Journal of the NACAA
ISSN 2158-9429
Volume 14, Issue 1 - June, 2021
Annual Ryegrass Response to Seasonal RyZup Smartgrass® Application
- Lemus, R. , Extension Forage Specialist, Mississippi State University Extension Service
Cox, M, Professor, Mississipppi State University
Rivera, J.D., Associate Professor, South Miississippi Brach Exp. Station
ABSTRACT
Annual ryegrass (Lolium multiflorum L.) is a cool-season forage annual crop in the southern USA used for livestock production due to its biomass potential and nutritive value. Productivity depends on proper nitrogen (N) fertilization and environmental conditions. Gibberellic acid (GA) has been proposed as a source of increasing production under cold temperatures and reducing N applications. The objectives of the study were determining the impact of RyzUp Smartgarss® (RZ, 40% GA w/w) in annual ryegrass biomass production and nutritive value when applied alone or in combination with different N sources and rates. The study consisted of two N sources [ammonium nitrate (AN, 34-0-0), and urea ammonium nitrate solution (UAN, 32-0-0)] that were applied alone at different rates or in combination with RZ (0.33 oz ac-1). Ammonium nitrate had a greater impact on biomass production and nutritive value when compared to UAN. There was no yield increase with RZ alone or in combination with N sources compared to N rates alone. Nitrogen removal was lower with RZ when compared to the untreated check. An improved nutritive value was observed with N-containing treatments when compared to RZ. The application of RZ might not be a profitable way to increase extra winter feed and extend the grazing season.
Abbreviations: N, nitrogen; RZ, RyzUp Smartgarss®; GDD, growing degree days; UC, untreated check; AN, ammonium nitrate; UAN, urea ammonium nitrate; CP, crude protein; ADF, acid detergent fiber; NDF, neutral detergent fiber; WSC, water-soluble carbohydrates; LAI, leaf area index; NDVI, normalized difference vegetative index; PLS, pure-live seed.
Keywords: Giberrellic acid, RyzUp Smartgarss®, nutritive value, biomass, nutrient removal.
INTRODUCTION
Early vigorous growth in fall and late maturity has made annual ryegrass (Lolium multiflorum L.) a popular forage crop in the southern USA. In Mississippi, approximately 40 to 50% of the warm-season pastures are planted in annual ryegrass to minimize the need for winter supplementation (hay). Climatic conditions such as temperature and precipitation play a major role in determining biomass production. Annual ryegrass is best adapted to cool, moist climates, but not to temperatures below 30 ºF (Lemus, 2010). Best growth occurs between 50 and 70°F. Thus, annual ryegrass grows well in early spring and fall. Nitrogen (N) is commonly applied to pastures in the fall and spring with rates ranging from 60 to 100 lb N ac-1. With the increase and fluctuation in fertilizer prices over the last 5 years, producers have considerably reduced nitrogen applications, affecting forage production and quality.
The role of N application to cool-season annual grasses during the winter months is mostly as a growth stimulant under cold conditions rather than an essential nutrient to help with biomass production and to sustain grazing (Rath, 2010). Due to the increase in N fertilizer cost, producers are seeking new technologies and management practices that can reduce or optimize N applications and use efficiency. The use of gibberellic acid (GA) to stimulate growth in cool-season annual grasses has been implemented for many decades, but environmental conditions can pose limitations (Wittwer and Bukovac, 1958). Rath (2010) has reported a 62% yield increase after 18 d when GA was applied alone to cool-season grasses in Australia.
RyzUp Smartgarss® (RZ) is a foliar plant growth regulator containing gibberellic acid (GA3 40% w/w/) that is recommended for use in pasture and forage crops to increase dry matter forage yield when cool weather conditions have the potential to limit growth. Gibberellic acid is a plant growth regulator (hormone) found in plants that promotes growth and cell elongation. The application of exogenous levels of gibberellic can increase the natural levels of GA in the plant tissue to induce longer and faster growth of leaves in the plant that could result in increased dry matter production and improved nutritive value. The application of this product is recommended when average daily temperatures range from 40 to 65 °F. Hall et al. (2010) reported that weather conditions and plant growth stage at the time of application have the greatest impact on RZ effectiveness. They also indicated that late spring applications were less effective and RZ reduces CP and increases fiber content.
