Incidence of cutting height (15 or 50 cm) of two corn hybrids on crop yield and nutritive quality of silage and lower stalk left in the field

摘要

This trial was carried out to evaluate the affect of cutting height (15 or 50 cm) of two corn hybrids on dry matter yield and the nutritional quality of silages and lower stalks left in the field. The nutritional quality was evaluated in terms of chemical composition, in vitro gas production and in situ degradability of dry matter (DM). Two hybrids, Pioneer 37P73 (Pioneer) and Dekalb 615 (Dekalb), were sown in plots in a complete randomize design with three replications. At the stage of half milk line 20 plants per plot were manually cut at 15 cm of height. In 10 plants the lower stalk below 35 cm was separated to obtain the lower stalk left in the field corresponding to the 50-cm cutting height. Six plants per plot were used to determine DM weight and the proportion of leaf, stalk, husk and grain. The rest of the plants of each plot were ensiled in plastic containers of 5 liters. For the in situ study, samples of silages and lower stalks were incubated for 0, 6, 12, 18, 24, 48 and 72 h in two steers (350 kg BW). Plants of Pioneer were 24% heavier and presented higher grain content than those of Dekalb. The increase in cutting height brought about a yield drag of 15% with a concomitant increase of a similar proportion in grain content, without differences between hybrids. The high cutting height silage was higher in DM (39,7 vs . 33,6%) and starch content (35.8 vs . 29.6%) and lower in neutral detergent fiber (NDF) content (35.8 vs . 39.0%). Cutting height or hybrid did not affect the kinetics of in vitro gas production, although the increase in cutting height improved the in situ digestion rate from 3.08 to 4.65%/h and the effective degradability (51.0 to 56.1%, at kp=5%/h: DE-5). The hybrid did not affect the lower stalk weight, neither the leaf/stem proportion nor the nutritive quality (NDF= 63.9%; DE-5= 41.1%), which was lower than that of the low cutting height silage. It is concluded that hybrid did not affect parameters under study and that although the increase in cutting height occasioned a yield drag, it was counteracted by the increase in silage nutritive quality and the additional biomass of lower stalk left in the field, which could be an extra benefit in periods of forage shortage.