QField for QGIS application for oil palm agronomist’s field visit and assessment

In formulating fertilizer recommendations, an agronomist has to visit the estate to assess the actual oil palm growth/condition and other factors such as nutrient deficiencies, field conditions, drainage issues, pest damage, etc. Conventional field assessment using manual handwriting requires a lot of paper and also results in double-handling of work when transferring the data into digital format. Other printed data such as block, soil, and terrain map are not practical to be used in the field or loaded in Androzic or Avenza Maps applications which are not interactive and cannot handle aerial photo data of the estate. An android application, QField for QGIS, has been explored and utilized to replace the conventional field assessment method. To start making an assessment, the agronomist has to tick the smartphone/tablet display to pop up the assessment form. Block data such as block name, leaf/soil analysis result, soil type, rainfall, etc., will be automatically shown, specific to the block where the agronomist is. The agronomist can then fill in the form by selecting multiple choices, such as poor, fair, and good, etc., or typing in the necessary information. The other pre-loaded data, such as block, soil & terrain map, and even aerial photos with original resolution can be shown and overlaid. Capturing georeferenced photographs and tracking can also be performed. Transferring assessment data into a spreadsheet and viewing georeferenced photographs can be done using QGIS software on the computer.


Field visit by the agronomist
One of the key elements of oil palm yield and profit is a judicious fertilizer recommendation, which is the main responsibility of agronomists.Apart from assessing nutrient analysis of leaf and soil, assessment of the actual field and palm conditions is also required to determine appropriate fertilizer rates [1].Goh et al [2] elaborate on the six most important criteria and indicators of palm health, such as uniformity of palms, fresh fruit bunch (FFB) yields, canopy sizes/color, leaf nutrient concentrations, soil fertility, and field conditions.Therefore, the agronomist has to visit the estate to assess these parameters before formulating fertilizer recommendations.
A good field assessment must be supported with historical data (yield, leaf analysis results, etc.) and maps (block, topography, soil, aerial photos, etc.).The agronomist requires these data during the field visit to see the 'big picture' of an estate, accelerate understanding of the block, and ease problem identification.These data and information are usually abundant and stored in separate and different 2 formats.The current field assessment system in PT Applied Agricultural Resources Indonesia (AARI) is the estate and block map loaded and opened in an Android application such as Androzic [3] or Avenza Maps for navigation, tracking, or marking purposes whilst field/palm assessment forms and other supporting historical information, on the other hand, are carried around usually in paper/hardcopy formats.The latter may be not so practical for easy reference and create doublehandling work in summarising the assessment back in the office.Moreover, the Android field navigation maps are usually not interactive and unable to handle aerial/drone images of estate areas.Therefore, there is room for improvement via digitalization of all the above operations for more effective and efficient field/palm assessment by the agronomist.

What is QField for QGIS?
QField for QGIS is a mobile geographic information system (GIS) application on an Android system, developed by OPENGIS.ch(Switzerland) and released under the GNU Public License.It is an opensource application and free to use and distribute.QField can be utilized to a broad extent of work scopes including in oil palm plantation as well as other sectors, such as Montagnetti and Guarino [4] used QField for facilitating the work of the archaeologist in the field that provides several benefits such as reducing registration and computerization time of inputting data into the database system, eliminating the digitization of field registers and all related paperwork.
In this paper, we wish to share AARI's experience using QField for QGIS application for field/palm assessment by agronomists.We will also elaborate on an example of steps to use QField (version 1.10.0-Uluru).We used QGIS Desktop (version 3.22.10)to create and extract the data from the QField project.As the applications are continuously developed over time, slight differences and more features may be encountered when using the latest versions of QField or QGIS Desktop in the future.We run the QField application smoothly on an Android tablet with the following specification: a) CPU: Exynos 9611 Octa-core 2.3 GHz, b) GPU: Mali-G72 MP3, c) RAM: 4 GB.Other Android tablets/smartphones with different specifications might result in a different experience.The methodology described in this paper specifically refers to oil palm agronomists' assessment method in AARI.

Raster data
Aerial photo/satellite image data of the estate are to be saved in GeoPackage format.The pyramid option must be checked and all levels of pyramids are also checked.This is to ensure the aerial photo data will be opened smoothly in the QField.The original resolution of aerial photo data may be maintained.Based on our experience, QField can still manage to open and display aerial photo data of large estates, say 5.000-10.000ha.Topographic or slope maps of the estate are to be saved in Tif format.