The objectives of the study were to determine the impact of RZ in annual ryegrass biomass production and nutritive value when applied alone or in combination with different N sources and rates throughout the growing season.
MATERIALS AND METHODS
The preliminary on-year study was conducted at the Henry H. Leveck Animal Research Farm at Mississippi State University (33º25’18.23” N, 88º47’31.88” W) on a Marietta fine sandy loam (Fine-loamy, siliceous, active, thermic Fluvaquentic Eutrudepts; USDA-NRCS Web Soil Survey) during the 2010-2011 growing season. The experimental design was a randomized complete block design with a split-plot arrangement and replicated four times. The main plots consisted of two N sources [granular ammonium nitrate (AN, 34-0-0) and urea ammonium nitrate solution (UAN, 32-0-0)]. The subplots consisted of eight treatment combinations within each N source and RZ (Table 1). Plots were 11 ft x 6 ft. Phosphorus and potassium were applied based on soil test recommendations. Three weeks before planting, glyphosate was applied at a rate of 2-pt ac-1 in 20 gals of water for weed control. ‘Marshall’ annual ryegrass was planted at a rate of 30 lb PLS ac-1 in October 2010 using an ALMACO precision cone planter (ALMACO, Nevada, IA). RyzUp Smartgarss® 40SG treatments were applied at a rate of 0.33 oz ac-1 per application. RyzUp and UAN solutions were applied to their corresponding treatments between 10 A.M. and 2 P.M. at wind speed less than 3 MPH using a handheld CO2 charged sprayer equipped with a 6-ft boom calibrated to deliver 25-gal ac-1 at 40 PSI. The spray pattern was a fine mist in a flat fan pattern. Non-ionic surfactant was added at a rate of 0.25% v/v to all treatments to keep a uniform application. Post-harvest treatments were applied 3 d after harvest to allow plant recovery. Ammonium nitrate was applied using a 6.0-ft-wide drop spreader (Model 6500, Gandy, Co., Owatonna, MN).
| Treatment | Description |
|---|---|
| Untreated Control (UC) | No nitrogen (N) or RyzUp (RZ) was applied. |
| 100 lb N ac-1 (N2X) | Ammonium Nitrate (AN, 34-0-0) or Urea Ammonium Nitrate solution (UAN, 32-0-0) were applied in split applications of 50 lb N ac-1. First application two weeks after grass emergence and the second application after the first harvest. Total application 100 lb N ac-1 season-1. |
| RyzUp (RZ2X) | RZ was applied two weeks after grass emergence and after the first harvest. |
| N2X+RZ2X | AN or UAN were applied in split applications of 50 lb N ac-1 along with RZ. The first application was two weeks after emergence and the second application after the first harvest. Total application 100 lb N ac-1 season-1. |
|
100 lb N ac-1 (N4X) |
AN or UAN was in split applications of 25 lb N ac-1. The first application was two weeks after emergence and three subsequent applications after each harvest. Total application 100 lb N ac-1 season-1. |
| N4X+RZ4X | AN or AUN was applied in split applications of 25 lb N ac-1 along with RZ applications. The first application was two weeks after emergence and subsequent applications after each harvest. Total application 100 lb N ac-1 season-1. |
| RyzUp, (RZ4X) | RZ was applied two weeks after emergence and after each subsequent cut. |
| 50 lb N ac-1, (N1X+RZ1X) | AN or AUN was applied at a rate of 50 lb N ac-1 two weeks after emergence followed by RyzUp application after the first harvest. Total application 50 lb N ac-1 season-1. |
Plots were harvested to a 3-in stubble height when at least 50% of the plots have reached a height of 10 to 12 inches. There were four harvests during 2011 [14 February (H1), 4 March (H2), 17 March (H3), and 19 April (H4)]. Plots were harvested using a Sensation mower, removing a 36-in swath from the center of the plot, to minimize border effect. Subsamples were collected for determining dry matter yields. Subsamples were oven-dried at 140 °F to constant weight, ground to pass through a 1-mm screen, and used for nutritive analysis. Samples were analyzed for CP, ADF, NDF, and WSC using the Foss-2500 NIR system (Foss North America, Eden Prairie, MN) and the grass hay equation developed by the NIRS Feed and Forage Testing Consortium (NIRSC, Hillsboro, WI). Nitrogen content was determined using a CN analyzer and used to calculate N removal by multiplying percent N time dry matter biomass yield. Normalized Difference Vegetative Index (NDVI) was taken using a Green Seeker (Trimble, Sunnyvale, CA). Leaf Area Index (LAI) was determined using an LAI-2000 canopy analyzer (Li-Cor, Lincoln, NE). °Brix levels were determined using a VEE GEE PDX-1 digital refractometer (VEE GEE Scientific, LLC, Vernon Hills, IL).
