Nitrogen fertilizer product and timing alternatives exist for forage production in the Peace region of Alberta

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1 Nitrogen fertilizer product and timing alternatives exist for forage production in the Peace region of Alberta R. E. Karamanos 1 and F. C. Stevenson 2 1 Viterra Inc., Barlow Trail SE, Calgary, Alberta, Canada T2C 4M5 ( rigas.karamanos@viterra.com); and Rogers Road, Saskatoon, Saskatchewan, Canada S7N 3T6. Received 2 July 2012, accepted 14 November Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/13 Karamanos, R. E. and Stevenson, F. C Nitrogen fertilizer product and timing alternatives exist for forage production in the Peace region of Alberta. Can. J. Plant Sci. 93: Four different N sources [ammonium nitrate (NIT), urea (UR), polymer-coated urea (PCU), and N-(n-butyl) thiophosphoric triamide-treated urea (AGR)] were applied to stands of pure meadow bromegrass (Bromus beibersteinii L.) or a 50:50 smooth bromegrass (Bromus inermis L.)alfalfa (Medicago sativa L.) mixture in late fall and early spring at four N rates (0, 60, 80 and 100 kg N ha 1 ) over a 3-yr ( ) period. The N treatments generally increased forage responses, but the response net revenue to N treatment was rarely positive and at times was negative, especially for PCU. On average, PCU resulted in lower yield and protein concentration, lesser N efficiency, and lesser profit relative to other forms of N. This difference was more pronounced in the spring and was less notable at Rycroft, the location with the bromegrassalfalfa mixture. Also, greater N fertilizer rates increased the yield, protein concentration, total N uptake, and profit for all fertilizer forms. The exceptions to the preceding were N fertilizer rate did not affect forage responses for PCU and at the location with the brome-alfalfa mixture. Urea or AGR provided satisfactory agronomic alternatives to ammonium nitrate when applied in early spring at sufficient rates. Key words: Bromus beibersteinii, Bromus inermis, Medicago sativa, urea, ammonium nitrate, urease inhibitor, N timing Karamanos, R. E. et Stevenson, F. C Il existe diffe rentes solutions a` l emploi et au moment d application des engrais azote s pour la production fourrage` re dans la re gion de la rivie` re de la Paix, en Alberta. Can. J. Plant Sci. 93: Quatre sources d azote [nitrate d ammonium (NIT), ure e, ure e enduite de polyme` re (PCU) et ure e traite e au N-(n-butyl) triamide de l acide thiophosphorique (AGR)] ont été applique es à des peuplements purs de brome des prés (Bromus beibersteinii L.) ou compose s àmoitie de brome inerme (Bromus inermis L.) et de luzerne (Medicago sativa L.) à la fin de l automne et au de but du printemps. Les applications ont été re alise es à quatre taux diffe rents (0, 60, 80 et 100 kg de N par hectare) pendant trois ans (de 2003 a` 2005). En ge ne ral, l application d azote intensifie la croissance du fourrage, mais la variation du revenu net attribuable a` une telle application est rarement positive et est parfois ne gative, surtout avec le PCU. En moyenne, le PCU diminue le rendement et la concentration de prote ines, re duit l efficacite du N et engendre moins de be ne fices que les autres formes d engrais azote s. L e cart est plus prononcé au printemps et moins évident a` Rycroft, ou` e tait cultive le mélange de brome et de luzerne. Par ailleurs, plus haut est le taux d application, et plus grands sont le rendement, la teneur en prote ines, l absorption totale d azote ainsi que le be ne fice re alise, peu importe le type d engrais azote. Le taux d application des engrais N n affecte toutefois pas la re action des cultures fourrage` res au