Here is some science for the home gardener looking to maximise their potato yield!
A short article published in the 2011 proceedings a conference entitled “New findings in organic farming research and their possible use of Central and Eastern Europe” compared soil water availability, soil temperature and tuber yield of potatoes grown with either a chopped grass mulch, a black textile mat and a control group with no mulch.
The article has been hanging around here for a while with thoughts of replicating it ourselves. There are some issues with the paper; being a conference paper it isn’t peer reviewed, it contains very little raw data, the methods aren’t described particularly well and it is possible that the experiment could have been designed in a way to control for some unaccounted for variables.
What the researchers did was plant potatoes at two sites in the Czech Republic to study for two years. At each site 4 replicates of the experimental and control groups were planted. One group was treated with a 25mm thick layer of chopped grass 14 days after planting, one group was planted in pre-cut holes in a black textile mat that had been placed over ridges dug into the plot, and the control group had no mulch added.
Over the course of two years the researchers measured soil temperature and soil water potential in each plot. At the end of the experiment they cultivated the potatoes and measured their size and total yield.
They found that soil temperature was higher under the black mulch than in the control. Strangely, they do not mention the soil temperature under chopped grass. Soil water potential was highest under chopped grass, with the control variant having slightly less water potential than black mulch.
Finally, the researchers found that under the chopped grass mulch the number of larger tubers was greater than in the other two groups, the total weight of smaller tubers were reduced and the total yield was significantly more.
Figure from article: increase in number of larger tubers and total yield in potatoes grown under grass mulch (GM) compared to black textile mulch and control conditions.
The discussion section of the paper points to an article which found that potato doesn’t grow as well under high soil temperature and low soil moisture, and the results of the study correspond to this earlier research.
As indicated above, there are some issues with the paper (which is part of the reason the thought of replicating the study and perhaps bettering it has crossed our minds). This type of study will usually include significantly more detail about the plots where the experiment was carried out. Details such as how the soil was treated over the past number of years, any differences in previous treatment or soil preparation methods are noted, graphical representation of how the plot was divided and how the selection of which treatment is to be applied to which plot was randomised are a common part of the methods and materials. The manufacturer and product details of the type of black textile used would be a detail that would enhance the ability to replicate the study. The lack of raw data on the number of potatoes cultivated at each size and how the statistical analysis was performed also cast some doubt on the reliability of the conclusions.
The result of the study is that, although it has some faults, it does give some direction to home gardeners who may be wondering whether to apply a mulch and, if so, what type of mulch to increase their own potato growing efforts.