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© 2008 Plant Management Network. A Comparison of Side-dressed Liquid Hog Manure to Urea Ammonium Nitrate in Corn William Deen, Associate Professor, and Amal Roy, Research Associate, Department of Plant Agriculture, University of Guelph, Guelph, ON, N1G 2W1; and Greg Stewart, Corn Specialist, Ontario Ministry of Agriculture and Food, Guelph, ON, N1G 2W1 Corresponding author: W. Deen. bdeen@uoguelph.ca Deen, W., Roy, A., and Stewart, G. 2008. A comparison of side-dressed liquid hog manure to urea ammonium nitrate in corn. Online. Crop Management doi:10.1094/CM-2008-1103-01-RS. Abstract Liquid hog manure is frequently spring-applied prior to corn planting, but concern regarding compaction, planting delays, and nitrogen losses have increased corn producer interest in side dressing. The objective of this study was to compare available nitrogen in side-dressed liquid hog manure versus 28% urea ammonium nitrate (UAN) in terms of fertilizer nitrogen equivalent, yield response, grain protein, soil compaction, and end of season soil nitrates. Field experiments were conducted at three sites in southwestern Ontario from 2003 to 2005. Three rates of liquid hog manure (zero, low, and high) and five rates of UAN (0, 53, 106, 159, 220 lb of N per acre) were applied at side-dress timing in corn. Available nitrogen in side-dress applications of liquid hog manure was equally effective as UAN in supplying corn nitrogen requirements based on comparisons of yield and grain protein concentration. Drier conditions at side-dress timing reduced soil compaction risks and yield reductions arising from possible root pruning were not observed. Side-dressed liquid hog manure should be applied at rates of available nitrogen that correspond to crop nitrogen demand, since like UAN, excess applied nitrogen will be susceptible to late season losses. Introduction In Ontario, an increasing number of hog producers are side-dressing liquid manure at the 4- to 12-leaf stage of corn. The side-dress timing has a number of benefits relative to the traditional preplant timing in either spring or previous fall. First, in most regions of Ontario, precipitation exceeds evapotranspiration during the winter and early spring months; consequently, side-dress applications should reduce risk of nitrogen losses both through downward movement of NO3, or as gaseous emissions of nitrous oxide. Significant corn nitrogen uptake and demand is not initiated until approximately the 6- to 8-leaf stage, nitrogen sources applied in advance of this stage have a higher potential risk of nitrogen loss. Second, by avoiding manure application at a preplant timing when soil water content in Ontario is typically high, compaction risk associated with high axle weight manure application equipment is reduced. Third, the optimal application window for corn in Ontario is relatively short, and spring pre-plant applications of liquid hog manure often must occur during this optimal planting window thereby reducing the likelihood of corn planting within an optimal window. Liquid hog manure contains nitrogen in the ammonium and organic form. While ammonium nitrogen is readily available, the organic fraction must be released through mineralization processes. Whether this latter fraction will be utilized by a corn crop if application occurs at side dress timing is uncertain. If unutilized by the crop, released organic nitrogen could cause elevated autumn soil nitrate levels which could be lost over winter. Another concern regarding side dress application is associated with negative effects of running manure application equipment between corn rows, particularly concerns regarding root pruning and soil compaction. The objective of this study was to compare available nitrogen in side-dressed liquid hog manure versus 28% urea ammonium nitrate (UAN) in terms of fertilizer nitrogen equivalent, yield response, grain protein, soil compaction, and end of season soil nitrates. Field Experiment Comparing Side-dressed Manure to UAN Field experiments were conducted during three site-years, consisting of three sites in southwestern Ontario from 2003 to 2005. Sites were located on hog farmer-cooperator fields. Previous crop in all years was corn. Soils in all three years were a grey-brown Podzolic, imperfectly drained, Listowel silt loam. Soils had relatively high levels of organic matter, phosphorus and potassium content as indicated in Table 1. Table 1. Site characteristics, planting, manure application, and harvest dates, 2003-2005.
