\ I f POTATO INVESTIGATIONS LABORATORY
Mimeo Report POL 64-2 October 1, 1963
LIMING AND FERTILIZATION OF POTATOES
D. R Hensel, Assistant Soils Chemist
Reasons for Liming
Most virgin and cultivated sandy soils in the Hastings area are naturally acid
', have a lov pH. This is due to the nature of the parent material from which they
are formed and also to the soil-forming process in the humid climate which leai.hed
out the basic elements such as sodium; potassium, calcium and magnesium. Periodic
iim'-ng as indicated by a pH test is necessary to replace the calcium and magnesium
'ken: up by the potato crop and lost by leaching, neutralize the acidifying effect
.' fertilizers, make the nutrients in the soil and fertilizer more available to the
plants reduce the leaching loss of ammonical nitrogen by heavy rains, reduce the
availability of aluminum, and improve structure of soil. Liming also increases
nitrification which is a precautionary measure against nutritional leaf roll of
Soil samples for pH determinations in indicating liming requirements should be
collected on old land in the fall immediately after the summer cover crop has been
turned under and on new land as soon as the land has been cleared and leveled but
before the cover crop is planted. However, if nutritional leaf roll has occurred in
potatoes grown on old land, the soil should be sampled in the spring soon after the
potatoes have been dug. In all cases, lime should be applied as soon as possible
after the soil samples have been collected and the pH determined in order to provide
additional time for the lime to react.
It is extremely important to obtain a representative soil sample from the field
being sampled. A tube, auger, or spade may be used to collect the sample. Each
type of soil should be sampled separately by taking from eight to ten plugs or
slices of the surface six inches over the area and mixing them together to make one
sample. Several such samples should be taken from each field, usually about one or
two per ten acres.
Soil Acidity (pH)
A soil pH of 5.5 is currently recommended for growing potatoes in the Hastings
section. Potatoes will grow at a higher pH than is recommended for them, but gen-
erally scab is less troublesome .n acid soils below pH 5.5. A pH of 6.0 or higher
should be avoided because certain microelements such as boron, copper, manganese and
zinc become less available on most soils at high pH levels. For average sandy soils
lime may be used on the basis of 200 pounds per acre of ground limestone (dolomite
or h:bh calcic limestone) or 120 pounds per acre of hydrated lime for each 0.1 pH
Kind of Lime
Dolomite is preferred for general use to maintain proper soil pH for potatoes
because of the magnesium it contains. High calcic limestone is preferred where more
rapid correction of acidity is desirable. Hydrated lime gives still faster correc-
tion of acidity but is more costly and difficult to use. It may be used in emergen-
cies where liming of new lands or those subject to leaf roll has been delayed until
The current fertilizer recommendations for potatoes in the Hastings area is
2500 pounds per acre of 6-8-8 or its equivalent. For example, 2,200 pounds of 7-9-9
would contain about the same amount of plant nutrients as 2,500 pounds of 6-8-8.
Higher analysis fertilizer are generally cheaper per unit of plant material.
Contents of Fertilizer
1. Nitrate Nitrogen.- For average conditions, one-fifth of the nitrogen should
be nitrate nitrogen. The fertilizer tag would then show 1.2 percent nitrate nitrogen
in a 6-8-8 fertilizer, or 1.4 percent in a 7-9-9 fertilizer. For new lands or
here nutritional leaf roll has been prevalent, the nitrate can be increased up to
one-third of the total nitrogen present.
2. Insoluble Nitrogen.- More than one unit of nitrogen from insoluble sources
generally can not be economically justified for use in potato fertilizer. Potato
season in the Hastings area is short, and the largest part of the growing season is
during cool weather. Breakdown of insoluble nitrogen material into an available
form would be slower during the cool weather.
3. Phosphorus.- Recommended rates of 200 pounds per acre of P205 are supplied
by 2,500 of --8-8. On newly cleared land, the phosphorus rates should be doubled.
This is shown by the data in Table 1.
Table 1. Yield of Size A Potatoes on Old and Newly Cleared Soil Fertilized
With Various Amounts of Phosphorus
Yields in Cwt./A
Lb. P205/A Old Soil Newly Cleared Soil
1960 1961 1960 1961
0 160 297 24 75
50 154 306 65 162
100 182 310 90 196
200 210 326 121 210
400 198 338 157 242
Use of high phosphorus ratios in the basic fertilizers together with sidedress-
ing of nitrogen and potassium, gave no reduction in yield at Potato Investigations
4. Potash and Chlorides.- Not more than one-half of the potash should be de-
rived from muriate (chloride) of potash, but the lower the better if harvest is to
be delayed beyond the average digging dates or if a dry season is encountered.
5. Magnesium.- The fertilizer should contain 2 percent soluble magnesia (MgO).
1. Leaf roll- Land which has shown nutritional leaf roll should be sidedress-
ed with approximately 30 pounds per acre of nitrate nitrogen or its equivalent.
2. Light Soils- Yields may be increased by applying 30 pounds of nitrogen
per acre about 40 days after planting. Similar sidedressing on dark sandy soils is
unlikely to prove beneficial unless heavy leaching rains have occurred early in the
growing season. Foliar sprays for supplemental fertilizer are not recommended at
the present time.
1. Hayslip, N. C. and Howard W. Burdine. Results of potato fertilizer experiments
in the Indiantown and Palm City area. Fla. Agr. Exp. Sta. Indian River
Field Lab. Mimeo Rpt. 59-3. April 28, 1959.
2. Hensel, D. R. Phosphorus Fertilization of Potatoes on Ona Fine Sand. Soil
Crop Sci. Soc. Fla. Proc. 22: 130-134. 1962.
3. Volk, G. M. and Nathan Gammon, Jr. Effect of liming and fertilization on yield
and correlation of nutritional leaf-roll of Irish potatoes. Fla. Agr.
Exp. Sta. Bul. 504. 1952.