Nitrogen management for brown mid rib sorghum sudangrass:

Results of the 2003 Valatie trial.  

Thomas Kilcer¹, Quirine M. Ketterings², J.H. Cherney²

¹CCE Rensselaer County , ²Dept. of Crop and Soil Sciences, Cornell University

Introduction

A brown mid rib (BMR) sorghum-sudangrass nitrogen (N) trial conducted on non-manured Hoosic soil at the Valatie Research Farm in Columbia County in 2001 showed that the greatest yields (15 tons/acre at 35% dry matter) was obtained when 200 lbs N/acre were applied in split applications. The split application increased N fertilizer efficiency which favors environmental stewardship. A yield plateau was not achieved at that application rate and no data on end-of-season soil nitrate levels were obtained. The 2002 season validated farmers experience of having a positive response to growing BMR sorghum-sudangrass on manured ground versus growing it in non-manured fields. Because of the wide range of optimum N rates generated by the research of the previous two years, further research was needed to determine optimum economic (split) N application rates.

Materials and Methods

In the 2003 growing season, we conducted a study at the Valatie Research Farm in Columbia County NY , on a soil that had received manure applications 19 months previous. The trial was conducted in the same field as the 2002 trial but on a separate part of the field that was in BMR sorghum sudangrass in 2002. The soil was an outwash derived Hoosic gravelly loam. The pH of the soil was 6.2 and the soil organic matter content was 2.4%. The site was classified as high in phosphorus (10 lbs/acre Morgan extractable P), high in potassium (220 lbs K/acre) and magnesium (345 lbs Mg/acre), and medium to high in Zn (0.9 lbs Zn/acre). Approximately 7,000 gallons of liquid manure was applied to the surface in November of 2001. Based on an estimated organic N release rate of 12% for the second year after application, we expected a release of 19 lbs of N/acre for the 2003 season. The field was chisel plowed and fitted in the middle of May to stimulate weed development. It was harrowed, and planted on June 2 using a John Deere grain drill dropping 66 lbs of seed per acre. Plot size was 6 ft x 10 ft with a harvest area of 3 ft x 5 ft. Each plot received the equivalent of 26 lbs of P₂O₅ in fertilizer before planting. The N rates for each cut were: 0, 50, 100, 150, 200 lbs N/acre. Because two cuttings were made, the total N applications were 0, 100, 200, 300, and 400 lbs N/acre. Nitrogen applications were in the form of urea (46% N) and applied just before one of the frequent rains to prevent volatilization losses. The entire trial was replicated four times. The sorghum sudangrass was harvested when the tallest plots were about 48 inches tall as measured at the horizontal curve of the tallest leaf. A 3.5-inch cutting height was used. The first harvest took place on July 29 and the second harvest occurred on August 28. These harvest dates were close to normal for this location and growing season. We determined yield and took sub samples to determine moisture content, nutrient concentrations, and forage feed quality. All samples were analyzed for total N, P, K, Ca, Mg, lignin, sugar, non-structural carbohydrates (NSC), neutral detergent fiber (NDF), digestibility of neutral detergent fiber (dNDF at 30 hr), and in- vitro total digestibility (IVTD at 30 hr) at the forage laboratory of DairyOne Cooperative Inc. in Ithaca, NY.  Milk2000 version 7.4, a software model developed at the University of Wisconsin , was used to estimate milk yields in lbs per ton and in lbs per acre. We used the alfalfa-grass Milk2000 worksheet with standard values for neutral detergent insoluble crude protein (NDICP; 2.4% on a dry matter basis) and ether extract (3.6% on a dry matter basis) as reported for sorghum-sudangrass silage in the 2001 Nutrient Requirements for Dairy Cattle (National Research Council, 2001). The 30 hour dNDF was multiplied by 1.16 to obtain an estimate of the dNDF at 48 hours (J.H. Cherney, unpublished, 2003).

