A place for potatoes in regenerative farming
There is often debate about how potatoes can fit into regenerative farming systems, but one grower is showing how the crop’s environmental credentials can be improved ...
As some landlords turn away from intensively cultivated crops, there is a risk that greater focus on no-till could further jeopardise the UK’s potato area.
John Bubb, who grows combinable crops, potatoes and flowers in east Shropshire, has long been focused on his farm’s soil health, but more recently he has been honing in on the farm’s potato practices with the help of a team of experts, and has seen significant improvements to both soil health and the bottom line.
As a first step, introducing cover crops ahead of potatoes and spring-sown flowers was a no-brainer on Mr Bubb’s light sandy soils to help build organic matter reserves.
The mix, grown ahead of the potato crop, consists of linseed, buckwheat, phacelia, vetch, clover and oats.
“We are trying to grow as diverse a mix as possible with as many species as possible, while still being affordable,” explains Mr Bubb’s agronomist, Ed Brown, who is head of agroecology for Hutchinsons.
They decided to move away from brassica species after various issues, most notably regrowth in the potato crop particularly when grazed, as well as slug issues.
And although spring oats have been excellent for soil structure, they are not included in the mix ahead of flowers as they tend to have a negative allelopathic effect.
With a catch crop also grown between oilseed rape (OSR) and wheat, a huge part of growing a potato crop regeneratively is what happens in the rest of the rotation, says Mr Brown.
This means taking a whole-farm approach to cultivations. Since the introduction of cover crops, soils have become more friable, so potato cultivation passes and depth can be reduced, says Mr Bubb.
“In the potatoes, we have been able to eliminate some passes, and we try not to plough, using a DTX machine instead. We have reduced the depth of the destoner, which has share tines on it to get rid of any pan, and we are also doing much less bed tilling.
“We have a lot of stones where we are, so stones are an issue and there is concern about bruising at harvest. We can get away without destoning some fields but on the whole, destoners still have a place in reducing bruising so there is work to be done there.”
All OSR and flowers are strip-tilled, and Mr Bubb says that across the whole farm, there is enough machinery to be able to do the right pass on the right day, in the right conditions.
While on the whole, pesticide use has been markedly reduced across the whole rotation, cutting down on blight sprays is a key challenge yet to be addressed.
Mr Brown says: “Getting away from routine prophylactic blight sprays is quite difficult, because when it goes wrong, it can go spectacularly wrong.
“We are trying to put in the groundwork now to build healthy soils and plants, and manage nutrition to make plants much more resilient to pathogens such as blight. Before too long we will start to pullback where we can.”
However, Mr Bubb has now man-aged to reduce nematicide use from 90 per cent of the potato area previously treated to just 8 per cent, which he puts down to rigorous soil testing, growing resistant varieties and keeping a wider rotation.
Mr Brown says: “For me, potato cyst nematode (PCN) is a symptom of an unbalanced soil and one that is lacking in diversity of the soil food web.
“If you are repeatedly damaging soils and killing off beneficial elements, then putting potatoes in on a regular basis, it is no surprise PCN has a chance to thrive because you are removing all the things that would naturally predate on that specific crop pest. Try to rebalance the soil food web so PCN is a very small part of it and never has the chance to thrive.”
Key to growing more resilient crops that are better able to cope with pest and disease has been to give the farm’s nutrition programme a complete rehaul with the help of Ian Robertson, Hutchinsons head of soils.
Mr Robertson says: “Every soil has a deep freeze full of loads of complex nutrients. First you need to test the soil to measure what is there, then look at what can be done in the rotation to cycle those nutrients back to the crop. A key part of this is all about management practices.”
In Mr Bubb’s soil, testing revealed 1,228kg of total phosphorus, but only 85kg was cycling.
“By using cover crops, fewer cultivations and biological inoculants, we are now getting more of that to cycle,” Mr Robertson explains.
“The best way to reduce chemical disturbance is to reduce fertiliser use and allow the soil to become more native, which will improve nutrient cycling.”
The addition of cover crops is improving nitrogen capture in the soil profile, and Mr Bubb now applies a carbon source alongside nitrogen to balance the carbon:nitrogen ratio and improve nitrogen use efficiency.
Crops are monitored throughout the growing season using SAP analysis to ensure the nutrition programme delivers everything it needs.
On the back of soil testing, the team has reduced artificial nitrogen from 210kg/ha to 180kg/ha; phosphorus from 80kg/ha to zero; and potassium from 330kg/ha to 154kg/ha.
Not wanting to ‘take their feet off the gas’ completely, PC25, a phosphate-solubilising bacterium is still being applied to ensure enough is available to the crop, but Mr Brown is hopeful they will be able to move away from this too.
Mr Robertson says: “There is plenty of phosphate in the soil to grow the crop, and we are now only applying potassium to meet crop demand. Potassium was being over-fed, which was having a negative effect on soil structure, collapsing the soil.
“Reducing the amount of potash and only feeding the crop requirement rather than offtake has had another effect on soil structure. We have reduced nitrogen to the lowest level we thought possible, but we may go lower again.”
At the end of last season, taking this tailored approach to crop nutrition resulted in a whopping £345/hectare difference in the bottom line.
In the hope of further tapping into organic nitrogen, Mr Bubb is trialling wheat grown in 50cm rows, and in May/June, establishing a clover living mulch which he hopes will survive within the rotation for five years until the next potato crop is grown.
Mr Bubb says: “The idea is to help with plant diversity, provide nitrogen to following crops, provide green cover to soil and act as a weed suppressant. Eventually, if we can get it working, we are looking at inter-row mowing to manage it in the spring and release nitrogen into the neighbouring plant, as well as trying some with DeCyst [trap crops] amongst the clover to help with PCN.”
Overall, these management changes have made the crop more resilient and profitable, with no noticeable impact on yield.
The increase in organic matter has also helped with water retention and reduced the amount and frequency of irrigation requirements.
Mr Brown says: “Now we are in this process of less tillage, more cover crops and residues, we are seeing physical organic matter in the ridge rather than just sand, which can dry out very quickly or cap so water runs off.
“When you get your head around the principles of regenerative agriculture, it is difficult to see how potatoes fit in.
“But we see it very much as three steps forward and only two steps back, which means over time you are still making progress with soil health.
“Potatoes are a really important home-grown food source, and John is on a soil type suited to growing potatoes, therefore we should be growing them, but we have a responsibility to do it better and have less of an impact.”
- Based five miles from Harper Adams University in Shropshire
- Sandy loam soil
- 160 hectares of potatoes grown one in six years
- Other crops include wheat, oilseed rape and flowers for confetti
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