EFFETS DE L’HUMIDITE DU SOL, DES DATES DE SEMIS ET DES MAUVAISES HERBES SUR LE RENDEMENT DES CEREALES

Abstract

Soil moisture and weeds were evaluated under two seeding dates on a St. André sandy loam to explain the increase in grain yield observed with the early sowing of oats (Avena sativa L.), barley (Hordeum vulgare L.), and wheat (Triticum aestivum L.). For each seeding date (early and late May), two soil moisture levels were obtained using the seasonal precipitation as the first level and by adding 25 mm of water/week as the second level. Weed cover was noted on each plot. A greenhouse experiment was conducted by simulating the soil moisture and soil temperature conditions measured in the field. In the field, early seeding and irrigation increased the yield of cereals but the yield differences observed between seeding dates were greater than the yield differences obtained between soil moisture levels. Soil moisture does not explain by itself the increased yield obtained with early seeding because the plots sown in late May and irrigated produced about 80% of the yield obtained on plots sown early and not irrigated. The regression analysis has shown that the soil thermal units between sowing and emergence and the total amount of water between emergence and heading explain more than 50% of the yield variation of cereals. Weeds did not play an important role. Greenhouse results were comparable to those obtained in the field although the importance of soil moisture was more evident. On light soils at La Pocatière, the yield of cereals is regulated by cool soil temperatures at seeding and by high soil moisture level between emergence and heading. These conditions are generally met when seeding is done in early May.