

In 1997 around five hectares (12 acres) of hemp was grown to evaluate harvesting and storage systems. Another goal was to produce 20 to 30 tonnes of raw material for evaluating the use of hemp stems in the manufacturing of medium-density fibre board (MDF). For the researchers increasing the whole stem yield was a major objective, regardless of fibre content and quality.

Sowing:

Generally the hemp was sown in a narrow row (12cm) corn drill. Nitrogen (120kg per ha) was applied to the seedbed before sowing. Some phosphate and potassium was also used depending on soil conditions. No fungicides, insecticides or herbicides were used during the process.

To assess the yield potential of early-sown fibre hemp, sowing date experiments were carried out in 1998 and 1999. It was found that early sowing “had a significant positive effect on the yield of stems” with a “steady decline in yield with delayed sowing.”

Tests showed that for maximum production hemp should be sown in late March, where possible, at a seed rate of 25–30 kg/ha. To reduce the risk of frost damage during April, early to mid-April sowing is advisable. This will produce the maximum biomass yield where fibre content and/or quality can be ignored, as is the case when producing a raw material for the fibre board industry.

The researchers found that hemp establishes itself within 10 days of sowing and grows slowly but steadily for the first month. The rate of growth increases subsequently and this crowds out any competing weeds that. By mid-June the hemp crop was generally free of any weeds. The researchers found that “the hemp flowered from mid-July to mid-August depending on sowing date and seed rate.”

Seed rate

A series of experiments were conducted to study the effect of density on stem dry matter yield using the variety Fedora 17. The results are presented in Table 1.

Effect of seed rate on stem yield

It was found that reducing the seed rate from 50 to 20 kg per hectare “resulted in a significant increase in stem yield in two of the three years.” The lower-seed rate plots also had fewer weak dwarf plants and significantly less Botrytis-infected plants.

The stem diameter also increased with a reduction in seed rate. Based on these results the traditional seed rate of 50 kg/ha “may not be the most appropriate where the objective is maximum biomass yield.” Tests reveal that a seed rate of 20–30 kg/ha produced the highest yields. It also resulted in a significant saving in seed costs of around £87/ha.

Varieties:

Seven varieties (Table 3) were sown in ’96, ’97 and 1998. The plots were sown from 10 to 20 April in each of the three years and harvested in late August/early September.

A sample of twenty stems was removed to the laboratory and all leaf and head material removed. The two fractions, (stem and leaf material) were dried separately. The stem yields (t/ha @ 15% m.c.) are presented in Table 3.

The stem length and % leaf Dry Matter (DM) were also calculated for these variety trials. The three-year mean figures are given in Table 4 along with the average loss of stem yield as the cutting height is increased from ground level to 20 cm.

The data shows that at harvest, an average 25% of the total biomass yield of hemp is in the form of leaf and flower material. This material is of no commercial value and is generally lost during the field drying and subsequent baling of the crop.

It is important, therefore, when recording the yield of hemp that only stem yields and not total biomass yields are quoted. Because a long stubble is left in hemp fields to aid drying of the cut crop, significant yield losses of around 15% are incurred. The average stem lengths recorded in these trials varied from 190 cm for Fedora to 225 cm for Lovrin.

The percentage fibre, as measured using a laboratory scutcher, varied from 29.4% for Felina to 35.4% for Kompolti. Fibre yields ranged from 2.70 to 5.98 t/ha over this series of trials.

Diseases:

Over the three years of the project the only disease encountered was Botrytis cinerea which is a fungus. High humidity combined with high temperatures can result in a high proportion of the weaker plants being killed by Botrytis. The large plants, while showing symptoms of the disease, usually survive to harvest.

Hemp is also susceptible to Sclerotinia. While both diseases can be controlled by spraying, in practice this will prove difficult because of the crop height. Further work on this aspect is required to establish if any economic increase in stem yield is possible.

Harvesting

As the researchers state “The density and height of a mature hemp crop can cause problems when cutting and baling hemp with existing farm machines.” Using part of the crop the performance of the following machines were evaluated.



