concurring in part, and in part dissenting.
Although remanding these causes to the State Board of Equalization and Assessment is the correct result, cogent reasons for the remand, as such reasons appear to me, are quite different from the very suspect bases suggested elsewhere in this court’s opinions in the present appeals.
For a centrally assessed taxpayer’s appeal from a decision by the State Board of Equalization and Assessment, the standard of review was expressed in Northern Natural Gas Co. v. State Bd. of Equal., 232 Neb. 806, 808-09, 443 N.W.2d 249, 252 (1989): “[T]he standard of review will be to search only for errors appearing in the record; i.e., whether the decision conforms to law, is supported by competent and relevant evidence, and was not arbitrary, capricious, or unreasonable.” When this standard of review is applied in the present appeals, the state board’s decision must be reversed.
The constitutional requirement that Nebraska property taxes *383be levied uniformly and proportionately, see Neb. Const, art. VIII, § 1, is a rule of uniformity which applies to both the rate of taxation and valuation of property for tax-raising purposes. Gordman Properties Co. v. Board of Equal., 225 Neb. 169, 403 N.W.2d 366 (1987). “[T]he object of the law of uniformity is accomplished if all of the property within the taxing jurisdiction is assessed at a uniform standard of value.” (Emphasis in original.) Carpenter v. State Board of Equalization & Assessment, 178 Neb. 611, 619, 134 N.W.2d 272, 278(1965).
Equalization of assessments has for its general purpose to bring the assessment of different parts of a taxing district to the same relative standard, so that no one of the parts may be compelled to pay a disproportionate part of the tax. Hacker v. Howe, 72 Neb. 385, 101 N.W. 255 (1904); Gordman Properties Co. v. Board of Equal., supra.
As a result of Trailer Train Co. v. Leuenberger, 885 F.2d 415 (8th Cir. 1988), issued on December 19, 1988, collection of the tax on personal property of Trailer Train, a centrally assessed car company-taxpayer in Nebraska, was permanently enjoined.
In the wake of Trailer Train, Natural Gas Pipeline Company (NGPL), as a centrally assessed “public service entity” within Neb. Rev. Stat. § 77-801 (Reissue 1990), requested that the state board equalize the value of NGPL’s personal property for 1989. At the time of the August 15,1989, hearing on NGPL’s request, valuations for centrally assessed car companies and air transportation carriers were undetermined, but were expected to be determined in December 1989.
At the equalization hearing, the Nebraska Department of Revenue (DOR) informed the board that a “unit valuation method” was used to establish the value of personal property owned by railroads and public service companies, a “valuation of the entirety of a company, as opposed to a summation of individual parts of a company.” Under the “unit valuation theory” or method, “particular assets . . . only develop value when there is an integrated use of [the] assets and the assets standing alone do not necessarily have an individual recognized value, [for example], a pipeline cut off at [a] county line would not necessarily have any value unless it’s interconnected in a *384complete unit.” In applying the unit valuation method, DOR “allocates a portion of that total [unit] value . . . based on various factors, depending on [the] industry it is. These factors are intended to identify specific things about the companies that contribute to its value. Such as investment income, and other similar features.” Although it is possible to determine a value for the various items of a centrally assessed taxpayer’s personal property, that process “is extremely difficult, there’s a lot of these types of property [that] do not carry value unless [they] are a part of the integrated unit.” Nevertheless, according to DOR, through “unit valuation,” personal property of railroad companies and public service entities is valued at “100 percent of market value.” In reference to NGPL’s equalization request, however, DOR used the 1989 “assessment sales ratio” for real estate in Nebraska’s 93 counties, that is, the aggregate assessment sales ratio for residential and recreational acreages, commercial and industrial real estate, and agricultural land, which produced a factor of “91.91 percent,” a weighted real estate average which was then applied to the value of NGPL’s personal property. The board accepted the 91.91 real estate factor and set the 1989 equalization rate for NGPL’s personal property at 91.91 percent.
