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Cropping systems for minimum or no tillage have been developed to produce corn (Zea mays L.) yields equal to or higher than yields obtained in conventional tillage systems, but limited research has been conducted with tillage systems involving corit and soybean [ Glycine max (L.) Merr.J rotations. The objective of this study was to compare different cropping sequences of corn, soybean, and wheat (Triticum aestivum L.) in conventional, strip, and no tillage. A field experiment was conducted on a Hartsell fine sandy loam (fine-loamy, siliceous, thermic Typic Hapludults). In 1981, corn yields with no tillage were 30o/o lower than those from conventional tillage systems. No corn yield differences were observed in 1982 and 1984 due to tillage or crop rotation; however, in 1983, strip and no tillage in conjunction with soybean in the rotation increased corn grain yields by 12%. Soybean yields in strip and no tillage decreased 16o/o compared to conventional tillage yields in 1981, but in subsequent years, soybean yields increased with those systems. A significant tillage x rotation interaction in 1981, 1982, and 1983 was caused primarily by a buildup of soybean cyst nematode (Heterodera glycines Ichinohe) (SCN) population with conventional tillage and continuous soybean. Rainfall affected soybean yields more with conventional tillage than with strip or no tillage. The conservation tillage systems (strip or no-tillage system) in combination with corn-soybean rotation for both full-season or double-cropped soybean gave the most consistent yield increase for the 4 yr.Published in Agron. J. 80:76-80(1 988).

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Information is needed on the relation between concentration of N in solution, CN, and the rate of N uptake by corn (Zea mays L.) roots in order to evaluate the soil and crop parameters affecting N fertilizer efficiency. Data on net N influx, In, vs. CN were obtained for N levels below 150 μM on corn plants of seven ages ranging from 15 to 58 days (2 weeks after tasseling). In was determined by measuring rate of N depletion from the solution in which corn plants grew. Both NH+4 and NO‐3 forms of N were used. The experiments were conducted in the growth chamber and greenhouse. Maximum influx, In‐max, occurred above 21 μM N concentration. Values of In‐max, varied with plant age and were greatest with 18 to 24‐day‐old plants and decreased exponentially to 58‐day‐old plants. In ceased when the averaged CN value decreased to 4 μM. This minimum N concentration varied little with plant age. Since the range of CN values where In varied was only 4 to 21 μM, the time period when CN is within this range for corn growing in the field is probably short so In will usually be at either In‐max or 0.