The total effect of legumes on subsequent crop yields may be divided into two categories: (i) the effect of the N that they supply, and (ii) the net effect of all other contributions. Knowing the size of these two effects, plus the N response of the subsequent crops, allows N fertilization to be optimized for decreased energy use and for reduced pollution potential. Because the size of the legume effects vary, a study was made to estimate them on a mesic, Typic Hapludalf soil at Lancaster, Wisconsin from 1967–1976. The crop species included alfalfa (A, Medicago sativa L.), corn (C, Zea mays L.), oats (O, Avena sativa L.), and soybeans [S, Glycine max (L.) Merr.] in five crop sequences: continuous C, CSCOA, CCCOA, CCOAA, and COAAA. Four N treatments: 0, 84, 168, and 336 kg/ha were applied only to C. Crop sequence phases were assigned to whole plots in a randomized, complete block design with the N treatments in subplots. There was a highly significant effect of years on all crops due to weather variation and crop variety changes. Soybeans and A did not respond to residual N. Alfalfa yields were the same in all rotations (7.6 ± 0.04 metric tons dry matter/ha/year). The mean 0 yield (Y, quintals/ha) response to residual N (kg/ha) was described by Y = Minimum C(18.4 + 0.0354N), 24.93. Both A and S increased yields of C following these legume crops. Most of the increase was due to their N contribution, which was estimated with a Mitscherlich‐Spillman N response model as 50, 66, 51, 25, 3, 84, 24, and 71 kg N/ha to CSCOA, CSCOA, CCCOA, CCCOA, CCCOA, CCOAA, CCOAA, and COAAA, respectively. The increases in C yields above that due to the legume N were estimated as the difference between the predicted maximum rotational and continuous C yields, specifically: 11, 8, 9, 4, 4, 11, 6, and 11 quintals/ha (in the same order as above).
Many farmers in the northern Corn Belt are reluctant to adopt notillage practices with continuous corn (Zea mays L.) because they fear that phenological development, stand establishment, and grain yield will be reduced compared with moldboard or chisel plowing. Mechanical removal of in‐row residue at planting may reduce or eliminate these problems. The objectives of this research were to determine the effects of surface crop residue and planter attachments on in‐row cover, seed placement, plant density, grain yield, and grain moisture content of notillage corn, and to determine if these effects changed with time. Three postharvest residue levels, residue removed, normal, and double, were compared from 1984 through 1990 on Rozetta and Palsgrove silt loam soils in southwestern Wisconsin. Average grain yields over the 7‐yr period ranged from 3.7 to 10.8 Mg ha−1. Seasonal effects, presumably due to weather conditions, accounted for >90% of the variability in grain yield. For the period 1984 to 1990, yield differences due to crop residue levels and in‐row residue removal techniques could not be declared statistically significant at the 5% level, given the limited size of the study. However, average yields with normal residue were 0.44 Mg ha−1 greater than where residues were removed. Because such a difference can be agronomically important, additional research seems warranted. In‐row residue affected planting depth and stand density emphasizing that uniform seeding depth is particularly important for successful no‐till corn production.
The genetic variation among and within strains of long‐time inbred lines of maize was investigated. Six inbred lines and male fertility restorer versions of four of these lines were obtained in 1963 from Corn Belt foundation seed stock organizations and the Iowa Agricuture Experiment Station. Significant variation was found among nonrestorer strains, restorer strains, and strain X strain crosses for nearly all of the eight quantitatively inherited characters studied. The Iowa non‐restorer and restorer strains (maintained by ear‐to‐row method) were significantly less vigorous than the other non‐restorer and restorer strains (maintained by selfing and bulking) for many comparisons. The restorer strain versions excelled over the nonrestorer versions from the same seed source in many comparisons. Vigor of strain X strain crosses was greater than the vigor of their parental strains for 34 of 35 comparisons where differences were significant. Variation within the Iowa WF9 strain was generally less than within the other four WF9 strains, which indicated that the ear‐to‐row procedure was more effective in maintaining a low degree of genetic variability within an inbred line. The time span between the year of release of a particular inbred and the commencement of this study showed little relationship with the variation among strains within the inbreds.
Long-term comparisons of alternative tillage systems are needed to evaluate their effect on corn (Zea mays L.) yield under the variable temperature and rainfall conditions of the Corn Belt. Our objective was to evaluate long-term effects of alternative tillage systems on corn growth and yield on low organic matter silt loam soils. The effect of no-tillage (NT), chisel plow (CP), and moldboard plow (MP) treatments on plant density and grain yield was measured from 1981 through 1990 on Palsgrove and Rozetta silt loam (fine-silty, mixed mesic Typic Hapludalfs) soils. Tillage treatments were randomly allocated to plots in 1981 and treatments were applied in subsequent years without rerandomization. Therefore, measurements over years on the same plot were treated as repeated measures. Grain yields for all tillage treatments were primarily affected by water stress, which varied with yearly weather conditions. Grain yield decreased approximately 0.3 Mg ha-1 per cm weighted water stress (WWS) for WWS >8 cm. No statistically significant yield differences among tillage treatments, when averaged over the 10-year period covered by the experiment, were detected. A combined analysis indicated that yield differences among tillage treatments did not depend on whether water stress or non-stress conditions occurred. Over half the variation in yearly differences in grain yield between tilled and NT treatments was explained by differences in plant density.Years were classified as stress or non-stress years on the basis of observed water stress and yearly weather factors. Variability among years was partitioned into variability among years within stress years and non-stress years. The difference in mean yields between ending (1989-90) and beginning years were used to investigate cumUlative effects of tillage treatments.
Six inbred lines and seven single crosses involving these lines were obtained from four Corn Belt foundation seed stock organizations and the Iowa Agriculture Experiment Station. The genetic variation among the strains within inbred lines and among single crosses of the same pedigree was investigated. The inbred strains were compared in testcrosses with three unrelated inbred lines and the single crosses were compared in nine double‐cross hybrids. Tests in 10 environments, five locations for two years, revealed significant differences for percentage moisture among strain testcrosses within all inbreds and for yield in all except two of the inbreds. Strains included pollen restorer (Rf) and nonrestorer (rf) versions, except for two lines in which only rf versions were available. Significant variations were obtained for Rf vs. rf strain testcrosses, among Rf strain testcrosses, and among rf strain testcrosses. The Iowa Rf strain testcrosses were not different from the remaining Rf strain testcrosses for yidd, but the Iowa rf strain testcrosses compared with the remaining rf strain testcrosses were significantly different for yield within three of the six inbreds and for moisture within five of the six inbreds. Among strains within double crosses there were significant differences for percentage moisture in eight hybrids and for yield in four hybrids. Yield differences were great enough to be of practical importance in some cases, whereas moisture differences were not considered of practical importance even though many were statistically significant.
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