Change Node: string to number

General
2

You can use $number() to convert

{
"datum": payload.datum,
"tijd": payload.tijd,
"temp": $number(payload.uplink_message.decoded_payload.temp_SOIL),
"humi": $number(payload.uplink_message.decoded_payload.water_SOIL),
"conduct": payload.uplink_message.decoded_payload.conduct_SOIL,
"batt": payload.uplink_message.decoded_payload.Bat
}

[edit] sorry you are using a change node and Jsonata edited above to reflect that