High Yields, High Hopes

This story has its origins in a comment made someone calling him/her-self Zeke on WUWT.

Benign, inexpensive and effective chemicals were largely developed by the Greatest Generation. The chemical inputs they developed allow us to grow 5 times as much food on the same land.

The replacements mandated by the environmentalists are genuinely toxic, expensive, and ineffective. The tainting of all of our products and innovations through top-down behind-the-scenes environmentalist NGOs etc. is indeed toxic.

The Git had during an earlier exchange estimated he would be harvesting potatoes yielding ~120 tonne/hectare which just happens to be The Git’s long-term average. Now the potato haulms are all but dead, a more careful assessment indicates a yield of 187 tonnes per hectare beating out The Git’s old record of 155 tonnes per hectare. Much to his surprise, The Git discovered that the world record is, according to Indo-Asian News Service | February 18, 2013, 108.8 tonnes per hectare. Whoda thunkit? The average yield for The Git’s part of the world (Tasmania) is 54 tonnes per hectare, well short of Zeke’s claimed “five times” increase using artificial fertilisers.


This 12 litre bucket holds the product of a single potato plant.


This bowl holds a small number of immature tubers that likely wouldn’t have grown much more in size due to the advanced maturity of the haulms. They would have made fine “seed”.

As for “toxic” and “ineffective”, The Git’s inputs are:

  • A 25–50 mm layer compost hoed in to a depth of ~ 100 mm (4”)
  • A tight handful of kelp meal per metre of row (39”)
  • A tight handful of sulphate of potash (K2SO4) per metre of row (39”)
  • When ridging was complete, a layer of wheat straw ~50–75 mm (2–3”) thick was place on the sides of the ridges
  • Dilute fish emulsion (Power Feed) mixed with seaweed emulsion (Seasol) at the manufacturer’s recommended rate applied fortnightly.

The potatoes were grown in 1 m (39”) wide and 8.5 metre (28 feet) long boxed in beds spaced 330 mm (12”) apart. The beds have 500 mm (20”) wide paths between using plastic weed-mat covered with hardwood sawdust for weed suppression. Including the path area in the per hectare calculation reduces the yield to 112.5 tonnes. The potato seed pieces (Tasmanian Pinkeye) were left intact and planted at a depth of 130 mm (5”). The rows were hilled twice bringing the centre of the ridge ~ 150 mm (6”) higher than the original soil surface. The sides of the ridges were then covered with a thick layer of wheat straw. The straw serves several purposes: it reduces water loss from the soil surface, it prevents the birds from breaking down the ridges while scratching for earthworms, it suppresses weeds and it feeds the soil as it breaks down.

This differs somewhat from the method used for the old record, since that was when The Git was growing commercially. The potatoes were grown using conventional row spacing of 750 mm (30”) and 380 mm (15”) between plants. The variety grown was Tasman (yield similar to Kennebec). Weekly maintenance of the ridges due to bird damage was needed until the potato haulms made that impossible. Losses due to greening were somewhat higher than the current method used in my retirement.


This image shows the potato crop mid-way through the growing season.

For interest’s sake, here are the soil test results from back then comparing the grass paddock with the 0.4 hectare (1 acre) market garden. The paddock was used for grazing sheep.

Element                                      Paddock       Market Garden
Calcium                                       1532 ppm      3059 ppm
Magnesium                                100 ppm        469 ppm
Potassium                                   88 ppm          268 ppm
Sodium                                        33 ppm          56 ppm
Iron                                              34.7 ppm       12.5 ppm
Manganese                                0.3 ppm         0.5 ppm
Copper                                        29 ppm          0.8 ppm
Zinc                                              3.6 ppm         18.5 ppm
Boron                                          0.07 ppm       0.14 ppm
Nitrate                                        2 ppm            63 ppm
Phosphorus                                173 ppm        463 ppm
Sulphur                                        1 ppm            10 ppm
Chloride                                      14 ppm          17 ppm
Organic matter                          8%                  14%
pH                                                5.8                  5.9
Cation Exchange Capacity      8.86                20.14

The current kitchen garden soil also differs from the original soil in that approximately 25 mm (1”) of sand was applied and mixed into the top 100 mm (4”) about a decade ago. The original soil was 50% silt and 50% clay.

While conventional potato production relies heavily on herbicides, insecticides and fungicides of varying toxicity, The Git has only ever needed to apply a fungicide to his potatoes once in 30 years of gardening (for Irish blight). He used an “organically approved” copper spray that he uses for black spot control on his apple trees. The only insect pest of note is the potato fly and that only ever affects exposed potatoes and they of course are green and unmarketable anyway. Keeping the tubers well covered prevents greening and potato fly. Weed control is accomplished by the cultivation hilling requires and in latter days the wheat straw mulch.