 Results and Discussion

Whereas drought affected the 2002 study, 2003 knew periods of major extended rainfall events. Prolonged cool and wet conditions delayed growth until the third week of June. Just prior to harvest in mid-July a tornado passed through the plots. This tornado uprooted 200+ trees in the neighboring orchard. The flattened sorghum sudangrass stand was erect again after 10 days. The second cut yield and quality was impacted by 14 days of continuous rain in the first half of August. This produced forage with an incredible 92% moisture level. It also, for the first time in four years, produced second cutting yields that were less than the first cutting yields. Yields increased from 12.3 tons/acre (35% dry matter) with only soil + residual manure N; to over 18.2 tons/acre with N applications of 150 lbs/acre of N per cut (Figure 2). Nitrogen application increased predicted milk yields (Table 1) mostly due to an increase in yield. The highest yields were obtained with a 150 lbs N/acre application per cut. The manure and soil derived N supplied 127 lbs of N for the two cuts over the entire season on the 0 N plots. The estimated soil N supply for a Hoosic soil for corn uptake is ~60 lbs N/acre according to the Cornell soils database (Ketterings et al., 2002). These results would suggest that about 50 lbs of N (127-60-18 = 49) were recycled from the previous BMR sorghum-sudangrass crop that was mowed but not removed.

Figure 2: Brown mid rib sorghum-sudangrass yield (left) and estimated milk yield per acre (right) as affected by the amount of nitrogen applied at the Valatie Research Farm, NY, 2003.

 Table 1: Yield, predicted milk production, nitrogen uptake, nitrogen uptake efficiency, and forage nitrate concentrations as affected by N application rates in a 2-cut BMR sorghum-sudangrass trial at the Valatie Research Farm, NY, 2003. The trial was conducted on a field that received approximately 7,000 gallons/acre manure surface applied in November 2001.

Note 1: Milk yield was predicted using Milk 2000 (http://www.uwex.edu/ces/forage/articles.htm#milk2000).

Note 2: Average values within columns with different letters (a,b,c) are statistically different (a = 0.05)

Dry matter yields increased with the application of 50 lbs N/acre. Although not statistically significant, a trend was seen of increasing yield with N application up to 150 lbs of N/acre per cut. Nitrogen uptake efficiencies were not significantly different among the treatments and averaged 30% higher than the much drier 2002 season. As compared to the N uptake efficiency of BMR sorghum sudangrass at the Mt Pleasant site (Ketterings et al., 2004), the N uptake efficiency at the Valatie farm was 50 – 100% higher. At the greatest yields, the crop removed 330 lbs of N/acre suggesting a much greater N need than for corn.

With these high N application levels comes a concern with potentially toxic nitrate levels in the forage. Nitrate in the forage is toxic above 1.76% and becomes a concern at concentrations of >0.88% nitrate ion (Dairy Herd Management, Nov 2001 p10). In spite of the much higher rainfall in 2003 as compared to 2002, the forage nitrate levels were similar. At the Valatie farm in 2003, the both cuttings showed a significant increase in forage nitrate concentration with increasing N rate. Absolute concentrations did reach a level of concern when N application rates were above 150 lbs N/acre per cut on first harvest. In the second cutting, nitrate levels were significantly increased, and above caution levels when 100 lbs of N/acre per cut or more were applied. Fermentation would reduce all nitrate concentrations below toxic; and dilution in a normal ration (50% forage and 50% grain) would drop them below even the caution level, further increasing the safety margin.       

Nitrogen addition did increase crude protein and lowered NDF but did not affect dNDF, or IVTD (Table 2). Milk per acre estimates strongly reflected the sorghum sudangrass silage yields. There were no significant differences in the milk/ton predictions (an indicator of forage quality) across all nitrogen fertilization levels. This continues to support the conclusion that N fertilizer application rates do not affect overall forage quality and that it is reasonable to evaluate the economics based on yield alone. These results are very similar to those found in two years of N trials for sorghum sudangrass at the Cornell Mt. Pleasant Research Farm (Ketterings et al., 2004).   

Table 2: Effect of N application on quality of BMR sorghum sudangrass grown at the Valatie Research Farm, NY, in 2003. The trial was conducted on a field that received approximately 7,000 gallons of manure in surface applied in November of 2001.

Note 1: Average values within columns with different letters (a,b,c) are statistically different (a = 0.05).

Conclusions

As with the 2003 Mt Pleasant study, nitrogen fertilization of BMR sorghum sudangrass did not affect total digestibility or fiber digestibility of the forage, but did reduce the NDF concentration and increased crude protein levels. The main impact of N application is on total yield. Because the 2002 study had fresh manure, and the 2003 was only residual manure, they could not be directly combined. The optimum economic N rate in 2002 was 80 lbs N/acre per cut returning $173/acre in a very dry season.  In 2003 the optimum economic N rate was 109 lbs N/acre per cut returning $375/acre in a season characterized by above normal rainfall. The high protein produced by BMR sorghum-sudan, enables expensive soy purchases to diminish.  This directly reduces the single largest source of imported phosphorus on Northeast dairy farms, improving their nutrient balance for this key nutrient.