PCU et ni celle observée a` l endroit ou` e tait cultivé le me lange brome-luzerne. Sur le plan agronomique, l urée ou l AGR constituent les meilleures solutions de rechange au nitrate d ammonium quand on les applique au de but du printemps, a` un taux suffisant. Mots clés: Bromus beibersteinii, Bromus inermis, Medicago sativa, ure e, nitrate d ammonium, inhibiteur de l ure ase, moment de l application des engrais N The total area dedicated to alfalfa, alfalfa mixtures and tame hay crops in western Canada in 2006 was estimated at approximately 9 million ha, of which 3.5 million ha were in Alberta, 4.6 million ha were in Saskatchewan and under 1 million ha were in Manitoba (Statistics Canada 2006). Alberta remains the top province for alfalfa acreage with 31.4% of the national area; a sizable portion of this established forage acreage is in the Peace River Region of Alberta. The two preferred forms of N fertilizer for broadcast application have been primarily ammonium nitrate (3400) and to a lesser degree urea (4600). Production of ammonium nitrate in western Canada, however, was discontinued in Also, information for alternative N fertilizer products is limited, especially for the Peace River Region of Alberta. In Saskatchewan, dribble-banding liquid N, especially when treated with a urease inhibitor, or placing N in the soil using a spokewheel applicator or coulter/disc system (but not knife banding), was recommended to avoid any potential problem of N loss (Saskatchewan Agriculture and Food 2005). Urea forms were equal to or superior to ammonium nitrate for fertilizing late-season grasses in Manitoba when conditions were not conducive for Abbreviations: AGR, N-(n-butyl) thiophosphoric triamide (NBPT)-treated urea; NIT, ammonium nitrate; PCU, polymer coated urea; UR, urea Can. J. Plant Sci. (2013) 93: doi: /cjps

2 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/ CANADIAN JOURNAL OF PLANT SCIENCE volatilization losses (Manitoba Agriculture, Food and Rural Initiatives 2006). This same publication recommended the use of banding solutions or urease inhibitor when there was a potential for volatilization losses. In southern Alberta, McKenzie et al. (2009) concluded that the efficacy for spring-broadcast urea and ammonium nitrate (NIT) were similar and greater, respectively, than for polymer coated urea (PCU) a study with irrigated timothy (Phleum pratense L.). In central and northern Alberta, spring temperatures are generally cool enough to allow early spring broadcast urea with minimal N loss. Research in Montana, however, has pointed to potential volatilization losses of urea when applied onto cold soil with moderate snow cover, albeit on frozen and wet soils (Engel et al. 2011). With this in mind, our objective was to assess whether the use of ammonium nitrate as a N source in northern Alberta can be substituted by N fertilizer products meant to minimize volatilization losses or urea applied when conditions are cooler. MATERIALS AND METHODS A 3-yr project ( ) was carried out at two locations in northern Alberta: (1) Peoria, a loam, ph 5.5 and 3.5% organic matter and (2) Rycroft, a sandy loam, ph 8.1 and 1.9% organic matter). The study was only continued at Peoria in Peoria had been seeded to meadow bromegrass (Bromus beibersteinii L.), whereas Rycroft was a 50:50 mixture of smooth bromegrass (Bromus inermis L.) and alfalfa (Medicago sativa L.). The treatment design included a factorial arrangement of time of fertilizer application (fall and spring), fertilizer form, and N fertilizer rate (0, 60, 80 and 120 kg Nha 1 ). Fertilizer forms included ammonium nitrate (NIT), urea (UR), polymer-coated urea (PCU), and N-(n-butyl) thiophosphoric