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© 2005 Plant Management Network. Nitrogen Fertilization Rate and Application Timing Effects on the Yield of Crabgrass Chris D. Teutsch, Assistant Professor, Southern Piedmont Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Blackstone 23824; John H. Fike, Assistant Professor, Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State University, Blacksburg 24061; Gordon E. Groover, Extension Economist, Department of Agricultural and Applied Economics, Virginia Polytechnic Institute and State University, Blacksburg 24061; and William M. Tilson, Research Associate, Southern Piedmont Agricultural Research and Extension Center, Virginia Polytechnic Institute and State University, Blackstone 23824 Corresponding author: Chris D. Teutsch. cteutsch@vt.edu Teutsch, C. D., Fike, J. H., Groover, G. E., and Tilson, W. M. 2005. Nitrogen fertilization rate and application timing effects on the yield of crabgrass. Online. Forage and Grazinglands doi:10.1094/FG-2005-0518-01-RS. Abstract Crabgrass (Digitaria species) is a summer annual grass that could provide high quality grazing for ruminant livestock in the mid-Atlantic region of the United States. However, little is known about managing crabgrass as a forage in this region. This study was designed to evaluate the effect of N fertilizer rate and application timing on the yield of crabgrass. Nine N rates ranging from 0 to 400 lb/acre were applied as a single application at seeding or as a split application, one-half at seeding and one-half after the first cutting. Averaged over years, first harvest yield ranged from 800 to 4000 lb/acre and increased as N rate increased with maximum dry matter production occurring at 255 lb of N per acre. Second harvest yield was greatest when N was applied as a split application. This effect was most pronounced with ample rainfall. Total dry matter production, averaged over years, ranged from 3000 to 9000 lb/acre and increased as N rate increased with maximum dry matter production occurring at 305 lb of N per acre. Results support current recommendations for summer annual grasses of applying N at 60 to 80 lb/acre at seeding followed by N at 40 to 60 lb/acre after each harvest and suggest that crabgrass could be managed in a similar manner. Introduction Crabgrass (Digitaria species) is a warm-season annual grass that is commonly considered a weed due to its prolific growth rate and spreading morphology. However, these species possess significant potential for supplying high quality summer forage for grazing livestock in the transition zone between subtropical and temperate regions of the United States. Research conducted in Oklahoma demonstrated that improved crabgrass is capable of producing 8000 to 10000 lb of DM per acre (3). In addition to high yields, crabgrass is also more digestible than other commonly used warm-season grasses (3). Although crabgrass is already a component of most cool- and warm-season pastures in the northern transition zone (1), no research has evaluated its potential as summer forage. In addition, no information is available on the productivity or management of improved crabgrass in this region. This study was designed to evaluate the effect of N fertilization rate and application timing on the yield of improved crabgrass. Procedures for Assessing Effect of Nitrogen Fertilization on Crabgrass Production
‘Red River’ crabgrass (Digitaria ciliaris (Retz.) Koel) was established on 7 May 2001, 16 April 2002, and 15 April 2003 near Blackstone, VA (Fig. 1). The soil series for all three years was a Wedowee sandy loam (fine, kaolinitic, thermic Typic Kanhapludults). Initial soil nutrient levels are shown in Table 1. A conventional seedbed was prepared and plots were seeded using a cultipacker type seeder and a seeding rate of 6.0 lb/acre. Nitrogen was applied at 0, 50, 100, 150, 200, 250, 300, 350, and 400 lb/acre either as a single application of ammonium nitrate at seeding or as a split application, one-half at seeding and one-half after the first cutting. Nitrogen treatments applied at seeding were incorporated into the seedbed by disking once with a finishing disk. All plots also received 100 lb/acre of P2O5 and 300 lb/acre of K2O before seeding. Bentazon [3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one 2,2-dioxide] herbicide was applied at a rate of 0.50 lb ai/acre on 31 May 2001 and 0.75 lb ai/acre on 11 June 2001 for the control of yellow nutsedge (Cyperus esculentus L.). Bentazon and carfentrazone-ethyl {Ethyl alpha, 2-dichloro-5-[4-(difluoromethyl)-4,5-dihydro-3-methyl-5-oxo-1H-1,2,4-triazol-l-yl]-4-fluorobenzenepropanoate} herbicides were applied at a rate of 0.75 and 0.23 lb ai/acre respectively, on 30 May 2002 and 6 June 2003 to control broadleaf weeds. Table 1. Soil nutrient levels (lb/acre) and pH for 2001, 2002, and 2003.
a Mehlich I extract was utilized. b Soil Test Recommendations for Virginia (1994). The experimental design was a randomized complete block with a two-factor (N rate and single versus split application) factorial treatment arrangement and four replications. Plot size was 9 × 20 ft. Plots were harvested on 5 July and 31 August 2001; 11 July, 15 August, and 3 October 2002; and 11 July, 14 August, and 22 October 2003 by clipping a 4-ft-wide strip through the center of each plot using a self-propelled sickle bar-type forage harvester (Fig. 2). Harvest was initiated when the forage reached the late boot stage, except for the last harvest in each year, which was harvested at seed maturity to simulate natural reseeding of volunteer stands (Fig. 3). The clipping height was 4 inches above the soil surface. A subsample of fresh forage was collected from each plot and dried in a forced air oven for 5 days at 140°F. Dry matter was determined and yields were calculated on a dry matter basis.
