Soil Fertility Considerations

Part of the Ruminant Livestock: Facing New Economic Realities Meetings

Fertilizer Prices

• Late January 2008: Nitrogen = $0.65/lb, P2O5 = $0.65/lb, K2O = $.0.41/lb

• Future Projection: Increasing costs!

• Management Options?• Continue as before

• Quit using synthetic fertilizer

• Use strategically

pH Effect on Element Availability

• When talking about fertilizers and fertility, begin by looking at soil pH.

• Soil pH has an effect on fixation and release mechanisms in soil

• Lime may be the cheapest “fertilizer”

Soil pH: Legume species

Species Tolerance to

pH < 6.0

pH Goal

Alfalfa Low > 6.5

Alsike Clover High > 5.5

BFT High > 5.5

Red Clover Medium 6.0-6.5

White Clover Medium 6.0-6.5

Kura Clover Medium 6.0-6.5

Source: Ohio Agronomy Guide, bulletin 472

Soil pH: Grasses

Species Tolerance to

pH < 6.0

pH Goal

Kentucky BG Medium 6.0 – 6.5

Orchardgrass Medium 6.0 – 6.5

Tall Fescue High > 6.0

Perennial RG Medium 6.0 – 6.5

Timothy Medium 6.0 – 6.5

Brome Medium 6.0 – 6.5

Source: Ohio Agronomy Guide, bulletin 472

Soil pH and Lime Application• Apply lime when soil pH is below optimum• It is the buffer pH number that determines the

lime application required to get the desired response

• Agronomy Guide recommendations are based on tons/acre of ag lime with an ENP of 2000 lbs/ton

• Lime is not very soluble, surface applications neutralize acidity slowly (may move downward approximately 1 inch/year)

• Implications for nitrogen fertilization (can increase losses)

Nitrogen Fertility

• Rate of nitrogen application is directly related to yield potential

• Nitrogen sources include synthetic fertilizer, livestock manure, compost, and organic matter release in the soil

• Cool season grass response is greatest in spring and in fall

• Pasture and hay fields with > 25% evenly distributed legumes do not need nitrogen application

Phosphorus (P)

• Needed at critical soil test level to ensure maximum forage production

• Rate recommended is not directly related to yield potential

• For every 7.5 – 10 lbs/acre of P2O5 added or removed from the soil, soil test P will change by 1ppm

Source: Robert Mullen, 3-6-07 presentation to Athens Grazing Council

Potassium (K)

• Poor potassium nutrition can result in poor forage production

• Application not related to yield potential

• For every 2 –6 lbs/acre of K2O added or removed, soil test K will change by 1 ppm

• High levels of soil K can be a problem:• Luxury consumption and high forage concentrations

• Can suppress magnesium uptake

Source: Robert Mullen, 3-6-07 presentation to Athens Grazing Council

Critical Soil Nutrient Levels for Forages: P and K

K at CEC:

Crop P 5 10 20

ppm (lbs/acre)

-------- ppm (lbs/acre)

---------

Legumes 25 (50) 88 (175)

100

(200)

125 (250)

Grasses 15 (30) 88 (175)

100

(200)

125 (250)

P critical levels based on crop, K critical levels based on CECSource: Robert Mullen, 3-6-07 presentation to Athens Grazing Council

Role of Soil Organic Matter• O.M. increases the water holding and nutrient

storage capacity of the soil• Critical to soil organisms that play a role in nutrient

release, decomposition, and breakdown of chemicals

• Release nutrients and increase nutrient availability to plants

• Buffers the soil system: in high organic matter soils macro nutrients are more available compared to low pH soils (What is a “high” OM soil?)

Pastures: Nutrient Cycling

• Removal rates for pasture are lower than for hay crop, but…

• Grazing livestock move nutrients and concentrate nutrients into patches

• Nutrients are lost from pastures as animal product, through volatilization, leaching, erosion, but…

• Purchased feeds and stored feeds fed to livestock on pasture can add nutrients

Pastures: Nitrogen Cycling

• 70% of nitrogen returned to pastures is in the form of urine

• The nitrogen application rate can be the equivalent of 1000 lbs/acre in a urine patch

• Leaching losses can approach 50% and 22% of nitrogen is lost to volatilization

• Negligible N-fixation under a urine patch

Source: Dave Barker, 2-9-07 OFGC conference presentation

Pasture Nutrient Cycling: Feces/Dung

• Phosphorus applications can amount to 220 lbs/acre in dung patches

• Soil K in camp areas are commonly 4 to 10 fold higher than the overall pasture average

• The nitrogen in dung can approximate urine N levels but is in an organic form and is more stable: volatilization losses about 5% and leaching losses about 4%

Source: Dave Barker, 2-9-07 presentation to OFGC conference

Nutrient (manure) Management in Pastures

• Higher stock density = better distribution

• Shorter occupation periods = better distribution

• Shade, water and minerals can concentrate manure

• Use water and minerals to spread distribution

• More intensive management can reduce fertilizer costs