Preparing or Upgrading Your Orchard Site - Growing Organic Orchard Fruits - page 128

Each 1 percent of soil organic matter adds up to about 20 pounds of
plant-available nitrogen per year. Soil temperatures and moisture affect the
actual amount of nitrogen released, which will be less in cold, wet soils. In
reasonably well-drained soils, organic matter concentrations of 5 percent
or more should provide sufficient available nitrogen for planting tree fruit
crops. Additional nitrogen may be needed later, as the trees mature and be-
gin bearing fruit.
Physical signs of low soil nitrogen are stunted and yellowish crop plants
and weeds on the planting site. If crop and weed growth are lush and vigor-
ous, and leaf colors are normally green, nitrogen deficiency should not be a
problem for your newly planted trees.
Ways to Add Nitrogen
Composts, manures, alfalfa pellets, alfalfa meal, soybean meal, feather meal,
fish emulsions and meal, and cottonseed meal provide moderate to slow ni-
trogen release into the soil. These products, their mineral contents, and their
uses in organic orchards are described in chapter 8 ➔ . If you need a quick
fix of nitrogen just before or at the time you plant your trees, nitrogen from
dried blood (blood meal) (12 percent N) is available almost immediately.
Blood meal must be used with care as it can damage plants when too much
is applied.
Sodium nitrate (also known as Chilean nitrate) (16 percent N) provides
nitrogen rapidly, but it is discouraged in organic crop production because of
its high sodium content (26 percent Na), which can damage sensitive plants
and contaminate groundwater. Certified organic growers should check with
their certifying organization before using sodium nitrate, as some organiza-
tions limit sodium nitrate to no more than 20 percent of the total nitrogen
applied, and some certifying organizations prohibit its use altogether.
Nitrogen-fixing green manure crops can help get your trees off to a good
start. Plow them under the year before planting. Clovers, beans, and peas
are typically used to fix nitrogen as green manure crops. Alfalfa establishes
more slowly than these crops and, depending on your location, is best left in