The main effect of the harvest was evaluated as repeated measures for biomass yield, LAI, NDVI, Brix, and nutritive value (Table 2). Data were analyzed by using the General Linear Mixed Model (GLIMMIX) of SAS (Cary, NC), and mean separation was done using the LSMEANS to compare least-squares means (LSMeans) of fixed effects at α = 0.05.
| Variance | Seasonal Yield | Harvest Yield | N Removal | LAI | NDVI |
|---|---|---|---|---|---|
| N Source (NS) | NS* | NS | 0.0004 | < 0.0001 | 0.0003 |
| Treatment (TRT) | 0.0019 | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 |
| NS*TRT | NS | 0.0212 | NS | NS | NS |
| Harvest Date (HD) | -- | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 |
| NS*HD | -- | < 0.0001 | 0.0032 | NS | NS |
| TRT*HD | -- | 0.0069 | NS | 0.0001 | < 0.0001 |
| °Brix | CP | ADF | NDF | WSC | |
| N Source (NS) | < 0.0001 | < 0.0001 | 0.0002 | < 0.0001 | < 0.0001 |
| TRT (TRT) | 0.0004 | 0.0006 | NS | 0.0085 | < 0.0001 |
| NS*TRT | NS | NS | NS | NS | NS |
| Harvest Date (HD) | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 | < 0.0001 |
| NS*HD | 0.0024 | < 0.0001 | < 0.0001 | < 0.0001 | 0.0010 |
| TRT*HD | NS | NS | NS | 0.0090 | 0.0010 |
| *NS = not significant at α = 0.05. | |||||
RESULTS
Weather
Weather conditions were monitored from September 2010 to May 2011. Precipitation was 4.2 inches below normal for the season (Table 3). Total precipitation during the duration of the study was 38.6 inches. The average temperature for the duration of the study was 58.2 °F. That is 1.6 °F above normal. There were 488 GGD above the normal for the time of the year and this is related to warmer temperatures from September to November and February to April.
| Month | Precipitation (inches) | Temperature (°F) | GDD1 |
|---|---|---|---|
| Sep | -3.1 | 4.1 | 129 |
| Oct | -2.3 | 2.2 | 68 |
| Nov | 1.9 | 1.7 | 25 |
| Dec | -3.6 | -3.7 | -36 |
| Jan | -4.0 | -0.3 | -1 |
| Feb | -2.6 | 2.4 | 89 |
| Mar | -0.7 | 3.0 | 61 |
| Apr | 9.4 | 4.7 | 137 |
| May | 0.9 | 0.4 | 16 |
| 1Growing degree days (GDD) base 50. | |||
Biomass Yield
Seasonal yield production was not affected by nitrogen (N) source and ammonium nitrate (AN) only produced a 2% greater yield than urea-ammonium nitrate (UAN). There was a treatment application effect on seasonal yield (Fig.1). No differences were detected among N-containing treatments and treatment with split applications of 25 lb N ac-1 over the season (N4X) yielded greater biomass. RyzUp Smartgarss® (RZ) treatments were not significantly different from the UC and no additive effect was produced in combination with N sources or rates.
