Fertilizing Seeded Forages in Saskatchewan

Seeded forages can be highly productive, but this productivity gradually declines as the stand ages. Research has indicated that fertilization can rejuvenate or revitalize a forage stand. But before you decide to fertilize, you need to assess the current status of your stand.

Some important questions to ask are:

• To what degree has the stand degraded with age?
  At least half of the remaining species should be desirable for forage production. Pastures or hay stands in good to excellent condition generally respond to fertilizer better than pastures with weeds or less productive grasses.
• Is it a mixed stand?
  The amount of legumes such as alfalfa will affect the amount of fertilizer required.
• Have you soil tested?
  Yield response to nutrients will vary from field to field. Coarse sands and gravelly soils will generally give a lower yield response to fertilizer than finer, sandy soils, loams or clays.
  Soil testing is an inexpensive way to tailor the nutrient application to the particular needs of the stand.
• Does it make economic sense to fertilize?
  Several economic studies have shown that higher yields alone do not necessarily translate into lower costs or higher profit so it is essential to understand the effect of fertilization on unit costs of production.

Fertilizer Effects on Forage Production

If you have assessed the field and determined that the stand is nutrient deficient, the short-term yield response to fertilizer will depend largely on moisture.

With adequate moisture, fertilizing seeded pasture and hay land can significantly increase yields across all soil zones in Saskatchewan.

Since moisture conditions are less predictable in dry areas of the province, yield responses tend to be more variable in these regions. Small responses to added fertilizer can occur even in dry years where plants are able to take advantage of early spring moisture and cooler temperatures. This extra growth in a dry year can be important when feed shortages are more likely.

Yields are usually more predictable in moister regions such as the moist Dark Brown, Black, and Grey Wooded zones of Saskatchewan.

On the moist Dark Brown soil at Scott, annual applications of 45 lbs. nitrogen (N)/acre plus periodic phosphate (P) applications more than doubled yields of smooth bromegrass stands (Table 1); annual applications of 90 lbs. N/acre plus periodic P more than tripled yields. The yields were slightly more than double that of unfertilized bromegrass, compared to 90 lbs. N/acre without P.

On Grey-Wooded soil at Pathlow, fertilizing with 80 lbs. N/acre, 40 lbs. P₂O₅/acre and 9 lbs. sulphur (S)/acre every second year nearly tripled production compared to unfertilized pasture in the year of application. A year after application, the yield was still one and half times more than unfertilized pasture (Table 1).

With the above fertilization rates applied every second year, the grazing capacity was increased by 70 per cent compared to unfertilized pasture because of greater stocking levels and a longer grazing season. Weight gains of the cows were also improved on the fertilized pasture.

Table 1: Examples of yield response to fertilization at various locations in Saskatchewan

Note: N=Nitrogen, P=Phosphorus, S=Sulphur. Multiply lbs./acre by 1.121 to convert to kg/ha

Removal of Nutrients by Haying or Grazing

Management systems affect the nutrient status of forage fields differently.

Hay production removes large amounts of nutrients directly from a field and if these nutrients are not replaced by either manure or commercial fertilizers, hay yields will decline over time.

Provided that the alfalfa has been adequately inoculated with rhizobium bacteria, most of the nitrogen will be supplied by nitrogen fixation from nodules in the alfalfa, but the rest of the nutrients will come from the soil. (See Table 2)

Table 2: Nutrients Removed in Hay Production (in lbs./acre)

Livestock grazing removes fewer nutrients than haying. This is because most of the nitrogen (N), phosphorus (P), potassium (K) and sulphur (S) consumed by livestock are excreted in the urine and feces. In some cases, extensive or in-field winter feeding systems can increase nutrients depending on the nature (bale grazing vs. stock piled forages) and intensity of the system.

Because of the high recovery of nutrients in in-field winter feeding systems, it is especially important to select appropriate sites to prevent nutrients from leaving the fields in spring runoff and to rotate sites (especially when bale grazing) to prevent excessive buildup of nutrients.

Despite the higher recovery of nutrients in pastures, they may still respond to fertilization. Under a grazing situation, nutrients can still be lost, immobilized and redistributed, leaving areas of the pasture deficient.

Generally, the first sign of nutrient deficiency in a hay stand or pasture is lower than expected production from plants that appear stunted and spindly.

Fall soil testing is the quickest method of determining the nutrient status of the soil and whether or not a nutrient deficiency is the problem. A soil test will also provide information about which particular nutrient or combination of nutrients (N, P, K, or S) is limiting growth.

If you have never taken soil samples before it is a good idea to consult with your local agrologist.

