Seeding and N Fertilization Effects on Yield and Quality of Brachytic Dwarf Brown-Midrib Forage Sorghum Hybrids.

Abstract

Brown midrib (BMR) forage sorghum (Sorghum bicolor (L.) Moench) silage is a reasonable alternative to corn (Zea mays L.) silage for areas with limited soil moisture. Traditional forage sorghum varieties are tall and prone to lodging, with low forage quality. Brachtyic dwarf BMR forage lines are shorter, lodging resistant and have higher forage quality. Newer, earlier hybrids have expanded the potential adaptation of forage sorghums to more northern areas. A two-year study was conducted during the 2014 and 2015 growing seasons using newly available brachytic dwarf BMR forage hybrids to determine the effects of different seeding rates and N (nitrogen) fertilization rates on forage dry matter (DM) yield and quality for two hybrids. The experimental design was split-split-plot with four replications. In each replication, main plots were two hybrids [AF7202 (early maturity) and AF7401 (late maturity)], subplots were two seeding rates (198,000 seeds ha-1 and 296,400 seeds ha-1), and sub-subplots were two N rates (123 kg ha-1 and 168 kg ha-1). Dry matter yield and forage-quality parameters were measured for each treatment. We observed significant differences between hybrids for all the parameters, except neutral detergent fiber digestibility (NDFD) in 2015. The early maturity hybrid, AF7202, had higher yields, higher starch content and net energy for lactation (NEL) levels than AF7401. The dwarf hybrid, AF7401, had higher crude protein (CP) content and NDFD than AF7202. AF7202 was more responsive to the higher N rate than AF7401. Crude protein was increased as N level increased for both hybrids. Other forage quality traits were unaffected by N rates. Neither variety responded to an increase in seeding rate. This study showed that the earlier brachytic dwarf forage sorghums, such as AF7202, managed with recommended seeding rates and possibly higher N rates, have good potential for high forage yield and quality in central Pennsylvania (PA).

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