triamide (NBPT)-treated urea (AGR). The polymer-coated urea was ESN (Agrium Advanced Technologies); urea was handtreated with NBPT at the recommended rate of 0.14% by weight sold under the trade name Agrotain (Agrotain International, St. Louis, MO) 2003 and In 2005, a pretreated urea product (Nitrogain) was used. An unfertilized control was also included in each replicate within each site (location by year combination). Combinations of these treatments were arranged in a randomized complete block design with five or six replications. Plot size was 1.8 m12 m. Each site received a blanket application of 100 kg P 2 O 5 ha 1 as triple super phosphate (0450), and 50 kg K 2 Oha 1 and 18 kg S ha 1 as potassium sulphate (005018) in the fall of 2002 together with the N treatments. fertilizer application was carried out in late fall (2002 Oct. 30, 2003 Nov. 03 and 2004 Oct. 21) with a Hege (Hege Equipment Inc Colwich, KS) applicator. The fall applications for 2003 (fall of 2002) and 2004 (fall of 2003) occurred on plots with snow cover of approximately 2.5 and 20 cm, respectively. fertilizer applications were carried out on 2003 May 01, 2004 Apr. 06 and 2005 May 04. Soils were partly frozen in 2002 and 2004, whereas soils were warm (average May temperature of C) in 2005 (National Climate Data and Information Archive 2012). A 1.5-m6-m portion of each plot in 2003 and 2004, and a 1.5-m5.2-m portion in 2005, was harvested on 2003 Jul, 10, 2004 Jul. 14, and 2005 Jun. 26. A second harvest was not performed because re-growth in the northern Alberta climate is too slow. Harvested plant material was dried at 608C to a constant weight. Plant sub-samples were ground ( B425 m) prior to assay. Total plant N was determined in a Kjeldahl digest (Huang and Schulte 1985). Protein was estimated from Kjeldahl N by multiplying by Nitrogen efficiency components were estimated from yield and N concentration data after Snyder and Bruulsema (2007). Three components were calculated as follows: PFP (partial factor productivity of applied nutrient): Y/F AE (agronomic efficiency of applied nutrient): (Y-Y0)/F RE (apparent crop recovery efficiency of applied nutrient): (U-U0)/F where Y is yield (kg ha 1 ), F is N fertilizer rate (kg N ha 1 ), Y0 is the yield of the no fertilizer treatment (kg ha 1 ), U is nutrient amount (kg N ha 1 ) in aboveground crop biomass with nutrient applied, and U0 is nutrient amount (kg N ha 1 ) in above-ground crop biomass with no nutrient applied. Net revenue data were calculated to assess the economic viability of N fertilizer treatments. Net revenue calculation was done on a plot basis using an equation adapted from Mason et al. (2007) and O Donovan et al. (2001) as follows: NR (YP)(FN) where NR is net revenue in $CAD per hectare, Y is crop yield (Mg ha 1 ), P is commodity price in $CAD Mg 1, F is the cost of each fertilizer form in $CAD Mg 1, and N fertilizer rate (kg N ha 1 ). Commodity prices ($CAD Mg 1 ) were as follows: bromegrass$65 and alfalfa-bromegrass mixture$95. Data were analyzed two ways with the PROC MIXED procedure of SAS (Littel et al. 2006), with the effect of replicate considered random, and the effects of site (location by year combination) and the applied treatments considered fixed. A separate residual variance for each site was modeled for all response variables. A corrected Akaike s information criterion confirmed the benefit of modeling heterogeneous residual variances. The first analysis included the control and a single classification factor for the analysis. The second analysis excluded control and the data considered in the factorial treatment design were time of application by fertilizer form by N fertilizer rate.

