You can set FeatureLayer.ValidateEdits=False or fix your service.
Your service defines the field as such:
{
"name" : "IrrigationType",
"type" : "esriFieldTypeString",
"alias" : "IrrigationType",
"editable" : true,
"length" : 2,
"domain" :
{
"type" : "codedValue",
"name" : "TreeIrrigationType",
"codedValues" : [
{
"name" : "Drip Irrigation",
"code" : "DI"
},
{
"name" : "Gator Bags",
"code" : "GB"
},
{
"name" : "Irrigation System",
"code" : "IS"
},
{
"name" : "Non-Irrigated",
"code" : "NI"
}
]
}
},
with the following Prototype attribute:
"prototype" : {
"attributes" : {
"IrrigationType" : " ",
"TreeType" : "GRA",
"TreeCondition" : null,
"TreeValue" : 0,
"TreeSize" : null,
"DatePlanted" : null
}
Validation check in the client fails because space is not one of the expected coded-value domain, so you might want to change the default value in your prototype attribute.