Knowledge of average yields that can be expected over a period of years from a soil mapping unit helps in the use of soil survey information. Soil surveys rely on yield estimates from experiments and field observations. In most cases these estimates are adjusted for the effects of soil‐water relationships and often must be extrapolated to similar soils for which no data are available. The objective of this study was to determine corn (Zea mays L.) yields on adjacent soils varying primarily in physiographic position, parent material, internal drainage, available soil water capacity, slope, and degree of erosion under the same general climatic influence and management over a long period. Corn yields were collected on 33 different soil mapping units over 24‐yr at the West Tennessee Agric. Exp. Stn., Jackson. Ten to 18 years of data were available for six of the soils, 5 to 9 yr for nine additional soils, and four yr or less for the others. Yearly mean yields across all soil mapping units ranged from 188 bu/acre in 1972 to 52 bu/acre in 1969. Yields were above 100 bu/acre in 15 of the 24 yr. The effect of physiographic position was not significant. Soils derived from sandy parent material and characterized by low available water‐holding capacity had yields about 58% of those obtained on soils derived from silty parent material and which were well, moderately well, somewhat poorly, or poorly drained. Mean yields of eroded soils averaged 90%, and severely eroded soils 73% of those on the uneroded soils. Data obtained from this study may be used in establishing soil management groups for corn production.
SUMMARYPotato seed tubers of six cultivars from commercial stocks and from stocks derived from stem cuttings (healthier seed) were fumigated with 2‐aminobutane 2 wk after lifting or treated with benomyl or thiabendazole in January. 2‐aminobutane prevented skin spot and gangrene developing on treated tubers. Experiments were planted at Rothamsted (clay with flints soil) and at Woburn (sandy loam soil) in 1973–75.Healthier seed produced more stems/plant than commercial stocks and yielded on average 8% more at Rothamsted in 1973 and 1974 and respectively 5 and 10% more at Woburn in 1973 and 1975. Seed treatments did not consistently affect stem numbers or increase yield although all treatments tended to decrease tuber size.Infection of stem bases and tubers by Polyscytalum pustulans and Rhizoctonia solani was usually less from healthier than from commercial seed and was decreased by benomyl and thiabendazole in 1973 and 1974. Infection by Helminthosporium solani of the skin around tuber eyes was greater from healthier than from commercial seed but was decreased by benomyl and thiabendazole. 2‐aminobutane sometimes decreased infection of tubers by P. pustulans and R. solani but neither of stem bases nor of tubers by H. solani. Gangrene on tubers uniformly wounded at lifting was not consistently affected by seed source or seed treatment.Treating seed with benomyl or thiabendazole in 1975 decreased skin spot and black scurf in tubers stored until March 1976. These treatments also decreased silver scurf on the produce of commercial seed at Rothamsted but gangrene was not consistently affected by seed treatments.
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