Figure 1. Influence of nitrogen and RyzUp applications on seasonal biomass production of annual ryegrass. Letters are for comparison of treatments. Treatments containing the same letters are not significant at α = 0.05.
Nitrogen sources did not affect harvest yields. Harvest yields were impacted by treatment applications. There were no differences between RZ treatment rates only and the UC (Table 4). No differences were noted among N application rates although the N4X produced a greater yield. N application in split applications of 25 lb N ac-1 had a greater harvest yield than the rest of the N rates. This is an indication of that smaller rates, but more frequent N applications can impact forage production and potential grazing days due to possible better N use efficiency. There was an N source x N rate interaction. Ammonium nitrate produced greater yields than UAN, except for N1X+RZ1X (Fig. 2). A significant harvest date x N source interaction indicated greater harvest biomass yield in April compared to the rest of the harvest dates (Table 7). Urea ammonium nitrate application had greater yields during H1 and H2 compared to AN (Table 5). A significant treatment x harvest date indicated the N containing treatments had greater harvest biomass yield when compared to RZ or UC treatments (Table 6). An increase in yield was also observed across harvest dates. This is expected since annual ryegrass production increases in March and usually peaks by mid-April.
| Treatment |
Harvest Yield (lb DM ac-1) |
N Removal (lb N ac-1) |
LAI | NDVI |
|---|---|---|---|---|
| UC | 1063 BC* | 22 C | 3.3 DE | 0.82 C |
| RZ2X | 919 C | 19 C | 3.1 E | 0.79 D |
| RZ4X | 100 C | 21 C | 3.1 E | 0.76 E |
| N2X | 1215 AB | 32 A | 4.0 AB | 0.84 B |
| N4X | 1324 A | 32 A | 4.3 A | 0.87 A |
| N1X+RZ1X | 1164 AB | 25 C | 3.5 CD | 0.79 D |
| N2X+RZ2X | 1309 A | 31 A | 3.8 BC | 0.84 BC |
| N4X+RZ4X | 1271 A | 29 AB | 4.0 AB | 0.85 AB |
| Brix (%) | CP (% DM) | NDF (% DM) | WSC (% DM) | |
| UC | 11.1 A | 15.1 BC | 43.2 D | 13.6 A |
| RZ2X | 11.1 A | 14.9 BC | 43.4 CD | 13.6 A |
| RZ4X | 11.2 A | 14.5 C | 42.8 D | 14.5 A |
| N2X | 9.4 B | 16.6 A | 44.2 ABCD | 11.7 B |
| N4X | 9.7 B | 17.2 A | 45.8 A | 11.1 B |
| N1X+RZ1X | 10.0 B | 15.0 BC | 43.7 BCD | 13.2 A |
| N2X+RZ2X | 9.9 B | 16.0 AB | 45.5 AB | 11.8 B |
| N4X+RZ4X | 9.7 B | 16.4 A | 45.2 ABC | 11.6 B |
| *Letters are for comparison of treatments within each variable. Treatments containing the same letters within a variable are not significant at α = 0.05. | ||||
Figure 2. Influence of N sources and rates on harvest biomass production of annual ryegrass. Letters are for comparison of treatments. Treatments containing the same letters are not significant at α = 0.05.
Nitrogen Removal
Significant seasonal nutrient removal was observed where AN has a 22% greater N removal than UAN. There were no differences in N removal among N-containing treatments although N1X+RZ1X had 39% lower removal than N4X (Fig. 3). Nitrogen removal of RZ treatments was not significantly different from the UC and the RZ4X has lower N removal than UC.
Figure 3. Influence of nitrogen and RyzUp applications on total nitrogen removal of annual ryegrass. Letters are for comparison of treatments. Treatments containing the same letters are not significant at α = 0.05.
