Nitrogen Fertilization Strategies for Annual Ryegrass Pastures

By Robert Kallenbach, State Forage Specialist, Matt Massie and Richard Crawford, Southwest Research Center, Mt. Vernon. University of Missouri Extension. Livestock operations as far north as southern Iowa are planting annual ryegrass pastures as an alternative to feeding hay in winter.
calendar icon 13 August 2007
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Missouri

Easy establishment, rapid autumn growth, and high forage quality are making annual ryegrass popular with dairy and beef farmers alike.

Annual ryegrass has several features that make it popular with livestock producers. When planted in late-summer, annual ryegrass can produce 2 to 3 tons of high-quality feed per acre before December and an additional 3 to 4 tons in the spring (Bishop-Hurley et al., 2001). Few other forage crops can produce this much forage for winter grazing. Annual ryegrass is able to achieve these yields in autumn because it continues to grow even after the first killing frost. Cold-tolerant cultivars can grow when average daily temperatures are below 39°F. In addition, the lack of true dormancy in annual ryegrass allows it to grow during warm spells in winter and to resume growth earlier in spring than many perennial cool-season grasses.

In addition to its rapid fall growth, the forage quality of annual ryegrass is outstanding. During vegetative growth, annual ryegrass has crude protein levels that exceed 20% and dry matter digestibility that approaches 75% (Dunavin, 1990). Because of its high quality, producers can successfully use annual ryegrass to feed both stocker cattle and lactating dairy cows. For example, stocker calf gains of 1.0 to 2.7 lb/day are common in the southern USA (Evers, 1995). In addition, milk yields of 85 lb/day have been reported for dairy cows grazing annual ryegrass pastures (Thom and Bryant, 1996).

Seed sales of cold-tolerant cultivars of annual ryegrass in Missouri have quadrupled over the past four years. However, we still have a lot to learn about the management of annual ryegrass for winter pasture in Missouri. There is little research about how to fertilize annual ryegrass that is grown outside the southern USA. Research from other regions suggests that annual ryegrass responds tremendously to N fertilizer, but proper fertilization rates and strategies for states outside the southern USA are lacking.

The overall objective is to determine the optimum rate and timing of N fertilizer for annual ryegrass in Missouri. Specific objectives are:

Objective 1: Determine the optimum N rate at planting to maximize fall growth of annual ryegrass for winter grazing.

Objective 2: Determine if N applications in late winter (March 1) are economical.

Materials and Methods

A three year field trial studying the impact of nitrogen rate and date of application on the yield and quality of annual ryegrass began in August 2002. This replicated (4x) experiment has 16 treatments: four N rates in autumn (0, 50, 100 and 150 lb/acre of N) followed by the either 0, 50, 100 or 150 lb/acre of N in early spring. The table below describes the rate and date of N applications for treatments.

 

Treatment N in Autumn Nearly spring
  N lb/acre
1 0 0
2 0 50
3 0 100
4 0 150
5 50 0
6 50 50
7 50 100
8 50 150
9 100 0
10 100 50
11 100 100
12 100 150
13 150 0
14 150 50
15 150 100
16 150 150
  • Cultural practices: The soil type is a Huntington silt loam. Thirty lb/acre of ‘Marshall’ annual ryegrass was broadcast seeded into a prepared seedbed in early September of 2002 and 2003. Soil P and K was maintained at the levels recommended by the University of Missouri Soil Testing Laboratory for cool-season grasses.

  • Design: Each of the sixteen treatments were replicated four times in a randomized complete block design with 64 total plots (4 replications x 16 treatments). Individual plots were 21 feet x 15 feet.

Measurements:

  • Forage yield was measured when plant height in an individual treatment reached 8 to 10 inches. This is the recommended height to begin grazing annual ryegrass. Weekly measurements of canopy height were recorded to guide harvests. Once a treatment reached 8 to 10 inches in height, forage yield was determined by clipping two 2.67 feet x 15 feet strips in each plot to a 3 inch stubble height.

  • Forage quality [crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF)] was measured at the same time as forage yield. Samples were dried at 125°F for 72 hours in a forced-air oven before being ground to pass a 1 mm screen. Crude protein, ADF and NDF were measured using NIRS with appropriate wet chemistry calibrations.

  • Tiller density was determined in fall and spring each year. Tiller density was measured by counting the tillers on plants taken from ten 2.5 inch diameter cores from each plot.

  • Total soil nitrogen to a depth of 40 inches was determined prior to application of N and in early June (after the growing season for annual ryegrass) each year. Samples were split into three sections: 0-10 inches, 10-20 inches, and 20-40 inches.

Results

During the 2002-2003 growing season, total season yields were more than 12,000 lb/acre for the best treatments. While the highest N rates provided the greatest yields, it appears that 50 lb/acre of N in autumn followed by 50 lb/acre in early spring provides enough N for annual ryegrass growth. While more N fertilizer would increase growth slightly, economic analyses suggest that applying 50 lb/acre in autumn followed by another 50 lb/acre in spring would be the most cost effective rate.

Forage quality samples showed that annual ryegrass is excellent forage. Samples for 2002-2003 showed that annual ryegrass averaged 24% crude protein and had acid detergent fiber values less than 22%. In short, few other forages can produce such excellent quality feed for winter and early spring grazing.

Soil samples taken to a 40 inch depth in June of 2003 showed that soil nitrate levels, 0 to 10 inches from the soil surface, were nearly 6 ppm when 150 lb/acre of N was applied in both autumn and spring, while all the other treatments had about 2 ppm of nitrate or less. At deeper depths, (10 to 20 and 20 to 40 inches from the surface) soil nitrate levels were less than 2 ppm for all treatments. This suggests that little N is lost due to leaching from annual ryegrass pastures at the rates of N we examined.

Conclusions

  • Annual ryegrass can produce more than 12,000 lb/acre of high quality forage. This production level makes it an excellent choice for many livestock operations.

  • Annual ryegrass should receive 50 lb/acre of N in autumn followed by another 50 lb/acre in early spring. Applying more N fertilizer than that is probably not economic.

  • At all but the highest rates of N fertilizer tested, little N is lost from annual ryegrass pastures due to leaching.
August  2007

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