Basic Workflow

In ofpetrial: Design on-Farm Precision Field Agronomic Trials

knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)

Here, we demonstrate a typical workflow of using the ofpetrial package to create a trial design through an example of two-input on-farm experiment trial.

library(ofpetrial)

Create experimental plots

Prepare plot information for the inputs

We start with specifying plot and machine information for inputs using prep_plot, which simply creates a data.frame of the specified information with some internal unit conversion of length (e.g., feet to meter).

#--- for nitrogen ---#
n_plot_info <-
  prep_plot(
    input_name = "NH3",
    unit_system = "imperial",
    machine_width = 30,
    section_num = 1,
    harvester_width = 30,
    plot_width = 30
  )

dplyr::glimpse(n_plot_info)

#--- for seed ---#
seed_plot_info <-
  prep_plot(
    input_name = "seed",
    unit_system = "imperial",
    machine_width = 60,
    section_num = 24,
    harvester_width = 30,
    plot_width = 30
  )

dplyr::glimpse(seed_plot_info)

Create experimental plots

Now that plot and machine specifications for the inputs are ready, we can create experiment plots based on them using make_exp_plots(). Since this is a two-input case, you create a list of plot information and the provided that to make_exp_plots() along with the path to the field boudary and ab-line files (you can alternatively provide those data as sf objects.).

input_plot_info <- list(n_plot_info, seed_plot_info)

exp_data <-
  make_exp_plots(
    input_plot_info = input_plot_info,
    boundary_data = system.file("extdata", "boundary-simple1.shp", package = "ofpetrial"),
    abline_data = system.file("extdata", "ab-line-simple1.shp", package = "ofpetrial"),
    abline_type = "free"
  )

The experiment plots created by make_exp_plots() is stored in exp_plots.

exp_data$exp_plots

exp_data$exp_plots is a list of experimental plots in sf. The first element is for nitrogen and the second for seed following the order of information you provided in input_plot_info. You can access the individual experiment plots (an sf object) like this.

exp_data$exp_plots[[1]]

We can visualize the layout of the experiment plots using viz() with type = "layout" option.

viz(exp_data, type = "layout", abline = TRUE)

As you can see, ab-lines for the applicator/planter and harvester were generated for each of the input. We will show how to export ab-lines later.

Assign rates

Let's now assign input rates to the experimental plots we just created. Before doing so, we need to prepare rate information for both inputs using prep_rate(). Here, design_type = "ls" (Latin Square) is used for both seed and nitrogen experiments (see this article for other design options and this article for changing rates manually.).

Prepare rate information

You can use prep_rate() to prepare rate information before assigning rates to the experimental plots. For nitrogen, exact rates were specified through the rates option, and trial design type is specified to be "ls" (short for Latin Square). For seed, the minimum and maximum rates, and the number of rates were specified. In this case, the code interally finds the rates automatilly for you.

#!===========================================================
# ! Assign rates
# !===========================================================
n_rate_info <-
  prep_rate(
    plot_info = n_plot_info,
    gc_rate = 180,
    unit = "lb",
    rates = c(100, 140, 180, 220, 260),
    design_type = "ls",
    rank_seq_ws = c(5, 4, 3, 2, 1)
  )

dplyr::glimpse(n_rate_info)

seed_rate_info <-
  prep_rate(
    plot_info = seed_plot_info,
    gc_rate = 32000,
    unit = "seed",
    min_rate = 16000,
    max_rate = 40000,
    num_rates = 4,
    design_type = "ls"
  )

dplyr::glimpse(seed_rate_info)

Assign rates

We can now use assign_rates() to assign rates to experiment plots.

trial_design <- assign_rates(exp_data, rate_info = list(n_rate_info, seed_rate_info))

Here is the visualization of the trial design done by viz.

viz(trial_design, abline = TRUE)

Along with the spatial pattern of the input rates, the applicator/planter ab-line and harvester ab-line are drawn by default.

Diagnose the trial design

The ofpetrial package offers several functions to check the soundness of a trial design (see this article for more details and examples).

Here, let's check the correlation between the seed and NH3 rates.

(
  cor_inputs <- check_ortho_inputs(trial_design)
)

The correlation coefficient is r round(cor_inputs, digits = 2), which is certainly acceptable.

Make a trial design report

After creating a trial design you can download a trial report that serves as a guide for implementing the trial as well as a reminder of the equipment sizes, plot specifications, and treatment levels that were chosen. The report is saved as an html document named "trial_design_report.html". Along with basic information about the design (total amount of inputs to be applied, number of replicates of each treatment level, plot size, etc.), the report also contains figures displaying how the provided ab-lines and machines will line up inside the trial plots.

make_trial_report(
  td = trial_design,
  folder_path = getwd()
)

Write the trial design files for implementation

Once you are satisfied with the trial design and the location of the ab-lines, you can write out all the necessary files as shape files for the machine operators to actually implement the trial.

write_trial_files(td, folder_path = getwd(), zip = TRUE, zip_name = "td-collection")

Here, all the shape files (trial dsign, applicator/planter ab-line, and harvester ab-line) are packed in a zipped folder, named "td-collection.zip".

ofpetrial documentation built on April 12, 2025, 1:28 a.m.