Nitrogen removal with AN application was 21% significantly greater than UAN. There was a treatment application effect in which N-containing treatments have a 49 and 42% greater removal compared to RZ and UC treatments, respectively (Table 4). N removal was also significantly higher in H1, H2, and H4 compared to H3 (Table 7). There was an 83, 61, and 33% greater N removal for H1, H2, and H4, respectively, when compared to H3. This could be related to N allocation to growth in March than earlier in the season under colder temperatures. A significant N source x harvest date indicated a decrease in N removal across the season (Table 5). Differences among N sources were observed during H3 and H4 in which AN had a 50 and 72% greater removal when compared to UAN.
| N Source | |||||
| Harvest | AN | UAN | AN | UAN | |
| Harvest Yield (lb DM ac-1) | Harvest N Removal (lb DM ac-1) | ||||
| H1 | 934 C* | 1064 C | 34 A | 32 AB | |
| H2 | 1091 C | 1356 B | 29 B | 30 AB | |
| H3 | 749 D | 693 D | 21 C | 14 D | |
| H4 | 1909 A | 1470 B | 31 AB | 18 CD | |
| Brix (%) | ADF (% DM) | ||||
| H1 | 13.3 A | 14.0 A | 20.7 C | 21.7 C | |
| H2 | 8.2 EF | 11.6 B | 32.2 E | 29.0 B | |
| H3 | 7.3 F | 9.4 CD | 31.9 E | 29.6 B | |
| H4 | 8.4 DE | 9.8 C | 29.1 B | 29.7 B | |
| NDF (% DM) | WSC (% DM) | ||||
| H1 | 39.6 D | 40.6 D | 13.7 BC | 15.0 AB | |
| H2 | 50.3 A | 45.6 B | 7.8 E | 11.7 D | |
| H3 | 49.4 A | 44.8 B | 8.5 E | 13.2 C | |
| H4 | 42.7 C | 40.8 D | 14.8 B | 16.4 A | |
| *Letters are for comparison of harvest dates and N source within each variable. Treatments containing the same letters within a variable are not significant at α = 0.05. | |||||
Leaf Area Index (LAI)
Leaf Area Index (LAI) is defined as the amount of leaf area per unit of ground surface area (Addai and Alimiyawo, 2015). Ammonium nitrate application increased LAI by 15% compared to UAN. Significant differences among treatments indicated that RZ did not increase LAI compared to the UC. However, N-containing treatments had greater LAI and those N treatments containing 1X and 2X RZ applications had lower LAI than N applied 4X during the season (Table 4). Significant LAI differences were detected among harvest dates. There was a decline in LAI with harvest date, but H3 has the lowest LAI compared to the rest of the harvest dates. A significant treatment x harvest date interaction indicated that LAI decreased within treatment with harvest date (Table 6). On the other hand, the UC and RZ treatments had much lower LAI than compared to those N-containing treatments.
| Harvest | ||||
| Treatment | H1 | H2 | H3 | H4 |
| Harvest Yield (lb DM ac-1) | ||||
| UC | 957 HIJKLMN | 912 IJKLMNO | 642 NOP | 1741 B |
| RZ2X | 769 LMNOP | 842 KLMNOP | 521 P | 1544 BCDE |
| RZ4X | 852 KLMNO | 1058 GHIJKLM | 752 LMNOP | 1338 DEFG |
| N2X | 1056 GHIJKLM | 1402 CDEF | 782 LMNOP | 1619 BCD |
| N4X | 990 HIJKLM | 1254 EFGHI | 869 JKLMNO | 2184 A |
| N1X+RZ1X | 1060 GHIJKL | 1183 FGHIJ | 621 OP | 1793 B |
| N2X+RZ2X | 1194 EGHI | 1587 BCD | 737 MNOP | 1718 BC |
| N4X+RZ4X | 1114 FGHIJK | 1551 BCDE | 843 KLMNO | 1578 BCD |
| LAI | ||||
| UC | 3.6 HIJ | 4.2 CDEFGH | 2.7 KLMN | 2.9 KLM |
| RZ2X | 3.8 FGHI | 4.0 DEFGH | 2.2 MN | 2.3 LMN |
