Dry matter yield and nutritive value of pea/wheat bi-crops differing in maturity at harvest, pea to wheat ratio and pea variety

Studies were conducted over 3 years to evaluate the effect of maturity at harvest (Year 1 and 2), pea content (Year 2) and pea variety (Magnus versus Setchey, Year 3) on the nutritional quality of inter-cropped, spring-sown, pea/wheat bi-crop forages. Herbage samples were taken at different stages of growth for separation of component crops (peas and wheat) and estimation of dry matter (DM) content, DM yield, chemical composition and in vitro digestible organic matter in DM (DOMD). The DM yields generally increased with maturity and the average bi-crop DM yields was highest in Year 3. Peas had higher crude protein (CP) and DOMD but lower neutral detergent fibre (NDF) and acid detergent fibre (ADF) than wheat. For both peas and wheat, the DM, CP, starch, NDF and DOMD at harvest were higher in the second cut (15 weeks after planting) than in the first cut (13 weeks after planting). The DM yield, CP, starch, WSC, NDF, ADF content of the bi-crops and their DOMD yields were all influenced by the stage of maturity and the proportion of peas to wheat in the bi-crops. The results show that inter-cropped spring sown pea/wheat bi-crops can be harvested between 13 and 16 weeks after planting. However, relative to other stages of maturity measured, harvesting when the wheat was at early to soft dough stage and the peas at yellow wrinkle pod stage appeared optimal. In comparison with the pea variety Magnus, the lower NDF and ADF, and higher CP, WSC, starch and DOMD in the pea variety Setchey suggests that the latter is nutritionally better. In deciding when to harvest, the chemical composition and stages of growth of both peas and wheat are important. However, because there is little decline in the quality of peas with maturity, it may be possible, in certain conditions (e.g. absence of lodging, infections or senescence in peas), to use the stage of maturity of wheat only as the index of the ideal time to harvest pea/wheat bi-crop for conservation as forage for ruminants