Rape swather:

“This machine is designed to handle oilseed rape with a straw length of approximately 1.5 m. It had great difficulty handling the hemp. The normal work rate is 2 to 7 ha/h. This was reduced to 0.8 ha/h or less on the hemp. Stubble height is very easily controlled.”

Drum - top drive mowers:

“These are designed for cutting grass silage. These mowers failed to handle the hemp.”

Disc - bottom drive mowers:

“These are available from 1.65 m to 4 m cut widths and handled the hemp crop easily. Work rate was up to 2 ha/h. These machines did not create a swath of the cut material and control of the stubble height is difficult. This cutting system required a follow-up windrowing operation. Suitable machines are available. A Stoll windrower was used very successfully on the Carlow site. Once cut and windrowed, the straw has to be gathered and made safe for handling, transport and storage. Again a number of approaches were tried.”



Hesston belt baler:

“This machine worked very well and had no problems baling the crop provided the swath width was narrower than the pick-up width of the machine.”

Welger fixed-chamber roller baler:

“Again, this machine is capable of baling hemp, but our experience suggests that belt-type balers are more suitable. For both types, bales of hemp weighed 220 to 250 kg”

Forage harvesting:

“Precision-chop forage harvesters fitted with rotary maize headers are capable of harvesting hemp and delivering a chopped material into conventional silage trailers. The chop length of these machines can be increased by reducing the number of chopping knives and reducing the drum speed. However, our experience suggests that the crop must be green and cut before natural retting sets in on the standing crop.”



Teagasc also evaluated aprototype machine which makes high-density polythene-wrapped. It’s stated that “Generally, the machine handled the hemp satisfactorily with bales weighing approximately 400 kg. The wrapped bales are suited to long-term storage and easily transported.”

Researchers also state that “the chopped material requires storage for up to one year under conditions that prevent deterioration of the material.”

End uses (MDF)

Researchers acknowledged that hemp has a wide range of end uses but expressed some concerns. It’s stated that “To fully exploit hemp an industrial infrastructure is required to separate the long blast fibres from the shorter hurd fibres.” Since this industry does not exist in Ireland “the concept of using the whole stem as a raw material for the fibre industry was investigated.”

At the time it was estimated that the MDF industry used approximately two millon tonnes of wood. It was suggested that replacing even 10% (200,000 tonnes) of this figure with whole hemp stems “would create a market for over 6,000 ha of hemp.”

The researchers argue that not only would this make more raw materials available for the MDF industry but that hemp would act as “a very useful break crop to the tillage sector.”



The hemp straw produced was baled and later chopped using a big bale chopper. The chopped material was mixed with wood chips at a ratio of 1:7.7 (13%) on a dry matter basis and incorporated into a MDF manufacturing process.

The resulting MDF board “passed all quality tests at the factory.” On the basis of these results the industrial experts were satisfied that hemp “could replace up to 20% of wood chips in their process.”



Serious problems arose, however, when commercial quantities of chopped hemp stems were introduced to the intake and conveyor systems at the factory. The loose long blast fibres caused damage to bearings, shutting down the whole intake system.

So while whole hemp stems are very suitable for MDF production, the material must be chopped in lengths of 2.5 cm to 10 cm with no fibres unravelling on the stems. At present no machinery is available to carry out this process satisfactorily.

The researchers stated that “For hemp to become a successful raw material source the fibre board industry requires the design of an efficiently chopping mechanism and a means of storing the harvested crop for up to twelve months without deterioration.”

Conclusions:

You can read the report in full here but below are the conclusions.

- Hemp can produce high yields of stem material, (10–14 t/ha) for processing.



- The crop can be produced on any arable mineral soil.



- Sowing in early to mid-April will ensure maximum yields.



- Seed rate can be reduced significantly, where fibre quality is not a priority.



- The crop can be produced without the aid of agrochemicals.



- Whole chopped hemp stems can be used up to a maximum of 20% inclusion rate in the manufacture of medium density fibre board (MDF).



- The development of harvesting and storage techniques are required before commercial development can take place.

Brian Houlihan is the curator of the Dublin Hemp Museum and regularly writes about hemp. Follow him on Twitter @dubhempmuseum and @houlihanbrian. You can also find the museum on Facebook.

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