| RZ4X | 4.0 DEFGH | 4.2 CDEFGH | 2.1 N | 2.3 LMN |
| N2X | 4.3 CDEFG | 5.5 A | 3.3 IJK | 2.9 JKL |
| N4X | 4.1 CDEFGH | 4.8 ABC | 3.7 GHI | 4.5 BCD |
| N1X+RZ1X | 4.5 BCDE | 4.7 BCD | 2.4 LMN | 2.6 KLMN |
| N2X+RZ2X | 4.4 CDEF | 5.1 AB | 2.5 LMN | 2.9 KLM |
| N4X+RZ4X | 4.5 BCD | 4.6 BCD | 3.2 IJK | 3.8 EFGHI |
| NDVI | ||||
| UC | 0.88 AB | 0.90 A | 0.80 D | 0.68 GH |
| RZ2X | 0.88 AB | 0.89 AB | 0.74 E | 0.63 I |
| RZ4X | 0.89 AB | 0.89 AB | 0.70 FG | 0.55 J |
| N2X | 0.89 AB | 0.92 A | 0.83 DC | 0.71 EFG |
| N4X | 0.89 AB | 0.92 A | 0.86 BC | 0.81 D |
| N1X+RZ1X | 0.89 AB | 0.89 AB | 0.74 EF | 0.65 HI |
| N2X+RZ2X | 0.88 AB | 0.91 A | 0.82 DC | 0.72 EF |
| N4X+RZ4X | 0.89 AB | 0.91 A | 0.81 D | 0.79 D |
| *Letters are for comparison of treatments and harvest dates within each variable. Treatments containing the same letters within a variable are not significant at α = 0.05. | ||||
Normalized Difference Vegetative Index (NDVI)
The Normalized Difference Vegetation Index (NDVI) is an indicator of the greenness of the plant (0 to 1.0) and it indicates possible seasonal changes in biomass, fertilizer response, and nutritional quality in annual ryegrass (Hogrefe et al., 2017). There was a significant difference among N sources in NDVI values. Despite the statistical significance, the difference between the two sources was only 2.5%. A significant treatment effect indicated RZ treatments had lower NDVI than the UC (Table 4). Among the N-containing treatments, RZ4X had the lowest NDVI value (0.76). Despite RZ4X having the lowest NDVI value there no is indication of N deficiency. Increasing the gibberellins levels in plant tissue by 4X application RZ seems to impact chlorophyll accumulation and leaf development. This could be related to less growth by reducing leaf area and yield. A significant harvest effect indicated that NDVI values decreased as plants tend to mature, this could be related to lower LAI, N translocation to seedhead production, and higher fiber accumulation in annual ryegrass (Table 7). There was a significant treatment x harvest date in which no difference was detected among treatments within H1 and H2 (Table 6). A decline in NDVI was observed in H3 and H4. Such decline could be associated with N utilization for growth and development in cooler temperatures that could delay growth during H1 and H2.
°Brix
Brix is the measurement of sugar, vitamins, minerals and proteins, and other solid contents that are in solution in the plant. There was a significant increase in Brix level (20%) with UAN application when compared to AN. The UC and RZ applications had a greater Brix level compared to the N treatments (Table 4). This could be due to reduced growth rates and greater soluble accumulation while N treatments created a dilution effect. There was an N source x harvest date interaction. Brix concentration was higher with UAN across harvests when compared to AN (Table 5). There was a linear decline in Brix levels with harvest date across both N sources, but such decline was greater with AN. Overall, there was a linear decline in Brix levels within the harvest date from H1 to H3 (Table 7). A slight increase in Brix level in H4 could be related to plant senescence and sugar accumulation.
