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Fertilizer Management

Nitrogen Management of Brown Midrib Sorghum x Sudangrass in the Northeastern USA

^a Dep. of Crop and Soil Sciences, Bradfield Hall, Cornell Univ., Ithaca, NY 14853
^b Cornell Cooperative Extension of Rensselaer County, 61 State St., Troy, NY 12180
^c Cornell Cooperative Extension of St. Lawrence County, 1894 State Hwy. 68, Canton, NY 13617

^* Corresponding author (qmk2{at}cornell.edu)

Brown midrib (BMR) forage sorghum [Sorghum bicolor (L.) Moench.] x sudangrass (Sorghum sudanense Piper) hybrids (S x S) have been considered as a possible forage alternative to maize silage (Zea mays L.) where maize planting is delayed due to wet soil conditions. Our objective was to determine the most economic rate of nitrogen (MERN) for BMR S x S grown in a two-cut management system with a split application of N. Six field trials were conducted in New York in 2003 and 2004. One trial followed a grass–legume sod; a second trial had received liquid manure 19 mo before S x S planting. The remaining four followed S x S, silage maize, and/or a small grain crop. The MERN ranged from 137 to 192 kg N ha^–1 cut^–1 with dry matter (DM) yield ranging from 7.8 to 9.7 Mg ha^–1 at the sites without additional N input. At the sites with prior N inputs, yield was higher (10.4–13.8 Mg ha^–1) and MERN lower. The apparent nitrogen recovery (ANR) at the MERN was highest (61–73%) for the sites with prior N inputs. Nitrogen application rates > 145 kg N ha^–1 cut^–1 decreased nitrogen use efficiency (NUE) to <15 kg DM kg^–1 N, while the ANR became <45%. We concluded that the MERN for BMR S x S grown in New York in a two-cut system following maize, small grains, or forage S x S is 125 to 145 kg N ha^–1 cut^–1. For sites that follow sod plow-down or recent manure application, N application rates should not exceed 40 to 60 kg N ha^–1 cut^–1.

Abbreviations: ANR, apparent nitrogen recovery • BMR, brown midrib • DM, dry matter • MERN, most economic rate of nitrogen • NUE, nitrogen use efficiency • S x S, sorghum x sudangrass hybrids

Received for publication December 11, 2006.