����������� N-P-K Fertilizer Requirements
and Recommendations in Pumpkins and Related Crops
����������������������������������������������� ������������ (J.M. Swiader)
1.� Nitrogen fertilization recommendations
Due to the various physio-chemical
transformations and mobility of N in most soils, chemical tests for
plant-available soil N can be highly inaccurate and misleading.� Subsequently, fertility recommendations for
N in pumpkins are not based on soil N tests, but rather are based primarily on
crop yield potential, with adjustments made for soil organic matter
content.� In Table 1, N fertilizer
recommendations are for a crop yield potential of 15-25 tons/acre, a relatively
high but achievable yield level.
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Table 1. Nitrogen fertilizer
recommendations in pumpkins�� ������������� (and related crops).z |
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�������������������������� soil organic matter content (%) |
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<
2 |
2-9.9 |
10-20 |
>20 |
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������� (lbs N/acre) |
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100-120� |
80 |
60 |
30 |
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zfor a yield goal of 15-25 tons/acre |
On sandy soils, and other soils with less
than 2% organic matter, it is common practice to split the N application, with
1/2 the N applied preplant, and 1/2 sidedressed when vines run.�
If the previous crop was soybean, a
credit of 30-40 lbs N/acre can be taken.�
If the prior crop was a legume vegetable, such as green bean or peas, a
credit of 20 lbs N/acre can be taken.�
However, in both cases, no credit should taken if pumpkins are to be
grown on sandy soils.� For each ton of
solid dairy or cattle manure applied, N recommendations can be reduced 3-4
lbs/acre.� If liquid sources of dairy or
cattle manure are used, subtract 10 lbs N/acre for each 1000 gallons/acre of
material applied.� However, in no case
should amounts of manure in excess of N fertilizer requirements be applied.
2.� Phosphorus (P) and potassium (K) fertilization
recommendations
P and K soil test levels.� As regards P and K
fertility requirements, pumpkins and winter squashes are classified as
demand-level �5� crops, which means they have a relatively high demand for P
and K.� Unlike N, however, P and K
fertilizer recommendations are based on the levels of plant-available nutrient
in the soil.� Optimum soil test levels
of exchangeable P and K for pumpkins are shown in Table 2 (next page).�
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Table 2.� Optimum soil test levels for P and K in �������������� pumpkins and related crops. |
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soil type |
soil
P1 |
soil
K |
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� (lbs/acre) |
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loam, silt, clay |
60-75 |
250-350 |
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sands |
60-75 |
200-300 |
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P and K fertilizer recommendations.�
When P and K soil tests are in the optimum range, P and K fertilizer
recommendations are set to a rate approximately equal to the amount removed in
the harvested part (pumpkin fruit) of the crop.� This is known as the �maintenance� level and is roughly equal to
10 lbs P/acre and 105 lbs K/acre.� Based
on these totals, and converting P and K to their respective oxide equivalents
(and increasing the P requirement 50% to account for fixation by soil
particles), the fertilizer maintenance requirement (FMR*) for P and K in
pumpkins for a yield goal of 20-25 tons fruit/acre calculates out to approximately
125 lbs K2O/acre and 50 lbs P2O5/acre.
When soil test results are below the
optimum range.� Additional P and K is
added in with the maintenance P and K level.�
Conversely, when soil test results are above the optimum range, P and K
fertilizer recommendations are reduced to approximately 1/4 to 1/2 the
maintenance levels.� These calculations
are factored in to the P and K fertilizer recommendations in Tables 3 and 4,
respectively.� The recommendations in
each table are based on a fruit-yield potential of 20-25 tons/acre, for plant
population densities of 1,850-4,500 plants/acre.� Note; soil test results are expressed in lbs/acre, while
fertilizer recommendations are given as P2O5 and K2O
equivalents.
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Table 3.� Phosphorus fertilizer requirements (P2O5)
in pumpkins for various levels of soil P fertility |
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expected
yield level |
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P1 soil test |
maximum |
95% |
90% |
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�(lbs P/ac) |
(lbs P2O5/ac) |
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100 |
� 0 |
� - |
�- |
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� 90 |
�30 |
� - |
�- |
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� 80 |
�60 |
�� 0 |
�- |
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� 70 |
�90 |
� 20 |
�- |
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� 60 |
120 |
� 50 |
� 0 |
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� 50 |
150 |
� 80 |
� 30 |
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� 40 |
180 |
110 |
� 60 |
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� 30 |
210 |
140 |
� 90 |
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� 20 |
240 |
170 |
120 |
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� 10 |
270 |
200 |
150 |
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P �maintenance� level (~
50 lbs P2O5/acre) |
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Table 4.
Potassium fertilizer requirements (K2O) in pumpkins for various levels of soil K
fertility |
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expected
yield level |
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K soil test |
maximum |
95% |
90% |
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�(lbs K/ac) |
(lbs K2O/ac) |
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400 |
� 60 |
� - |
�- |
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300 |
150 |
� 60 |
�- |
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280 |
160 |
� 70 |
� 10 |
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260 |
180 |
� 90 |
� 30 |
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240 |
200 |
110 |
� 40 |
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220 |
210 |
120 |
� 60 |
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200 |
230 |
140 |
� 80 |
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180 |
250 |
160 |
� 90 |
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160 |
260 |
170 |
110 |
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140 |
280 |
190 |
130 |
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120 |
300 |
210 |
140 |
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100 |
310 |
220 |
160 |
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�80 |
330 |
240 |
180 |
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�60 |
350 |
260 |
190 |
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�40 |
360 |
270 |
210 |
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K �maintenance� level (~
125 lbs K2O/acre) |
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