| Harvest |
Harvest Yield (lb DM ac-1) |
Harvest N Removal (lb N ac-1) |
LAI | NDVI | |
| H1 | 999 C* | 33 A | 4.1 B | 0.89 B | -- |
| H2 | 1223 B | 29 B | 4.6 A | 0.90 A | -- |
| H3 | 721 D | 18 C | 2.8 D | 0.79 C | -- |
| H4 | 1689 A | 24 B | 3.0 C | 0.69 D | -- |
| BRIX (%) | CP (% DM) | ADF (%DM) | NDF (% DM) | WSC 9% DM) | |
| H1 | 13.7 A | 20.4 A | 21.2 C | 40.1 C | 14.4 B |
| H2 | 9.9 B | 15.9 B | 30.6 A | 47.9 A | 9.8 D |
| H3 | 8.3 D | 15.6 B | 30.7 A | 47.1 A | 10.9 C |
| H4 | 9.1 C | 11.0 C | 29.4 B | 41.8 B | 15.6 A |
|
*Letters are for comparison of harvest dates within each variable. Treatments containing the same letters within a variable are not significant at α = 0.05. |
|||||
Nutritive Value
Crude protein was 17% significantly higher for AN compared to UAN. Significant treatment differences were observed between N-containing treatments and RZ. No differences were reported between UC and RZ treatments, however, RZ CP concentrations were lower than the UC (Table 4). A similar reduction in CP concentration with the RZ application has been reported by Hall et al. (2010). No significant differences were observed among N-containing treatments. Crude protein concentrations were significantly affected by the harvest date. There was a linear decrease in CP from H1 and H4 resulting in a 46% CP difference (Table 7). This is expected as annual ryegrass increase in maturity.
Nitrogen sources significantly impacted ADF concentrations. Such differences represented a 4% increase in ADF concentration for AN compared to UAN. Harvest date impacted ADF concentrations with no differences between H2 and H3, but H1 had 33% lower ADF than the mid-season harvests (Table 7). There was an N source x harvest date interaction. Differences in ADF concentrations were lower for H1 within UAN application (Table 5). The same trend followed AN application, although no differences occurred between H2 and H3. Acid detergent fiber concentrations increased with harvest date due to an increase in maturity.
Differences were detected among N sources for NDF concentrations. Ammonium nitrate had a 6% greater NDF concentration than UAN. Neutral detergent fiber concentrations were significantly lower for UC and RZ treatments when compared to the N-containing treatments (Table 4). Fiber concentrations were affected by harvest date with H2 and H3 having higher concentrations compared to H1 and H4 (Table 7). A significant N source x harvest date interaction indicated an increase in NDF concentration in mid-season compared to the H1 and H4 and such increase in NDF concentration was higher for AN application (Table 5). There was a treatment x harvest date interaction. Neutral detergent fiber concentrations increased across treatments for all harvest dates; however, NDF concentrations were more consistent among treatments for all harvest except for H2 and H3 where N-containing treatments had greater fiber concentrations than UC or RZ treatments (Table 8). This indicated that greater increases in ADF concentrations occurred during the mid-season harvests.
| Harvest | ||||
|---|---|---|---|---|
| Treatment | H1 | H2 | H3 | H4 |
| NDF (% DM) | ||||
| UC | 39.8 JK* | 48.1 BCD | 44.0 EFGHI | 40.8 IJK |
| RZ2X | 40.6 IJK | 46.0 CDEFG | 44.8 DEFGH | 42.3 GHIJK |
| RZ4X | 39.9 JK | 44.5 DEFGH | 44.8 DEFGH | 42.0 HIJK |
| N2X | 40.0 JK | 50.3 AB | 46.7 BCDEF | 39.7 JK |
| N4X | 39.4 K | 49.0 ABC | 48.9 ABC | 45.9 CDEFG |
| N1X+RZ1X | 40.7 IJK | 48.2 BCD | 45.6 CDEFGH | 40.3 JK |
| N2X+RZ2X | 40.2 JK | 50.0 AB | 52.0 A | 39.9 JK |
| N4X+RZ4X | 40.3 JK | 47.6 BCDE | 49.9 AB | 43.1 FGHIJ |
| WSC (% DM) | ||||
| UC | 14.5 BCDEFGH | 9.6 MNOP | 13.2 EFHHIJ | 17.1 AB |
| RZ2X | 13.8 CDEFGHI | 12.2 HIJKLM | 12.5 GHIJKL | 15.9 ABCDE |
| RZ4X | 15.1 ABCDEFG | 12.9 FGHIJK | 14.7 BCDEFGH | 15.3 ABCDEF |
| N2X | 13.8 CDEFGHI | 6.7 P | 9.8 LMNOP | 16.5 ABC |
| N4X | 15.0 ABCDEFG | 8.7 NOPQ | 8.2 OPQ | 12.5 GHIJKL |
| N1X+RZ1X | 13.5 EFGHI | 10.6 JKLMNO | 11.3 IJKLMN | 17.6 A |
| N2X+RZ2X | 14.8 BCDEFGH | 7.2 P | 9.0 NOPQ | 16.3 ABCD |
