Soils

John Hart, Mark Mellbye, William Young, and Thomas Silberstein

Nutrient Management for Annual Ryegrass Grown for Seed in Western Oregon

This article is a draft of the first half of a new publication.

Annual ryegrass is grown for seed on Dayton, Bashaw, and similar poorly drained soils in western Oregon. Dayton soil is found on broad flat areas of the southern Willamette Valley floor and is called “white soil” by growers. Bashaw soil is formed on the low lying and gently concave areas associated with narrow stream valleys and at the edges of some hill slopes. These soils are not well suited to perennial grass production because of poor drainage that results in water standing on the soil surface. Recommendations in this guide assume production in these settings.

The guide also assumes disease, pest, and weed control are adequate. For example rust, slugs and annual bluegrass are controlled. Lack of pest control cannot be overcome by the addition of nutrients. A healthy plant with an adequate root system is required to receive the greatest return from your fertilizer investment.

Annual ryegrass can be established by planting in a prepared seedbed or with volunteer seedlings from the previous year’s crop. Using volunteer seedlings for stand establishment reduces establishment cost and yield. The yield reduction is caused by competition among plants. To take advantage of the cost saving from a volunteer stand without a reduction in yield, either herbicide is sprayed to establish rows or heavy grazing with sheep is used to reduce competition. Recommendations in this guide apply to both methods of establishing a stand. Only minor adjustments to nutrient applications are needed for the traditional burn and no-till, volunteer seeding, or plowing and disking methods of stand establishment. Volunteer stand establishment should only be used when soil pH and nutrient levels are adequate since nutrients aren’t incorporated at planting.

The recommendations provided assume little if any rotation of annual ryegrass with other crops, and stand establishment by row spraying volunteer seedlings is used only in alternate years. The recommendations apply to commonly grown varieties of annual ryegrass.

The average seed yield for annual ryegrass is approximately 2000 lb/a. The recommendations in this guide, especially for nitrogen, are adequate for production of much higher seed yields; for example, more than 3000 lb/a seed yield is possible with these recommended nutrient levels on sites where soil pH and drainage do not limit yield. Higher amounts of nutrients than recommended by this guide are not required for seed yield above 2000 lb/a.

Research for this guide was performed over the past 50 years on a combination of large and small plots throughout the Willamette Valley. Several research projects evaluated grazing on annual ryegrass seed yield. No reduction in seed yield from grazing was measured when grazing began before the onset of stem elongation and continued until all meristems of primary tillers were removed. In these studies, grazing began in late February or early march and ended in early to mid-April. Sufficient nutrient and moisture for regrowth and seed developments is necessary during the post-grazing period if seed yield is to be maintained.

Sample and analyze soil to estimate need for lime, phosphorus, potassium, calcium, and magnesium. Annual soil tests are not necessary. Sampling and testing soil every other year or every third year is sufficient. If possible, sample soil after tilling. A single sample should represent only 40 acres, a single soil type, or the same management practices in a field. If you have questions about sampling or testing soil, contact the local Oregon State University Extension office for assistance. A List of Analytical Laboratories Serving Oregon is available at: http://eesc.orst.edu/agcomwebfile/edmat/html/em/em8677/em8677.html and a general Soil Test Interpretation Guide, EC 1478 is available at: http://eesc.orst.edu/agcomwebfile/edmat/EC1478.pdf. Ordering information of printed copies is given at the end of this publication.

Nutrient management can be addressed by answering the following four questions: 1) how much should be applied, 2) when should the material be applied, 3) how should the material be applied, and 4) what material should be used. This guide primarily provides answers to amount to be applied and timing or when to apply the material.

For nutrients except N, a fall preplant or banded at planting application is assumed when the crop is planted with a drill. No fall fertilizer is recommended when the stand is established with volunteer seedlings. Volunteer stand production is recommended when soil pH is above 5.3, soil test P is above 25 ppm, soil test K is above 150 ppm, soil test Ca is above 10 meq/100 g soil, and soil test Mg is above 0.5 meq/100 g soil. Avoid volunteer stand establishment on fields with soil pH below 4.8.

Rate and timing recommendations for nitrogen are based on plant demand. Annual ryegrass growth and nitrogen uptake information is needed to provide application timing. Figure 1 provides information about amount of aboveground biomass and nitrogen accumulation for ungrazed annual ryegrass.

The total aboveground biomass of approximately 9000 lb/a was comprised of 2700 lb/a seed and 3 t/a straw. Slow early growth occurs in the fall and winter. Depending on year and if fields are grazed, between 500 and 1000 lb/a of dry matter is accumulated by mid-March. Growth is rapid and linear from early April to early June.

Figure 1. Biomass accumulation and N uptake for annual ryegrass grown on a Dayton,
Concord or Malabon soil in the southern Willamette Valley.

