STUBBLE HEIGHT EFFECTS ON MICROCLIMATE, YIELD AND WATER-USE EFFICIENCY OF SPRING WHEAT GROWN IN A SEMIARID CLIMATE ON THE CANADIAN PRAIRIES

In the semiarid region of the western Canadian prairies, seeding direc tly into standing cereal stubble is gaining popularity. This four year study was conducted at Swift Current, SK, to determine how seeding in to tall (>30 cm high), short (about 15 cm high) and cultivated cereal stubble altered the microclimate thereby affecting the growth and yiel d of hard red spring wheat (Triticum aestivum L.). The treatments were deployed immediately before seeding on plots that had overwintered wi th tall stubble. Seeding wheat into tall stubble increased grain yield and water use efficiency by about 12% compared to wheat seeded into c ultivated stubble. Yield and water use efficiency for wheat seeded int o short stubble were intermediate to the other stubble treatments. As well, wheat seeded into tall stubble grew taller than wheat seeded int o the cultivated stubble. Further, there was a tendency for spring whe at 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 prop ortion as stems, and to have a lower harvest index than the other trea tments. Growing season evapotranspiration (ET) was not Effected by stu bble height. When the seedlings were small, compared to cultivated stu bble, tall stubble altered the microclimate near the soil surface by r educing the daily average windspeed, soil temperature, and incoming so lar radiation, and increasing the reflected solar radiation. Throughou t much of the growing season, potential ET at the soil surface, measur ed with minilysimeters, was significantly lower in the tall stubble. T all stubble, compared to cultivated stubble, increased the proportion of ET that was transpired by the wheat. As well, reduced windspeeds an d increased photosynthetic area may have increased the efficiency of n et carbon assimilation. To increase grain yields, producers in the sem iarid prairies who direct-seed spring wheat are advised to seed into s tubble left sanding as tall as practical (at least 30 cm).