3 KARAMANOS AND STEVENSON * N FERTILIZER AND FORAGE PRODUCTION 153 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/13 For this analysis, responses to N fertilizer were assessed with polynomial contrasts rate across and among fertilizer forms and sites. Where contrasts indicated important responses to N fertilizer rate, means derived from the preceding analysis of variance was analyzed with the PROC REG procedure of SAS (SAS Institute, Inc. 2004) to obtain regression coefficients. All statistical tests were declared significant at P B0.05. RESULTS AND DISCUSSION An analysis was conducted to determine whether the response for each applied treatment was different from the untreated control. Differences relative to control were often significant with some notable exceptions (Fig. 1 and Table 1). Additionally, the site treatment interaction always was significant (P B0.001), thus indicating that the differences between treatments and control likely varied among sites. In general, more significant differences relative to control were noted: Peoria 2003 Peoria 2004/2005Rycroft. This is in agreement with findings by Whitehead et al. (1995) under different environmental conditions, who observed that response of forage grasses to N fertilization varied with site, year and season. The authors attributed this to variation in the soil N supply and the crop N requirements. Some of the other highlights from our analysis were that yield differences almost always were significant at all site sites except Rycroft 2003 where almost none of the differences were important. Yield differences for PCU treatments vs. control at Peoria 2003 and especially Peoria 2005 were not important. Protein concentration often was greater with applied treatments at all sites except at Rycroft 2004, where one UR and two AGR treatments results in significantly less protein concentration than the control. In terms of profitability, most positive effects of applied treatments on profitability occurred at Peoria At remaining sites, almost all of the important differences were negative and most negative instances occurred mainly for PCU and at Peoria Fertilizer affected (P B0.001) all forage responses tested in this study (Table 2). The PCU resulted in Fig. 1. A summary of differences relative to the untreated control (treatment minus control) at five sites in northwest Alberta, Dots mark the point estimates of the differences. Error bars represent confidence intervals for differences, and intervals not including zero indicate statistically significant differences (a0.05). NIT represents ammomium nitrate, UR represents urea, AGR represents Agrotain, and PCU represents polymer-coated urea.

4 154 CANADIAN JOURNAL OF PLANT SCIENCE Table 1. Forage response to combinations of time of N application, fertilizer form, N fertilizer rate (kg ha 1 ), and an untreated control at five sites in northwest Alberta, Yield (Mg ha 1 ) Protein conc. (g kg 1 ) Net revenue ($ ha 1 ) Peoria Rycroft Peoria Rycroft Peoria Rycroft Treatment Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/13 Control NIT UR PCU AGR NIT UR PCU AGR LSD lower yield and protein concentration, lesser N efficiency, and lesser profit compared to other products when data were averaged across sites. This is in contrast to findings by Malhi et al. (2004) in central Alberta, who reported that when N was applied in April, the effectiveness of surface applied urea on grasslands can be improved by some slow release products; however, economic analysis of their data showed that added expense of the coated fertilizer makes its application non-practical. The other fertilizer forms all had similarly greater responses, with one exception. Table 2. Forage response to fertilizer form average across five sites in northwest Alberta, Urea had protein concentration intermediate to those for PCU and AGR/NIT. The effect of fertilizer form interacted (PB0.015) with site and time of application, except for protein concentration where fertilizer form interacted (P0.02) with N rate in addition to site and time of application. The negative effect of PCU for forage responses was notable in the spring (Table 3). Generally speaking, these form effects mostly occurred at the Peoria sites and occurred less frequently and to a lesser degree at Rycroft in For protein concentration, the nature of the site by Variable NIT z UR AGR PCU LSD Yield (Mg ha 1 ) Protein conc. (g kg 1 ) N uptake (kg ha 1 ) AE (Mg ha 1 per kg N ha 1 ) y PFP (Mg ha 1 per kg N ha 1 ) y RE (kg N ha 1 per kg N ha 1 ) y Net revenue ($ ha 1 ) z NIT, ammonium nitrate; UR, urea; AGR, Agrotain; PCU, polymer-coated urea. y AE, agronomic efficiency of N; PFP, partial factor productivity of N; RE, apparent crop recovery efficiency of N.

