(b) Any irrigation district may enter into an agreement with the United States or any department, bureau or agency thereof in pursuance of the federal laws governing such department, bureau or agency, or with any person or corporation for the establishment, construction and completion of the necessary irrigation works as provided in this act, and may in such contract or agreement provide for the payment of the cost of establishing and constructing such works by the levy and collection of assessments against the lands benefited and/or by annual payments from funds raised by the collection of water rentals, tolls or charges from persons furnished water for the irrigation of their lands: Provided, That before any assessments shall be extended on the tax roll against any lands in the district, or the contract providing therefor becomes effective, the board of directors in the district shall file an action in the district court in which the greater part of said district is located, for the approval of any such contract and for the approval of the proposed assessments. A copy of the proposed schedule of assessments shall be attached to the petition or embodied therein. Service of process shall be deemed sufficient upon the publication of a notice in three issues, a week apart, in some newspaper of general circulation in the district. Said notice shall be addressed "To the landowners of Irrigation District No. ______ in __________ County, Kansas:" (the number of the district and the name of the county to be filled in) and said notice shall state that a description of the various tracts of land in the district and the respective amounts of assessments proposed for each tract, as fixed by the board, may be examined in the office of the clerk of said district court. It shall not be necessary that the notice contain the description of the various tracts of real estate, or of the total real estate, within the boundaries of the district. Such notice shall specify a date not earlier than thirty days after the date of the first publication of said notice and not later than forty days thereafter within which any qualified owner of land within the district shall file his answer, or other pleadings, to said petition challenging the assessment against his property, if he believes a proposed assessment against his property is either: Too high; erroneously computed; or not uniformly assessed in proportion to other tracts within the district.Upon trial of said cause, the court shall hear evidence concerning the correctness and uniformity of assessments and may modify the schedule of assessments in accordance with such evidence. The court hearing such evidence shall review the schedule of assessments as proposed by the board of directors and shall not disturb the findings and assessments of the board unless the proposed assessments are manifestly disproportionate. The assessments as determined by the district court shall be final and a conclusive determination that all such proposed assessments have been made in proportion to the benefits conferred upon such properties by reason of the improvements to be constructed, and such assessments shall constitute a perpetual lien on the properties so assessed, until paid. The approval of the proposed contract by the trial court, together with any approved changes or modifications of the same, shall be final and binding upon the parties signatory to said contract. For the purpose of defraying the expenses of organizing the district and the maintenance, operation, management, repair and improvement of such irrigation works, including salaries of officers and employees, the board may collect water rentals or service charges, or may levy assessments therefor, or by a combination of methods.