Mycorrhiza likes clay - High resolution soil texture maps reveal a conserved correlation of maize mycorrhization to soil particle size across years and fields

Soil particle size distribution determines the soil water and nutrient availability, but the spatial variance of the soil texture is often unknown in agricultural fields. This knowledge gap limits demand-oriented and ecological nutrient and water management of crops. It also hampers our understanding of the crop resource use in the field as mediated by soil microbes such as the arbuscular mycorrhizal symbioses. To better understand to which soil conditions maize-mycorrhiza associations respond, we used proximal sensing of soil texture to map within-field variation soil particle size in high spatial resolution and related soil texture to the mycorrhization of organic maize.

To obtain the soil texture maps, we used the mobile sensor platform Geophilus electricus [1]. This proximal soil sensing system deploys a multi-sensor approach to discriminate soil properties by simultaneously measuring the electrical resistivity (up to 1.5m depth) via rolling electrodes and the natural gamma activity, whilst a DGPS guarantees the required precision in geo-referencing during mapping [2]. After calibration of the sensor data with soil samples of the selected fields, the final output is a high-resolution map of the mean soil particle diameter (MPD), which was then used as the independent variable in correlations with the mycorrhization of maize.

The soil texture mapping took place for three investigated fields in 2020 at an organic farm in Lower Saxony, Germany, which is dominated by sandy soils and on which a crop rotation with maize was deployed. The plant and soil sampling took place in 2017, 2020 and 2021 at the respective sites with maize. For each field, the sampling of soils and plants occurred equidistantly in 12 parallel transects along the moving lane direction. We analyzed plant and soil C/N, P, K, Mg, soil pH and organic matter and root colonization by native mycorrhizal fungi during the maize culture.

According to our expectations, we found that the MPD and the clay fraction are accurate describers of the soil P, N, Mg and C_org concentrations for the three years and fields in the crop rotation, while soil K was not responding to the soil texture. Interestingly, we also found a conserved correlation between root colonization by arbuscular mycorrhizal fungi and the MPD of the soil surrounding the roots of the sampled plants. Lower MPD (i.e. higher clay contents) gave rise to stronger maize-mycorrhiza root associations. This response pattern was conserved in years markedly different in mean annual temperature and precipitation. However, the lowest rates of root colonization by mycorrhizas were observed in the dry year of 2020.

We discuss that precision farming technologies may have the potential to guide the management of crops for improved and microbe-assisted resource use. 

 

 

[1] Lück, E., & Rühlmann, J. (2013). Resistivity mapping with GEOPHILUS ELECTRICUS—information about lateral and vertical soil heterogeneity. Geoderma, 199, 2–11. [2] Meyer, S. et al. (2019). Creating soil texture maps for precision liming using electrical resistivity and gamma ray mapping. In Stafford, J. V. (Ed.) Precision Agriculture’19 Proceedings of the 12th European Conference on Precision Agriculture Wageningen (pp. 92). Wageningen, The Netherlands: Wageningen Academic Publishers.