Quantifying links between topsoil depth, plant water use, and yield in a rainfed maize field in the U. S. Midwest

Agricultural production in highly variable soils is a challenge, especially when those soils are shallow. Precision agriculture techniques were developed to improve yields and minimize spatial and interannual variability in profit. In the Central Claypan region of the Midwest United States, many of the precision agriculture techniques were based on the assumption that topsoil depth controlled plant available water, and therefore yield. But this assumption has not been empirically tested. In this study, we use measurements of sap flow installed on maize plants with a gradient in topsoil depth, caused by a claypan layer. We hypothesize that plants with higher water use have higher yield, plants in areas with thicker topsoil have higher water use, and soils in the areas with thicker topsoil have higher soil water content. Sap flow sensors were installed on 5 plants each at three locations with topsoil depths of 19.6 cm (shallow), 21.6 cm (medium), and 30.5 cm (deep) from June - September, 2022. An ANOVA analysis demonstrates that the average total season transpiration at the deep site (279 mm) was significantly larger than at the shallow site (151 mm), while the medium site was in the middle with transpiration not significantly different from either shallow or deep sites (218 mm). At the end of the season, the plants were harvested and total biomass and grain yield were measured. Increase in plant transpiration was significantly related to both increases in biomass and yield. Finally, we measured volumetric soil water content at each location and found higher soil water content at the site with thicker topsoil. Our results demonstrate the link between topsoil depth, soil water content, plant transpiration, and yield. These findings will help improve precision agriculture techniques in areas with highly variable topsoil thickness.