Morgan, D., Associate Area Agent, LSU AgCenter
Gentry, G.T., Associate Professor, LSU AgCenter
Gurie, J., Research Associate, LSU AgCenter

ABSTRACT

Evaluating Best Management Practices (BMPs) is critical in determining environmental impacts from agricultural fields, regardless of cropping system. Research has shown that the utilization of BMP’s can reduce the amount of nutrients and sediment leaving the field or pasture. The first year of a multi-year study conducted at the Dean Lee Research Station in Alexandria, Louisiana was implemented to evaluate the effect of winter forage planting methods on sediment and nutrient runoff. Conventional tillage, conservation tillage and untreated/unplanted control methods for establishment of winter annual ryegrass were compared. Results showed phosphate and total phosphorus concentrations were higher from over-seeded plots than drilled, conventionally prepared, and unplanted.

Introduction

Winter forages play a key role in most livestock grazing systems found in the Southeastern United States.  It is recognized that annual ryegrass (Lolium multiflorum) is perhaps the most popular, with an estimated 2.5 million acres planted for grazing in the US each year and can provide 3-5 tons of dry matter per acre of high quality forage while extend the grazing season (Ball and Lacefield, 2011). Planting methods vary and can depend on factors such as available resources, location, and conditions, but may prove to have an effect on the success of a winter grazing program. Conventional planting methods require soil disturbance and may cause possible erosion and/or nutrient loss, but may facilitate seed emergence and stand establishment sooner than other methods. However, due to increasing concern over environmental impacts and water quality, conservation tillage is now a widely-used means to protect soils from erosion and compaction, while reducing production costs (Holland, 2004). 

Soil covered by grassland vegetation has been demonstrated to effectively limit movement of sediment and nutrients from pastures (Butler, Ranells, Franklin, Poore and Green, Jr., 2006; Butler et al., 2008; Schwarte et al., 2011) .  Permanent warm-season perennial grasses provide substantial protection for pastures across the southern region during the spring and summer months. Additionally, winter planted forages may also help to maximize soil protection during the heavier, seasonal rainfall months. Movement of soil and nutrients across the landscape is greater from poorly drained soils than from well-drained soils (Butler et al., 2008), which are typical of many bottomland pastures in central and southern Louisiana. These high-clay soils may be particularly vulnerable to movement of water-borne substances, such as nitrogen and phosphorus, from pastures to nearby waterbodies when grass cover is disturbed (Butler et al., 2008). Determining environmental impacts from agricultural fields, regardless of cropping system, is critical in reducing what is referred to as non-point source pollution. Non-point source pollution is derived from many diffuse sources and is not discharged directly into a waterbody from a direct source or point of origin. It is largely unregulated and therefore can be difficult to reduce.

Treatments to help establish annual cool-season forage plants while reducing the  disturbance of warm-season perennial grass have been extensively evaluated in the region (Mooso, Feasel, and Morrison, 1990; Evers, 2012). Even so, soil and nutrient movement in runoff water from pastures receiving these treatments have not been assessed. Determining effects of pasture management and associated livestock grazing on water quality of streams and needed BMPs in the southern humid region is particularly important because of the considerable extent of grazing lands in the region  (Agouridis, Workman, Warner, and Jennings, 2005).

To determine these effects, a study was implemented at the Dean Lee Research Station in Alexandria, Louisiana in October, 2013 to evaluate the effect of winter forage planting methods on sediment and nutrient runoff.

Materials and Methods

Conventional and conservation tillage methods to establish winter annual ryegrass were compared and tillage treatments included:  1) Conventional tillage (COV) - plots were disked twice (4 inch depth), fertilizer was applied, seed broadcast and the plot packed using a field culti-packer; 2) No-tillage (SOD) - sod was undisturbed and fertilizer and seed were broadcast (sod-seeding); 3) No-tillage  (DRL) - sod was minimally disturbed and ryegrass planted using no-till drill and fertilizer broadcast; 4) Unplanted/untreated/ungrazed control (CON) - sod was undisturbed with no ryegrass planted or urea applied. All plots were treated with one quart/A of glyphosate to reduce competition from summer annuals.

Each treatment was replicated in a Randomized Complete Block design and each plot received 175lbs DAP/A (18-46-0) + 90 lb ammonium sulfate/A (21-0-0-24) according to soil test recommendations at the beginning of the study. Plot size was approximately 0.11A (4800 ft2) on corrugated pastures and was “flash” grazed with 16 mature cows once forage reached an average height of 8.3 inches. Additional post-grazing urea applications were applied at 30 lb nitrogen/A throughout the grazing season. Approximately 13 rainfall events resulted in collection of runoff from the plots from October through April, 2014. Automatic ISCO 6712 water samplers were used collect field runoff from each plot and samples were submitted to the W.A. Callegari Environmental Lab in Baton Rouge, La and analyzed for total solids (sediment), total phosphorus, phosphates, potassium, and nitrates according to standard laboratory protocol.