5 KARAMANOS AND STEVENSON * N FERTILIZER AND FORAGE PRODUCTION 155 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/13 Table 3. Forage response to time of N application and fertilizer form average at five sites in northwest Alberta, Peoria Rycroft Treatment Yield (Mg ha 1 ) NIT z UR AGR PCU NIT UR AGR PCU LSD Protein concentration (g kg 1 ) NIT UR AGR PCU NIT UR AGR PCU LSD N uptake (kg ha 1 ) NIT UR AGR PCU NIT UR AGR PCU LSD AE (Mg ha 1 per kg N ha 1 ) y NIT UR AGR PCU NIT UR AGR PCU LSD PFP (Mg ha 1 per kg N ha 1 ) y NIT UR AGR PCU NIT UR AGR PCU LSD Table 3 (Continued) Peoria Rycroft Treatment RE (kg N ha 1 per kg N ha 1 ) y NIT UR AGR PCU NIT UR AGR PCU LSD Net revenue ($ ha 1 ) NIT UR AGR PCU NIT UR AGR PCU LSD z NIT, ammonium nitrate; UR, urea; AGR, Agrotain; PCU, polymercoated urea. y AE, agronomic efficiency of N; PFP, partial factor productivity of N; RE, apparent crop recovery efficiency of N. fertilizer form by time of application was different. At Peoria 2003 and 2004, and Rycroft 2003, the effect fertilizer form by time of application combinations was generally similar to that averaged across sites. Protein concentration did not respond to fertilizer form and time of application at Peoria 2005, but at Rycroft 2004 protein concentration was greater for PCU vs. other forms, especially in the spring. Fertilizer form also affected forage responses through interactions (PB0.014) with site and N fertilizer rate. When examining responses across sites, maximum forage response was often achieved with 100 kg N ha 1 of all forms except PCU and urea for protein concentration (Fig. 2 and Tables 4 and 5). Also, greater N fertilizer rates increased the response of yield, protein concentration, total N uptake, and profit for all fertilizer forms except PCU where the effect of N fertilizer rate generally was not important. The site portion of the sitefertilizer form N fertilizer rate interaction for yield, protein concentration, total N uptake, and profit mostly occurred because the effect of N fertilizer rate was not statistically significant at both Rycroft sites. The site by all treatment interaction for protein concentration was not considered because of the complex nature of the responses and the difficulty to come up with a meaningful interpretation. For RE, N fertilizer rate on average was not statistically important

6 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/ CANADIAN JOURNAL OF PLANT SCIENCE Fig. 2. A summary of differences for linear contrast comparing N fertilizer rates (1 0 1) for each fertilizer form at five sites in northwest Alberta, Additionally, the interaction between different form (e.g., NIT-AGR: NIT minus AGR) and the linear contrast for N fertilizer rate also are summarized. Dots mark the point estimates of the differences. Error bars represent confidence intervals for differences, and intervals not including zero indicate statistically significant differences (a=0.05). NIT, ammomium nitrate; UR, urea; AGR, Agrotain; PCU, polymer-coated urea; RE, apparent crop recovery efficiency of N.

7 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/13 Table 4. Forage response to fertilizer form and N fertilizer rate (kg ha 1 ), and an untreated control at five sites in northwest Alberta, Yield (Mg ha 1 ) Protein conc. (g kg 1 ) N uptake (kg ha 1 ) Peoria Rycroft Peoria Rycroft Peoria Rycroft Variable Site z NIT y Slope x (0.007) (0.005) (0.005) (0.012) (0.010) (0.063) (0.090) (0.312) (0.165) (0.023) (0.073) (0.080) (0.132) (0.003) (0.118) UR Slope (0.011) (0.004) (0.007) (0.011) (0.001) (0.009) (0.053) (0.082) (0.105) (0.072) (0.003) (0.098) (0.106) (0.002) AGR Slope (0.012) (0.017) (0.023) (0.006) (0.036) (0.180) (0.147) (0.120) (0.008) (0.006) (0.108) (0.170) (0.103) (0.047) PCU Slope (0.012) (0.017) (0.023) (0.006) (0.036) (0.180) (0.147) (0.120) (0.008) (0.006) (0.108) (0.170) (0.103) (0.047) z Site represents location by year combinations. y NIT, ammonium nitrate; UR, urea; AGR, Agrotain; PCU, polymer-coated urea. x Linear slope coefficient (SE in parentheses) from regression of means. KARAMANOS AND STEVENSON * N FERTILIZER AND FORAGE PRODUCTION 157