Total precipitation was similar across years but distribution varied (Table 2). Precipitation levels in August-September 2004 and May-June 2005 were below normal, versus July 2005 when levels were above normal. Corn heat unit (1) accumulation over the growing season was 2840, 2921, and 3260 units for 2003, 2004, and 2005, respectively. Table 2. Mean monthly precipitation (inches) for the period 2003-2005
The eight treatments used in the study consisted a low manure rate (2000, 3064 and 2526 gal/acre for 2003, 2004, and 2005, respectively) and a high manure rate (3700, 4492, and 5266 gal/acre for 2003, 2004, and 2005, respectively) also applied at side-dress timing, four non-zero rates of UAN (53, 106, 159, and 220 lb of N per acre) applied at side-dress timing, and two unfertilized control plots (UAN at 0 lb of N per acre, manure at 0 gal/acre), where the zero manure rate was trafficked like the non-zero manure rates. In 2003, treatments consisting of manure at 0 gal/acre and 28% UAN at 250 lb of N per acre were not included. Manure characteristics are given in Table 1 and application dates are listed in Table 3. Manure was side-dress applied using a 3000-gal Nuhn liquid manure tank with in-tank agitation and equipped with a Nuhn Row-Crop Injector (Nuhn Industries, Sebringville, ON). Manure was injected to a depth of approximately 8 inches beneath the soil surface on a 30-inch spacing. Applications were made each year when the corn was approximately 20 inches tall and in the 10- to 12-leaf stage. Individual plots were six, 30-inch corn rows wide by 300 to 500 ft in length, depending on year. Treatments were arranged in randomized complete block design and were replicated three times. Table 3. Manure analysis results, 2003-2005
Grain yield was measured after physiological maturity using a AGCO R42 (AGCO Corp., Duluth, GA) combine equipped with a GrainGage (Juniper Systems Inc., Logan, UT) volumetric yield measurement system. Four rows of the entire plot length were harvested and yields were calculated and expressed on a 15.5% moisture basis. Grain samples were taken at harvest (2004, 2005) and analyzed for protein content using a Dickey John OmegAnalyzerG (Dickey John, Auburn, IL) whole grain analyzer. Samples were taken to 10 inches pre-side-dress (2003 and 2004), approximately one month after application, and post harvest. A composite sample was generated by combining five samples taken along the length of the plot. For the post harvest timing, soil was sampled to a depth of 20 inches in 0 to 10 and 10 to 20-inch depth increments. Samples for each date were analyzed for ammonium (NH4+-N) and nitrate (NO3--N). Frozen samples were thawed, dried, and ground to pass through a 2-mm sieve. A 10-g subsample was extracted using a 2M KCl solution (4), and filtered using Whatman or Fisher Brand filter paper. Concentrations of ammonium and nitrate were determined spectrophotometrically using a Technicon TRAACS-800 (Technicon Systems Inc., Emeryville, CA) auto-analyzer. Soil penetration resistance in the surface 20 inches was measured every 0.6 inch using a Rimik recording penetrometer (Rimik PTY Ltd., Toowoomba, Australia) from a minimum of five positions per plot. At each position, measurements were taken from in-row, wheel-track inter-rows, and non-wheel-track inter-rows. On the same day that penetration resistance measurements were conducted, volumetric soil moisture in the surface 6 inches was also determined for each position using time domain reflectrometry (7). Dry bulk density was determined at depths of 2 to 4-inch and 6 to 8-inch again from in-row, wheel-track inter-rows, and non wheel- track inter-row positions from five positions per plot. Bulk density samples were collected using 2-inch-diameter by 2-inch-high aluminum cores. Data were analyzed for each year using an analysis of variance appropriate for a randomized complete block design using the Mixed Procedure of SAS ver 8.02 (SAS Institute Inc., Cary, NC). Treatments were considered to be fixed effects and blocks were considered to be random effects. Soil bulk density, penetration resistance, and soil nitrate data were analyzed over depth using a split-plot model which considered depth as a whole-plot factor and a fixed effect. When the F-test from the ANOVA was significant for treatment differences, an LSD means separation test was calculated (P < 0.05). Corn Grain Yield Corn grain yield was responsive to nitrogen in all three years (Fig. 1) with an average yield difference of approximately 25.1 bu/acre between the check treatment and the high rate of UAN. Treatment effects were consistent across years, although average yields varied across years. In 2004 and 2005, the 53 lb of N per acre UAN rate resulted in yields equal to higher rates of UAN, but when averaged across the three year period, 106 lb of N per acre was required to maximize yield. The maximum economic rates of nitrogen (MERN), calculated using a quadratic plateau function (2) and assuming a corn price after drying and trucking of $2.8/bu, and nitrogen cost $0.50/lb of N, were 114, 71, and 55 lb of N per acre in 2003, 2004, and 2005, respectively.