In addition to sediment and nutrient runoff data, forage growth and dry matter were also recorded. In order to simulate a winter grazing scenario, grass was harvested in the treated plots by 16 mature cows averaging 1250 lbs for a period of 2-4 hours. This method more closely resembles a highly intensive grazing system, however was necessary to remove forage in a timely manner while adding the impact of grazing animals.  Forage samples were collected prior to each grazing and grazing was initiated when forage reached 8-10 inches in height.  A 39” square frame was used to randomly select three areas across each plot.  Forage height was recorded and forage within the square was clipped to a height of 2-3 inches and dried in a forced air oven at 131 ° Fahrenheit for 48 hours.  Samples weights were then recorded for dry matter calculations.

Data for solids, phosphorus, phosphates, nitrates, and potassium are expressed as a percent of the total collected for the season and as percent collected for each month where rainfall was sufficient to causes runoff. The runoff data were analyzed using the GLIMMIX Procedure of SAS (SAS Institute Inc., Cary, NC), with Tukey-Kramer method (p<0.05) used for mean separation, while the forage data were analyzed using the MIXED Procedure of SAS, with Tukey-Kramer method (p<0.05) used for mean separation.

Results and Discussion

Sampling Events

Sample collections began shortly after planting and initial fertilizer applications in late October. For the sampling period, a total of 21.25” of rain was recorded, with more than 57% of that during the last 2 ½ months (Figure 1.).  Collections occurred from the corrugated, clay loam pastures when a rainfall event approached a total of ½ - ¾ “. Based on weather station data (located at the Dean Lee Research Station in Alexandria, LA), 64 hourly rainfall amounts were recorded during the study period, with only 13 of them measuring greater than ½”.  There was insufficient total rainfall during the month of December and resulted in no collections for that month.

Figure 1. Rainfall, expressed in inches, collected from October through April.

Water Quality Results

Results are expressed as a percent of total collection for each analyte across the season. There were no differences across treatments for solids, nitrates, or potassium in collected samples. However, phosphates from SOD plots were greater (P=0.012) than DRL plots but were not different than COV or CON treatment plots (Figure 2). Figure 3 shows that most phosphates left the field early in the study and losses are likely to be from the initial fertilizer application that was applied at planting when very little forage was present. Total phosphorus in collected runoff was greater (P=0.002) in SOD compared with DRL and CON but was not different than COV (Figure 4).

Figure 2. Phosphates expressed as a percent of total phosphates across treatments. Bars with different superscripts are significantly different (P<0.05).

 

We hypothesize that these findings are likely to be a result of the nutrients being broadcast onto non-tilled soil surface instead of a tilled or semi-tilled surface, all with little or no forage covering the soil. This scenario resulted in the nutrient being exposed to environmental conditions on the soil surface with little or no protection. The fact that most phosphates left the plot early in the study when very little forage was present indicates that this may be a result of  less phosphate being utilized by the plant and/or lower filtering of runoff water by the presence of forage. Vegetation on the soil surface has been reported to reduce sediment, nutrients and pathogens leaving pastures (Butler et al., 2006; Butler et al., 2008; Schwarte et al., 2011) by as much as 31%.

 

 
Figure 3. Percent phosphate (lines) collected over the grazing season and monthly rainfall (bars).

 

Although, we did not use incorporation of the fertilizer as part of our study, the degree of soil disturbance may have played a role. Incorporation is an established Best Management Practice (BMP) for reducing soluble nutrients in runoff water, but may not always be practical or possible. The very nature of incorporation results in soil disturbance and Tabara (2003) showed that incorporation reduced the losses of dissolved reactive phosphorus and total phosphorus by as much as 30-60%, depending on source and application rate. Therefore, in pastures with very little slope some soil disturbance may result in lower amounts of phosphates and total phosphorus leaving the field. Figures 3 and 5 show the nutrient runoff over the course of the experiment as they relate to monthly rainfall totals. Both nutrient levels exceeded 55% of the total runoff at the beginning of the study and decreased over time. It is interesting to note that phosphate and total phosphorus runoff was less than 10% from January through April, when the heaviest rainfall events occurred.

 

Figure 4. Total phosphorus expressed as a percent of total phosphorus collected. Bars with different superscripts are significantly different (P<0.05).

 

Figure 5. Percent total phosphorus (lines) collected over the grazing season and monthly rainfall (bars).

