incorporated during tillage, is best used to increase
usually called starter fertilizer, may be a good idea even
the nutrient level of the bulk of the soil. It is especially
in warmer climates when planting early. It still might be
useful to build P and K when they are very deficient.
cool enough to slow root growth and release of nutrients
Broadcasting with incorporation is usually done in the
from organic matter. Including N as part of the starter
fall or in spring just before tillage. Broadcasting on top
fertilizer appears to help roots use fertilizer P more
of a growing crop, called topdressing, is commonly used
efficiently, perhaps because N stimulates root growth.
to apply N, especially to crops that occupy the entire soil
Starter fertilizer for soils very low in fertility frequently
surface, such as wheat or a grass hay crop. (Amendments
contains other nutrients, such as sulfur, zinc, boron,
used in large quantities, like lime and gypsum, are also
or manganese.
broadcast prior to incorporation into the soil.)
Splitting N applications is a good management
There are various methods of applying localized
practice—especially on sandy soils, where nitrate is easily
placement of fertilizer. Banding small amounts of
lost by leaching, or on heavy loams and clays, where it
fertilizer to the side and below the seed at planting is a
can be lost by denitrification. Some N is applied before
common application method. It is especially useful for
planting or in the band as starter fertilizer, and the rest
row crops grown in cool soil conditions—early in the
is applied as a sidedress or topdress during the growing
season, for example—on soils with high amounts of sur-
season. Although unusual, sometimes split applications of
face residues, with no-till management, or on wet soils
K are recommended for very sandy soils with low organic
that are slow to warm in the spring. It is also useful for
matter, especially if there has been enough rainfall to
soils that test low to medium (or even higher) in P and
cause K to leach into the subsoil. Unfortunately, relying
K. Band placement of fertilizer near the seed at planting,
on sidedressing N can increase the risk of reduced yields
croP vALue, fertILIzer costs, And fertILIzer rAtes
The cost of N fertilizer is directly tied to energy costs, because so much energy is used for its manufacture and transport. The costs of other fertilizers are less sensitive to fluctuating energy prices but have been increasing, nevertheless. Use of fertilizers has increased worldwide, and dwindling global reserves combined with the increase in fuel and other input costs to manufacture them have recently led to large price increases.
Most agronomic crops grown on large acreages are worth around $400 to $1,000 per acre, and the fertilizer used may represent 30% to 40% of out-of-pocket growing costs. So, if you use 100 pounds of N you don’t need, that’s perhaps around $65/
acre and may represent 10% or more of your gross income. Some years ago, one of the authors of this book worked with two brothers who operated a dairy farm in northern Vermont that had high soil test levels of N, P, and K. Despite his recommendation that no fertilizer was needed, the normal practice was followed, and N, P, and K fertilizer worth $70 per acre (in 1980s prices) was applied to their 200 acres of corn. The yields on 40-foot-wide, no-fertilizer strips that they left in each field were the same as where fertilizer had been applied, so the $14,000 they spent for fertilizer was wasted.
When growing fruit or vegetable crops—worth thousands of dollars per acre—fertilizers represent about 1% of the value of the crop and 2% of the costs. But when growing specialty crops (medicinal herbs, certain organic vegetables for direct marketing) worth over $10,000 per acre, the cost of fertilizer is dwarfed by other costs, such as hand labor. A waste of $65/acre in unneeded nutrients for these crops would cause a minimal economic penalty—assuming you maintain a reasonable balance between nutrients—but there may also be environmental reasons against applying too much fertilizer.
211
Building SoilS for Better CropS: SuStainaBle Soil ManageMent