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Soil & Fertility


Soil

Deep sandy to loamy soil with a pH of 6.5 to 7.5 is ideal for early cucurbits. Heavier soils, while more productive, should be used for main season production. Most soils in Utah are suitable for the cucurbits provided they are well drained, fertile, and do not have a buildup of salt. Crop rotation is necessary. Remember that squash, pumpkins, and cucumbers are related to cantaloupe and watermelons and most insects and diseases are common to all cucurbits.

Most of the cucurbits are quite sensitive to herbicides in soil, so pay special attention to site selection if residual herbicides have been used in the past. Crop rotation is another important consideration. Other cucurbits should not be planted within at least two years of related crops (cucumbers, squash, melons, watermelon, pumpkins or gourds). Plant residue from these related crops serves as a host for plant diseases and insects that may infect or infest the next cucurbit crop. Plant residues from the prior crop should be completely buried at the bottom of the furrow to facilitate decomposition. A well-tilled field will help produce a smooth, fine seed bed for uniform planting and emergence. Several weeks before planting, prepare the field for planting. If soils have drainage issues, create 6-8 inch raised beds. A very loose, somewhat dry soil is ideal for transplanting to ensure good soil contact with the transplant root ball or seed.

Fertility

Prior to planting, have the soil tested to determine nutrient needs and deficiencies (Table 5.2). Soil sampling approaches, forms, test details, and interpretation can be accessed through the Utah State University Analytical Laboratories (www.usual.usu.edu). Organic growers find it is a good idea to incorporate composted organic matter before planting to sustain soil fertility. An initial application of 5 tons per acre of high quality compost of known nutrient analysis may be helpful. This can be broadcast over the whole field or banded and incorporated into the individual rows.

A common practice is to add ⅓ to ½ of the required nitrogen fertilizer and all the phosphorous and potassium prior to planting. This fertilizer is either broadcast or banded. In soils with high P and K levels, broadcasting all of the fertilizer is acceptable. This is done before plowing or disking, then worked into the soil during normal field preparations. Banding is a good method to ensure the fertilizer is near the plant and makes sense for crops like winter squash and pumpkins where wide row spacings are common. Fertilizer bands should be 3 inches beside and 3 inches below the seed or transplant to minimize salt injury during establishment. Often transplanted cucumbers and summer squash are “watered in” with starter fertilizer containing high P levels applied at one quarter to one half pint per plant. Starter fertilizer is applied in addition to the fertilizer that was broadcast or banded.

Table 5.2. Phosphorus (P2O5 ) and Potassium (K2O) for Cucumber, Pumpkin, and Squash based on soil test results.

Phosphorus Test Results Lb/ acre Potassium Test Results Lb/acre
0-14 100-150 0-74 100-150
15-29 70-100 75-149 50-100
30-45 40-70 150-199 25-50
46-60+ 0-30 200+ 0-25

Use the higher amount when soil test values are in the lower part of the range.

Nitrogen (N) – Up to 50 lbs. N/acre can be applied prior to planting. Higher rates of N at planting may cause seed or transplant establishment problems. An additional 50-100 lbs. N/acre is often applied in two applications, the first when vines begin to run and again around first flowering. Use the smaller amount if the site has added manure, compost or when cucurbits are grown after a legume crop (beans, alfalfa, etc.).