Forage Production

Data was collected throughout the grazing season to determine the effect of planting method on forage production (dry matter) and the grazing interval. Our results showed total dry matter (DM) was not affected and yields were 12,773, 13,331, and 15,476 lbs/A for SOD, DRL, and COV, respectively. At each grazing, average pounds of DM per acre and average plant height were not different across treatments. However, the average number of days after planting each treatment was grazed during the grazing season was different across treatments (P=0.001; Figure 6). This finding indicates that the average day of each grazing was earlier for the COV plot compared with the SOD and DRL plots. The days at first grazing was not different across treatments and was 62, 65 and 71 days for COV, DRL and SOD, respectively, while the interval between grazing for the COV and DRL plots were 39 days compared with 46 days for the SOD plot. This scenario allowed the COV and DRL plots to be grazed five times during the 6 month study, compared with four times for the SOD treatment.

According to current recommendations (Twidwell, 2007), producers desiring to have winter pastures available for grazing prior to January 1 need to plant into a prepared seed bed in late September or early October. Planting forages using the conventional prepared method typically enhances seed to soil contact and plant emergence, thus allowing grazing to begin earlier than other types of planting methods and agrees with the results from our study.  The resulting additional grazing opportunities may be beneficial to producers who have limited hay resources during the winter grazing season.

Figure 6. Average days after treatment grazed for all grazing opportunities within each treatment. Bars with different superscripts are significantly different (P<0.05).

Conclusions

The objective of this study was to evaluate conservation tillage and conventional tillage planting methods and their effect on water quality and forage production. Our data showed that even though sod-seeding is considered a no-till practice and has been shown to reduce sediment and nutrient runoff in other studies, phosphates and total phosphorus concentrations were higher using this method compared with other methods in our study. One must be cautious in the interpretation of a single year of data as environmental conditions change from year to year and sod-seeding pastures with annual ryegrass may in fact be beneficial under certain circumstances if early grazing is not required. However, during the study period, with the environmental conditions that occurred, some soil disturbance resulted in decreased movement of phosphates and total phosphorus with no differences in total forage production. This also allowed one additional grazing opportunity compared with no soil disturbance.

Acknowledgements

The authors thank The Louisiana Master Farmer Program (LMFP) for the use of sampling equipment and support throughout the study. This study and data collected will be incorporated into the environmental stewardship trainings and field days that the LMFP participates in.

References

Agouridis, C. T., Workman, S. R., Warner, R. C., and Jennings, G. D. (2005).  Livestock grazing management impacts on stream water quality: a review.  Journal of the American Water Resources Association, 41, 591-606.

Ball, D. M. and Lacefield, G. D. (2011). Ryegrass for Forage. Circular 11-1, Oregon Ryegrass Growers Seed Commission, Salem, OR

Butler, D. M., Franklin, D. H., Ranells, N. N., Poore, M. H., and Green, Jr., J. T. (2006). Ground cover impacts on sediment and phosphorus export from manured riparian pasture.  Journal of Environmental Quality, 35, 2178-2185.

Butler, D.M., N.N. Ranells, D.H. Franklin, M.H. Poore, and J.T. Green, Jr.  (2008).  Runoff water quality from manured riparian grasslands with contrasting drainage and simulated grazing pressure.  Agriculture, Ecosystems and Environment 126, 250-260.

Evers, G.  (2012).  Effect of autumn sod treatment on overseeded annual ryegrass production and Coastal bermudagrass recovery.  Crop Sci. 52, 1430-1436.

Holland, J.M. (2004). The envornmental consequences of adopting conservation tillage in Europe: reviewing the evidence. Agriculture, Ecosystems, and Environment 103,1-25

Mooso, G.D., J.I. Feazel, and D.G. Morrison. (1990). Effect of sodseeding method on ryegrass-clover mixtures for grazing beef animals. Crop Sci. 3, 470-474.

Schwarte, K.A., J.R. Russell, J.L. Kovar, D.G. Morrical, S.M. Ensley, K.J. Yoon, N.A. Cornick, and Y. Cho.  (2011).  Grazing management effects on sediment, phosphorus, and pathogen loading of streams in cool-season grass pastures.  Journal of Environmental Quality 40, 1303-1313.

Tabara, H. (2003). Phosphorus loss to runoff water twenty-four hours after application of liquid swine manure or fertilizer. Crop Sci. 32, 1044-1052.

Twidwell, E. (2007). Planting winter pasture best way to winter cattle. Cattle Today. Retrieved March 5, 2015 from http://www.cattletoday.com/archive/2007/September/CT1178.shtml.

 

 

 

---