If you are a potato plant then a sweltering summer can be too much of a good thing. New studies show a clear correlation between increasing temperature and decreasing yield.
It might be true that climate change can heat up the Danish summer and transform Denmark into the tourist paradise of the future. However, if you prefer a steady supply of Danish-grown potatoes on your dinner table, you should be asking for cool summers.
Warming of the Danish summer weather is not exactly good news for potato farmers. New studies indicate that the optimal temperature in the potato growing season is around 15° C and that for each 1° C increase in temperature the dry matter yield falls by 10 percent. Temperature is even more important than the level of nitrogen fertilisation.
These results were found by postdoc Zhenjiang Zhou from the Department of Agroecology at Aarhus University in the course of his PhD studies, which included crunching data from three years of field experiments. One of the things that he investigated was the effect of temperature and nitrogen levels on potato dry matter production and the underlying mechanisms affecting it.
Potatoes prefer cool
He found that the temperature is the most important parameter for potato growth but that the amount of added nitrogen also has a significant impact on yield in that increased nitrogen fertilisation increased the potatoes' production of dry matter.
- My own studies based on the three years of field experiments on soil classified as JB1 (sand) showed that the economically optimal application of nitrogen was 183 kg N per ha. If they are fertilized with less than 120 kg N per ha then nitrogen will not be the most important limiting factor for dry matter production; instead, it would be the temperature, says Zhenjiang Zhou.
He was able to measure the potatoes' nitrogen requirement with a precision all the way down to 10 kg nitrogen per ha with the aid of remote sensing and simulation models developed at Aarhus University. Remote sensing means that the potatoes could be measured from a distance without the need for physical contact with them. This data could be used in the simulation models that could thus contribute to the understanding of how potatoes react to various levels of irrigation with water containing nitrogen (N fertigation).
- The studies showed that remote sensing and simulation models can be used as tools to estimate the nitrogen status of potatoes and thus set up guidelines for nitrogen fertilisation. This means that the farmer can apply nitrogen to his potatoes throughout the season in a more flexible and intelligent way thereby saving money, increasing yield and protecting the environment, says Zhenjiang Zhou.
Big water savings
Zhenjiang Zhou also compared two different types of irrigation - gun and drip irrigation - and the effect of irrigation strategies and N fertigation on potato growth, yield and nitrogen utilisation.
The results showed that even allowing the potatoes to get thirsty from time to time did not reduce yield - on the contrary, this strategy improved irrigation efficiency significantly.
- With the amount of rain falling in Denmark this means that significant water savings can be made, says Zhenjiang Zhou.