Lecture 11 - Rangeland Fertilization

Why Fertilize Rangelands?

Increase Yield of Forage (and therefore gains in grazing animals)

Alter plant composition

________: fertilize to get

High Returns:

• Irrigated Pasture or hayland w/ 25 inches of precip

• Naturally subirrigated pastures and hayland

Moderate Returns

• Cool-season grass/legume mixtures with 15-25 inches precip

• Midwest tallgrass

• Saline subirrigated

• Wetlands pastures

1. Locations where Soil Moisture is not a limiting factor

2. Locations with deep, well-drained soils

3. Locations where a soil nutrient is limiting plant growth!!

Where to Fertilize?

The Law of the Minimum

“The growth or distribution of a species is dependent on the one environmental factor most critically in demand.”– Justus von Liebig

Steps to Fertilization of Rangeland

1. Verify soil nutrient deficiency

• Soil tests

• Observe plant symptoms

2. Smaller-scale fertilizer trials

• Measure actual field response

3. Larger-scale application

Airborne Nutrients:

• C, H, O

Soil Nutrients

• Macro:

  • N, P, K, Ca, Mg, S

• Micro:

  • B, Cu, Fe, Cl, Mn, Mo, Zn

Plant Nutrients

Proteins, amino acids, etc

• Humus and mulch layers

• Immobile

• Unavailable for plant use

Ammonium compounds

• Bound to soil colloids and O.M particles

• Slightly mobile

• Slightly available to plants

Nitrates

• Soluble in soil solution

• Highly mobile

• Highly available to plants

Soil Nitrogen

Especially important for legumes/legume mix areas

Most western soils (N great plains and west) have ample, but S. great plains and Coasts may be deficient

Soluble phosphorus vs insoluble phosphorus

Solubility affected by pH (6-7pH = greatest)

Soil Phosphorus

Most of West has adequate Potassium and Calcium

Midwest, Northeast, Southeast, and PNW often need potassium and calcium additions

Especially gulf and S. Atlantic coasts

May counter the tendency of Nitrogen fertilizers to “acidify” the soil

Be careful with “luxury consumption” of K

Potassium/Calcium

Sulfur is especially beneficial for annual grass/clover rangelands (California) and sandy-soil legume ranges (Nebraska)

Other nutrients are less common as problems…

Sulfur and Others

Fertilizer Labels

By law, US fertilizers are required to be sold with a guaranteed analysis

• Elemental

• Oxide

Season of Fertilizer Application

Best time to apply depends on:

• Amount and distribution of rainfall

• Type of plants present

• Kind of fertilizer

In general, must match AVAILABILITY to time of plant growth

Method of Fertilizer Application

Broadcast Dry

Drilling/banding into soil

Liquid spray

• Mix with herbicide/insecticide

Manure

Biosolids

Mulch

Other Fertilizers

Grass Response to Nitrogen

Increases vigor, production, seeding, rooting, drought survival of C3 grasses

Less dramatic results on C4 grasses (but requires lower rates)

Altering Plant Competition Through Fertilization

Grasses

• Nitrogen favors C4 over C3

Grass/Legume

• High N stimulates grass and reduces legume production

• High phosphorus stimulates legume and reduces grass production

High, annual inputs of N may favor C3 annual grasses (i.e.– WEEDS!), and can be costly

Alternative approach:

• Match the plants to the existing soil nutrients, let succession improve the site over time

Fertilizing Wildlands: Pitfalls