AgronomyWaging War on Waste

Waging War on Waste


[deck]Why improving potato crop quality in the field could be the key to reducing waste.[/deck]

Waste is a reality for all potato operations. Just how much waste varies, and the degree of waste often differs from season to season. Canadian growers commonly view waste as potatoes unusable for fresh market, processing or dehydration because they do not meet minimum size, grade or quality standards. Potatoes disposed of due to low market value caused by overproduction—typically referred to as cull potatoes—are also considered waste.

Solanum, a potato processor in the United Kingdom, is taking a broader view on potato waste. According to a report posted to the British Potato Council website entitled War on Waste in the Potato Supply Chain, the company is planning to dramatically reduce waste in the supply chain by improving quality in the field. Inefficiencies and waste occur throughout the potato production and supply chain, but Solanum’s agronomy director maintains that the most important area to address regarding waste prevention is how the crop is grown and managed in the field.

Bruising is one of the leading contributors to potato crops failing at field level.
Bruising is one of the leading contributors to potato crops failing at field level.

In 2008, Solanum initiated a five-year project dubbed War on Waste in collaboration with a large supermarket chain. Its goal is to assess the level of waste produced in the potato supply chain and come up with practical solutions for reducing it.

According to the BPC report, the War on Waste project found that for every 1,000 tonnes of potatoes produced for a retail crop, just 583 tonnes eventually made it to the consumer. The project also determined that about half of these losses occurred directly on the farm. Six per cent of potatoes failed at field level before or soon after lifting began, due to size, quality or bruising problems. Defects removed during initial grading—including damaged, misshapen, scabbed and green tubers—resulted in a further 12 per cent loss, while storage waste accounted for five per cent. During the packing phase, size grading took out another two per cent while post-washing defects removed 22 per cent.

Causes of Waste

The War on Waste project team categorizes the key causes of potato waste as follows:

Field failure:

  • Unsuitable soils
  • Lack of irrigation
  • Pests and diseases

Gross defects:

  • Over/undersized tubers
  • Misshapen tubers
  • Green tubers
  • Mechanical damage

Storage waste:

  • Skin disease
  • Weight loss
  • Loss of skin brightness

Post-washing loss:

  • Greens
  • Mechanical damage
  • Skin disease

The project has an overall waste reduction target of 12 per cent. Central to this goal is an agronomic plan for tackling wastage in the field that focuses on three key areas—soil, seed and water.

The War on Waste team believes many potato defects are caused by soils, which may be inherently unsuitable, harbour pests or have poor moisture retentiveness. Quality soils typically save between 10 to 40 per cent on cultivation and input bills, while producing a 15 per cent improvement in packing out-turn.

Growers are urged to consider extending or following different crop rotation practices, introducing brassica or green manure crops. Better crop programming along with raising organic matter levels, will  help reduce waste.

Soil structure, as well as pest and disease pressure, should be examined before planting, while cropping history is another important consideration. Solanum is building a database of soil information across its grower group to keep track of how well crops are performing in each field.

Soil structure is crucial, and compaction is a key reason for poor crop consistency and loss of marketable yield, according to Solanum. Misshaped tubers are the main defect caused by poor soil structure, but scab risk is also increased.

The War on Waste team maintains seed should be integrated with ware programs to improve quality. In addition, tuber size distribution can be optimized through physiological and chronological aging. Solanum field staff members carry out detailed in-field examinations before a particular crop is lifted in order to highlight any potential problems which will need to be managed in-store.

Better use of water is another key aspect in preventing in-field damage and subsequent waste. The War on Waste team believes that fewer crops should be targeted in areas where irrigation is limited rather than risking wholesale rejection. Greater attention to irrigation scheduling is also important. The team stresses that rain guns, for example, are quite variable and should be phased out—replacing them with drip irrigation typically increases yields by five to 10 per cent.

Actions can also be taken during harvest to prevent waste potatoes, such as ridge rolling to reduce greening. Rapid store loading and cooling can also minimize potential damage.

Preventative agronomic measures like these will help, but in reality, potato growers will still have to deal with some potato waste or cull potatoes every season.

Cull Potatoes

Cull potatoes may accumulate any time during the year, but several periods are especially critical. At planting, potato waste material may accumulate when seed pieces or tubers are discarded due to size (slivers) or disease problems. At harvest, potatoes that do not make grade due to size, disease, or defects are sorted out and discarded prior to moving the crop into storage. Any time potatoes are removed from storage, those that are diseased, damaged, out of grade, or in oversupply are once again culled and discarded.

Allowing cull potatoes to accumulate without proper disposal practices can have undesirable consequences, which include the following:
• cull potatoes can be a source of late blight inoculum, leaf roll virus and other diseases that can spread to a grower’s own fields and neighbouring fields;
• rotting cull potatoes can produce offensive odours and attract undesirable insect pests; and
• decomposing potato piles provide a point source for nutrient leaching to ground and surface waters.

Waste Control Guidelines

In the document entitled Agricultural Waste Management, the P.E.I. government and Environment Canada provide a number of practical guidelines for growers to deal with potato waste management.  The guidelines cover several areas, including value-added processing, animal feed, composting and land spread.

Dehydration of cull and other waste potatoes is a very effective and efficient method of turning a waste material into a value-added product. This process dehydrates the raw potato into dry material such as potato flakes and granules which can then be used to create new potato and other food products.

Cull potatoes and processing vegetable wastes are an excellent energy source suitable for finishing rations in beef feedlots. Cull potatoes and processing plant wastes can be ensilaged and used as animal feed. For example, potato culls and processing plant wastes can be ensilaged by placing them in layers in silos with well-wilted hay crop silage at a 2:1 ratio. A mixture of three parts potato waste to one part chopped hay can also be ensilaged.

The composting of cull potatoes is an environmentally acceptable method of disposal. To obtain the correct amounts of carbon and nitrogen, potatoes must be mixed with other materials for effective composting. Common materials that are mixed with potatoes include sawdust, straw and solid manure.

Spreading cull potatoes over frozen ground during the winter is another effective disposal method, but care must be taken to evenly distribute the potatoes and not dump them in piles to ensure freezing. Maximum application rates should not be more than 10 tonnes per acre. In addition, growers should avoid fields that will be planted later with potatoes, since cull potatoes can introduce nematodes, weed seeds and other soil-borne diseases to the field.

The accumulation of cull potatoes occurs year-round on farms, as well as at fresh pack and processing operations. Managing cull potatoes and associated dirt and plant debris needs to be incorporated into the normal management routines of growers, fresh packers, and processors.

It’s apparent that some potato waste is unavoidable, but  there are ways to limit the impact on yields. In the fight against waste, a grower’s best defence is knowledge about the proper preventative agronomic measures.

Lukie Pieterse is a consultant and writer with decades of experience in the potato sector, from growing his own drip-irrigated potatoes to writing international potato news. Tuber Talk is an insider’s take on the issues impacting the industry.

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