As the result of the Trailer Train injunction, the state board faced a dilemma. If the value of NGPL’s personal property were equalized with the value of other centrally assessed taxpayers’ personal property, Trailer Train’s personal property, which might have a value of “zero” for tax purposes as a result of the federal injunction, would become part of the equalization equation and perhaps necessitate a corresponding reduction in the tax value of NGPL’s property, since the property of Trailer Train and NGPL apparently belong to the same general class. To avert that possibility, the State resorted to the 91.91 percent factor produced from the aggregate sales ratio of Nebraska real estate, although it was admittedly possible to achieve a value based on personal property of centrally assessed taxpayers — perhaps difficult, but, nevertheless, possible. Consequently, DOR resorted to real estate values to equalize the value of NGPL’s personal property. In that process, DOR used values of real estate, nondepreciable *385property with value ascertainable by different methods, in order to determine value for personal property, which is valued in relation to retail cost less depreciation. Thus, DOR’s equalization method was not an attempt to compare apples with oranges, but an abortive attempt to establish a comparative similarity between oranges and orangutans. The absolute dissimilarity of property and essentially different values prevented an equalization under DOR’s methodology. Were the adjustment of values made according to DOR’s employed method, which was incorporated into the board’s decision, there would truly be inequality in equalization. There is no factual basis for the board’s equalization order; hence, the board’s decision is arbitrary, unreasonable, and capricious and must be set aside.
In Sommerfeld v. City of Seward, 221 Neb. 76, 80, 375 N.W.2d 129, 132 (1985), we stated: “It has long been a rule in Nebraska that a court, including the Supreme Court, will decline to pass upon constitutionality of legislation unless such determination of constitutionality is necessary for proper disposition of an action.” Therefore, if chronology has rendered the subject matter of L.B. 1 “irrelevant to equalization,” as other members of this court believe, what is really irrelevant is any discussion about the constitutionality of L.B. 1, now Neb. Rev. Stat. §§ 77-103 and 77-103.01 (Reissue 1990). That same critique applies to this court’s comments about L.B. 7.
However, since the court has proceeded to express certain views and conclusions regarding the legislation in question, some additional comment is in order lest silence give consent and tacit approval to the constitutionally unwarranted conclusions in other opinions expressed today. So, “Once more unto the breach, dear friends, once more.”
This court has concluded that in the context of the present appeals, L.B. 1 is irrelevant and, in view of the chronology, could not be retroactively applied at the peril of offending the anticommutation of tax provision in Neb. Const, art. VIII, § 4. Yet, the fact is that L.B. 1 has never actually been applied to the appellants’ claims for equalization, and, additionally, the state board’s previous equalization order has been set aside, resulting *386in proceedings anew before the state board. Thus, the equalization order and consequent equalization-ordered levies have vanished. There remains the unanswered question about what tax statutes apply when the board considers the appellants’ applications on remand. The lapse of time would seem to have obviated concerns about the chronology inasmuch as the state board, as a result of these appeals, has yet to enter an order pursuant to the appellants’ applications, and several events, including the enactment of L.B. 1, have transpired, or will have transpired, before the board considers the appellants’ application on remand. An intriguing question arises concerning the law applicable to the prospective equalization proceedings, but that question, and perhaps an even more fascinating answer, must await another day which undoubtedly will come.
