Forages: Fertility Management

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Pub 811: Agronomy Guide > Forages > Fertility Management

Excerpt from Agronomy Guide for Field Crops
Order OMAFRA Publication 811: Agronomy Guide for Field Crops

• Nitrogen
  • Table 3-6. Nitrogen Recommendations for Improved Grass Hay or Pasture
  • Table 3-7. Phosphate Recommendations for Forages Based on OMAFRA-Accredited Soil Tests
• Phosphate and Potash
• Plant Analysis
  • Table 3-8. Potash Recommendations for Forages Based on OMAFRA-Accredited Soil Tests
• Micronutrients
  • Table 3-9. Interpretation of Plant Analysis for Alfalfa
• Manure
• Liming

Nitrogen

Forage stands that are more than 50% legume do not require nitrogen fertilizers. For nitrogen recommendations, see Table 3-5, General Nitrogen Recommendations - Perennial Forages, and Table 3-6, Nitrogen Recommendations for Improved Grass Hay or Pasture.

Grass stands containing less than one-third legumes require large amounts of nitrogen to optimize yield. Where conditions permit, it is generally more profitable to reseed to mixtures containing legumes. It can be profitable to fertilize grass stands consisting of productive species such as bromegrass, orchardgrass or timothy. The use of nitrogen will also increase the protein level in the grass. The rates of nitrogen recommended for grass stands have been developed on the basis of the price of nitrogen relative to the value of hay (see Table 3-6). Make the first application for hay or pasture as early as possible in the spring, followed by a second application after the first cut and a third application after the second cut. To avoid the danger of nitrate toxicity, apply no more than 170 kg/ha (150 lb/acre) of nitrogen at any one time.

Nitrogen deficiency in forages shows up as a general yellowing and stunting of the plants. It may show in the lower parts of the plants first. In legumes, a nitrogen deficiency usually indicates poor nodulation and/or low soil pH.

¹Make first application before May 10 and second application after the first cut. Make a third application after the second cut only if there is reasonable assurance of a third cut.

² For stored feed: Where manure is applied, reduce the fertilizer application according to the type and amount of manure (see Manure). For pasture: Reduce all rates by one-third because of recycling through manure and urine.

The most profitable rate of nitrogen application is also affected by the relative prices of hay and nitrogen, which can be expressed as a nitrogen/hay price ratio. This ratio is calculated by dividing the cost of nitrogen, in dollars per kilogram of actual N, by the value of the hay, in dollars per kilogram.

a) To determine the cost per kg of actual nitrogen, divide the cost per tonne of fertilizer material by 10 times the percentage of nitrogen in the fertilizer. Include application costs.

Cost of N/kg = Cost of nitrogen fertilizer per tonne ÷ 10 x (% Nitrogen in fertilizer)

b) To determine the value per kg of hay, divide the value per tonne by 1,000. The value of the hay may be the anticipated selling price, or it may be the cost to replace that hay with other feeds in the ration.

c) To determine the nitrogen:hay price ratio, divide the cost of N per kg by the value of the hay per kg.

Nitrogen/hay price ration = Value of hay/kg ÷ Cost of N/kg

¹ HR, MR, LR, RR, and NR denote, respectively, high, medium, low, rare and no probabilities of profitable crop response to applied nutrient. Profitable response to applied nutrients occurs when the increase in crop value, from increased yield or quality, is greater than the cost of the applied nutrient.
² Where manure is applied, reduce the fertilizer application according to the amount and quality of manure (see Manure)
³ For use only where seed is banded directly above the drilled fertilizer.

Phosphate and Potash

Phosphate and potash recommendations are given in Table 3-7, Phosphate Recommendations for Forages Based on OMAFRA-Accredited Soil Tests, and Table 3-8, Potash Requirements for Forages Based on OMAFRA-Accredited Soil Tests. For information on the use of these tables or if an OMAFRA-accredited soil test is unavailable, see Fertilizer Recommendations.

When direct-seeding on soils that require phosphate fertilizer, establishment may be improved by the placement of a high phosphate fertilizer 5 cm (2 in.) directly below the seed. Using a grain drill with fertilizer and grass seed attachments, this placement may be accomplished by drilling the fertilizer through the furrow opener and dropping the forage seed on a firm soil surface directly behind the furrow opener. Usually it is advisable to firm the soil surface immediately after seeding.

