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Long-term fertility experiments with replications are often statistically analyzed as split plots in time. Years are often shown to be significantly different and the inconsistency of treatment effects over years enters into significant year-by-treatment interactions which are difficult to interpret. The objectives of this study were to evaluate long-term fertility experiments by stability analysis and relative stability and to observe possible benefits of these analyses to complement conventional analysis of variance procedures. Stability analysis which is the linear regression of treatment yield on the location/year envi· ronment mean yield was performed on long-term wheat (Triticum tu~stivum) and coro (Zea mays L.) fertility trials. Stability analysis on wheat data from the Magruder Plots, indicated that beef manure applications (269 kg N ha·') responded poorly compared to the NPK treatment when environment means were low (<2.0 Mg ha·') and visa versa when environment means were high (>2.0 Mg ha-'). Similarly, anhydrous ammonia applied as sidedressing in an irrigated coro experiment at Mead, NE, was found to be superior to ureaammonium nitrate applied either pre-plant or sidedressed when environment means were less than 8.0 Mg ha _,. Stability analysis provided a simple method of interpreting significant year-by-treatment intelilctions detected in analysis of variance models from these longterm experiments. Stability analysis may also be useful for multilocation experiments and continuous site experiments where treatments are applied to the saine plot year to year. However, stability analysis may be misleading when employed on continuous site experiments where autocorrelations are present year to year.A MAJOR PURPOSE of long-term fertility trials is to . provide a measure of the effect of the environment over time on the consistency of treatment effects. Assessing year-by-treatment interactions in long-

Renewed interest in low‐input and sustainable crop production has rekindled interest in long‐term agronomic research. Research plots that have been monitored continuously since the late 19th Century exist in several states. Twenty‐five experiments have been identified that have been monitored for over 25 yr; 12 of these are more than 50 yr old. Yield and treatment records provide valuable information on the effects of cropping systems, tillage, manuring, and fertilization practices on yields and on soil physical and chemical properties, Most of these very early tests were non‐replicated studies using large plots and crop rotation systems. Four of America's oldest, continuous agronomic research tests were reviewed in more detail: (i) Illinois' “Morrow Plots” (c. 1876), (ii) Missouri's “Sanborn Field” (c. 1888), (iii) Oklahoma's “Magruder Plots” (c. 1892) and (iv) Alabama's “Old Rotation” (c. 1896). All of these are listed on the National Register of Historical Places. These studies document that long‐term crop production can be sustained and improved in different regions and on different soils of the USA. Long‐term studies have shown that crop rotations and attention to recognized and established soil fertility practices, which may or may not include legumes and manuring, are essential to maintaining high, sustained production.

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Critically acid soils (pH < 5.0) now exist in the major wheat (Triticum aestivum L.) production areas of the Southern Great Plains. This condition has encouraged the identification and development of hard red winter (HRW) wheat genotypes that can tolerate higher amounts of soluble soil AI. The objectives of this research were to identify Al‐tolerant HRW genotypes better adapted to soils high in soluble Al and to determine alternative gene sources. Seedlings were grown in nutrient solutions containing 0.18, 0.36, and 0.72 mM AI. As a measure of tolerance, the degree of staining on root tips of 5‐d‐old seedlings was visually scored after exposure to hematoxylin. A total of 156 HRW pureline cultivars, ancestors, and parental lines used in HRW breeding programs was classified into four tolerance levels, i.e., very susceptible (54%), moderately susceptible (15%), intermediate (14%), and tolerant (17%). Several ancestors from other wheat classes showed intermediate or tolerant responses including ‘Kenya 58’, ‘Mediterranean’, ‘Purplestraw’, and ‘Red Fife’; yet, the predominant ancestor of HRW wheat, ‘Turkey’, was very susceptible. Eight of the 16 tolerant USA cultivars shared similar pedigrees, and thus probably shared the same source(s) of Ai tolerance (i.e., ‘Sonora 64’ and ‘Trapper’). Confirmed sources of tolerance in remaining cultivars included ‘Centurk’ and ‘Prelude’, although several were derived from parents classified as very susceptible. Nine of the 15 intermediate USA cultivars were separated into two groups based on their distantly related Al‐tolerant parents (Kenya 58 and Prelude vs. Mediterranean). In summary, AI tolerance in HRW wheat could not be traced in a single lineage to any single ancestor or to a set of closely related lines. These results provide an information base to test for different genes among sources and to help develop recommendations of more tolerant cultivars for acid soils high in soluble AI.