It is difficult to accept this court’s conclusion that application of L.B. 1 to a 1989 equalization “would result in commutation of a tax, in violation of Neb. Const, art. VIII, § 4,” especially when Steinacher v. Swanson, 131 Neb. 439,268 N.W. 317 (1936), is offered as support for that conclusion. Decided in 1936, Steinacher dealt with legislation obviously intended to ease some of the burden from property tax liability during the Depression years, a time for many, it is safe to say, when money was not all that plentiful. The questioned legislation in Steinacher provided that property taxes, otherwise payable in a lump sum, could be paid in installments of 5 years for personal property and 10 years for real estate. According to the Steinacher court, that legislative transformation of a lump-sum payment into installment payments violated the anticommutation prohibition in Neb. Const, art. VIII, § 4, because “if the legislature has the power to extend the time in which taxes must be paid, as was done in the instant case, it could repeat the extensions or extend them for such a duration of time that it would amount to a remission of the tax.” 131 Neb. at 448, 268 N.W. at 322. As a more accurate analysis of the Steinacher situation, the time value of a monetary lump-sum payment vis-a-vis installment payments results in the unconstitutional reduction of the amount due from the tax liability. In a consideration of L.B. 1 on its face, *387that is, a facial challenge based on Neb. Const, art. VIII, § 4, which is exactly the nature of the question that others have unnecessarily undertaken to answer, just how application of L.B. 1 results in a reduction of any tax liability is unknown. To reach the “commutation” conclusion expressed today, much more information is required for the factual premises necessary as the bases for such conclusion, information which is understandably absent in view of the sequence of events leading to and during pendency of the present appeals.
In passing on L.B. 7, the court assails the Legislature’s expressed objectives and considerations for enactment of the legislation. Legislative expressions of purpose, considerations, or reasons underlying enactment of L.B. 7 (Neb. Rev. Stat. § 77-202(11) (Reissue 1990)) appear in § 1 of that bill, whereas the provision for tax exemption of railroad rolling stock appears in § 2 of the bill. Those legislative expressions in § 1 may be characterized as a preamble for the actual exemption specified in § 2. A statutory preamble is a declaration or explanation of the reasons for enactment of the legislation and objectives sought to be obtained by the legislation. Griffith v. New Mexico Public Service Commission, 86 N.M. 113, 520 P.2d 269 (1974). While a statutory preamble may express legislative motives and inducements for enactment of legislation, the preamble is not an essential part of the legislation. Portland Van & Storage Co. v. Hoss, 139 Or. 434, 9 P.2d 122 (1932). Although language in a legislative enactment may provide a manifest indication of the objective to be achieved through the legislation, a court, with or without an expression of a legislatively avowed objective, has the duty to determine whether the Legislature has constitutionally exercised its power reasonably related to a valid governmental purpose or interest. See State ex rel. Spire v. Northwestern Bell Tel. Co., 233 Neb. 262, 445 N.W.2d 284 (1989). Therefore, apart from the legislatively expressed objectives, purposes, reasons, motives, or inducements pertaining to L.B. 7, the judicial determination is whether L.B. 7 is unconstitutional on account of the exemption for a railroad’s rolling stock.
Neb. Const, art. VIII, § 2, in part provides that “[t]he Legislature may classify personal property in such manner as it *388sees fit, and may exempt any of such classes, or may exempt all personal property from taxation.” Generally, “the Legislature has plenary power over taxation except as limited by the Constitution.” State ex rel. Meyer v. McNeil, 185 Neb. 586, 587-88, 177 N.W.2d 596, 598 (1970).
Tax classifications must be based on a real and substantial difference, having a reasonable relationship to the subject of the particular legislation. Moeller, McPherrin & Judd v. Smith, 111 Neb. 424, 255 N.W. 551 (1934). Tax classifications which do not rest on real differences of situation and circumstances violate the uniformity clause of the Nebraska Constitution. See State ex rel. Meyer v. McNeil, supra.
