"Zoom-in" – January on the wheat field at the Open-Air Laboratory Lauresham (Germany)

In the overview recently published on this website, the aim was to illustrate the different weather conditions in January in the growing regions. Today, the aim is to "zoom in" again and take a closer look at the current datasets for the Open-Air Laboratory.

The wheat cultivation for the Year On The Field project is integrated into a long-term experimental archaeological project on early medieval agriculture. Thus, one of the institution's aspirations is not only to document every single step of work on the arable land, but also to carry out draught measurements and soil analysis as well as to collect climate data. The growth of the cereals is also closely observed. There is consequently a large database to draw on for further research. Let's start with the temperatures:

Fig. 1 Temperature trend in January (red maximum and blue minimum temperatures in Celsius)

The graph above first makes it clear that temperatures in January have so far been quite mild and mostly above freezing. Especially at the beginning of the month, the maximum temperatures during the course of the day were unusually high at almost 14° Celsius (57° F), although such peaks were also observed repeatedly in previous years (2021: 21.1. 11°C, 28.1. 12.1°C; 2020: 16.1. 14.7°C, 31.1. 14.9°C). Overall, it is noticeable that the trend in minimum temperatures has also continued to move upwards over the course of the past three years and will most likely not fall below the minus 5°C mark in 2022.

Temperatures above 5°C also favour the germination of weeds such as cranesbill (Geranium pusillum), Persian speedwell (Veronica persica) or annual meadow grass (Poa annua).

Coupled with a mild autumn, it is therefore not surprising that the weed pressure on the wheat cultivation area in Lauresham is already not to be underestimated. In some cases - as in the case of the neophyte dock (Rumex crispus) - these weeds will be reduced by hand weeding in spring.

Fig. 2 Weeds in the wheat field in January (Veronica persica on the left and Rumes crispus on the right).

Another reason for the comparatively high weed pressure could have been the furrow depth of only 13cm on average when ploughing with a (re)constructed mouldboard plough.

Detail of the ploughing process back in October 2021

It is also worth looking at soil moisture and rainfall in the wheat field:

Fig. 3 Recording of rainfall (blue) and soil moisture (different shades of red represent different soil depths) in the wheat field

The general amount of precipitation in January (measured up to Jan 25th) is rather below average with 40mm. Accordingly, there was a tendency for soil moisture to decrease at soil depths of up to 10 cm, especially in the second half of January. Basically, the soil as a whole can still be described as well saturated down to the maximum depth of 90cm that we measured. The wheat can therefore access sufficient water at its current stage of development with a root depth of about 6 cm. As expected, growth in January was only slight. On Jan. 4th, the wheat was on average in stage 22 on the BBCH scale. On Jan 25th, this state was only slightly changed with a value of 23-24 and is still in the middle of the development phase called tillering. During this time, the cereals mainly form side stems before they finally start to "shoot" in the spring.

Fig. 4 Development stage of wheat on Jan 25th (BBCH scale stage 23)