Fertilize Pastures Now For Fall Growth

Adequate fertilization can increase pasture forage production between .5 and 2 tons per acre.

Published on: Jul 25, 2013

By Dan Undersander

With the general forage shortage this year, producing additional forage by all available means will benefit most farms. One of the vastly under-appreciated forage sources is pasture. Pastures that are not fertilized will generally produce good growth in the spring and then run out of nutrients and, though remaining green through the fall, will produce little late-season tonnage. Adequate fertilization in the fall can easily increase pasture forage production from 0.5 to 2 tons per acre.

In addition to nitrogen the major minerals needed by livestock that may be deficient in pasture forage are calcium, phosphorus, magnesium, potassium and sulfur.  Average pasture forage mineral levels are shown in table 1.

Fertilize Pastures Now For Fall Growth
Fertilize Pastures Now For Fall Growth

Soil test
Calcium content of forage increases as the legume content of the stand increases (table 1). Calcium content is lower in grasses than legumes. This mineral is usually adequate in pasture and hay to meet the needs of lactating and growing cattle, though some grass pastures may not have sufficient calcium for animal needs.  Liming can add calcium to the soil in addition to raising soil pH to be more favorable to legumes.

Phosphorus content is similar across forage types but is higher in pastures than in hay crops.  Forage content of this mineral is usually adequate for lactating and growing cattle. Pastures with soils testing low or forage testing below 0.3% phosphorus may increase forage mineral content and plant growth if fertilized with 12 to 15 pounds per acre

Magnesium content in forage is higher when legumes are present. Magnesium is seldom deficient for pasture growth in the Midwest, however forage content of this mineral in grass forages can be marginal for lactating cows. High potassium and nitrogen levels can reduce availability of magnesium to cattle consuming the forage.

Potassium content is similar in grasses and legumes. Pasture forage for good yield are about 2.0% of dry matter for grasses and 2.5% for legume. Animals need potassium for milk production, maintenance of body fluids, nerve impulse transmission, muscle contraction, and the maintenance of enzyme systems. Little potassium is removed from the farm by milk or meat production. Most potassium is excreted in animal urine. So potassium will move from the pasture to wherever the animals urinate.

Sulfur fertilization of pastures was seldom needed in the past because pastures used to receive enough sulfur in the acid rain.  Since environmental standards have reduced acid rain, many pastures now need sulfur fertilization. Animals need sulfur for rumen bacterial growth and protein synthesis.  Each ton of forage needs about 5 pounds per acre sulfur.

August. 1 is a good time to fertilize pastures to maximize fall growth.  By then any spring applied nitrogen has been used to produce previous forage crops. Mineral deficiencies for good growth are often may be  indicated by green rings of grass growth around manure in the pasture.  Nitrogen and other needed nutrients can be applied at the same time. 

All pastures with less than 40% legume need about 50 pounds per acre nitrogen for fall growth.  Soil and tissue testing can tell if any other minerals are lacking for good pasture growth. Nutrients, other than phosphorus, move quickly into the soil and are taken up by the pasture plants. Animal mineral needs above those shown in table 2, are most economically met with additional animal mineral supplement.

Undersander is a University of Wisconsin Extension and research forage agronomist.

Table 1. Mineral content of pasture forages

 

Calcium

Phosphorus

Magnesium

potassium

Sulfur

Pasture type

% Dry Matter

Grass

0.43 ± .22

0.38 ± .08

0.22 ± .05

3.38 ± .71

0.32 ± .07

Mixed mostly grass

0.75 ± .22

0.38 ± .08

0.26 ± .05

2.76 ± .71

0.33 ± .07

Mixed mostly legume

1.99 ± .22

0.35 ± .08

0.29 ±.05

2.65 ± .71

0.30 ± .07

Data from Edward B. Rayburn, WV Extension Specialist

 

Table 2. Pasture forage tissue mineral levels needed for good growth.

Nutrient

--% of DM--

Nitrogen

2.5 to 4.0

Phosphate (P2O5)

0.25 to 0.45

Potash (K2O)

2.25 to 3.40

Calcium, legume

                grasses

0.70 to 2.50

0.30 to 0.50

Magnesium

0.25 to 0.70

Sulfur

0.25 to 0.50

 

-- ppm --

Boron

25 to 60