There is a real and substantial difference between railroad rolling stock, tax-exempt under L.B. 7, and property of other common carriers. Transportation of Nebraska products to market is essential to this state’s economy. Among Nebraska’s chief products is grain harvested in this state. It is self-evident that expeditiously getting Nebraska-harvested grain into the stream of interstate commerce, which frequently involves grain shipments to mills and ports at some distance from Nebraska, is vital to the strength of our state’s economy. Large and usually rapid interstate shipments by rail are readily distinguishable from the relatively smaller quantities moved by motor carriers. I am unaware of any planeloads of grain moving by air carriers within or departing Nebraska. Therefore, although this court feels that mention of “restrictions or conditions” somehow constitutionally damns L.B. 7, the “conditions” might well apply to something as common as the weather, including inclemency, climatic conditions which the Postal Service considers in the expression “Neither snow, nor rain, nor heat, nor gloom of night stays these couriers from the swift completion of their appointed rounds.” Then again, in retrospect, maybe comparing postal service to railroad operations is a bad example. However, all the sundry and imaginative interpretations regarding a legislative preamble for a statute are beside the point, since the preamble is not part of the tax exemption in L.B. 7 for railroad rolling stock. What is important is the classification by which railroad rolling stock is tax-exempt personal property. There is a reasonable and *389legitimate basis for the exemption of railroad rolling stock under L.B. 7. For that reason, courts should decline to inquire into the wisdom, policy, or justness of valid legislative action. As we noted in Spence v. Terry, 215 Neb. 810, 816, 340 N.W.2d 884, 887 (1983): “Reasons underlying valid legislation are left first to the Legislature and ultimately to the electorate.”
Turning to some of the court’s comments in view of Trailer Train v. Leuenberger, 885 F.2d 415 (8th Cir. 1988), especially the statement “[Ejven if this state’s present classification of property as exempt and not exempt was to be found valid under Nebraska’s constitution, it could not withstand muster under federal law,” Trailer Train does not support such assertion, for the court in Trailer Train stated: “The purpose of § 306 of the 4-R Act is to prevent tax discrimination against railroads in any form whatsoever.... It does not encroach upon a state’s right to tax its citizens as it sees fit, as long as that tax does not discriminate against railroads.” 885 F.2d at 416-17. What Trailer Train does teach is that Nebraska’s tax structure does not exist in some provincial and pristine environment or in a vacuum, hermetically sealed to the law of the land. As federal protection against a state’s discriminatory taxation of property is extended to various entities, consequences of property tax exemptions under state law will have to receive the most careful attention lest exemptions result in imposition of a disproportionate share of the tax burden on federally protected entities and thereby prevent collection of a tax revenue from those protected entities. The bell some hear as a death knell is really the signal for round 2 in the tax fight after Trailer Train.
Also, some of this court criticizes Stahmer v. State, 192 Neb. 63, 218 N.W.2d 893 (1974), but as we recently noted in Banner County v. State Bd. of Equal., 226 Neb. 236, 252, 411 N.W.2d 35,45 (1987), the Nebraska “Constitution... must be read as a whole.” The constitutional requirement of uniformity or equality in taxation extends only to those objects of taxation which the Legislature has determined to be property subject to the tax burden. U.S. Cold Storage v. Detroit Assessors, 349 Mich. 81, 84 N.W.2d 487 (1957). See, also, T. Cooley, ATreatise on the Constitutional Limitations Which Rest Upon the Legislative Power of the States of the American Union (8th ed. *3901927). As the court observed in State v. Willingham, 9 Wyo. 290, 294, 62 P. 797, 798 (1900):
[T]he State may tax all, or it may select for taxation certain classes, and leave the others untaxed. Considerations of general policy determine what the selection shall be in such cases, and there is no restriction on the power of choice unless one is imposed by constitution. . . . [The constitutional requirement of uniformity in taxation] merely obliges the Legislature to impose an equal burden upon all those who find themselves in the same class. . . . To be uniform, taxation need not be universal.
Requisite deference to each constitutional provision concerning taxation and exemption of property will be no small task and will be one which both the Legislature and this court will encounter again.
Next, there is the view expressed by some of the court that
the classification set forth in L.B. 1 is unconstitutional because it is not based on a real and substantial difference between “machinery and equipment used for business purposes or center pivot or other irrigation systems of a type used for agricultural or horticultural purposes” and machinery and equipment used for other purposes.