| N4X+RZ4X | 14.4 BCDEFGH | 10.2 KLMNO | 8.2 OPQ | 13.7 DEFGHI |
|
*Letters are for comparison of treatments and harvest dates within each variable. Treatments containing the same letters within a variable are not significant at α = 0.05. |
||||
Water-soluble carbohydrates (WSC) concentrations were affected by N sources. Urea ammonium nitrate had a 25% increase in WSC compared to AN. Water-soluble carbohydrate concentrations were also affected by treatment applications. Nitrogen-containing treatments with multiple applications had lower WSC concentrations than the UC, RZ, and a single N application (Table 4). This is usually correlated with less biomass production and greater accumulation of nutrients. There was a harvesting effect on WSC where concentrations were higher in H1 and H4 compared to mid-season harvests (Table 7). Water-soluble concentrations were also affected by an N source x date interaction. There were lower WSC concentrations in mid-season harvests for both N sources and concentrations were higher for UAN applications compared to AN (Table 5). A significant treatment x harvest date interaction indicated no differences during H1; however, higher WSC concentrations were observed during H4. This could be related to an accumulation of WSC due to reaching the reproductive stage (Table 8). Across H2 to H4, N-containing treatments tend to have lower WSC concentrations compared to UC and RZ applications.
CONCLUSIONS
This one-year study indicated that RyzUp Smartgrass® did not increase dry matter biomass when applied alone or in combination with two different N sources and rates. Although increases in nutritive value (CP and WSC) were observed in RZ treatments, such increases were related to slow growth which decreases the amount of metabolizable energy and nutrients to promote faster plant growth rates. RyzUp applications are recommended in temperatures ranging from 40 to 65 °F. Despite the temperatures being within the recommended range during the application for the duration of the study, results indicated that annual ryegrass growth was limited by the RZ application, and no additive benefits were observed with the N sources. Normalized difference vegetation index indicated that RZ treatments had lower values, which could be related to chlorophyll dilution that could restrict photosynthetic activity and impact growth rate. Although RZ is a non-selective growth promoter, it should not be used as an alternative to replacing fertilization practices in forage crops. Under the environmental conditions and fertilization practices for this study, there was a very little benefit that can warrant the economic investment due to a limited time window for optimum response and producers need to consider the benefits in the context of the farm system (grazing days, animal performance, and forage nutritive value, and forage utilization). Despite RZ applications referred to as having a minimal economic cost ($3 to $5 per acre), they provided minimal benefits over N alone and can only increase the cost of dry matter yield in the short term. The addition of the RZ to N application had a 10 to 15% cost increase. Therefore, the application of RZ might not be a profitable way to increase extra winter feed and extend the grazing season in the region. Further research on the timing of application and RZ rates is needed under the environmental conditions present during the winter months in the southern USA and to include other cool-season annual forage crops such as small grains.
CONFLICT OF INTEREST
The authors declare that there is no conflict of interest.
ACKNOWLEDGEMENT
This manuscript is based on work that is supported by the Mississippi Agriculture and Forestry Experiment Station and the National Institute of Food and Agriculture, U.S. Department of Agriculture, Hatch project under accession number 1016223, Project Number MIS-164010. Thank you to Valent BioSciences (Libertyville, IL) for providing funding for this study.
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