Corn: Phosphate and Potash

Excerpt from Agronomy Guide for Field Crops (Chapter 3)

Order OMAFRA Publication 811: Agronomy Guide for Field Crops

Table of Contents

1. Introduction
2. Seed Placed Fertilizer
3. Maximum Safe Rates of Fertilizer
4. Updates on Corn: Phosphate and Potash
5. Related links...

Introduction

Adequate phosphorus and potassium are necessary for optimum corn growth and yield, although the response to these nutrients is not as evident as with nitrogen. Phosphorus deficiency does not show any obvious symptoms, although phosphorus-deficient plants will be stunted and may have a darker green or purplish colour (see Plate 1). Purple leaves may also be an indication of cool weather stress or root injury (see Plate 3). Potassium deficiency symptoms appear on the lower leaves of the plant first, showing as yellowing and browning beginning at the tip and proceeding back along the outside margin of the leaf (see Plate 1 and Plate 4). Both of these nutrients will exhibit "hidden hunger," where yields are reduced by a deficiency of one or both of these nutrients even though no deficiency symptoms are visible.

Plate 1. Colour Plates Guide to Nutrient Deficiency Symptoms. Reprinted with permission of the Saturday Evening Post © 1957 (renewed) BFL&MS, Inc.

Plate 3. Purple corn. Purple leaves on corn caused by cool weather stress or root injury. This is not usually an indication of phosphorous deficiency.

Plate 4. Potassium deficiency shows up on lower leaves first, as yellow and browning at the leaf tip, and proceeds back along the margin of the leaf.

Phosphate and potash recommendations for corn are presented in Table 3-21. Phosphate and Potash Recommendations for Corn Based on OMAFRA-Accredited Soil Tests.

For information on the use of this table or if you do not have an OMAFRA-accredited soil test, see the section Fertilizer Recommendations.

Where soil tests indicate that large amounts of phosphorus and potassium are required, the major portion may be broadcast and incorporated in the fall or spring. However, where soil tests show a requirement for these nutrients, a fertilizer containing nitrogen (preferably in the ammonium form) and phosphorus, or nitrogen, phosphorus and potassium should be applied as a starter at planting. All of the phosphorus and some of the potassium may be applied in a band 5 cm (2 in.) to the side and 5 cm (2 in.) below the seed (see Table 2-30. Maximum Safe Rates of Nutrients).

Seed Placed Fertilizer

Fertilizers to be applied with the seed should contain nitrogen (in the ammonium form), must be low in salt and must not contain either urea or diammonium phosphate (see Table 2-30. Maximum Safe Rates of Nutrients). They must also be distributed uniformly to avoid toxicity to the germinating seed. Application of more than 15 kg P₂O₅/ha (13 lb P₂O₅/ac) with the seed (in 75-cm (30-in.) wide rows) is not recommended.

Maximum Safe Rates of Fertilizer

Applying too much fertilizer to corn may result in crop injury, either from excessive salts or ammonia. The more concentrated the fertilizer, and the closer it is to the seed, the greater the risk of crop injury and the lower the safe rate. Maximum safe rates are given in Table 2-30. Maximum Safe Rates of Nutrients. Note that slight reductions in crop growth and yield are possible with these application rates under adverse weather conditions.

Updates on Corn: Phosphate and Potash

• Phosphorus Requirement Table - Field Crops
• Potassium Requirement Table - Field Crops

Related links...

• Corn
• Soil Fertility & Crop Nutrition

| Top of Page |