Nutrient Management Research Database

Abstract

Fertilizer can be managed more precisely when both the total nutrient demand and thedaily rate of nutrient accumulation of the crop are known. The results of two studies arepresented for high-yielding irrigated potatoes grown in Minnesota and in Oregon. Closelymatching nutrient availability with crop demand is essential for producing profitable yieldsof high quality potatoes, while minimizing unwanted nutrient losses to the environment.

Summary

Nitrogen

Approximately two-thirds of the total plant N is accumulated in the first few months following planting. There-fore, an adequate availability of N must be maintained in the root zone to support this rapid uptake. This is not a simple task,since excessive early season N can increase the susceptibility to brown center, hollow heart, and delays in maturation, while excessive N during the late season can reduce the specific gravity of the tuber and the skin set. Petiole testing is frequently useful for monitoring N availability and determining the need for supplemental fertilization.During the time of maximum growth during the midsummer, the plants accumulated up to a maximum of 7 lb N/A/day.

This large amount of N can come from N already in the soil,
N released from organic matter, N in the irrigation water, or
from fertilization. Since yield and quality suffer when N is
over- or under-supplied, close monitoring of the plant N status
is recommended.

Phosphorus

The rate of plant P uptake generally peaks
during the middle of the growing season, with a daily demand
of between 0.4 and 0.9 lb P/A/day depending on the variety
and location. The amount of P present in the soil solution at
any time is generally low and is regulated by the buffering
capacity of the particular soil. Each soil has a different capacity to replenish the roots with soluble P from mineral and
organic sources.

When P concentrations are inadequate to meet peak
demands, tuber size and yield are diminished. Fertilizer P is
generally applied prior to planting based on soil tests, but monitoring petiole P concentrations is also common for determining
the need for additional mid-season P. Sprinkler application of
soluble P can be effective for supplementing the P supply if
active roots are very near the soil surface. With a full plant
canopy, potato root density will typically be high near the soil
surface. This is important since P fertilizer applied through
the sprinkler system rarely moves more than a few inches into
the soil. A week or two may be required before a response to
added P is measurable, so applications should be made in
advance of possible deficiencies.

Potassium

Potatoes typically accumulate more K than
any other nutrient. During the peak uptake period, daily accumulation rates can exceed 5 to 14 lb K/A/day, and over 600
lb K/A was accumulated by the crop. An adequate supply of
K can help prevent a variety of tuber quality defects, such as
blackspot bruising, low specific gravity, and poor storage quality. Excessively high K may also be detrimental and should be
avoided. Potassium application rates should be based on soil
testing and crop removal rates.
The majority of K fertilizer is usually applied prior to
planting. At typical application rates, there is no consistent
difference between K sources. At high K application rates,
K2SO4 or a blend of KCl and K2SO4 may tend to produce slightly
larger potato yields with higher specific gravity compared with
KCl alone. The timing and rate of application, as well as the
product blend, are important considerations when making K
applications to potatoes.

Potatoes (cv. 'Russet Burbank') were fertilized with a total of 325 lbs N, 220 lbs P2O5, and 240 lbs K2O per acre. Preplant fertilization accounted for 16&, 45%, and 95% of these rates.

Plants were harvested at 6 times in the season. Plant tissue was analyzed for dry matter and nutrient content.

A maximum daily growth rate was measured 90-100 days post planting, which occurred 20-30 days after the peak nutrient demand.

Nutrient deficiency during the period of maximum uptake would have limited the growth rate during the period of maximum growth.

This result show the importance of timing fertilization to maximum crop demand.