An agrologist can provide information about:

• How to sample;
• Where you can send the soil for analysis;
• Interpreting the results from the lab; and
• The appropriate timing, placement, formulation and amount of fertilizer for your forage stand.

Fertilizing to Address Nitrogen Deficiencies

Nitrogen deficiencies in forage grasses include:

• Slow plant growth;
• Yellow-green leaves; and
• Browning and/or dying of leaf tips and margins.

Grass crops will almost always respond to nitrogen fertilizer. Since in most cases fertilizer is being broadcast on existing stands, spring and early summer precipitation after application will determine the amount of nitrogen that actually enters the soil and is available to the stand.

Pure stands are generally more prone to deficiencies than mixtures of grass and alfalfa. This is because properly inoculated alfalfa has the ability to fix atmospheric N.

Amounts will range from 70-200 lbs. N/acre depending on growing conditions. Alfalfa inoculated with rhizobium forms nodules within the root system. Under normal growing conditions, these nodules supply nitrogen to both the alfalfa and some to its companion grass and can significantly improve the production of the pasture.

In terms of cost-effectiveness, no other measure can match the value of including inoculated alfalfa in pasture and hay seeding. Threshold amounts of 40 to 50 per cent alfalfa in a mixed hay stand and 30 per cent in a pasture stand may provide adequate nitrogen within the stand.

Adding nitrogen to stands with greater percentage of alfalfa may be uneconomical as it may actually decrease the amount of fixation that occurs within the alfalfa nodules. Too much nitrogen can also overstimulate grass production at the expense of the legumes.

When grasses are grown with legumes it is important to adjust fertilizer nitrogen rates based on the amount of alfalfa in the stand. For stands below the threshold percentages of alfalfa, the fertilizer rate should be reduced by the percentage of alfalfa remaining in the stand.

Example: If the mixture contains 25 per cent alfalfa, the fertilizer rate should be reduced by 25 per cent of the amount recommended for a pure grass stand.

Urea is the most widely used source of nitrogen fertilizer. It has high nitrogen content relative to its cost per pound. If urea is broadcast, some of the nitrogen may be lost by volatilization or gassing off.

Generally speaking, volatilization will be lower when urea is applied during the wetter and cooler conditions that occur in early spring (March and April). Drying surface soil and rising temperatures as spring progresses increases the probability of ammonia volatilization.

Ideally, a manager should attempt to apply nitrogen immediately before a moderate rain event (1/2 inch), allowing urea to dissolve and move into the soil; however, this is not always possible. Since urea supplies about half the nitrogen in liquid nitrogen fertilizer UAN (28-0-0), similar care should be used with the timing of UAN applications.

A urease inhibitor, for example - Agrotain has been shown to reduce volatilization losses for surface applied urea and UAN.

Depending on moisture, and as a rough rule of thumb, you can expect the following response for each pound of N/acre applied:

Fertilizing to address Phosphorus Deficiencies

Phosphorus is often the next most deficient nutrient within a mixed stand (it may be first in a pure stand of alfalfa).

Symptoms of P deficiency include:

• Stunted or slow growing plants;
• Blue-green colour (grass);
• Purple-shaded leaves and stems (legumes); and
• Delayed maturity.

Phosphorus deficiencies can be corrected with an annual application of 25 lbs. P₂O₅ /acre on established stands. Responses to annual low application rates of phosphorus will vary but they are generally best during good soil moisture conditions.

An alternative practice may be to incorporate 100-200 lbs. P₂O₅ /acre before seeding; this amount will supply the stand for several years.

Mono ammonium phosphate (12-52-0, 11-55-0) is the most common form of fertilizer phosphorus. Liquid phosphorus fertilizers are also available and are effective.

Because phosphorus is relatively immobile in the soil broadcasting is an effective way to apply it. Banding P fertilizer into existing stands is recommended only where feasible.

Fertilizing to address Potassium Deficiencies

Potassium is important for:

• Winter survival;
• Stand persistence;
• Disease resistance;
• Root development; and
• Yield.

Potassium is generally adequate in most soils but can be limiting on light textured Gray Soils. Application of 100 lbs. K₂O/acre should be considered when soil test potassium is less than 250 lbs. /acre in the top six inches of the soil.

Banding or spreading potassium fertilizer on established forage are effective ways to apply potassium.

Fertilizing to Address Sulphur Deficiencies

Sulphur is essential in plant protein formation and legume nodule formation. Alfalfa is a high user of sulphur. Sulphur levels may be adequate in the Brown and Dark Brown soil zones of Saskatchewan and may be deficient in the Black and Gray Wooded soils.

