Investing in a lower carbon footprint from growing through to storage – British Potato Review

Andrew Goodinson, Agronomist, and Potato Specialist at Hutchinsons, offers advice and insights to help growers ensure the best results from their potato crops. Based in Herefordshire, Andrew has been working for Hutchinsons for 17 years and looks after 8000 ha of farmland, including the Welsh borders, south Shropshire and Worcester. Most of the potato crops he looks after are destined for the crisping or processing markets.

Every business has a part to play in reducing carbon emissions, but potatoes are resource intensive therefore meeting carbon targets is particularly challenging for them.

Nevertheless, there are several steps that can be taken that can help reduce carbon footprint which will not impact on yields, says Andrew. Overall carbon footprint should be measured by crop tonnage rather than area, as seed or salad potatoes typically yield 30t/ha, whilst ware can produce 60t/ha, he said.

“We need to establish just one industry- accepted method to look at and measure how much carbon goes into producing potato crops. A good place to start is by assessing on- farm activities necessary to growing potatoes and exploring ways to reduce them.”

These include machinery selection, cultivations, fuel, fertiliser, irrigation pesticide application as well as storage.

One of Andrew’s principal pieces of advice is to avoid overworking soils. In many cases, the depth of cultivations and frequency of bed tilling can be reduced, in some cases eliminating the de-stoning operation, making important savings, he said.

Over cultivating soils increases wearing of parts, fuel costs, reduces soil organic matter and increases carbon loss.

“We also need to look at soil structure, because it affects nutrient availability and uptake. Any remedial cultivations using machinery contribute to the carbon footprint, so activities need thinking through, to determine how much is necessary.

“There are benefits from shallower working in the different soil types, yet many growers still cultivate soils deeper than necessary. Reducing cultivation depth from 43cm to 35cm can give a 25% reduction in fuel usage with no impact on yield, so it provides a good start to reducing carbon footprint, particularly as it reduces energy use without taking a toll on yield.”

However, growers need to remain flexible with their strategies he cautioned, noting there are times when weather conditions dictate strategies.

Fertiliser has a high carbon footprint, not only in its manufacture but also on-farm application, so keeping chemical fertiliser inputs to a minimum is important, says Andrew.

“We need to be enhancing N-use efficiency, and solid N is the most carbon-hungry, so perhaps we need to look at using more liquid fertilisers, manures and cover crops to boost nutrition.”

Liquid fertilisers are efficient and can be placed into the soil, he adds.

“New nitrogen capture products are being trialled currently, with interesting results. The Omnia Farm Management System measures carbon content using the ‘Gold Soil’ test which details exactly what is going on in the soil, including ratios and balances of nutrients, so nutrition decisions can be tailored according to need.

“During the growing season, regular sap or tissue testing is also key to understanding plant efficiency and any deficits can be dealt with. It is important to take samples early in the morning across a range of potato crops to see if there is a trend rather than focusing on any imbalance in one field.”

Andrew does not recommend top-dressing at tuber initiation with ammonium nitrate, noting that it tends to end up in the ridges. Instead, an application of methylated urea releases nitrogen over a period of time, which is more efficient than solid nitrogen, and can be mixed with a blight spray therefore reducing a pass through the crop. “Sometimes you have to balance the crop needs with the carbon footprint. For example, a bio-stimulant will always add benefit but also add to the carbon tally. However, they make the plant more efficient, so there is a pay-off.”

When it comes to irrigation, for which the water itself can have a carbon footprint, there can also be an associated footprint from the fuel used by the machinery or pump, he said.

“Some growers still prefer to use a rain-gun over trickle irrigation, and both use similar machinery to transport water to the field, but the efficiency of these systems varies. If you are running a generator or pump for a gun, energy requirement for the fuel has to be included, and much of that water is likely to evaporate, run off or miss the target before it gets to the crop, reducing efficiency.”

Other on-farm practices, such as desiccating twice compared with flail and spray, because of their fuel use, can also impact on the carbon footprint.

“Reducing the carbon footprint of potatoes will be an ongoing challenge with different systems and supply chains having different targets and measures. However, resource efficiency is central – making the most of the inputs we apply by maximising best practices, product choice and timings.

“We can focus on building resilience into growing potatoes, which will always be beneficial to aid building yield whilst reducing inputs where possible.”

Cover crops are often thought of as a silver bullet thanks to their ability to improve soil conditions and build fertility, playing an important role in the battle to keep inputs to a minimum without compromising quality or yield.

As such, they are integral to the carbon footprint of growing potatoes, says Andrew. Decisions on cover crops should take into account the grower’s priorities, which may be to provide wild bird seed, biofumigant activity, as well as soil structure, so he advises against using the same strategy on all the fields.

“Growing cover crops helps restructure soil as well as contributing to building soil organic matter (SOM). As such, they minimise the carbon extracted from the soil when growing potatoes, although this is a very slow process. Moreover, if you have sandy soils, they have low SOM and low carbon, making it difficult to get them to hold onto nutrients they also have lower water retention as they drain faster.”

Other methods for improving SOM include incorporating farmyard manures, chopping straw after a cereal crop, or adding grass leys into the rotation can also contribute to improved soil structure.

