����������� 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.

 

 

Table 1. Nitrogen fertilizer recommendations in pumpkins��

������������� (and related crops).z

 

 

�������������������������� soil organic matter content (%)

 

< 2

2-9.9

10-20

>20

 

������� (lbs N/acre)

 

100-120�

80

60

30

 

 

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).�

 

 

 

Table 2.� Optimum soil test levels for P and K in

�������������� pumpkins and related crops.

 

 

soil type

soil P1

soil K

 

 

 

� (lbs/acre)

 

 

loam, silt, clay

60-75

250-350

 

 

sands

60-75

200-300

 

 

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.

 

 

Table 3.� Phosphorus fertilizer requirements (P2O5) in pumpkins for various levels of soil P fertility

 

 

 

expected yield level

 

 

P1 soil test

maximum

95%

90%

 

 

�(lbs P/ac)

(lbs P2O5/ac)

 

 

100

� 0

� -

�-

 

 

� 90

�30

� -

�-

 

 

� 80

�60

�� 0

�-

 

 

� 70

�90

� 20

�-

 

 

� 60

120

� 50

� 0

 

 

� 50

150

� 80

� 30

 

 

� 40

180

110

� 60

 

 

� 30

210

140

� 90

 

 

� 20

240

170

120

 

 

� 10

270

200

150

 

 

P �maintenance� level (~ 50 lbs P2O5/acre)

 

 

 

 

 

 

 

 

 

 

 

Table 4. Potassium fertilizer requirements (K2O) in pumpkins for various levels of soil K fertility

 

 

 

 

expected yield level

 

 

K soil test

maximum

95%

90%

 

 

�(lbs K/ac)

(lbs K2O/ac)

 

 

 

 

 

 

 

 

400

� 60

� -

�-

 

 

300

150

� 60

�-

 

 

280

160

� 70

� 10

 

 

260

180

� 90

� 30

 

 

240

200

110

� 40

 

 

220

210

120

� 60

 

 

200

230

140

� 80

 

 

180

250

160

� 90

 

 

160

260

170

110

 

 

140

280

190

130

 

 

120

300

210

140

 

 

100

310

220

160

 

 

�80

330

240

180

 

 

�60

350

260

190

 

 

�40

360

270

210

 

 

 

 

 

 

 

 

K �maintenance� level (~ 125 lbs K2O/acre)