Date: December 13, 2001
Category: Agronomy Subject: Late-Fall Fertilization
Late-Fall Fertilization: Now would be a good time for
late fall fertilization. The benefit of a well-timed late season application
includes: good winter color, increased rooting, enhanced carbohydrate
reserves, and earlier spring green-up (without surge growth). Furthermore,
late fall applied nitrogen (N) can substitute for early spring fertilizer,
postponing the need for spring fertilization until around mid-May. The
unseasonably warm temperatures this fall have delayed (postponed) typical
start dates for late season fertilizer N. Generally, Thanksgiving is a
good calendar date for late fall fertilization. However, the above average
temperatures this fall have prolonged shoot growth activity later into
the fall period. Timing is critical to the success of late season N. Specifically,
active shoot growth at the time of late-fall applied N can encourage surge
growth (excess shoot growth) and increase winter kill, low temperature
disease, and freeze-stress injury. Late-fall applied N is not only dependent
on proper timing (after shoot growth ceases and before low-temperature
decline in color), but eary-fall fertilization (September) is also important
in ensuring good color through the fall period to maintain green, photosynthetically
active tissues. Good late-fall color afforded by early fall fertilization
is essential to maximizing the benefits of late-season N.
Nitrogen rates ranging from 1.0 to 1.5 pounds per 1,000 square feet can
be used in late fall using complete fertilizers with ratios (N-P205-K2O)
such as 4-1-2 or 3-1-2 (i. e., analysis such as 20-5-10 or 15-5-10, respectively).
Many N fertilizer sources are suitable for late season application including
water soluble N (i. e., urea) as well as most slow-release N (SRN) sources.
However, on sandy rootzones where the potential for nitrate leaching is
high, SRN sources such as coated nitrogen (SCU or polymer), IBDU, and
methyleneureas are recommended in late fall. At least 25 to 30% of the
total N should be derived from SRN to achieve the maximum slow-release
benefits. SRN fertilizers which release their N through microbial decomposition
and therefore are temperature dependent (i. e., natural organic), should
be avoided in late fall because soil temperatures are too cold for N release
to provide any of the benefits associated with late season fertilization.