“Ideally, cover crops should be planted the year before potatoes, and should be in the soil by mid-September so that they have time to accumulate a good root structure and plenty of biomass before winter sets in.”

Benefits from such activities can include improving soil structure from stabilising aggregates. Soils that have been well-maintained for more than five years need fewer cultivations and crops establish more quickly.

“Of course, there are times when compaction occurs, and if you think that you need to sub-soil, first take a spade and dig a hole check how deep the compaction is. Subsoiling when there is no real need can create more damage to the soil than any potential benefits.”

Choice of cover crop depends on the outcomes the grower is seeking, and he recommends looking at the different components of several mixes.

“If you are looking for something that is deep rooting to improve the soil structure, then a brassica such as oil radish, or some mustards, can be very useful. However, if you opt for a brassica and already have oilseed rape in the rotation, then you need to be aware of the risks of club root”

He points out that some cover crop species are not winter hardy, so should be planted early enough for them to have developed good root systems which will remain in the ground during the cold weather.

Nutrient retention is another important benefit from cover crops, and he notes that phacelia, buckwheat and linseed can work well as they provide a mix of forbs, cereals and legumes.

“Forbs, which are herbaceous plants not related to grasses, have large root structures and can be particularly good at holding nutrients. Above-ground biomass can also be useful in alleviating the weight of heavy winter rainfall on the soil, and improved soil structure helps improve infiltration.

“Nonetheless, when choosing cover crops, a mix is better, particularly when the species in a mix complement each other, as this can help ensure against weather extremes because different species will thrive in different weather conditions.”

Moreover, mixes have the reputation of being more effective weed suppressants than a single species and having legumes in the mix with grasses help compensate for the decreases in nitrogen availability for the following crop.

“Planting more than one species can help fulfil multiple goals that producers often want the cover crop to achieve, but there are trade-offs.”

Some growers report increased slug numbers, while others have observed higher wireworm counts after growing cover crops.

“These need to be balanced against the bigger picture, and appropriate measures taken to control slugs and wireworm may need to be taken.”

Andrew goes on to talk about biofumigants and trap crops, explaining that biofumigants are topped and macerated and the biomass incorporated into the soil, while trap crops stimulate the pest to hatch but it is not then. able to complete its lifecycle.

“Trap crops for PCN are wild solanaceous species, such as black nightshade, which can stimulate PCN hatching through the release of root exudates, similar to those produced by potatoes. While PCN are able to invade the roots of trap crops, they cannot establish feeding sites and consequently their development ceases.”

PCN trap crops include Solanum sisymbriifolium, Solanum nigrum (black nightshade), and Kenyan Broad-Leaf, also known as Garden Huckleberry (Solanum melanocerasum).

“Biofumigants may impact on any number of pests and diseases, whereas trap crops are quite specific for the type of pest, such as a member of the solanum family for PCN or radish being used for cyst nematodes in beets.”

Andrew explained that when growing biofumigants, the aim is to get as much bulk as possible, then top it to a height of about 20cm. Kick-starting the reaction to release the gases is challenging and is why the crops need to have a lush physiology, he said. This is because lush crops are easier break down with maceration implements and so have a better chance of liberating biofumigant volatiles.

Maceration techniques such as hammer- flail topping, or the use of other flat blunt tines, also aid volatile production by bruising tissues as well as chopping, leading to greater cellular destruction.

“The more damage you can achieve, the more effective the release of isothiocyanates (ITCs) and other biocidal products. The ideal situation is to incorporate biofumigants which have high glucosinolate concentrations and high biomass to generate a high potential for biofumigation, whilst having a lower dry-matter/lignin content to avoid problems with accessibility to the glucosinolate and myrosin cells.”

He pointed out that trap crops and biofumigants need to be planted earlier than cover crops, which can make it more difficult to fit them into the rotation as it means losing a period of production.

“If you opt for a trap crop, think where it might best fit into your rotation, it might be worth considering whether it might fit in better after an early harvested crop, such as forage rye, then the trap crop, followed a late- sown winter cereal”

Now is a good time to check storage facilities, clean them and make any necessary repairs to ensure they provide the best possible energy performance, advised Andrew. “Last year’s conditions at harvest are likely to have left silver scurf, black dot and fusarium spores in the store, so vacuuming, washing and disinfecting them will help keep this year’s crop in the best possible condition in store.”

Potato boxes will normally have been stored outside and therefore subjected to UV light, which will have killed the spores. “Any old or dirty fridges and fans will impact on storage efficiency, so they need to be checked and cleaned. Inspect the store thoroughly for any air leaks, sealing them and optimising insulation will make a difference to your energy use and carbon footprint”

Last year, store loading was protracted, which meant that in many cases the doors could not be closed promptly enough, affecting temperatures and drying, so for this year he suggests fitting screens.

Andrew also reminds growers that they should ensure that boxes are stacked in a way that leaves the alleys sufficiently wide to encourage the airflow to go through the boxes, and that stacks are the same height.

“Depending on the age and condition of the potato store, adopting these practices could significantly reduce energy use and your carbon footprint.”