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Influence of previous cropping sequence on compression characteristics of an aggregated soil
344 POSTERS
I. TILLAGE AND PLANT GROWTH
INFLUENCE OF PREVIOUS CROPPING SEQUENCE ON COMPRESSION AGGREGATED SOIL D.A. ANGERS,
CHARACTERISTICS
OF AN
B.D. KAY and P.H. GROENEVELT
University of Guelph, Ontario Agricultural College, Resource Science, Guelph, Ont. NIG 2WI (Canada)
Department
of Land
It has been suggested that different cropping sequences alter the type and content of soil organic matter and thereby can change the strength and size distribution of soil aggregates. Modification of aggregation may influence the compactibility of agricultural soils. A uniaxial compression device was used to measure the compaction characteristics of beds of aggregates taken from plots with different cropping histories, ranging from continuous corn to continuous bromegrass. Compression curves relating bulk density to applied pressure were obtained at different water contents. The bulk density and total porosity under standard compaction ( 0 . 1 M P a load and 50% water saturation) and the compression index were determined. Organic matter content (OM), particle density, aggregate size distribution, aggregate tensile strength (Y) and aggregate bulk density were also measured. The total porosity under standard compaction (N5o) was correlated to both OM and cropping history. OM and cropping histS~y were not correlated, presumably due to the short duration of the cropping sequences. OM was positively correlated to NS0 and this was attributed to its influence on intra-aggregate porosity. On the other hand, the influence of cropping history on N. 0 was attributed to its influence on inter-aggregate porosity. Soils from p~ots with a recent history in bromegrass had larger values of inter-aggregate porosity under compaction than soils from plots under continuous corn. This was attributed to larger aggregate strength and increased proportion of larger aggregates (I-5 mm) under bromegrass than under continuous corn. Compression characteristics of aggregate beds were found to be significantly influenced by changes in aggregation due to previous cropping sequence. The results suggest that the maintenance of appropriate levels of organic matter content and the incorporation of grass in rotation with corn increase the resistance of the soil to compaction.
POPULATION DYNAMICS OF THE EUROPEAN CORN BORER (Ostrinla nubilalis IN RELATION TO CONSERVATION TILLAGE
(H~bner)),
E. C. BERRY USDA-ARS,
Corn Insects Research Unit, Ankeny,
IA (U.S.A.)
Population dynamics of the European corn borer (ECB) (Ostrinia nubilalls (H~bner)) were studied in 5 tillage systems in continuous corn and corn-soybean rotations in Iowa during 1976 to present. Tillage systems consisted of plow tillage, surface tillage, till-plant, and no-tillage. The percentage of plants
I. TILLAGE AND PLANT GROWTH
INFLUENCE OF PREVIOUS CROPPING SEQUENCE ON COMPRESSION AGGREGATED SOIL D.A. ANGERS,
CHARACTERISTICS
OF AN
B.D. KAY and P.H. GROENEVELT
University of Guelph, Ontario Agricultural College, Resource Science, Guelph, Ont. NIG 2WI (Canada)
Department
of Land
It has been suggested that different cropping sequences alter the type and content of soil organic matter and thereby can change the strength and size distribution of soil aggregates. Modification of aggregation may influence the compactibility of agricultural soils. A uniaxial compression device was used to measure the compaction characteristics of beds of aggregates taken from plots with different cropping histories, ranging from continuous corn to continuous bromegrass. Compression curves relating bulk density to applied pressure were obtained at different water contents. The bulk density and total porosity under standard compaction ( 0 . 1 M P a load and 50% water saturation) and the compression index were determined. Organic matter content (OM), particle density, aggregate size distribution, aggregate tensile strength (Y) and aggregate bulk density were also measured. The total porosity under standard compaction (N5o) was correlated to both OM and cropping history. OM and cropping histS~y were not correlated, presumably due to the short duration of the cropping sequences. OM was positively correlated to NS0 and this was attributed to its influence on intra-aggregate porosity. On the other hand, the influence of cropping history on N. 0 was attributed to its influence on inter-aggregate porosity. Soils from p~ots with a recent history in bromegrass had larger values of inter-aggregate porosity under compaction than soils from plots under continuous corn. This was attributed to larger aggregate strength and increased proportion of larger aggregates (I-5 mm) under bromegrass than under continuous corn. Compression characteristics of aggregate beds were found to be significantly influenced by changes in aggregation due to previous cropping sequence. The results suggest that the maintenance of appropriate levels of organic matter content and the incorporation of grass in rotation with corn increase the resistance of the soil to compaction.
POPULATION DYNAMICS OF THE EUROPEAN CORN BORER (Ostrinla nubilalis IN RELATION TO CONSERVATION TILLAGE
(H~bner)),
E. C. BERRY USDA-ARS,
Corn Insects Research Unit, Ankeny,
IA (U.S.A.)
Population dynamics of the European corn borer (ECB) (Ostrinia nubilalls (H~bner)) were studied in 5 tillage systems in continuous corn and corn-soybean rotations in Iowa during 1976 to present. Tillage systems consisted of plow tillage, surface tillage, till-plant, and no-tillage. The percentage of plants