A change in elevation producing a change in yield is not a ridiculous statement when you consider the hundreds of thousands to millions of dollars spent every year on laser levelling and forming to enhance field drainage. If the numbers support the results you have to determine if elevation is a factor, or is something else may be causing this effect.
Given that drainage is an issue and that a 50mm depression in a field may pool water for extended periods of time during the wet season, severely reducing yield and even killing a proportion of the crop. An almost imperceptible ridge through a field, even 150mm or 200mm above the height of the rest of the field often produces a higher yield. Every grower in the industry is aware of this. What the intent is to find if there is actually a correlation between these slight changes in in-field elevation and yield. Of course this will not be the end of the story, finding a positive or negative correlation is not an end in itself, but provides an indication of one variable to consider.
One of the papers at the recent international conference for precision agriculture in St. Louis, advised producing a scatterplot between soil electromagnetic conductivity and yield, as a correlation has been found between these variables. In our part of the world, given our seasonal rainfall, drainage and therefore in-field elevation does make a difference in yield.
Unfortunately none of the tools mentioned are giving me the option of using a raster as an input layer, and none of them are allowing me to add more than one FC at a time.
I have an interpolated raster of crop yield, based on yield monitor and GPS data, and an elevation raster developed from LiDAR collected at 1 point per sqm. I would like to avoid going back to the original point data due to the high numbers of points to deal with.
I am currently limited to ArcGIS Advanced with Spatial Analyst. A couple of tools I have looked at require 3D analyst, and if I have to purchase that down the track some time then so be it, but for now I have this limitation.
Sorry for the long-winded explanation, but for decades there has been a suspected association between changes in in-field elevation, even small ones, and yield. Until recently we have not have the tools to measure/collect or to analyse the data that we now have available to us. As we do our analysis our results are reviewed by statisticians/biometricians to maintain rigour.
Regards
Rod Nielson
GIS Officer
Herbert Cane Productivity Services Ltd.
Ph: 07 4776 5660
Mob: 0403 215 594
Email: rnielson@hcpsl.com.au
Fax: 07 4776 1811