Abstract:

To study the changes in agronomic traits and fermentation quality of maize silage harvested at different stages of grain development in desert irrigated areas and to screen for the best-performing maize silage cultivars in the Third Division area， four silage-specific and 11 grain-feeding maize varieties were evaluated， and agronomic traits determined. Silages were prepared at the grain-filling stage， and when the milk line reached the 3/4 milk stage， 1/2 milk stage and 1/4 milk stage， of grain development. Nutrient composition， fermentation quality and in vitro digestion were measured after 60 days of fermentation， and the agronomic traits， nutrient composition， fermentation quality and digestion characteristics were used as evaluation indexes for the multi-factor evaluation of the 15 maize varieties using the similarity priority ratio method. It was found that silage corn plant height， cob position， fresh dry herbage yield， whole plant fresh weight， stalk fresh weight， cob fresh weight， seed fresh weight， dry matter （DM）， crude protein （CP）， water soluble carbohydrates （WSC）， starch content and metabolizable energy increased incrementally as grain development progressed， and reached a peak at the 3/4 milk stage. Among the varieties， Dafeng 30 had the highest fresh herbage yield， Jinyu 9 had the highest DM content， Xinsiyu No. 10 had the highest CP content， Xianyu 696 had the highest WSC content， and Tunyu 765 had the highest starch content， with values significantly different from other varieties （P<0.05）. Conversely， the contents of neutral detergent fiber （NDF）， acid detergent fiber （ADF）， the ratio of ammonia nitrogen：total nitrogen （NH₃-N∶TN）， the organic matter digestibility （OMD） and the gas production rate decreased incrementally as the reproductive period progressed， and ADF， NDF and NH₃-N/TN were lowest at the 3/4 milk line stage. Among the varieties， ADF content was the lowest in Xinsiyu No.12， NDF content was the lowest in Xinsiyu No.10 and NH₃-N∶TN was the lowest in Xinsiyu No.11 at the 3/4 milk line stage， with their values significantly different from other varieties （P<0.05）. OMD and gas production rate peaked in the filling period， with Xianyu 696 having the highest OMD and Xinsiyu No. 10 having the highest gas production rate， with both significantly different from other varieties （P<0.05）. The pH of the silage of each maize variety initially decreased and then increased at different grain-development stages， while the lactic acid （LA） content initially increased and then decreased， and there was no significant pattern of change with fertilizer in acetic acid and propionic acid. The silage pH value was lowest when harvested at the 1/2 milk line stage， and the variety with lowest pH was Tunyu 765. Silage LA content was highest when harvested at 1/4 milk line stage， with Xinsiyu No.12 significantly higher than from other varieties （P<0.05）. In summary， harvest of silage maize at the 3/4 milk line stage produced high yielding and high quality silage forage， and the multi-factor scores of Xinwo No.1， Tunyu 765 and Dafeng 30 were highest among the tested varieties. Therefore these three varieties are recommended for planting in the Third Division area of Xinjiang and in ecologically similar regions.

Key words: Xinjiang, silage corn, agronomic traits, fermentation quality, drought irrigation, digestibility