The additional 50 lbs of N uptake above that estimated from manure N and soil organic matter mineralization when no N fertilizer was applied may suggest higher N credits from the mowed sorghum sudangrass of the previous year. Research suggests that mowing sorghum sudangrass “whenever stalks reach 3 – 4 feet tall, increases root mass five to eight times compared to unmowed stalks and forces roots deeper” (Managing Covercrops Profitably, pg 80). This carryover of additional N to the next crop is a major potential benefit that needs to be quantified further for both N recommendations and nitrate safety factors.

The 2002 season at Valatie was ideal for nitrate accumulation.  The 2003 season, with its heavy rainfall, was the opposite, yet it still accumulated toxic levels of nitrate at the highest N application rates. With the potential for high manure applications to meet the N needs of the crop and the inherent inaccuracy of manure application on most farms, there is need for caution where the forage is directly consumed (grazed) as the sole or nearly sole forage. 

There is a tremendous interest expressed by farmers in using manure as the primary source of N for BMR sorghum sudangrass. Direct comparisons are needed to investigate N uptake efficiency of manure N. In addition, it is of high interest to farmers to investigate the possibility of split applications of manure. This may reduce the need for fertilizer as well as reduce N losses to the environment.  Both factors may greatly expand the potential demand for this crop.

The maximum yield obtained at the Valatie site in 2003 was 83% of full season corn grown on a neighboring site. When BMR sorghum sudangrass was grown with a double crop triticale at the same site, both crops combined produced a yield greater than the 21.8 tons of the full season corn silage at the site, and 14% more potential milk/acre.  This rotation needs to be studied further.  There is already a tremendous interest from farmers and Soil Conservation for this new cropping system, with multiple research proposals in New York , Vermont , and New Hampshire being developed to study it. 

The primary focus for field trials with BMR sorghum sudangrass this next season is the utilization of manure as the primary N source. A subset study is planned to determine nitrogen recycling from the tremendous root system produced by BMR sorghum sudangrass

 References

1.      Cerosaletti, P., Q.M. Ketterings and T. Kilcer (2002). 2001 Delaware County BMR sorghum sudangrass trials "What's Cropping Up?" 12(3): 1-3.

2.      Guyer, P.Q. and D.D. Duey (1986). Estimating corn and sorghum silage value. Univ. of Neb. Coop. Ext. Publ. G74-99-A, Univ. of Nebraska , Lincoln , NE.

3.      Ketterings, Q.M., G. Godwin, J.H. Cherney, S. Beer and T.F. Kilcer (2004). Nitrogen management for brown mid rib sorghum sudangrass: Results of two years of studies at the Mt Pleasant Research Farm.What’s Cropping Up? 14(2): x-xx.

4.      Ketterings, Q.M., S.D. Klausner, and K.J. Czymmek (2003). Nitrogen guidelines for field crops in New York . Second Release. Department of Crop and Soil Sciences Extension Series E03-16. Cornell University , Ithaca , NY . 70 pages.

5.      Kilcer, T., Q.M. Ketterings, T.W. Katsvairo and J.C. Cherney (2002). Nitrogen management for sorghum sudangrass: how to optimize N uptake efficiency? "What's Cropping Up?" 12(5): 6-9.

6.      National Research Council (2001). Nutrient requirements of dairy cattle. 7^th edition. National Research Council. National Academy Press, Washington , D.C. 408 pages.

7.      SARE, (1998),  Managing Cover Crops Profitability, Handbook Series #3

 Acknowledgment and For Further Information

             This research was funded by a research grant from Townsend and Garrison Inc. For further information on BMR sorghum sudangrass projects in New York contact Thomas Kilcer at the Rensselaer Cooperative Extension Office (tfk1@cornell.edu or 518-272-4210) or visit our websites (http://nmsp.css.cornell.edu/projects/bmr.asp or  http://www.cce.cornell.edu/rensselaer/ Agriculture/new%20bmr_sorghum.htm).

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