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Exciting Results from Commercial Experience of Biennial Cropping of Glen Ample Raspberry

Andrew Cranston

Boxford Suffolk Farms

Introduction 

Biennial cropping is not a new technique to this or other raspberry producing countries. Experiments were conducted in the 1970’s at the Scottish Crop Research Institute and the Experimental Horticulture Stations Brogdale, Luddington and Stockbridge House, using a range of varieties. These experiments identified some major advantages from utilising this method of production most notably, a reduction of the labour costs involved in cane management which were quantified for biennial versus traditional/annual systems.  In addition, fruit was found to be more accessible to pickers, picking rates increased and for some varieties, the total yields per unit area of ground enhanced.

Based upon the results of these trials several growers established commercial plantations employing the biennial system in the late 1970’s and early 80’s.  At the time, however, in the majority of cases these plantations were not served with the sophisticated trickle irrigation and fertigation systems that are available today. As a result due to fluctuating water and nutrient supplies, cane vigour, number, fruit size and ultimately yield suffered.

The use of unsuitable varieties, excessively wide row spacing, too high cane numbers, lack of effective shelter from the wind, poor soil conditions and inadequate cane management also meant that many plantations failed to achieve their full potential.

Finally, as the result of rampant and (at the time almost uncontrollable) Phytophthora infection and the sudden loss of Dinoseb in oil for effective primocane control, this system of crop production lost favour with the majority of the industry.

In recent years, ADAS Horticulture have been encouraging growers to re-consider biennial cropping to reduce labour costs of picking and cane management and to break the life cycle of some persistent insect pests and diseases. The majority of growers now produce raspberries on intensive systems, on sites with free-draining soils, good shelter (under polytunnels in most cases), with irrigation/fertigation and using improved management techniques. It may therefore be possible to overcome some of the difficulties that occurred when biennial cropping was employed on commercial farms in the 1970’s and 1980’s.

Why Boxford Suffolk Farms Considered Biennial Cropping

At Boxford Suffolk Farms, we have had some recent experience of planting and establishing long cane raspberry plantations. We have been impressed by the fact that picking rates have increased, leading to a corresponding decrease in picking costs. We have also noticed that fruit size was increased in comparison to a normal annual cropping system. It also became apparent using this system that the number of healthy viable buds which produce fruit and yield is more important than the cane height itself. The practice of growing healthy canes with high numbers of viable buds is vital to the production of high yields and we realised that this could be achieved better if we separated the production of primocane production from fruiting cane production.

In 2002, we therefore decided to establish Glen Ample on our farm in a system of production tailored to biennial cropping.

The Concept of Biennial Cropping

Biennial cropping refers to the production of a crop every second year.  Raspberry growth is divided into two distinct phases:-

·      The vegetative phase which we all refer to as the spawn or primocane stage.

 

·      The fruiting phase, which refers to primocanes that become dormant and receive a chilling period, over-winter and then break bud and produce fruit in what is their second growing season.

Biennial cropping involves the separation of these two phases in the field. In an established plantation, fruiting canes are tied in to their final cropping position and the flushes of spawn removed from beneath them throughout the majority of their growing season, using Croptex Steel.

When dormant in the winter, the old fruiting canes are cut out to ground level and the following spring/summer spawn is allowed to grow on its own to produce canes for fruiting in the following year.

To prevent all fruit being produced in one season and none in the next, plantations on a farm are managed in such a way that in any one season, half of them are in the fruiting and half in the vegetative phase.

The System Employed on Our Site

Firstly we planted short cane ample in 2002

At Boxford Suffolk Farms, our soil is a deep silty loam, which is ideal for raspberry growth. The site is flat and well sheltered with poplar windbreaks.

In the spring of 2002, we planted traditional ‘short cane’ Glen Ample on an area of 2 hectares. We planted into raised beds covered in black polythene at a spacing of 45cm between canes. The beds were spaced at a distance of 2.4m from bed centre to bed centre. The crop could be covered with 8 metre multi-bay tunnels (3 rows per tunnel). The site was split into two separate irrigation blocks.

Plantation Set Up

In 2003, both blocks were cropped normally, each producing a yield of 8 tonnes/ha. In the autumn of 2003, the blocks were managed differently. In the first block, the primocanes produced during the growing season were retained at a traditional density of 8 per metre of row with a view to maintaining a traditional annual cropping system. These were tied in to the support system for cropping normally in 2004.