For tax purposes, property is either real estate or personal property. L.B. 1, now § 77-103 (Reissue 1990), amends the statutory definition of “real estate,” formerly contained in § 77-103 (Reissue 1986), and expands the previous definition, so that the meaning of “real estate” now includes “pipelines, railroad track structures, electrical and telecommunication poles, towers, lines, and all items actually annexed to such property, and any interest pertaining to the real property or real estate.” Also, for purposes of taxation, L.B. 1 supersedes the common-law test to determine whether an item is a fixture or personal property and thereby eliminates the test for a fixture which this court used in Northern Natural Gas Co. v. State Bd. of Equal., 232 Neb. 806, 443 N.W.2d 249 (1989). As a consequence of L.B. 1, an article’s actual annexation to real estate is the test to determine whether the item is a fixture and, therefore, part of the real estate. When used on real estate, each of the items added in the expanded definition of “real estate” in *391§ 77-103 (Reissue 1990) is rendered immobile and becomes stationary as the result of some physical connection to the real estate. For instance, a pipeline is usually buried in the ground which it crosses, while structures such as electrical and telecommunications poles and towers are immobile when part of the structure is buried in the earth to support the remaining part above ground or when such items are securely fastened to buried foundations for additional support.
In contrast with the stationary aspect of those items within the definition of “real estate” in L.B. 1, a “center pivot,” as part of an irrigation system, is self-propelled and, therefore, mobile machinery which consists of a single pipe or arm connected by a swivel to a fixed anchor or pivot usually located in the center of a field to be irrigated. The swivel arm, as the radius from the pivot point, is elevated and supported by towers which move on wheels along a constant circumferential path around the pivot. Water passing from the well near the pivot point is sprayed by sprinkler nozzles located on the arm as it sweeps the field much in the manner of the hand of a clock. Thus, the center pivot may be disconnected from the pivot point at one irrigation site and moved to another site for irrigation. See, Irrigation 327 et seq. (C. Pair 5th ed. 1983); M. Kay, Sprinkler Irrigation, Equipment and Practice 85 et seq. (Batsford Academic & Educational Ltd. 1983); II Academic American Encyclopedia 281 et seq. (1986). Irrigation systems used for agricultural and horticultural purposes may also consist of movable surface pipes as conduits for water sprayed from sprinklers attached to the pipes, thereby allowing mobility from one irrigation site to another. Therefore, mobility of a center pivot and other surface irrigation system distinguishes the foregoing property from those items which the Legislature has defined as “real estate” in L.B. 1.
Since it is extremely unlikely that there are mobile microwave towers or portable pipelines, in substance and effect, the Legislature has, by express definition, defined and classified some property as “real property” for taxation controlled by Neb. Const, art. VIII, § 1, and has, by specifically excluding certain types of property from “real estate,” correspondingly defined and classified particular items as personal property for *392the purposes of taxation controlled by Neb. Const, art. VIII, § 2, and Neb. Rev. Stat. §§ 77-201 et seq. (Reissue 1990). Therefore, the definition of “real estate” in L.B. 1 and the exclusion of certain property from statutorily defined “real estate,” namely, a center pivot or other irrigation system of a type used for agricultural or horticultural purposes, have a rational basis and are, therefore, reasonable and not arbitrary or unfounded.
Even if this court had concluded that the business “machinery and equipment” provision of L.B. 1 was unconstitutional, that provision is distinct from “center pivot or other irrigation systems of a type used for agricultural or horticultural purposes” and is clearly severable pursuant to the express severability provision in L.B. 1, § 4. See, State v. Monastero, 228 Neb. 818, 424 N.W.2d 837 (1988); Ewing v. Scotts Bluff Cty. Bd. of Equal., 227 Neb. 798, 420 N.W.2d 685 (1988); State ex rel. Douglas v. Sporhase, 213 Neb. 484, 329 N.W.2d 855 (1983).
In any event, these causes are remanded for proceedings before the State Board of Equalization and Assessment. With that disposition, I concur.