CSV data
For assessments that allow selecting multiple items (e.g.nutrient deficiency), a list of categories is to be created in a CSV file, for example in Table 1 below.Assessment items with the same category list can also use the same CSV file.Severe -many

Creating a QField project
A QGIS project is to be created, for example, named 'Field assessment'.All vector, raster, and CSV data are to be added to the project.The layer order from top to bottom is as follows: vector point, vector line, vector polygon, raster, and CSV data.In the 'Assessment form' layer, the Attribute layout editor in the Attributes Form is to be selected in Drag and Drop Designer.The necessary fields are to be dragged into Form Layout.We can also create a tab group of data in the Form Layout when necessary.
The widget type of attribute form of basic fields ("Block name", "Estate", "Ha", "Soil", etc.) is to be set as Text Edit.The default value is set using an expression to extract field value from the overlaid block layer.The example below is the expression to extract the "block name" field from overlaid block layer attribute data.

array_to_string(overlay_intersects('Block layer name', "Block name"))
For fields that will extract historical data in JPG format such as "Rainfall" etc., the widget type of attribute form is to be set as Attachment with a Simple copy of Storage type, and its Default value is also set using an expression, similar to the above example.
For fields to store assessment data that only allow selecting 1 item such as "Canopy size", the widget type of attribute form is to be set as Value Map.Numbers in numerical order are to be added as many as the list of categories required.For the "Nutrient deficiency" field that allows multiple selections, the widget type of attribute form is to be set as Value Relation.Layer value is taken from CSV data loaded in the project (example shown in Table 1), the Key column is "No", the Value column is "Category", and the Description column is "Category".The option Allow multiple selections must be checked.
For fields to store geotagged photographs data, the widget type of attribute form is to be set as Attachment with Select Existing file of Storage type.The storage path is to be set as Relative to Project Path and Storage mode is File Paths.The Integrated Document Viewer type is Image with Auto Width and Height of image size.
Before finalizing the QField project, the styling of vector and raster data is to be set in such a way that it is comfortable to be seen on the android Tablet or smartphone ie.red color for the 'assessment form' point, simple line for block layer, Categorized based on soil name for soil map, Singleband pseudocolor with updated canvas option selected for Min/Max Value Settings for Terrain data, etc. QField project can be created by selecting Package for QField option in the QFieldSync plugin.After the project is created, the project folder is to be copied into the internal storage of an Android tablet/smartphone.

Opening data in the QField project
To open the QField project, the Open local file option on the first page of the QField application is to be selected, then a file with extension .qgs is to be opened.All layer lists including the styling will be shown the same as in the QGIS Desktop.We can show/hide the layer as well as the layer's label by long-pressing the layer name.The current location is indicated by a blue dot on the screen.

Starting the assessment
To do the assessment, the 'assessment form' layer is to be selected and then the mode is to be set to Digitize mode.The green-plus button on the right-bottom of the screen is to be pressed to add a point and start the assessment (or just tick the screen if we use a stylus pen).An assessment form including basic data will pop up.We created 5 tabs of group data as shown in Figure 2 which are 1) 'Block detail' containing basic data of the block as well as historical data, 2) 'Assessment form' to be filled in by the agronomist, 3) 'Other notes' to accommodate any important things apart from in the assessment form (only possible using an android tablet/smartphone equipped with stylus pen), 4) 'Photo' to capture geotagged photographs, and 5) 'Date/time to store date & time data automatically.Block detail data automatically corresponds to which block the point is located.Once the assessment is done, a point will be marked on the screen (Figure 3).We can modify or delete the assessment point if necessary.
To start the tracking, the 'tracking' layer is to be long-pressed until the options pop up, then Setup tracking is to be selected.We can set the constraint based on time, distance, or both.The agronomist also can make use of pre-loaded maps such as aerial photos, soil, and terrain maps to support his/her assessments, for example, identifying and quantifying yellowish palms (original resolution is maintained) as shown in Figure 4, low-lying area for drainage analysis (terrain map is rendered based on updated canvas) as shown in Figure 5, etc.
If all assessments are done, the data will be automatically saved in the 'assessment form' layer in the QField project.Since all assessment points are displayed on the screen (Figure 6), the agronomist can review the assessment points that have already been created to ensure the visit plan is completed.

Extract the data after the visit
QField project folder in the internal storage of the Android tablet/smartphone is to be copied into the computer or laptop.The project file with extension .qgs is to be opened in QGIS Desktop.The 'assessment form' layer contains all assessment data including geotagged photographs (Figure 7).
The assessment data are still in vector format and need to be converted into a spreadsheet for further analysis or uploading into the database system.This can be done using the Export to Spreadsheet tool in the QGIS processing toolbox.The Export formatted values instead of raw values option must be checked.The spreadsheet data can be opened using the spreadsheet application on the desktop (Figure 8).

Pros and cons of using QField oil palm field assessment
We gained many advantages when using QField for oil palm field assessment.However, there are still some limitations that required attention to avoid problems when conducting the field assessment.The main pros and cons of QField for oil palm field assessment are summarized in Table 3 below.

Figure 1 .
Example of historical data of (a) rainfall and (b) annual leaf analysis in jpg format

Figure 7 .
Figure 7. QField project is opened in QGIS Desktop

Figure 8 .
Figure 8. Example of field assessment data in the spreadsheet

Table 1 .
List of categories for nutrient deficiency assessment

Table 2 .
Table 2 below shows the example of a Value Map of "Canopy size".List of categories of "Canopy size" assessment