8 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/13 Table 5. Apparent crop recovery efficiency of N (RE) and net revenue from N fertilizer application at five sites in northwest Alberta, RE (kg N ha 1 per kg N ha 1 ) Net revenue ($ ha 1 ) Peoria Rycroft Peoria Rycroft Variable Site z NIT y Slope x (0.490) (0.340) (0.300) (0.860) (0.710) UR Slope (0.700) (0.280) (0.460) (0.760) (0.040) AGR Slope (0.550) (0.660) (0.010) (2.110) (0.210) PCU Slope (0.770) (1.100) (1.590) (0.440) z Site represents location by year combinations. y NIT, ammonium nitrate; UR, urea; AGR, Agrotain; PCU, polymer-coated urea. x Linear slope coefficient (SE in parentheses) from regression of means. 158 CANADIAN JOURNAL OF PLANT SCIENCE

9 KARAMANOS AND STEVENSON * N FERTILIZER AND FORAGE PRODUCTION 159 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/13 (P 0.09), but at Peoria 2005 greater N fertilizer reduced RE especially for NIT and PCU. For AE and PFP, greater N fertilizer rates decreased efficiencies for all fertilizer forms (Table 5). This reduction was more notable at Rycroft 2003 and particularly Peoria Rycroft sites were established on a 50:50 smooth bromegrassalfalfa mixture and the Peoria sites were established on a pure stand of meadow bromegrass. It is generally believed that forage stands dominated by legumes are not as responsive to N as stands dominated by grass species are (Alberta Agriculture, Food and Rural Development 2004), although Malhi et al. (2004) demonstrated the need for additional N by alfalfagrass mixtures in northern climates. However, observations at the site level indicated the forage dry matter yield was indeed more responsive to N fertilizer rate at Peoria compared with Rycroft (results not shown). Therefore, it is not surprising to find that the effect of N management strategies deviated from overall responses at the location including alfalfa. The Rycroft 2004, and Peoria 2004, had growing season (April 01 to harvest) precipitation for 2004 of 272 mm, which was 140 mm greater than in Greater soil moisture availability for 2004, relative to other years, likely resulted in greater mineralization from organic N sources that in turn results in more responses to the different N management practices for Rycroft 2004 vs It would be expected that fertilizer form would have minimal if no impact on forage plant physiology, and consequently the efficiency of plants to convert N into yield. Therefore, the generally lesser N uptake and efficiencies for PCU relative to other forms would implicate reduced N availability as the reason for these dry matter yield and protein concentration differences among fertilizer form. Greater labile N availability from alfalfa at Rycroft would explain why N availability effects via fertilizer form were generally not important at these sites. However, in cropping systems such as at the Peoria site, AGR and UR may be useful alternatives to NIT. Warmer spring conditions may have contributed to differences in responses at the Peoria site in 2005 compared with those in 2003 and Table 6. Comparison of net revenue from fall versus spring N fertilizer application in at five sites in northwest Alberta, Peoria Rycroft N rate (kg ha 1 ) Net revenue ($ ha 1 ) LSD Economic responses were assessed based on average forage price and fertilizer cost as ANOVA for ranges in the forage prices and fertilizer costs resulted in exactly the same conclusion. In terms of profitability, these analyses indicate that inferior agronomics (particularly yield) for PCU correspond with poor economics (Table 5). In fact, these results question the need for N fertilizer for forage production in the Peace region. However, these calculations are highly sensitive to the price assigned to forage, which we may, in fact, have undervalued. For example, the price for which a forage is sold might be different from the price a livestock operator might assign to this forage if he grew and fed it himself. Although the site timerate and site fertilizer rate interactions were significant for net revenue, it does not appear to be a consistently better time to apply N to improve profits (Table 6); in two sites there was no effect of time, in two spring was better, and in one site fall application resulted in higher net return (two rates only). This is not dissimilar to the findings of Campbell et al. (1986), who found that fertilizer applied to forages in Swift Current and Scott, Saskatchewan, in April generally gave the highest net returns, but sometimes October and/or November applications provided as good or better results. These authors further observed that net returns were highly dependent on the occurrence of early spring precipitation, with fertilizer application being profitable in wetter years, and on whether the forage was sold for hay or fed on the farm, and were greater for NIT than UR. CONCLUSION When considering optimal yield and protein concentration for forages grown in the Peace region of Alberta, AGR was found to be a satisfactory substitute for NIT especially when spring applied. In terms of biomass production alone, all N fertilizer forms, except PCU, provided maximum yields when applied in the fall or spring. The adoption of either N management strategy will also be influenced by the prevailing economic conditions. Therefore, the unique environmental conditions of the Peace region provide opportunities for spring applications for select N fertilizer forms. Alberta Agriculture, Food and Rural Development Management practices to maintain and rejuvenate forage crops. [Online] Available: department/deptdocs.nsf/all/crop5016 [2012 Mar. 26]. Campbell, C. A., Leyshon, A. J., Ukrainetz, H. and Zentner, R. P Time of application and source of nitrogen fertilizer on yield, quality, nitrogen recovery, and net returns for dryland forage grasses. Can. J. Plant Sci. 66: Engel, R., Jones, C. and Wallander, R Ammonia volatilization from urea and mitigation by NBPT following surface application to cold soils. Soil Sci. Soc. Am. J. 75: Huang, C. L. and Schulte, E. E Digestion of plant tissue for analysis by ICP emission spectroscopy. Commun. Soil Sci. Plant Anal. 16:

10 Can. J. Plant Sci. Downloaded from pubs.aic.ca by Alberta Government Library on 08/09/ CANADIAN JOURNAL OF PLANT SCIENCE Littell, R. C., Milliken, G. A., Stroup, W. W. and Wolfinger, R. D SAS system for mixed models. 2nd ed. SAS Institute, Inc., Cary, NC. 813 pp. Malhi, S. S., Gill, K. S., McCartney, D. H. and Malmgren, R Fertilizer management of forage crops in the Canadian Great Plains. Rec. Res. Devel. Crop. Sci. 1: Manitoba Agriculture, Food and Rural Initiatives Fertilizing forage stands. [Online] Available: ca/agriculture/crops/forages/bja03s04a.html [2012 Mar. 26]. Mason, H., Navabi, A., Frick, B., O Donovan, J. and Spaner, D Cultivar and seeding rate effects on the competitive ability of spring cereals grown under organic production in northern Canada. Agron. J. 99: McKenzie, R. H., Bremer, E., Pfiffner, P. G., Middleton, A. B., Dow, T., Oba, M., Efetha, A. and Hohm, R Yield and quality responses of irrigated timothy to fertilizer application in southern Alberta. Can. J. Plant Sci. 89: National Climate Data and Information Archive Daily data report for May 2005 [Online] Available: weatheroffice.gc.ca/climatedata/dailydata_e.html?timeframe 2&ProvALTA&StationID29633&dlyRange j &cmdB1Go&Month5&Year2005&Day0 [2012 Oct. 01]. O Donovan, J. T., Harker, K. N., Clayton, G. W., Newman, J. C., Robinson, D. and Hall, L. M Barley seeding rate influences the effects of variable herbicides rates on wild oat. Weed Sci. 49: SAS Institute, Inc SAS/STAT 9.1 user s guide. SAS Institute, Inc., Cary, NC. Saskatchewan Agriculture and Food Fertilizing perennial forages. [Online] Available: docs/crops/forage_pasture/forage_management_production/ fertilizeforages.asp?firstpickcrops&secondpickforage_ Pasture&thirdpickForage%20Management_Production [2012 Mar. 26]. Snyder, C. S. and Bruulsema, T. W Nutrient use efficiency and effectiveness in North America: indices of agronomic and environmental benefit. International Plant Nutrition Institute, Norcross, GA. Statistics Canada census of agriculture. [Online] Available: [2012 Mar. 26]. Whitehead, D. C Grassland nitrogen. CAB International, Wallingford, UK. 385 pp.