Data Science for Agriculture
How to manage and manipulate data for agricultural research
Your advisor is pleased with the results so far and asks you to compile some soils data for each of the stations. You decide to check for an R package that will help you and find the soilDB package. You read in the documentation that the package provides functions to query the NRCS Soil Data Access web service for SSURGO soil data. This sounds like the perfect tool for your project.
Install the soilDB package. Use the Fort Cobb Micronet layer with the SDA_query_features() function from the soilDB package to download soil mapping unit information for each station. Merge the resulting data frame with your existing SpatialPointsDataFrame.
SDA_query() function. You find an example query that does part of what you want:
mukeys <- c(381911,381889);
qry <- paste0("SELECT mukey, cokey, comppct_r, drainagecl
FROM component
WHERE mukey IN (",
paste(mukeys,collapse=","),
")");
soil.data <- SDA_query(qry)
Modify the code so that the query returns information for only the mapping unit keys (mukey) for each of the Micronet stations.
You notice that the above code returns multiple values for each mukey. That is, there are multiple soil types (components) for each mapping unit. Use filter() to keep only the soil components (cokeys) within each mukey that have the largest coverage within the mapping unit (i.e. where comppct_r is greatest). Merge this data frame with your Micronet SpatialPointsDataFrame.
These results are good, but they do not yet contain the surface sand percentage. After some reading you determine that the sand percentage is contained in the variable sandtotal_r in the chorizon. Copy and modify the code for your previous query so that you select the cokey, hzdept_r and sandtotal_r from the chorizon table where the cokey is in the filtered list of cokeys from the prevous problem.
This is almost what you need except that you now have multiple horizons for each soil type. Filter the output to only include the surface sand percentage for each soil type (i.e. where the horizon depth hzdept_r is least).