In the semiarid region of the western Canadian prairies, seeding directly into standing cereal stubble is gaining popularity. This four year study was conducted at Swift Current, SK, to determine how seeding into tall (>30 cm high), short (about 15 cm high) and cultivated cereal stubble altered the microclimate thereby affecting the growth and yield of hard red spring wheat (Triticum aestivum L.). The treatments were deployed immediately before seeding on plots that had overwintered with tall stubble. Seeding wheat into tall stubble increased grain yield and water use efficiency by about 12% compared to wheat seeded into cultivated stubble. Yield and water use efficiency for wheat seeded into short stubble were intermediate to the other stubble treatments. As well, wheat seeded into tall stubble grew taller than wheat seeded into the cultivated stubble. Further, there was a tendency for spring wheat grown in tall stubble to produce more dry matter and more leaf area, to have a lower proportion of dry matter as leaves and a higher proportion as stems, and to have a lower harvest index than the other treatments. Growing season evapotranspiration (ET) was not Effected by stubble height. When the seedlings were small, compared to cultivated stubble, tall stubble altered the microclimate near the soil surface by reducing the daily average windspeed, soil temperature, and incoming solar radiation, and increasing the reflected solar radiation. Throughout much of the growing season, potential ET at the soil surface, measured with minilysimeters, was significantly lower in the tall stubble. Tall stubble, compared to cultivated stubble, increased the proportion of ET that was transpired by the wheat. As well, reduced windspeeds and increased photosynthetic area may have increased the efficiency of net carbon assimilation. To increase grain yields, producers in the semiarid prairies who direct-seed spring wheat are advised to seed into stubble left sanding as tall as practical (at least 30 cm).
