S.K. Lee, D. D. Minner, N. E. Christians and H. G. Taber
Introduction
The fundamental concept of a slow-release fertilizer is that it releases its nutrients at a more gradual rate that allows maximum uptake and use of nutrients by plants while minimizing the losses due to leaching, volatilization, or unnecessary turf growth (Sartain, 2002). This may reduce the number of fertilizer applications required to maintain plant growth at desired levels and allow greater rates of fertilizer to be applied in a single application. Slow- and controlled-release N sources reduce leaching potential under adverse climatic and edaphic conditions as well as provide other benefits such as reduced burn potential, extended release over time, and lower labor costs (Fry et al., 1993).
Methylene ureas are a class of slow-release N that were promoted during the 1960's and 1970's (Sartain, 2002). These products predominantly contain intermediate-chain-length polymers. The total N content of a methylene urea polymer is 39 to 40%, with between 25 and 60% of the N present being cold-water insoluble N (CWIN) (Christians, 1998). Unreacted urea N content generally is in the range of 15 to 30%. The objective of this study was to compare urea and methylene urea (Nutralene®) by measuring clipping dry weight, root dry weight, root organic matter, and amount of NO3-N leached from a soil column at 146 and 293 kg•ha-1 and four mixing depths (0, 7.6, 15.2, and 22.9 cm) on a sand-based system.
Materials and Methods
This study was conducted for 12-weeks in a greenhouse at Iowa State University. Ames, Iowa. The experimental design was a randomized complete block with 16 treatments and four replicates. Methylene urea (Nutralene®), a slow-release N source, and urea (46-0-0), a fast-release N source, were the N sources. Both materials were evaluated with four mixing depths of 0, 7.6, 15.2, and 22.9 cm and evaluated with two application rates (146 and 293 kg•ha-1). Urea for surface application was applied weekly at 12.17 and 24.42 kg•ha-1, giving a total of 146 and 293 kg•ha-1 during the 12-week study period, respectively.
Local mason's sand that met the United States Golf Association (USGA) specification was used as the growing medium (USGA Green Section Staff, 1993). The sand was packed into a 7.62 cm diameter polyvinyl chloride (PVC) pipe lined with a clear plastic sleeve. The PVC pipe was capped at the bottom, and the plastic sleeve tied off at the bottom with fine holes punched into it facilitate drainage while keeping the sand in place. The plastic sleeve had a length of 38.1 cm, and the root zone depth was 30.5 cm. The columns were sodded with mature sod of Poa pratensis L. harvested and watered 300 ml each week. Greenhouse temperature during the night and day was 19.4-22.2 ºC, respectively.
Modified Hoagland solution was used that enabled proper levels of nutrients to be maintained in the root zone (Pellett and Roberts, 1963). The N fertilizers were applied on 4 Nov. 2002. Grass clippings were taken from each tube at two-week intervals. At the end of the study, root dry weight and organic matter weight for roots were measured. All leachate was collected from the cup under the PVC pipe for final nutrient analysis. Nitrate-N of the leachate was analyzed by using the cadmium-reduction method (Bremner, 1965).
Data were subjected to analysis of variance by using the Analysis of Variance (ANOVA) procedure, and mean separation was performed by the least significant difference (LSD) method wit the Statistical Analysis System (SAS, 1987).
Results
Significant effects on clipping dry weight were found in all treatments and interactions with exception of N rate X mixing depth and N source X N rate X mixing depth (Table 1). For this reason, each factor was reported independently at each mixing depth of the other factors (Table 2). In 0 cm mixing depth, both of urea and Nutralene® had no difference within same rate. However, Nutralene® of 293 kg•ha-1 rate produced 96-437 % more clipping dry weight than urea of 293 kg•ha-1 rates in 7.6, 15.2, and 22.9 cm mixing depth. Nutralene® of 146 kg•ha-1 rate had 142 % clipping dry weight than urea of 146 kg•ha-1 rate in 7.6 cm mixing depth.
There were significant main effects and interaction effects of N source X mixing depth observed on root dry weight and root organic matter (Table 1). Urea at a rate of 293 kg•ha-1 rate resulted in more root dry weight and root organic matter than Nutralene® at the 293 kg•ha-1 rate applied at the 0 cm mixing depth. Conversely, Nutralene® at a rate of 293 kg•ha-1 rate produced more root dry weight and root organic matter than urea of 293 kg•ha-1 rate applied at the 7.6 cm mixing depth. Nutralene® at a rate of 146 kg•ha-1 rate had 72 and 63 % more root dry weight and root organic matter, respectively than urea at a rate of 146 kg•ha-1 rate applied at the 15.2 cm mixing depth.