Approximately 100 to 125 lb N/a is taken into the aboveground portion of the crop when 90 to 135 lb/a spring N fertilizer is applied. Straw N concentration is about 1% and seed N concentration is about 2%. Slightly less than half the N is removed in the seed.

The maximum N uptake rate was approximately 1.5 lb/a/day during the latter part of March and first of April. Grazing will delay biomass accumulation and N uptake.

Nitrogen

Fall Nitrogen

A fall nitrogen recommendation of 20 pounds nitrogen per acre is based on burn/drill management. A seed yield increase from the application of fall N is not documented. Recent work with volunteer establishment did not produce an increase in seed yield from fall N application, Figure 2. When volunteer stand establishment is used, N can be applied over the crop during a row spray operation. Similar to conventionally planted annual ryegrass, use of fertilizer at planting can promote early growth, and provide additional forage for grazing. The limited choice of phosphorus fertilizer materials, primarily ammonium phosphates, causes nitrogen to be added if phosphorus is to be banded at planting. Typically 15 to 25 lb N/a would be added if 30 lb P₂O₅/a are supplied.

Table 1 provides clean seed yield from annual ryegrass receiving 15 to 25 lb N/a banded at planting and an additional 40 lb N/a as a preplant broadcast application. The crop residue was either burned or chopped and plowed into the seedbed. A seed yield of approximately 200 lb/a is necessary for the differences to be statistically significant. A yield increase of at least 80 lb/a seed is necessary to pay for the cost of 40 lb N/a. The statement is based on nitrogen costing $0.35 lb and the price of seed at $0.15/lb. Little or no increase in seed yield was measured when the annual ryegrass crop was established from a volunteer stand and rows were established with a winter herbicide application. A December application of 20 lb N/a as a liquid sprayed over remaining rows provided an insufficient seed yield increase to recoup cost of application, Figure 2.

Table 1. he influence of residue management, fall nitrogen application and spring nitrogen rate on
annual ryegrass seed yield. The data was collected from plots near Shedd, Oregon, from 1983 through 1985
and are treatment averages.

Figure 2. Annual ryegrass clean seed yield response to herbicide and fertilizer
treatments for establishment of rows in a volunteer stand. The fertilizer was
liquid 20-3-3-3 applied over the row being established at the rate of 10 g/a in December.

Spring nitrogen

Nitrogen is supplied to annual ryegrass from a variety of sources. These sources are crop residue, nitrogen supplied annually by the soil, and fertilizer nitrogen added in the spring. rate of 100 to 140 pounds nitrogen per acre. Nitrogen from the soil is supplied at a rate of 60-100 pounds nitrogen per acre, depending on soil drainage. Poorly drained soils with more than 5% organic matter produce less seed yield increase from N application than other soils. Poorly drained soils should receive the lower spring rate of N, 100 pounds nitrogen per acre. Nitrogen rates higher than 150 lb/a have not been shown to benefit seed yield. Higher than needed use of N is an expense not recovered in additional seed production and increases the need for lime compared to nitrogen application between 100 and 140 lb/a.

Figure 3. Annual ryegrass seed yield response to spring nitrogen application rate.

Figure 3 shows the relationship of annual ryegrass seed yield and spring nitrogen application from three research efforts spanning almost 50 years. The recently completed work explored the greatest range in spring N application rates of any field trial, but the conclusion from any of the trials is quite similar. In each study, approximately 120 lb N/a was sufficient for optimal annual ryegrass seed yields. A single rate for all situations is not logical since drainage, organic matter, and management differ for fields. A nitrogen application of 100 lb/a may be adequate for a poorly drained high organic matter soil where 140 lb/a is needed on a well-drained soil with a lower organic matter content. Thus, spring applications of 100 to 140 lb N/a are recommended.

Straw management differences have little effect on nitrogen needs. Residue removal, burning or disking has little short-term effect on nitrogen supply to an annual ryegrass seed crop. Table 1 presents annual ryegrass seed yield when residue is burned or chopped and plowed into the seedbed. When adequate spring N was applied, 120 lb/a, the seed yield from treatments with straw burned was identical to the seed yield for treatments where straw was incorporated.
The recommended nitrogen rate does not change when currently registered growth regulators for grass seed, Apogee® and Palisade® are used.

Timing

In non-grazed fields, the maximum daily rate of nitrogen uptake, 1.5 lb/a, occurs in late March or early April (Figure 1). Apply N in late March to mid-April. The nitrogen can be applied in a single or split application. No advantage was gained from a split application when some or all the nitrogen is applied in early April. Avoid nitrogen applications on fields with standing water. Delay N application until no standing water remains. In fields that are grazed, apply spring nitrogen as soon as sheep are removed from the field.

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