EFFECTS OF CROP RESIDUES ON PRODUCTION OF BARLEY, BROMEGRASS AND ALFALFA IN THE GREENHOUSE AND OF BARLEY IN THE FIELD

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Abstract
Barley (Hordeum vulgare L. cv. Conquest), bromegrass (Bromus inermis Leyss. cv. Magna), and alfalfa (Medicago media Pers. cv. Beaver) were grown together in a greenhouse in soil amended with ground straw or chaff. Additions of 8,970 kg/ha of rapeseed (Brassica napus L. cv. Target and B. campestris L. cv. Echo) and wheat (Triticum aestivum L. cv. Manitou) straws reduced barley grain and straw production and bromegrass dry matter production at the first harvest. Alfalfa dry matter production at the first cut increased where wheat and Echo rape straws were incorporated in the soil, but not where Target rape straw was used. Subsequent harvests of bromegrass and alfalfa showed no effects that were consistent between two independent experiments. On Span rape stubble in the field, barley produced 3,600 kg/ha of grain where a rape swath had lain the previous fall, compared with a production of 3,300 kg/ha elsewhere. This difference was significant (P < 0.01) and correlated with a difference in soil nitrogen. A second experiment where 6,730 kg/ha of rape straw were incorporated in summer-fallowed soil containing 22 ppm of nitrogen in the top 61 cm, barley yields averaged 5,100 kg/ha and were not affected by the added straw. The results are interpreted as showing that rapeseed residues in Melfort silty clay loam are not more deleterious than wheat residues to subsequent crops and that the principal cause of yield reductions is a deficiency of available nitrogen in the soil caused by microbial activity on the crop residues.

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