. 1987. Effects of nutrient availability and subsoil bulk density on corn yield and nutrient absorption.Can. J. Soil Sci. 67:281-292.A 4-yr study was conducted to determine the extent to which soil fertility and subsoil bulk density limit corn yields at the Elora Research Station. In one treatrnent, soil was replaced to a depth of I m with a highly fertilized soil:peat:perlite artificial medium (AM). Two other main treatments consisted of the natural soil with either a recom-. mended fertility (RF) or a very high fenility (vHF) treatment. plots were irrigated using a trickle system . Corn (Zea mays L.) yields on the artificial medium were the same as those on the VHF treatment in all 4 yr. This was unexpected because of a high subsoil bulk density (1.5 Mg m-r in the Bm and 1.8 Mg m-: in the Ck horizons). Grain dry matter yields on the VHF treatment were considerably higher than those on the RF treafinent (7.8 compared to 5.3 t 1tu-t) and were higher than the average yield (6.1 t ha-t) on the best treatrnent in a previous long-term fertility experiment at Elora. The response appeared to be due to all three macronutrients. Some response to N and K was expected, but the response to P, which was a major portion of the total response, was unexpected. It is concluded that subsoil bulk density is not a significant limitation on this soil when adequate water and nutrients are provided. The marked response to phosphorus application above recommended rates may indicate a need to re-evaluate the fertility requirements of high-yielding corn hybrids. (Miller 1981(Miller , 1983
. 1987. Effects of subsoil bulk density, nutrient availability and soil moisture on corn root growth in the freld. Can. J. Soil Sci. 67:293-308.In a 4-yr study, root growth in the upper 50 cm of a silt loam soil (Gleyed Melanic Brunisol) was equal to or greater than that in a low-density artificial medium (soil:peat:perlite) in spite of a high bulk density in the soil (1.5 Mg m : in the 15-to 45-cm depth). We suggest that, due to the natural structure of the Bm horizon, the resistance to root growth is much less than would be expected from bulk density or penetrometer resistance measurements. Marked increases in P and K fertility in the surface soil had only minor effects on either the total length or distribution of roots although the shoot growth was markedly increased. Neither total root length nor root distribution were altered by irrigation during 1981, the only year a moisture variable was included. During a 2-wk dry period in July, prior to anthesis, soil water potential on the nonirrigated plots decreased to -1.5 MPa in the upper 15 cm and to -0.
A centrifugation procedure is described for producing different degrees of compaction in both wet and dry soils. To ensure uniform distribution of water in the test samples, appropriate quantities of crushed ice are mixed with the oven‐dry soils 24 h prior to the centrifugation step.
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