Broadcasting fertilizers containing sulphate-sulphur, such as ammonium sulphate (21-0-0-24), that contains 24 per cent SO₄-S, are very effective in addressing sulphur deficiencies.

Fertilizing with Manure

Animal manure is a useful source of plant nutrients as well as an excellent soil amendment (Table 3).

Not all nutrients in manure are immediately available to plants. Research indicates that yield responses of manure-treated alfalfa and grass-alfalfa stands approach the yields obtained with similar rates of nitrogen and phosphorus applied as commercial fertilizers. Manure application must be timed to minimize problems with fouling of the forage.

To minimize the risk of nutrient runoff to adjacent water bodies, manure should not be applied to frozen ground.

Table 3: Typical Nutrient Contents of Fresh Cattle Manure and Swine Effluent

Fertilizer Timing and Methods

Spring fertilization should occur as soon as the field permits equipment travel. Early spring application of nitrogen is generally the most effective because conditions that can result in losses due to leaching, runoff and volatilization are relatively low. Late fall applications can also be effective and may be more practical where road bans, time constraints or wet soils may delay application in early spring.

Broadcasting is the most common method of application of nitrogen onto existing stands. It is better to fertilize fewer acres with higher rates (45-55 lbs. N/acre) than more acres at lower rates (18 - 27 lbs. N/acre) but fertilizing at excessive rates of 180 lbs. N/acre or higher may lead to toxic concentrations of nitrates in forage grasses. The risk is especially high after a killing frost.

Nitrogen applications can be split, but split-applications of N have given variable results. Splitting annual applications of nitrogen fertilizer should be used only in high moisture areas or under irrigation. Split applications of less than 45 lbs. N/acre (i.e. two 22 lbs. /acre applications) are not recommended.

Because phosphorus is relatively immobile in the soil, banding fertilizer into existing stands is recommended only where feasible. Extra care should be taken to prevent damage to the stand. This means using low disturbance disc or knife openers at reduced speeds.

Although potassium deficiencies are rare, K can be broadcast directly onto forage stands.

Like nitrogen, sulphate is a relatively mobile nutrient so ammonium sulphate fertilizers can be broadcast on forage stands.

Economic Considerations

The costs of fertilizing must compete economically with alternative sources of feed such as purchased hay or rented/purchased pasture.

The profitability of fertilizing seeded forages depends on:

• The additional yield;
• Harvest efficiency;
• Fertilizer and application cost;
• Fertilizer storage;
• Transport;
• Interest charges; and
• Current livestock and forage prices.

As these factors change, so will the economics of fertilization.

A long-term grazing-fertility study at AAFC Brandon Research Station where fertilizer was applied at soil test recommendations and when stocking rates were adjusted to production levels showed that net revenue was greatest in a non-fertilized mixed grass alfalfa stand.

Unfertilized pure grass had the lowest variable cost of production, but was not the most profitable because fixed costs were high relative to low productivity. On the other hand, fertilizing pure grass increased variable costs making it expensive relative to the gain in yield.

Fertilizing a mixed stand of alfalfa and grass was not as profitable as the non-fertilized mixed stand treatment.

Inputs were higher and adding fertilizer at soil test recommendations - without adjusting for percentage of alfalfa in the stand - actually reduced the alfalfa over time. Cost effectiveness of the added production was further reduced as benefits of N fixation by the legume disappeared along with the alfalfa. This may have been avoided by adjusting the nutrient level to take into account the percentage of alfalfa in the stand (see example in Fertilizing to Address Nitrogen Deficiencies section above).

Other Considerations

Fertilizing forages can result in several non-economic payoffs including:

• Improved livestock gains;
• Less risk of invasion by weeds;
• Less susceptible to disease or insect infestation; and
• Better wind and water soil erosion protection.

Increased production can also help increase forage carryover which can be important in times of drought.

Fertilization and proper grazing management extend the productive lifespan of a pasture. This reduces the need for more aggressive and costly forms of rejuvenation like cultivation and reseeding. The savings on rejuvenation will offset a portion of the annual fertilizer costs.

Through a balanced, long-term fertilizer program, more cattle can graze on the existing land base.

This helps save:

• Seeding, fencing, and water site costs if new land is required to meet this additional demand; or
• Taxes and interest charges if additional pasture is purchased.

As a result, producers are less dependent on rented pasture and the uncertainty of long-term tenure and rental charges.

Fertilization can also reduce the need to purchase additional land and can reduce transportation costs if this land is further away.

The fertilizer industry promotes sustainability and stewardship through awareness and adoption of the 4R nutrient stewardship principles; the Right Source applied at the Right Rate, Right time and Right placement.