Estimates of available nitrogen were made using manure analyses (Table 3) and the Ontario Ministry of Agriculture and Food assumption that 20% of the organic fraction is available in the year of application (5). At the low rate of application, available nitrogen was estimated at 60, 144, and 132 lb of N per acre in the year of application for the three respective study years. Using this assumption, 6.4, 13.6, and 5.8 lb of N per acre, respectively was derived from the organic fraction through the process of mineralization. Variations in manure nitrogen application rates reflect annual variation in manure nitrogen content and the challenge to apply intended rates using commercial equipment. In 2003, the estimate of available nitrogen for the low manure rate was lower than the calculated MERN; however, grain yield was equal to yield at MERN, indicating the possibility of non-nitrogen benefits associated with liquid hog manure. In 2004 and 2005, available nitrogen estimates in the low rate of manure exceeded MERN values, and resulted in yields equal to yields at MERN. Grain yield for low rates of manure application equaled yields of the high manure rate. The low rate of manure produced a fertilizer equivalent of 153, 57, and 131+ lb of N per acre in 2003, 2004, and 2005, respectively. Lack of correlation with estimates of available nitrogen reflect variation in N responsiveness across years, and the potential for yield increases to be associated with non-nitrogen benefits of manure (3,6). Grain yield of the two check plots did not differ (Fig. 1). Even though manure side dressing occurred at a relatively late stage of 10 to 12 leaves, soil and root disturbance associated with manure injection operations did not reduce yield. Clearance of most existing commercial equipment does not enable applications beyond the 12-leaf stage. An earlier manure side-dressing operation could further decrease risk of injury to corn roots. Earlier side-dress timing also could be beneficial in that it opens a new application window, and reduces trampling injury of corn on field headlands. Lack of difference in check yields also indicates that compaction from high manure tanker axle weights was not a problem. Soil bulk density or penetration resistance did not differ across the two check treatments at any of the depths evaluated in any of the three years (data not shown). Mean bulk density values across all years ranged from 1.2 to 1.3 g/cu cm. Shallow compaction that may have occurred due to manure tank axle weight appears to have been alleviated by subsequent loosening of soil by the injection implement. Deep soil compaction did not occur possibly as a result of low soil moisture levels associated with mid season application timing. Soil moisture at a 6-inch depth was 38 and 25% v/v in 2004 and 2005, respectively. The soils used in this study had relatively high organic matter contents (Table 1) which could also reduce risk of compaction due to high axle weights. Corn Grain Protein Ontario producers have speculated that nitrogen present in the organic form in liquid hog manure will mineralize during the corn grain fill period thereby increasing grain protein concentrations. This effect was not observed in this trial. Available nitrogen at the time of application had a greater influence on grain protein than any other factor. Grain protein content was not increased by liquid hog manure application in comparison to UAN treatments (Fig. 2). While grain protein content of the low manure rate in 2004 exceeded the 53 lb of N per acre treatment, the estimated available nitrogen in this treatment, as indicated above, was 144 lb N/acre with only an estimated 13.6 lb of N per acre of this amount derived from organic nitrogen (5).
