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Title: YIELD INDEX AND REMOTE SENSING TO CONFIRM WATERSHED SUBSURFACE FLOW PATHWAYS

Author
item Gish, Timothy
item Walthall, Charles
item Daughtry, Craig
item KUNG, SJ - UNIVERSITY OF WISCONSIN

Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/21/2003
Publication Date: 1/3/2005
Citation: Gish, T.J., Walthall, C.L., Daughtry, C.S., Kung, S.J.S. 2005. Yield index and remote sensing to confirm watershed subsurface flow pathways. Journal of Environmental Quality. 34:275-286.

Interpretive Summary: Subsurface soil water dynamics can influence crop growth as well as the fate of surface applied fertilizers and pesticides. In this study, a protocol using primarily ground-penetrating radar (GPR) was extended to the watershed scale while yield data and color infrared imagery were used to confirm the areal location of the subsurface flow pathways. A normalized differential yield index (NDYI) was introduced that utilizes corn grain yield from drought and optimum weather conditions to identify locations within a field crop growth is influenced by subsurface water. Results showed that whenever GPR-identified flow pathways were within 1.5 m of the soil surface there was a beneficial impact on yield. Regions where yield appears to be influenced by subsurface water flow (NDYI) were well correlated to the GPR-identified subsurface flow network. Likewise, color infrared imagery showed good visual relationship with the GPR-identified flow pathways. This research suggests that remote sensing and yield monitor data may be important tools for determining regions were subsurface water is converging and eventually leaving agricultural land.

Technical Abstract: A GPR protocol for identifying the subsurface flow pathways was extended to a small 3.2 ha watershed, uncertainty discussed, while yield and remote sensing data were evaluated for confirming the areal extent of the subsurface flow pathways. Yield data was normalized to facilitate comparison of within field corn grain yield patterns during climatically different years. Corn grain yield was normalized by subtracting the mean and dividing by the variance for every 10 m x10 m block within the watershed. A normalized differential yield index (NDYI) was subsequently developed by subtracting the normalized corn grain yield representing a drought year from a normalized yield representing near optimal climatic conditions. Regions influence by subsurface water flow should have a large positive NDYI while regions that were not influence by subsurface flow would be represented by a negative NDYI. Whenever GPR-identified flow pathways were within 1.5 m of the soil surface there was a beneficial impact on yield. Regions where yield appears to be influenced by subsurface water flow (NDYU) appear to be visually correlated to the subsurface flow network. Likewise, color infrared imagery showed good visual relationship with the GPR-identified flow pathways. This research suggests that remote sensing and yield monitor data may be important tools for determining regions were subsurface water is converging and eventually leaving agricultural land.