Carbon dioxide THE WORLD OF C arbon dioxide is a molecule that consists of one atom of carbon (C) and two atoms of oxygen (O), hence CO2. CO2 mixed with water under pressure produces the prickly soda experience and plants take it up from the air, use water taken up from the soil and with energy from the sun make sugars in the green parts of the plant: photosynthesis. This invisible gas also acts as a greenhouse gas: more of it stores more heat in the air as less solar radiation is bounced back to space. Without CO2 it would be much colder on earth. All in all a very useful substance. This is my third column about carbon dioxide. Two years ago I dedicated one to the effects of CO2 induced climate change such as higher temperatures, especially inland and more erratic rainfall with more dry spells and more intense showers. So even with the same amount of rainfall more irrigation will be needed as part of the water would run off or drain to the subsoil. More heat waves could affect the quality as secondary growth and reducing sugars affect fry colour. When investing in potato such effects should be taken into account I wrote. Last year a column on the Cool Farm Tool – Potato: a computer program for farmers to calculate how many kg of CO2 emission is associated with the production of one ton of potatoes. This may vary between say seventy – where yields are high, manure is used and rain is abundant - and two hundred kg where yields are low, much nitrogen fertiliser is used and irrigation water has to be pumped from great depths. In 1960 the concentration of carbon dioxide in the air was 315 parts per million (ppm) or 0.0315 % of the air. The figure shows the measurements at Hawai, in summer it is lower than in winter because plants use it in summer. Presently the concentration is 315 ppm and by 2050 it will be over 550 ppm, double as much as the air contained before the beginning of POTATO R ESEARCH the industrial revolution that started in the United Kingdom with the invention of the steam engine by James Watt around 1770. Researchers at Wageningen University in the mid nineties grew potato plants at ambient – 350 ppm at the time – and double that concentration of 700 ppm in separated compartments of a green house. They also planted potatoes outside in so called open top chambers either or not with CO2 enriched atmosphere. On average a yield increase of 38 % was found with later maturing varieties benefitting most. A few years later two European Union funded networks, one called CHIP: Changing Climate Impact on Potato Yield and Quality, across Europe recorded yield increases for the 2050 scenario of 550 ppm between 29 and 54 %. This was followed by a number of trials where both ambient CO2 and O3 (ozone) concentrations were increased. Ozone has a negative effect on crop growth and is expected to move up from the 2000 concentration of 50 parts per billion (ppb) to 60 ppb. Here it was found that the higher ozone levels reduced the positive effect of CO2. Dr Keith Jaggard and his colleagues in the UK last year reviewed the scientific literature on CO2 and O3 effects and concluded that the 2050 CO2 level of 550 ppm potato yields will be 36 % higher due to CO2 but reduced by 7.5 % due to increased ozone resulting in a 28.5 % yield increase. Rice and wheat benefited only 6 % and tropical grasses such as maize and sugar cane will lose yield up to seven percent as they do not benefit from more carbon dioxide in the air. This is good news for the potato and there is more. The carbon dioxide in the air enters the leaves through small entrances – stomata – that at elevated CO2 close a bit as there is enough CO2 in the leaf interior for photosynthesis. Hence less water is transpired through the stomata so the crop needs less water. The potato crop will use 11 % less water with 28.5 % higher yields. With 2 degrees higher temperatures the frost free period in Europe is extended with 3 weeks. Model calculations show that a 50 t per hectare crop will then yield 60 t, add to this 28.5 %, another 17 t and ordinary crops that now yield 50 t/ha within 40 years may yield 77 t. Not all things related to climate change seem threatening. ● Anton Haverkort anton.haverkort@wur.nl Potato World 2012 • number 1 29 Pagina 28
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