TITLE: Measuring root system stiffness in maize or sorghum
AUTHORS: Ashley N. Hostetler, Jonathan W. Reneau, Erin E. Sparks

[DESCRIPTION]
Plant mechanical failure has been evaluated with proxy measures that quantify root failure strength. However, understanding the force-displacement rate to reach that failure strength is currently a gap in the field. The force-displacement rate is called the root system stiffness. Here, we outline the steps necessary measuring root system stiffness in maize or sorghum using a new tool developed by our lab called SMURF (Sorghum & Maize Under Rotational Force). 

[GUIDELINES]
Plant Material:

Plant maize or sorghum seed under standard planting procedures. No specific field conditions are required. 
Maintain research fields. 

 

 

Device:

A device, called SMURF (Sorghum and Maize Under Rotational Force), was designed to non-destructively measure the root system stiffness of large grain root systems (Figure 1A). The SMURF applies rotational displacements and measures a force. Below we outline the components of the SMURF as a general overview of the device. 

The SMURF consists of a physical body, electronics, powertrain, sensors, and software (Figure 1). 

The physical body consists of (Figure 1A):
A 3D-printed case housing the electronics and powertrain (Figure 1A-1)
A battery pack (Figure 1A-2)
A set of arms with straps to attach the device to the plant (Figure 1A-3)
A sensor housing case for the load cell (Figure 1A-4)
A rotational foot for device grounding (Figure 1A-5)

The internal electronics are run via an Arduino microcontroller connecting a motor driver, load cell amplifier, and Bluetooth module (Figure 1B). 

The powertrain consists of:
A brushed DC motor
A lead screw
A battery 

A 10 kg load cell (sensor) 

A custom-built iPad application controls the device (Video 1)

 

 
 Video 1: Custom-built iPad application controls the device



[STEPS]
SECTION: Before Operating the SMURF:
1. Open the Device Controller iPad application (Video 1). 

SECTION: Before Operating the SMURF:
2. Hold the SMURF horizontally and power on. 

SECTION: Before Operating the SMURF:
7. Click button: “Fully Retract Foot”. This will re-home the device (Video 1).  

SECTION: Before Operating the SMURF:
5. Click button: “Save Researcher ID” (Video 1).

SECTION: Before Operating the SMURF:
4. Enter Research ID (e.g. researcher name/initials/identifier) in iPad application (Video 1).

SECTION: Before Operating the SMURF:
3. Calibrate the load cell in the absence of a load.

SECTION: Before Operating the SMURF:
6. Click button: “Go to Testing Screen” (Video 1).

 

SECTION: Operating the SMURF:
8. Attach the device with the two arms as low as possible on the plant while avoiding brace roots. 

 

SECTION: Operating the SMURF:
9. Enter Plant ID into the text box (Video 1). 

SECTION: Operating the SMURF:
10. Select appropriate Test Type (Video 1).

 

SECTION: Operating the SMURF:
11. Click button: “Get Initial Height” (Video 1)

 

SECTION: Operating the SMURF:
12. Click button: “Small Flex Test” or “Large Flex Test” to start the testing cycle (Video 1) 

A Small Flex Test should be used for any small or mutant plants, whereas a Large Flex Test is the default for all healthy plants. 

 

SECTION: Operating the SMURF:
13. Click button: “Accept Results” or “Reject Results” (Video 1) 

“Accept Results” prompts the data directory to save the data.
“Reject Results” prompts the device to go back to the original testing screen.

SECTION: Operating the SMURF:
14. Click button: “Move to Next Plant,” which will fully retract the foot and make the device ready for the next testing cycle (Video 1)