Informing precision agriculture: Small-scale spatial variability in herbicide, weed, and crop dynamics

Authors: Schneider, Sharon

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 2/15/2019
Publication Date: 5/19/2019
Citation: Papiernik, S.K. 2019. Informing precision agriculture: Small-scale spatial variability in herbicide, weed, and crop dynamics. 14th IUPAC International Congress of Crop Protection Chemistry. Paper P4.29.

Interpretive Summary:

Technical Abstract: As increasingly precise herbicide application technology is developed, there is a need for more information about the spatial variation in weed and herbicide dynamics. In hilly landscapes, soil properties vary due to soil formation processes and soil erosion. Here, extensive research of one eroded landform provides an example of the small-scale spatial variability that may affect precision agriculture applications. The site was a single ridge that measured 70 m in length from the summit to the toeslope. A detailed soil survey described 5 soil series along a transect. Surface soil organic carbon concentrations were 3.7x lower in eroded landscape positions than in depositional positions, with concomitant differences in soil nutrients, bulk density, soil moisture, and other properties. We measured the sorption of 6 herbicides and 5 herbicide metabolites and found that for most compounds, the sorption Kd was 1.5 to 6x higher in depositional positions than in eroded positions. This trend is consistent with many reports of herbicide sorption increasing with increasing organic carbon concentration. However, this trend did not hold for metolachlor: in both laboratory and field studies, metolachlor sorption/dissipation was the same in all landscape positions. In this landform, crop and weed emergence varied by landscape position. Crop and weed emergence was sometimes slower in eroded landscape positions than in depositional positions; biomass was consistently lower in eroded landscape positions and plants were slower to develop. These considerations are important for precision agriculture herbicide applications. In this example landform, depositional positions might be expected to demonstrate higher sorption (less bioavailability) of soil-applied herbicides, while both crop and weed plants are expected to be larger, requiring/tolerating a higher dose. The differences in weed and crop emergence and growth may reduce the cost-effectiveness of herbicides and sensor technology. Potential effects of small-scale spatial variability in soil properties and plant development on herbicide efficacy should be accounted for in precision agriculture approaches, but this is complicated because trends are not consistent for all herbicides.