CROPPING SYSTEMS FOR SPRING AND WINTER CEREALS UNDER SIMULATED PASTURE - SWARD STRUCTURE

The feasibility of using mixtures of spring-planted spring and winter cereals for pasture in central and southern Alberta was demonstrated previously. In the current study cropping system treatments consisting of: spring cereal monocrops (SMC), either oats (Avena sativa L.) or barley (Hordeum vulgare L.); winter cereal monocrops (WMC), either winter wheat (Triticum aestivum L.) or winter triticale (x Triticosecale Wittmack); binary mixtures of the spring and winter cereals planted together as intercrops (IC) in the spring at the same time; and a doublecrop (DC) system where the winter cereal was planted into the spring cereal after one clipping were grown during 2 yr at Lacombe, Alberta. Pasture was simulated by clipping the stands five times, beginning at the joint stage of the spring cereal and four times subsequently at about 4-wk intervals. Prior to each clip, tiller weight, tiller density, tiller height and leaf area index (LAI) were measured in each sward. Differences for yield among treatments within systems did not occur, so small differences in sward structure were considered to be due to a compensatory interaction of yield components which stabilized yield and were ignored. Sward structure appeared to explain differences among systems for yield distribution. Tiller density and LAI of the SMC and spring component of the IC and DC became relatively small as the season advanced, especially after cut 2. Tiller density and LAI of the WMC were maintained at high levels throughout the season after cut 1. After cut 2 the winter cereal components of the IC and DC were responsible for the maintenance of total tiller density and LAI in their respective swards. Average seasonal total LAI were 3.36, 3.02, 1.87 and 1.17 cm2 cm-2 in the WMC, IC, DC and SMC. Late planting and competition for light from the taller spring cereal component delayed tillering of the winter cereal component in the DC compared with the IC during midsummer (cuts 2 and 3) resulting in the low average LAI. In contrast, planting the spring and winter cereal components at the same time (IC) resulted in a relatively stable total tiller density, high average LAI and yield. Thus the superior yield distribution of the IC, shown previously, was due to the complementary way in which spring and winter cereal tillers responded to clipping when planting occurred at the same time.