It shall be the duty of the soil erosion committee to notify the board of supervisors, the county assessor and the landowner within fifteen days after the performance of each contract by the county or separate soil erosion district, giving the assessor the name of the landowner, the legal description of the land, the amount to be paid to the county or district, and how payable, and to the landowner a notice that a special assessment will be made against his land by the assessor for the amount determined by the committee, and presented to the next meeting of the board of supervisors beginning more than ten days thereafter for approval. The assessor shall, at the next meeting of the board beginning more than ten days after such notice, file with the board of supervisors, in duplicate, on appropriate forms, keeping a copy thereof on file in his own office, an assessment of the land for a special improvement tax thereon equal to the amount fixed by the committee, and payable as provided by the contract. It shall be the duty of the board of supervisors at said meeting to hear any objections to such assessment, by the landowner or the holder of any lien thereon, and to determine the amount of the assessment, not to exceed the amount fixed by the committee, and to approve the assessment as finally determined. The clerk of the board shall forthwith certify such assessment to the tax collector of the county upon the duplicate of the assessment filed by the assessor. In event such assessment be not returned to or acted upon by the board at the first meeting for any reason, it may be returned, considered and acted upon at any subsequent meeting. When approved, such assessment shall be a lien upon the land subordinate only to the lien of other taxes, prior and subsequent, and no delay or irregularity in the giving of notices, the making of the assessment, the hearing and approval thereof, or the certification thereof to the tax collector, shall affect the validity of the assessment if the work was actually done upon the land and the amount of the assessment does not exceed the contract price. Appeals may be taken to the circuit court of the county as in other cases of assessments for taxation, by the landowner or the holder of any lien upon the land. Nothing herein contained shall prevent any landowner from making payment to the tax collector of the estimated amount to become due under his contract, or any part thereof, in advance of the time the same becomes due, and the tax collector shall receive any payment so tendered, and give the landowner credit therefor against the assessment when made.