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Nitrogen Management of Brown Midrib Forage Sorghum in New York

Sarah E. Lyonsa, Quirine M. Ketteringsa, Greg Godwina, Debbie J. Cherneyb, Jerome H. Cherneyc, John J. Meisingerd, and Tom F. Kilcere

a Nutrient Management Spear Program, Department of Animal Science, Cornell University, Ithaca, NY, b Department of Animal Science, Cornell University, Ithaca, NY, c Soil and Crop Sciences Section of the School of Integrative Plant Science, Cornell University, Ithaca, NY, d USDA-ARS Beltsville Agricultural Research Center, Beltsville, MD, and e Advanced Agricultural Systems, LLC, Kinderhook, NY

Introduction

Forage sorghum is a drought and heat tolerant warm-season grass that can be used for silage on dairy farms. It can be a good alternative to corn silage in New York particularly during drought years or in the case of delayed planting in the spring. Forage sorghum requires soil temperatures of at least 60°F for planting, which normally occurs in early June in New York. Forage sorghum could also be a good fit for double cropping rotations because its later planting date gives time for an early May harvest of a forage winter cereal. Between 2013 and 2017, we conducted 13 N-rate trials across three regions of New York to evaluate nitrogen (N) needs for a brown midrib (BMR) forage sorghum variety (Alta Seeds AF7102).

Trial Set-Up

The trials were planted between early June and early July in central New York (eight trials) and northern New York (five trials). Of the northern New York trials, three were on commercial farms. The other trials were on Cornell research farms. Two of the three trials on commercial farms were conducted on fields with recent manure or legume histories. For eleven of the trials, sorghum was planted at a 1-inch seeding depth and 15-inch row spacing (15 lbs/acre seeding rate). The remaining two trials were planted either with a 30-inch or 7.5-inch row spacing. Five N-rates as Agrotain®-treated urea (Koch Agronomic Services, LLC, Wichita, KS) were broadcasted at planting (0, 50, 100, 150, and 200 lbs N/acre) with two additional N rates (250 and 300 lbs N/acre) for one of the central New York locations. The forage sorghum was harvested at the soft dough stage, which occurred between September 20 and October 14. Harvest was done using a 4-inch cutting height and dry matter (DM) yield was measured. This allowed for determination of the most economic rate of N (MERN), the N use efficiency (NUE), and the apparent N recovery (ANR). The NUE and ANR are measures of N efficiency. The NUE is the amount of N taken up in relation to yield, and is calculated by subtracting the yield when no N was applied in the spring from the yield when N was applied, and dividing that value by the N rate applied (NUE [lbs DM/lbs N] = [Triticale yieldN rate – Triticale yield­0 N]/N rate). A higher NUE means that more of the N that was applied was taken up by the sorghum. The ANR is the amount of fertilizer N recovered, calculated by subtracting the N in the forage when no N was applied from the N in the forage when N was applied, and dividing that value by the N rate applied (ANR [%] = [Forage N of Nrate – Forage N of N0]/N rate).

Results

The crop yield response to N could be separated into three yield response groups: (1) no response to N addition (MERN = 0; two trials), (2) no yield plateau (MERN > 200 kg N ha-1; four trials), and (3) a yield plateau between the lowest and highest N rates (seven trials) (Figure 1). The two trials on fields at commercial farms with a recent manure or legume history did not respond to N addition (group 1 trials, panel A). The trial in group 1 with the lowest yield (5.3 tons DM/ac) was planted with a 30-inch row spacing, which resulted in weed issues that likely impacted crop performance. Trials in group 2 (panel B) were either very responsive to N addition or had N uptake limitations, most likely reflecting weather or soil drainage issues. The trials in group 3 (panel C) had MERNs ranging from 134 to 234 lbs N/acre, averaging 181 lbs N/acre. Yields at the MERN for group 3 trials ranged from 6.7 to 10.4 tons DM/acre and averaged 8.9 tons DM/acre. On average, for responsive sites (so excluding group 1 trials), forage sorghum required approximately 20 lbs N/acre per ton DM. On average, for each ton of DM, 25 lbs of N was taken up by the sorghum. For group 3, higher N rates led to lower ANR and NUE (Figure 2). For these trials, NUE at the MERN averaged 56 lbs DM/lbs N and ANR at the MERN averaged 83%.

 

Figure 1: Impact of N application on forage sorghum yield for 13 trials from 2013 to 2017. Sorghum was harvested at the soft dough stage. Two trials did not respond to N (A), four trials did not have a yield plateau (B), and seven trials had a yield plateau between the lowest and highest N rates (C). Differences are likely due to sites native N supply, weather conditions, agronomic practices, and/or soil properties (see text for further details). Different symbols represent different sites within each group.

Figure 2: Forage sorghum nitrogen use efficiency (NUE, A) and apparent N recovery (ANR, B) as impacted by N application rate for seven trials with a most economic rate of N between the highest and lowest N rates. Different shapes represent different trials within each group.

Conclusions and Implications

Forage sorghum can be a good alternative to corn silage in years of drought, delayed corn planting, or as part of a double crop rotation with forage winter cereals. The BMR forage sorghum in this study, grown on N-limited sites, needed around 180 lbs N/acre, or around 20 lbs N per ton of DM, and yielded between 7 and 10 tons DM per acre. Fields with recent manure or legume histories supplied sufficient N, resulting in no crop response to additional N for the forage sorghum. Applying N beyond the N needs of the crop will result in reduced N use efficiencies. In addition, stands with row spacing greater than the recommended 15 inches may result in weed or other stand issues that could impact performance.

Acknowledgements

This work was supported by Federal Formula Funds, and grants from the Northern New York Agricultural Development Program (NNYADP), New York Farm Viability Institute (NYFVI), and Northeast Sustainable Agriculture Research and Education (NESARE). For questions about these results, contact Quirine M. Ketterings at 607-255-3061 or qmk2@cornell.edu, and/or visit the Cornell Nutrient Management Spear Program website at: http://nmsp.cals.cornell.edu/.

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