Potash may be more effective in promoting persistence if it is applied within the 6 weeks before the start of the fall rest period. Potash deficiency is occasionally found in alfalfa, showing symptoms of small, light dots on the leaflets. These dots can be on any part of the leaflet but are usually concentrated near the margins (Plate 20). Grasses and clovers are much less likely to show potash deficiency symptoms. Phosphate, if required, may be applied with the potash or at other times of the year. Phosphate deficiency symptoms are rare and non-specific in forages, but a shortage of phosphate may manifest itself as stunting and poor winter survival of legumes.

Plate 20. Potassium deficiency in alfalfa is indicated by small, light dots near margins of the leaflets.

Plant Analysis

When analyzing forage legumes, sample each species separately. Cut the plant at normal mowing height at the late bud stage. See Table 3-9, Interpretation of Plant Analysis for Alfalfa. Plants suspected of nutrient deficiency, however, should be sampled as soon as the problem appears. For sampling at times other than heading, and for species other than alfalfa, samples should be taken from both deficient and healthy areas of the field for comparative purposes. A soil sample should be taken from the same area and at the same time as the plant sample.

100 kg/ha = 90 lb/acre

¹HR, MR, LR, RR, and NR denote, respectively, high, medium, low, rare and no probabilities of profitable crop response to applied nutrient. Profitable response to applied nutrients occurs when the increase in crop value, from increased yield or quality, is greater than the cost of the applied nutrient.
² Where manure is applied, reduce the fertilizer according to the amount and quality of manure (see Manure).
³ A rating of "NR" may mean reduced yield or quality of crops primarily due to magnesium deficiency. Natural levels above 251 occur occasionally on clay and clay loam soils but are not expected to cause problems because soils naturally high in potassium are usually also high in magnesium.

Micronutrients

Boron

Boron is important for alfalfa, however, its application is not required on all soils. A deficiency shows up mainly on high-pH, sandy soils. Boron applications are recommended on all sandy soils and, in particular, the sandy loam and loam soils in the area east of the Niagara Escarpment up to and including Frontenac County. Boron deficiency is seen most frequently on droughty soils under dry conditions.

A shortage of available boron to the alfalfa plant first affects flowering and reduces seed-set. As the deficiency becomes more serious, the youngest upper leaves of the plant become yellow to red in different plants (Plate 21). Growth can be severely stunted and winter hardiness reduced.

Plate 21. Boron deficiency appears on the upper leaves of alfalfa, becoming yellow to red and stunting growth.

Values apply to the plant cut at normal mowing height at the late bud stage.

¹ Yield loss due to nutrient deficiency is expected with nutrient concentrations at or below the "critical" concentration.
² Maximum normal concentrations are more than adequate but do not necessarily cause toxicities.

Boron deficiency can usually be corrected or prevented by an application of 1.0-2.0 kg/ha of boron broadcast annually. Boron should not be banded at seeding.

Do not apply mixtures of herbicides and fertilizers to crop foliage unless recommended by competent authorities. For further details on boron deficiency and on methods of application, visit the OMAFRA website at www.ontario.ca/crops.

Sulphur

Sulphur deficiency has not been observed on forages in most of Ontario. The sulphur in acid precipitation falling on Northeastern and Southern Ontario is sufficient for crop requirements. There have been scattered reports of sulphur deficiency in alfalfa in Northwestern Ontario on sandy soils with low organic matter. The appearance of sulphur deficiency is similar to nitrogen deficiency with general yellowing of the plants.

Other Micronutrients

Deficiencies of copper, zinc or manganese have not been observed in forages in Ontario.

Manure

Manure is an excellent source of nutrients and can substitute for manufactured fertilizers. It is an excellent source of nitrogen for grasses and, when applied after the first or second cut, can give a forage yield and quality boost. Apply liquid manure as soon as possible after harvest, before re-growth. Application to older grass-alfalfa stands will give the largest benefit. Do not apply manure to perennial forage legumes when there is snow cover, because ice frequently forms under the manure and can kill the plants.

Liming

Legumes generally are not tolerant of acid soil conditions. Acid soils should be limed 1 year before seeding at rates indicated by soil tests. (Soil Acidity and Liming) Applying lime to established stands is not normally profitable.