A yield function averaged over the 3 years of this study and adjusted to 12% moisture and 20% harvest losses was used to calculate the profit maximization conditions based on the assumption that inputs will be used to the point where marginal revenue (hay sales) equal marginal costs (N and hay harvest costs). The variable cost of harvesting hay was assumed to be $25 per ton and all other costs are assumed to be held constant (10). Data were analyzed using the general linear model procedure from SAS (SAS Institute, Cary, NC). Only the N rate effect was considered for the first harvest since plots did not receive the split N application until after the first harvest. Regression analysis was performed on raw data using Sigma Plot 9.0 (Systat, Point Richmond, CA). In 2001, only two harvests were made and the second harvest was similar in maturity to the third harvest in 2002 and 2003. Therefore, the final harvest from each year was grouped for analysis and discussion. Nitrogen fertilization rates resulting in maximum yield for each harvest were calculated using corresponding regression equations. Rainfall and Temperature Severe drought in 2002 and excessive rainfall in 2003 resulted in the driest and wettest growing seasons, respectively, ever recorded at the Southern Piedmont Agricultural Research and Extension Center, Blackstone, VA. Precipitation for the crabgrass growing season (May to September) was near normal in 2001, 6.5 inches below normal in 2002, and 20 inches above normal in 2003 (Fig. 4). The drier-than-normal conditions in 2002 were magnified by the extremely dry winter of 2001-2002. For the period of August 2001 to April 2002, rainfall was more than 14 inches below normal resulting in dry soil conditions in the spring of 2002. Temperatures for the growing season were normal for 2001, 1.9°F above normal for 2002, and 2.4°F below normal for 2003.
Nitrogen Rate and Application Timing Effects on Dry Matter Yield
Analysis of variance combined across years indicated significant year × treatment interactions (P < 0.05) for yield. Due to these interactions, yields are presented by year. An application timing × N rate treatment interaction was found for second harvest in 2002 and 2003 and for the final harvest in 2003 only. Interaction means will be presented for these harvests only. Main effects will be discussed for all other harvests. First harvest. Yield increased in a quadratic manner as N fertilization rate increased (P < 0.001) (Fig. 5). Maximum yield was obtained when 280, 206, and 295 lb of N per acre were applied at seeding in 2001, 2002, and 2003, respectively. The lower maximum response to N observed in 2002 was likely related to lower rainfall (Fig. 6). In 2002, N rates above 200 lb/acre had a negative effect on yield compared to approximately 300 lb/acre in 2001 and 2003.
Second Harvest. Yield increased with N rate in both years (Fig. 7). The yield response for the split application was quadratic in nature compared to a linear increase when all the N was applied at seeding. Splitting the N application had a more pronounced effect in 2003. This was likely due to more favorable soil moisture during that growing season. These results show that the response of crabgrass to summer fertilization is moisture dependent.
Final Harvest. Although final harvest yield increased (P < 0.03) with N rate in 2001 and 2002 (Fig. 8), the rate of change was relatively small. In 2003, N rate did not significantly impact final harvest dry matter production. Although splitting the N application increased final harvest yield in 2001 and 2002, the differences were relatively small (Fig. 9).
Season Total. Total yield for the growing season ranged from approximately 3000 to 9000 lb of DM per acre and increased as N application rate increased in all three years (P < 0.001). Maximum yield was obtained when 329, 268, and 344 lb of N per acre were applied for the 2001, 2002, and 2003 growing seasons, respectively (Fig. 10). The economic application rate was likely in the range of 150 to 250 lb of N per acre and will be impacted by environmental factors such as temperature and precipitation, and N fertilizer cost. Splitting N applications increased total yield in only one year out of three (Fig. 11).
