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 p reviously. In the current study cropping system treatments consisting of: spring cereal monocrops (SMC), either oats (Avena sativa L.) or ba rley (Hordeum vulgare L.); winter cereal monocrops (WMC), either winte r wheat (Triticum aestivum L.) or winter triticale (x Triticosecale Wi ttmack); binary mixtures of the spring and winter cereals planted toge ther as intercrops (IC) in the spring at the same time; and a doublecr op (DC) system where the winter cereal was planted into the spring cer eal after one clipping were grown during 2 yr at Lacombe, Alberta. Pas ture 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, ti ller height and leaf area index (LAI) were measured in each sward. Dif ferences for yield among treatments within systems did not occur, so s mall differences in sward structure were considered to be due to a com pensatory interaction of yield components which stabilized yield and w ere ignored. Sward structure appeared to explain differences among sys tems for yield distribution. Tiller density and LAI of the SMC and spr ing component of the IC and DC became relatively small as the season a dvanced, especially after cut 2. Tiller density and LAI of the WMC wer e maintained at high levels throughout the season after cut 1. After c ut 2 the winter cereal components of the IC and DC were responsible fo r 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 lig ht from the taller spring cereal component delayed tillering of the wi nter 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) resulte d in a relatively stable total tiller density, high average LAI and yi eld. Thus the superior yield distribution of the IC, shown previously, was due to the complementary way in which spring and winter cereal ti llers responded to clipping when planting occurred at the same time.