aw5598, 5599, 5600, 5601: several carbon changes

Models/SoilPropertyType.cs

@@ -10,7 +10,7 @@ namespace FarmMapsAPI.Carbon.Models
         public double OM_Corr { get; set; }
         public double Bulk_Density { get; set; }
         public double Clay_Content { get; set; }
-        public double Depth { get; set; }
+        public int? Depth { get; set; }
         public bool Depth10 { get; set; }
     }