he ObjectContext instance has been disposed and can no longer be used for operations that require a connection.

public partial class ApplicationFormFarmersSolarPower
    {
        
        public int Id { get; set; }
        public string UniqueId { get; set; }
 
        //[Required(ErrorMessage = "Please select District.")]
        public  string District { get; set; }
 
        //[Required(ErrorMessage = "Please select Tehsil.")]
        public  string Tehsil { get; set; }
 
        //[Required(ErrorMessage = "Please select SubTehsil.")]
        //public string SubTehsil { get; set; }
        //[Required(ErrorMessage = "Please select District.")]
        public  string DistrictName { get; set; }
 
        //[Required(ErrorMessage = "Please select Tehsil.")]
        public  string TehsilName { get; set; }
 
        //[Required(ErrorMessage = "Please select SubTehsil.")]
        public string SubTehsilName { get; set; }
 
        public string Village { get; set; }
}

[HttpGet]
        public JsonResult GetTehsil(string districtID = "")
        {
            List<Tehsil> allTehsil = new List<Tehsil>();
            int ID = 0;
           
            if (int.TryParse(districtID, out ID))
            {
                using (FarmerBDContext db = new FarmerBDContext())
                {
                    allTehsil = db.Tehsils.Where(a => a.DistrictId.Equals(ID)).OrderBy(a => a.TehsilName).ToList();
                 
                }
            }
 
            if (Request.IsAjaxRequest())
            {
                return new JsonResult
                {
                    Data = allTehsil,
                    JsonRequestBehavior = JsonRequestBehavior.AllowGet
                };
            }
            else
            {
                return new JsonResult
                {
                    Data = "Not Valid request",
                    JsonRequestBehavior = JsonRequestBehavior.AllowGet
                };
            }
        }

<script type="text/javascript">


    $(document).ready(function () {
        $("#DistrictName").change(function () {

            var districtID = parseInt($("#DistrictName").val());
            
            if (!isNaN(districtID)) {
                var ddState = $("#TeshilName");
                ddState.empty();
                ddState.append($("<option></option").val("").html("Select State"));
                
                $.ajax({
                    url: "@Url.Action("GetTehsil", "Home")",
                    type: "GET",
                    data: { "districtID": districtID },
                    
                    dataType: "json",

                    success: function (Data) {
                        $.each(Data, function (i, valueOf) {
                            ddState.append(
                                    $("<option></option>").val(valueOf.TehsilId).html(valueOf.TehsilName)
                                );
                        });
                        console.log(JSON.parse(data));
                    },
                    error: function () {
                        alert("Error This is It!");
                    }
                });
            }
        });