Agriculture Reference
In-Depth Information
Nitrogen.
The nutrient most often deficient in orchards is nitrogen, for three
reasons: First, nitrogen is needed in greater amounts than any other miner-
al nutrient. Second, nitrogen is not derived from the mineral portion of the
soil, coming instead from the atmosphere by way of nitrogen-fixing plants
and microorganisms. Third, nitrogen is negatively charged, as are soil and
organic matter particles. Rather than binding to these particles like Ca or
++
K , nitrogen is repelled and washes from the root zone or volatizes into the
+
atmosphere.
Although nitrogen is essential and needed in large amounts, too much
nitrogen forces excessive, lush growth that is highly susceptible to damage
from pests and diseases and creates dense canopies that reduce air move-
ment, further increasing disease problems. Excess nitrogen also delays fruit
crop bearing; reduces flower bud and fruit formation; results in large, soft,
poorly colored fruits; and creates excessive, erect shoots, thereby increasing
pruning requirements and complicating training.
In orchards that are transitioning to organic and in newly planted organic
orchards, nitrogen deficiency can be severe and often limits tree survival and
health. Proper site preparation, combined with careful orchard floor manage-
ment and supplemental nitrogen fertilizers, should prevent most nitrogen de-
ficiencies from developing.
Research has demonstrated that organic apple orchards with low, al-
though acceptable, amounts of nitrogen have better crops and healthier
trees than those orchards with high, although still acceptable, amounts of ni-
trogen. The amount of nitrogen needed depends on the crop and variety. In
apples, for example, 'Stayman', 'Turley', 'McIntosh', 'Jerseyred', 'Gravenstein',
'Starr', 'Summer Pippin', and 'Britemac' require less nitrogen than 'Red Deli-
cious', 'Rome Beauty', 'Golden Delicious', and 'Jonathan'.
Potassium.
Potassium is abundant in many soils across North America. De-
ficiencies can arise in orchard production because some fruits are relatively
rich in potassium and large amounts of the nutrient are transported off-site
in the harvested fruits. Potassium, although often considered rather immob-