No N source and rate effects for NO3-N release was found in 0 cm mixing depth. Interestingly, the 146 kg•ha-1 Nutralene® rate provided less leached NO3-N with more clipping dry weight, root dry weight, and root organic matter than plants that received urea at 146 kg•ha-1 applied at the 7.6 cm mixing depth. Nutralene® at a rate of 293 kg•ha-1 rate at the 22.9 cm mixing depth also produced 18 ppm leached NO3-N with more clipping dry weight, root dry weight, and root organic matter compared to urea at a rate of 146 kg•ha-1 rate in 22.9 cm mixing depth that produced 174 ppm leached NO3-N.
Literature Cited
Bremner, J.M. 1965. Inorganic forms of nitrogen. 1179-1237. In C.A. Black et al. (ed.) Method of soil analysis. Part 2, Argon. Monogr. 9. ASA, Madison, WI.
Christians, N.E. 1998. Fundamentals of turfgrass management. Ann Arbor, MI.
Fry, J.D., D.O. Fuller, and F.P. Maier. 1993. Nitrogen release from coated ureas applied to turf. International Turfgrass Society. 7:533-539.
Pellett, H.M. and E.C. Roberts. 1963. Effects of mineral nutrition on high temperature induced growth retardation of Kentucky bluegrass. Agron. J. 55:473-476.
Sartain, J.B. 2002. Foot for turf: slow-release nitrogen. Ground Maintenance.
SAS. 1987. SAS/STAT User's Guide. Version 6. Statistical Analysis System Institute, Inc., Cary, NC.
United States Golf Association Green Section Staff. 1993. USGA recommendations for a method of putting green construction. USGA Green Section Record. 1-3.
Table 1. Summary of analysis of variance indicating significant source effects on total clipping dry weight, root dry weight, root organic matter, and amount of leached NO3-N.
| Source | df | Total clipping dry weight | Root dry weight | Root organic matter | Amount of leached NO3-N |
|---|---|---|---|---|---|
| N-source (NSO) | 1 | ** | * | * | ** |
| N-rate (NRT) | 1 | ** | ** | ** | NS |
| Mixing depth (MD) | 3 | ** | ** | ** | ** |
| NSO _ NRT | 1 | * | NS | NS | NS |
| NSO _ MD | 3 | ** | ** | ** | NS |
| NRT _ MD | 3 | NS | NS | NS | ** |
| NSO _ NRT _ MD | 3 | NS | NS | NS | * |
*, ** Significant at the 0.05 and 0.01 probability level, respectively. NS = not significant.
Table 2. Response of Poa pratensis 'Unique' fertilized with Nutralene® or urea at two rates and four depths of fertilizer incorporation. Values are means of four measurements.
| Nitrogen source | Rate (kg•ha-1) | Total clipping dry weight (g/m2) | Root dry weight (g/m2) | Root organic matter (g/m2) | Leached NO3-N (ppm) |
|---|---|---|---|---|---|
| Depth = 0 cm | |||||
| Nutralene® | 146 | 200 cdez | 157 ef | 140 defgh | 17 d |
| Nutralene® | 293 | 331 ab | 236 b | 209 b | 13 d |
| Urea | 146 | 265 bc | 194 bcde | 169 bcde | 9 d |
| Urea | 293 | 385 a | 305 a | 265 a | 13 d |
| Depth = 7.6 cm | |||||
| Nutralene® | 146 | 191 cde | 135 ef | 121 efgh | 25 d |
| Nutralene® | 293 | 322 ab | 219 bcd | 193 bcd | 13 d |
| Urea | 146 | 79 fg | 136 ef | 112 fgh | 92 bc |
| Urea | 293 | 60 g | 103 f | 96 h | 33 cd |
| Depth = 15.2 cm | |||||
| Nutralene® | 146 | 161 def | 175 cde | 156 bcdef | 45 cd |
| Nutralene® | 293 | 208 cd | 228 bcd | 196 bc | 115 ab |
| Urea | 146 | 67 fg | 102 f | 96 gh | 40 cd |
| Urea | 293 | 106 efg | 168 de | 152 cdefg | 167 a |
| Depth = 22.9 cm | |||||
| Nutralene® | 146 | 117 defg | 150 ef | 138 defgh | 64 bcd |
| Nutralene® | 293 | 324 ab | 232 bc | 212 ab | 18 d |
| Urea | 146 | 64 fg | 148 ef | 135 efgh | 27 d |
| Urea | 293 | 123 defg | 182 bcde | 165 bcdef | 174 a |
| LSD (0.05) | 99 | 61 | 56 | 64 | |
z Values in a column followed by the same letter are not significantly different based on LSD at 0.05 probability.
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ISU Turfgrass:2003 Turfgrass Report | College of Agriculture |
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