Soil Nitrogen Soil nitrate content in 2003 and 2004 measured prior to manure or UAN application was the same for all treatments at 36 and 17 ppm, respectively (Table 4). Nitrate content at this timing was much higher across all treatments in 2003 possibly due to a 10-day difference in date of sampling. Table 4. Soil nitrate-N concentrations for liquid hog manure and UAN application rates, 2003 to 2005. The interaction between treatment and year was significant for soil nitrate content measured 4 to 8 weeks after manure/UAN application. In 2003 and 2004 soil nitrate-N concentrations increased with increasing UAN rate. In 2005 UAN rate had no effect on soil nitrate content measured four weeks after application. Rainfall during the 4 to 6 week period following application was at normal levels in 2003 and 2004, but was high in 2005 (Table 2). High rainfall in 2005 may have caused significant nitrogen losses in that year. Only in 2005 was it observed that the high rate of manure caused increased soil nitrate concentrations in comparison to UAN treatment, possibly resulting from mineralization of the organic fraction of the manure. Post harvest soil nitrate concentrations were affected by treatment only in 2003 (Table 4). At the 0- to 10-inch depth, concentrations increased with increasing UAN rate. Soil nitrate concentrations of the manure application treatments only differed from the high UAN application rate. At the 10 to 20-inch depth differences only occurred between the check and the highest UAN application rate. In 2004 and 2005, soil nitrate-N concentrations did not differ for any of the treatments suggesting that significant losses of nitrogen had already occurred. Conclusions Side-dress applications of liquid hog manure appear able to substitute for UAN in supplying corn nitrogen requirements. Fertilizer nitrogen equivalent values for manure were variable due to variations in nitrogen responsiveness across years, and possible non-nitrogen benefits of manure. Negative yield impacts resulting from soil compaction and root pruning due to the side-dress application process were not observed. Available nitrogen in liquid hog manure treatments resulted in soil nitrate values during the grain fill period that were equivalent to corresponding UAN nitrogen treatments. Delayed nitrogen availability due to mineralization of the organic nitrogen fraction during the grain fill period of corn did not result in increased protein concentration of grain for the manure treatments, probably due to the fact that nitrogen derived from the organic fraction represented a relatively small percentage of the total available nitrogen in liquid hog manure. Growers that side-dress liquid hog manure into corn may reduce compaction risks associated with preplant applications, increase timeliness of corn planting by eliminating preplant manure application operations, reduce potential nitrogen losses associated with preplant manure applications, and reduce UAN requirements. Like UAN, side-dress liquid hog manure should be applied at rates of available nitrogen that correspond to crop nitrogen demand, since like UAN, excess applied nitrogen is susceptible to late season losses. As was evidenced in this study, additional attention is required to address the difficulties and constraints associated with applying desired manure nitrogen rates. Literature Cited 1. Brown, D. M., and Bootsma, A. 1993. Crop heat units for corn and other warm-season crops in Ontario. OMAF Factsheet, Agdex 111/31. Ontario Ministry of Agric. & Food, Toronto, Canada. 2. Bullock, D. G., and Bullock, D. 1994. Quadratic and quadratic-plus-plateau models for predicting optimal nitrogen rate of corn: a comparison. Agron. J. 86:191-195. 3. Lalande, R., Gagnon, B., Simard, R. R., and Cote, D. 2000. Soil microbial biomass and enzyme activity following liquid hog manure application in a long-term field trial. Can. J. Soil Sci., 80:263-269. 4. Malpassi, R. N., Kaspar, T. C., Parkin, T. B., Cambardella, C. A., and Nubel, N. A. 2000. Oat and rye root decomposition effects on nitrogen mineralization. Soil Sci. Soc. Am. J. 64:208-215. 5. Ontario Ministry of Agriculture, Food and Rural Affairs. 2002. Agronomy guide for field crops. Publ. No. 811. Ministry of Agriculture, Food and Rural Affairs, Queens Printer, Toronto, Canada. 6. Persson, J., and Kirchmann, H. 1994. Carbon and nitrogen in arable soils as affected by supply of N., fertilizers and organic manures. Agric. Ecosyst. Environ. 51:249-255. 7. Topp, G. C., Davis, J. L., and Annan, A. P. 1980. Electromagnetic determination of soil water content: Measurements in coaxial transmission lines. Water Resour. Res. 16:574-582. |