Nitrogen Management for Crabgrass With other warm-season annual grasses, N fertilization in the range of 180 to 265 lb/acre increased dry matter production and crude protein (4,6,7,8). In the current study, maximum dry matter yield of crabgrass was obtained when more than 300 lb of N per acre was applied with normal rainfall. Dalrymple (2) also found that crabgrass yield increased from 2400 to 7100 lb of DM per acre as N rate increased from 0 to 240 lb/acre. The economic range would be less than 300 lb of N per acre and likely lies between 150 and 250 lb/acre. This is in general agreement with the observations of other researchers that were summarized by Fribourg (5). Although splitting annual N applications for summer annual forages is widely advocated, little data are available to validate this practice (5). Applying one-half of the N at seeding and one-half after the first harvest in the current study resulted in increased dry matter production in only one of three years. This may indicate that the split application strategy used in the current study did not appropriately allocate N during the growing season. Observations show that crabgrass growth is restricted during periods of limited moisture. This may indicate that a larger proportion of the total annual N should be allocated during the portion of the growing season when the chance of good soil moisture is greatest. In the mid-Atlantic region this would typically be during the first part of the growing season (June). Results from the current study showed agronomic yield response for the first harvest up to approximately 150 to 200 lb of N per acre depending on the year. However, this rate of N applied at seeding could result in the accumulation of dangerous levels of nitrate in some years (9). In the current study, second harvest yields responded well to the split N application. However, due to a greater likelihood of drier conditions following the first harvest, care should be exercised with summer N applications to avoid excessive nitrate accumulation in crabgrass. In addition, high rates of N fertilization on sandy soils can also contribute to nitrate leaching into the ground water. Profit Maximizing Levels of Nitrogen Fertilization The array of profit maximizing levels of N is shown in Table 2. This example uses market hay prices that should reflect the values for farmers selling hay and using hay in livestock enterprises. For mathematical simplicity all costs other than N and hay are held constant. This assumption does not imply that other factors such as the cost of P and K and forage quality should not be considered when making the decision to apply N. However, for most grass hay production systems, N is the largest single input cost under a farmer’s control, at approximately 25% of preharvest costs and will have the most influence on profitability (10). Interpretation and use of Table 2, must be tempered with the knowledge that farm-level yields will vary based on soil type, slope, harvest methods, rainfall, and other micro and macro nutrients that might influence yield response to N. The most important concepts for farmers and professionals to recognize are that, (i) profit maximizing levels of N fertilization are seldom static and will change as prices change, (ii) some price combinations should result in recommendations not to apply N fertilizer, and (iii) fertilizing to achieve maximum yield is never profitable. Table 2. Profit maximizing levels of N fertilization (lb/acre) based on varying input prices of N and output prices of haya.
a Hay variable harvest costs remained constant at $25 per ton. b Asterisk denotes negative values, indicating no fertilizer should be applied at these prices. Conclusions Nitrogen fertilization increased the yield of crabgrass grown as forage. In most cases N rates that maximized yield resulted in accumulation of dangerous levels of nitrate in the forage tissue. However, moderate nitrogen rates in the range of 100 to 225 lb/acre led to profitable yields under general production and pricing conditions and minimized nitrate accumulation. These findings support the general recommendations to apply N at 60 to 80 lb/acre at seeding followed by 40 to 60 lb/acre after each harvest or intensive grazing for summer annual grasses and indicate that crabgrass can be safely managed in a similar manner. The responsiveness to N fertilization and ability to persist through natural reseeding may make crabgrass an excellent summer forage for livestock in the mid-Atlantic region of the United States. Literature Cited 1. Burns, J. C., McIvor, J. G., Villalobos, L. M., Vera, R. R., and Bransby, D. I. 2004. Grazing systems for C4 grasslands: A global perspective. Pages 309-354 in: Warm-Season (C4) Grasses. L. E. Moser, L. Sollenberger, and B. Burson, eds. Agron. Mongr. 45. ASA, CSSA, and SSSA, Madison, WI. 2. Dalrymple, R. L. 1975. Crabgrass N response on a low fertility soil. Pages 34-40 in: Crabgrass as a Forage. Publication No. CG-75. The Noble Foundation, Ardmore, OK. 3. Dalrymple, R. L. 1999. Crabgrass: A synopsis. Pages 1-5 in: Crabgrass for Forage: Management from the 1990s. NF-FO-99-18. The Noble Foundation, Ardmore, OK. 4. Edwards, N.C., Jr. 1966. The response of sorghum-sudan hybrids to nitrogen fertilization. M.S. Thesis, Mississippi State University. 5. Fribourg, H. A. 1974. Fertilization of summer annual grasses and silage crops. Pages 189-212 in: Forage Fertilization. D. A. Mays, ed. ASA, CSSA, SSSA, Madison, WI. 6. Hart, R. H., and Burton, G. W. 1965. Effect of row spacing, seeding date, and nitrogen fertilization on the forage yield and quality of Gahia-1 pearl millet. Agron. J. 57:376-378. 7. Jung, G. A., Lilly, B., Shih, S. C., and Reid, R. L. 1966. Studies with sudangrass. I. Effect of growth stage and level of nitrogen fertilization upon yield of dry matter; estimated digestibility of energy, dry matter and protein; amino acid composition; and prussic acid potential. Agron. J. 56:533-537. 8. Sumner, D. C., Martin, W. E., and Etchegaray, H. S. 1965. Dry matter and protein yields and nitrate content of Piper sudangrass (Sorghum sudanense (Piper) Stapf.) in response to nitrogen fertilization. Agron. J. 57:351-354. |
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