Aphids are a potential threat as they not only reduce the vigour of the plants they suck the sap from; they also transfer bacterial, fungal and viral diseases between plants. During the growing season here, there is an abundance of ladybirds whose larvae eat aphids, as do the small birds such as fairy wrens and diamond birds. The Git also grows calendulas (English marigolds) and nasturtiums around the edge of the garden and these provide a nectar source for insects that also predate on aphids.

The Git is somewhat perplexed by his yields since the theoretical maximum according to ever so many experts is 90 tonnes per hectare. He even met a conventional grower who achieved yields greater than 90 tonnes in a trial he conducted some twenty years ago. However, that grower concluded that the extra costs attendant on achieving the higher yield were greater than any pecuniary gain. So, the question arises as to the economic viability of The Git’s methods. Thirty years ago, when he was young and fit, he made many cubic metres of compost by hand. These days, in his retirement, he is mainly concerned with reducing the labour component of vegetable growing due to chronic arthritis. Back in the 1980s he made a modest income supplemented by being paid to labour in his neighbour’s orchards. It’s not something you would do because of the income; you do it because you love the lifestyle. It’s highly likely that The Git could reduce his labour by adopting artificial fertilisers, synthetic pesticides, fungicides and herbicides, but that would mean a greatly reduced yield and worse, a great deterioration in flavour. And the latter is something no Pompous Git worth his salt will ever countenance!

While Gurgling/Gaggling/Goggling/Giggling [delete whichever is inapplicable] around the Interwebs, The Git came across some potato growers trialling a method of increasing potato yields that he had contemplated attempting sometime in his retirement. The world record for a single potato plant was 168 kg according to The Idaho Potato Museum, having been achieved in 1974 by Englishman, Eric Jenkins. The Git suspected that this was done by gradually building a tower for the potato plant to grow up in a manner similar to the description here. Sinfonian’s experience and that of many others appears to be that it can’t be done. It seems to The Git that you need to achieve two contradictory things. First, you only leave a small growing plant tip by assiduously topping up the soil. But, and this is a big but, you need to maximise the area of leaves photosynthesising carbon “pollution” and water into the starches that the potato tubers’ dry matter largely consist of.

What is needed is a sufficiently long growing season for fully grown haulms to continue increasing the size of the tubers that have set. One blog had a comment that tubers do not set on side branches of the haulm and that was the reason for the failure, but here’s a photograph of The Git’s Tasmanian Pinkeyes happily setting tubers above the soil surface on side branches!


Of course the watering would need to be carefully controlled and considered. Watering spuds prior to and at flowering increases the number of tubers. Watering after petal-fall only increases the size of the existing tubers.

Then inspiration struck. What Jenkins probably did was choose a variety setting many shoots that were encouraged to, initially at least, grow sideways, not vertically. Thus the plant would have a much larger leaf area than the usual crowded potato plant. If, like the Pinkeye, it set tubers liberally along the haulms, judicious covering of the lower parts of the haulms would encourage the tubers that remained dwarfed in the photograph above to grow to full size.

Further, Jenkins was unlikely to have been aware of the effect of carbon “pollution” on crop growth. Organic market gardeners in India have been putting curtains of greenhouse film around the edges of their garden beds to concentrate the carbon “pollution” generated by the decomposing organic matter in the soil where it’s needed — in contact with the plants’ leaves rather than blowing away. A further increase in much-needed carbon “pollution” could be achieved by piping the gasses leaving a compost heap to where they can best be utilised — in the garden. This is a concept The Git remembers discussing with Bill Mollison these many long years ago while munching on Vogel bread sandwiches and discussing the downfall of Western civilisation. But back then carbon dioxide wasn’t “carbon pollution”, it was plant food.

A Footnote

Pinkeyes aren’t usually grown as a maincrop potato variety; they are very much sought after as an early. Back in the 1980s, The Git discovered that harvesting Pinkeyes in late winter, a 4–6 weeks before the first earlies were hitting the market, that he could sell Pinkeyes for three times the price compared to harvesting them as earlies in summer. The Git’s heavy soil and late frosts prevented bringing potatoes on any earlier. Leaving the Pinkeyes to mature, the yield per plant was at least three times that when harvesting the immature spuds.

The Git also sold a great deal of garlic fresh for a significant premium in the month before the cured product came to market. He was competing with tired old imports that were not only dehydrated, but also sprouting. Unlike the fresh garlic, there was no aroma. Sadly, garlic competed with leeks in the garden space and they were also one of the most remunerative crops to grow.

Successful market gardening is as much about marketing as it is about being a competent grower of vegetables.


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