In the second block, all of the primocanes that had developed during the 2003 season were retained and tied to the support system at a high density of 12-16 canes per metre of crop row. During the 2004 season, we removed all new spawn or primocanes as they developed using Croptex Steel and Wayfarer.

Yield Results in 2004

Given that both blocks are of an identical cropping area, In 2004, we assessed the development of fruiting laterals, and recorded yields.

Cropping Profile and Yields

As you can see from our figures, the increase in number of canes and removal of primocane competition in the biennial block gave rise to more than double the volume of fruit. We found that the increased yield came about through an increased number of laterals in the biennial plantation and an increase in berry size.

In addition, it is worth noting that we picked a higher percentage of class 1 fruit from the biennial plantation:

Biennial 96%

Traditional 87%

Picking Costs in 2004

The table is based on the actual picking averages for the 2004 season based on the minimum agricultural wage of £4.85 and £7.27 for overtime using a picking team of 40:

Traditional

Biennial

·        We discovered that the pickers could pick more quickly in the biennial block than they could in the traditional block.

·        In the biennial block, the pickers picked 6.06kg per hour in comparison to 4.21kg per hour in the traditional block.

·        Based on a squad of 40 pickers working for an 8 hour day, picking at a rate of 6.06kg per hour, a total of 1940kg was picked in a day. This cost us £1,552 to pick.

·        In contrast, picking the traditional block with the same number of pickers for 8 hours at a rate of 4.21kg per hour, we could only pick a total of 1347kg. To pick the same volume (1940kg) as we picked from the biennial block, required overtime working and a total cost of £2,658, some £718 more to pick the same quantity of fruit.

·        To prevent having to pay overtime to pick the same quantity of fruit in the traditional system, we would need 57 pickers to pick the 1,940kg. This however, still equates to an increase in picking costs of £350 per tonne and an increase in labour requirement of 18%.

·        In terms of productivity, we calculated that when picking the biennial block, we achieved an increase in productivity of 44%.     

Pruning and Cane Management

The table compares our calculated costs of pruning and managing canes on a traditional and a biennial system of production.

*Projected cost

Advantages Of Pruning A Biennial Plantation

·        In practice, we found that pruning a biennial plantation is more akin to a primocane plantation and can be carried out in winter, when there is less pressure on labour.

·        The pruning can be semi-mechanised and can be carried out by a less experienced team and therefore less supervision.  

Other Advantages of Biennial Cropping to Boxford Suffolk Farms

We are all under continuing pressure to protect all of our raspberry plantations using polythene-clad tunnels. However, given the exceptionally poor returns received for our fruit in 2004, very few of us are keen to purchase covers for raspberry crops.

In a biennial crop however, only half of our plantation needs to be covered each year resulting in reduced investment on polythene. Although the tunnels nee to be erected and dismantled each season, the potential changes to planning laws over tunnels could lead to us having to do this routinely anyway. There is also the potential to use the same tunnels on a later primocane fruiting variety, thus reducing the capital investment required on tunnels.

In contrast, with a traditional plantation, twice the investment is required to cover the crop, although once in position, the only costs incurred are those for erecting the polythene on an annual basis. A major disadvantage of covering traditional crops every year is that it can give rise to excessive primocane growth in hot seasons, leading to higher pruning costs.

The biennial system offers us improved spray penetration of both primocane growth and fruiting canes (as the two phases are grown separately). In addition, we find that we can manage our fertigation and nutrition more accurately as well as an opportunity to break pest and disease cycles.

Although history of biennial cropping suggests that plantations lose their vigour rather more quickly when grown in this way, leading to shorter plantation life, we are unconcerned about this. If we can consistently achieve the yield improvements and cost savings highlighted above, we would be prepared to lose longevity of the plantation.

Challenges for 2005  

Our challenge for next year is to design an improved system of support for the fruiting laterals and to achieve optimum vegetative growth and bud development in the primocane phase of growth. 

Conclusions (3 Points) 

·        In 2005 we plan to continue to grow raspberries on a biennial system. 

·        We would urge other farms to trial biennial cropping. 

·        Can we afford another season like 2004 in the raspberry industry?