Nitrogen management for brown mid rib sorghum-Sudangrass:

Results of the 2002 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-Sudan grass nitrogen (N) trial conducted in the cold and wet 2000 growing season on a Hoosic soil at the Valatie Research Farm in Columbia County showed that N application increased yields but little was gained by increasing the N application beyond 100 lbs/acre at planting. The greatest yields (15 tons/acre at 35% dry matter) were obtained when 200 lbs N/acre were applied in split applications. Split application increased the N fertilizer uptake efficiency (% of the fertilizer application that is taken up by the crop) and was likely to have favored environmental stewardship. However, since the highest N application in that study was 200 lbs N/acre, a yield plateau was not achieved at that application rate and no data on end-of-season soil nitrate levels were obtained. Farmers in the region reported having a greater success in growing BMR sorghum-Sudan on manured ground versus growing it in non-manured fields.  Thus, further research was needed to determine optimum economic (split) N application rates on both manured and un-manured fields.

Materials and Methods

In the 2002 growing season, we conducted a study at the Valatie Research Farm in Columbia County NY, on a soil that had received manure applications in the past (Figure 1). 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). The previous crop consisted of two years of weed growth that had been clipped once each summer. Glyphosate was applied in early October 2001. Approximately 7,000 gallons of liquid manure was applied to the surface in November of 2001. Per 1000 gallons, the manure contained 44 lbs total N, 22

lbs ammonium-N, 15 lbs P₂O₅ and 30 lbs K₂O. The field was plowed and fitted on June 4/5, 2002. Planting was done on June 6, using a John Deere grain drill at 68.7 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 and 90 lbs of K₂O in fertilizer before planting. The N rates for each cut were: 0, 50, 100, 150, 200 lbs N/Acre. Because the weather only allowed for two cuttings, the total N applications were 0, 100, 200, 300, and 400 lbs N/A. Nitrogen applications were in the form of ammonium sulfate (21% N) to prevent volatilization losses. The entire trial was replicated four times. The BMR was harvested when the tallest plots were 38 inches tall as measured at the horizontal curve of the tallest leaf. Based on earlier field trials conducted in Columbia and in Delaware County (see the article by Cerosaletti and others in “What’s Cropping Up?” (2002) 12(3): 1-3), we expected this stand height to provide optimum forage quality. A 3.5-inch cutting height was used. The first harvest took place on July 31 and the second harvest occurred on October 8. These harvest dates were a month later than normal due to limited biomass production during the drought. 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-Sudan grass 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). Soil samples (0-8 inches) were taken immediately after the first and second harvests and were analyzed for nitrate.

 Results and Discussion

           The drought greatly reduced yields and only permitted two cuts to be taken. Yields increased from 8.6 tons/acre (35% dry matter) with only manure N, to over 11 tons/acre with N applications above 50 lbs/A 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 50 lb. N application per cut.  The manure and soil derived N supplied 126 lbs of N for the two cuts over the entire season on the 0 plots.  When 50 lbs N was applied per cut (100 lbs N total), almost 200 lbs of N were removed per acre

            Dry matter yields increased with the application of N but an application rate of 50 lbs N per cut per acre was enough for maximum yield. Forage quality, expressed in milk per ton, was not affected by applications over 50 lbs N/acre per cut either. As was found at another N study at the Mt. Pleasant Research Farm, N addition did increase crude protein and lowered NDF but did not affect dNDF, IVTD, or lignin concentration (Table 2). The increase in crude protein was greater in the second cut most likely because of a decreased amount of N available from the manure. Nitrogen uptake efficiency decreased with N application rate although the trend was only significant for the second harvest. As compared to the N uptake efficiency of BMR sorghum sudangrass at the Mt Pleasant site, the N uptake efficiency at the Valatie farm was twice as large.

Figures 2 (see link below)

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 brown mid rib sorghum-Sudan grass trial at the Valatie Research Farm, NY, 2002. The trial was conducted on a field that received approximately 7,000 gal./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)

Table 2: Effect of N application on quality of BMR sorghum sudangrass grown at the Valatie Research Farm, NY, in 2002. The trial was conducted on a field that received approximately 7,000 gallons of manure in surface applied in November of 2001.