Concurrent recurrent selection experiments were conducted for five cycles to compare three methods of selection for grain yield in maize (Zea mays L.): (1) combining ability with an inbred line (Inbred Tester Method), (2) combining ability with the broad‐base parental population (Parental Tester Method), and (3) yield S2 lines per se (S2 Progeny Method). The 15 selected populations were then crossed with the parental population and with another broad‐base synthetic to evaluate changes in general combining ability, and also were tested as randommated and selfed populations per se.A significant linear increase in general combining ability over cycles was obtained for all methods, but the Inbred Tester Method was significantly more effective than the other two methods (4.4% gain per cycle, compared with 2.4 and 2.0% for the Parental Tester and S2 Progeny Methods, respectively). There was no significant difference among methods for yield of random‐mated selected populations when adjustments were made for differences in rate of inbreeding.The results indicate that the inbred tester used was homozygous recessive at many important loci. This would result in larger testcross variances and more successful selection of dominant favorable alleles than is possible with a broad‐base tester, which probably has intermediate gene frequencies at most loci. The slow progress in combining ability improvement with the S2 Progeny Method suggests that this method also was not effective in fixing dominant favorable alleles.

High costs of labor, fuel, and machinery; need to conserve moisture; loss of soil from erosion; and desire to double crop are some of the factors considered in the trend towards no‐tillage methods of planting crops. No‐tillage planting of corn in Pensacola bahiagrass (Paspalum notatum Flugge) sod and small grains such as rye (Secale cereale L.) was compared to conventional planting “rotavating, disking, and planting” for 3 years on Lakeland fine sand (Typic Quartzipsamment). When Pensacola bahiagrass was treated with paraquat + residual herbicide before planting corn by the notillage method, it recovered quickly and competed with the corn for water and nutrients. Corn (Zea mays L.) planted no‐tillage had lower yields than when conventionally planted, but after corn harvest the bahiagrass growth was adequate for grazing. Adding extra N to the no‐tillage corn increased yields of both corn and grass. Corn under no‐tillage in rye treated with paraquat + residual herbicides generally yielded about the same as conventionally planted corn. Pensacola bahiagrass when treated with glyphosate in combination with other herbicide was almost all killed and offered little competition to the corn. Forage yield in the fall was only 37% of yield after paraquat‐residual herbicide application. The effectiveness in controlling broadleaf weeds with atrazine, cyanazine, alachor, linuron, and combinations of these herbicides varied seasonally, but had no significant effect on corn yields. Weed growth at corn harvest was considerably less on the no‐tillage plots; however, after 3 years of continuous no‐tillage corn perennial weeds were beginning to appear while few perennial weeds were observed in the conventionally planted corn.

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Three methods of breeding for higher grain yield in maize (Zea mays L.) were compared: (a) recurrent selection for combining ability with the parental population (Parental Tester method), (b) recurrent selection for combining ability with an unrelated inbred line (Inbred Tester method), and (c) recurrent selection for yield of S2 progenies per se (S2 Progeny method).After three cycles of selection for grain yield had been completed with each of the three methods, the nine resulting selected populations were evaluated for grain yield (a) as random‐mated populations (synthetics), (b) as selfed populations (bulked S1 lines), and (c) in crosses with 11 unrelated testers. Significant differences among the breeding methods were noted for the second and third cycles of selection, but not for the first cycle. The Parental Tester method produced the highest yielding random‐mated (syn‐3) population; whereas the S2 Progeny method produced the highest yielding selfed population. Average combining ability with unrelated testers for all three methods was increased significantly (5.2%) by the second and third cycles of selection, but there was no significant difference among methods. Although the Inbred Tester method resulted in significant improvement in yield of selfed populations, it was inferior to the other two methods for population improvement in the over‐all evaluation.Selfing one generation resulted in over 70% reduction in yield of the first cycle populations, which indicates that dominance is of considerable importance in the base population. Inbreeding depression was progressively less drastic in the second and third cycle populations, particularly with the S2 Progeny method.

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