Core cultivation and fertilizer

Agronomists and turf managers have made remarkable strides in developing and improving natural grass playing fields for soccer, rugby, football, lacrosse, field hockey and baseball. Virtually any athletic field where heavy traffic occurs will benefit from sound management. The present surfaces are far more advanced than those that existed prior to the era of the first generation of artificial turf. Still, communities and schools across the United States continue to endure a never-ending plight of muddy, bare sports fields with hard surfaces. Maintaining a healthy, natural field without breaking the budget requires going back to the basics of turf management.

Compaction is the enemy

Most sports fields begin the season with a solid cover of green turf. Northern turf is usually ryegrass, bluegrass/ryegrass mixtures or turf-type tall fescue. Southern turf is usually hybrid or common bermudagrass. No single variety of turf is immune to wear and tear from daily use, and drought conditions only make the situation worse.

Compaction is the bane of nearly all turf surfaces, but compaction is not always due to human activity. Just plain wetting and drying of clay-type soils causes a hardness that acts as a barrier to water percolation and air movement. Pounding, cleated foot traffic common to sports fields hastens compaction of all soil types. This traffic, combined with the ripping and tearing from game activities, increasingly reduces turf cover as the season progresses.

Core cultivation is the best defense

Sports fields should be core cultivated (aerified) at least twice a year: once in late summer or early fall and again in mid to late spring. At these times, the weather is more conducive to root formation and regeneration of vegetative cover. The cores can be removed or broken up by dragging them back over the surface several times. By reincorporating the same soil into the holes, turf managers save on the cost of topdressing or sand. Care should be taken not to incorporate straight sand into clay soil as the distinctly different layers act as barriers to percolation. While not as functional as core cultivation, solid tines can also be used to improve air and water movement. Topdressing following solid tine use is a good consideration.

Nurturing the soil

Core cultivation is an important cultural practice to use in growing superior turfs for sports fields. Timely slow-release fertilizer applications also have a direct benefit to the grass. Soil microorganisms use nutrients to enrich the life of the soil.

A healthy turf environment, one that provides air, moisture and food, will support an active microbial population.

A well-nourished soil has billions of both single-celled and multicelled organisms whose primary function is to break down decay-resistant plant tissue (thatch) and soil organic matter. In the process, they create humus, which helps to keep the soil porous and serves as the medium for banking and exchanging nutrients for plant utilization. They also extract and make insoluble elements from soil complexes soluble for later plant uptake.

Football players pounding the field with their cleats increase compaction.

Under adverse conditions, such as compacted soils that are often too wet or too dry, the numbers of microorganisms decline drastically. Remember, soil micro-organisms require the same environment as you do: air, moisture and food.

Fertilizers and microbial activity

Ureaform and methyleneurea fertilizers are unique among nitrogen sources. The carbon (C) in the nitrogen-carbon linked polymers provides the energy microorganisms need to exist and multiply, while the nitrogen (N) is their food source. Like higher life forms, carbon is necessary for energy. Nitrogen is the chief component of proteins and amino acids. The only other fertilizers that provide useful carbon are natural organic materials with C to N ratios rarely narrower than 12 to 1. The C to N ratios of ureaform (UF) and methyleneurea (MU) are approximately 1-to-1. Decomposer microbes use both elements to fulfill immediate and long-term nutritional and energy requirements.

As microorganisms carry on their life processes, they return nitrogen to the soil in the ammonium (NH4+) form. Even in poor soils there is an inherent population of beneficial microorganisms that exist symbiotically with living plants. Core cultivation, and the use of UF and/or MU fertilizers will enhance their numbers. The result is a complexity of benefits, chiefly a deeper and more vigorous root system.

Soil microorganisms require lesser amounts of other nutrients, many of which are available in soil organic matter and plant residue. Phosphorus is essential to the chemical transfer of energy in all living cells. Occasional applications of phosphorus can be as important to the health of microorganisms as they are for turf and other plants.

Fertilizer release rates and solubility

Ureaform and methyleneurea fertilizers are both slow-release N sources. Rates of these fertilizers are governed by the percentage of water insoluble nitrogen (WIN) and sparingly soluble nitrogen in each. Ureaform 38-0-0 is marketed under the trade name Nitroform by Nu-Gro Technologies, Inc. It contains over two-thirds water insoluble nitrogen, with most of the remainder being sparingly soluble (occluded). Ureaform is highly resistant to leaching, even in sandy soils under heavy rainfall. It releases nitrogen over eight or more months of the growing season. Nitroform is particularly well suited for use in seedbeds, directly under sod and for soil incorporation following core cultivation. It is widely used in container nursery production.

Nutralene methyleneurea 40-0-0 contains approximately one-third WIN and two-thirds sparingly soluble nitrogen. Nitrogen release is initiated by hydrolysis, followed by microbial action to provide 12 to 16 weeks of color response without excessive growth. Both have low salt indexes, which means a reduced risk of phytotoxicity, even in the event of overapplication.

Seeding, fertilizing and core cultivation

Plant roots typically show a positive response when ureaform and phosphorus are placed directly in the rootzone. In established turf, the only way to accomplish this is to apply both materials directly after core aerification. Incorporate by dragging across the surface with the pulverized cores or other topdressing material. Slit-seeding following core cultivation will place even more of the seed and fertilizer in the soil and will help break up the cores. Caution should be taken if using more soluble or faster releasing nitrogen sources as root pruning and other phytotoxicity may occur.

Suggested rates for ureaform and phosphorus

Following core cultivation, apply 130 to 220 pounds of ureaform 38-0-0 per acre (3 to 5 pounds per 1,000 square feet) plus 2 pounds per 1,000 square feet of P2O5 equivalent in a phosphate fertilizer over the topdressing or pulverized core material. Then drag or brush to move the material into the holes. Note: Where dragging or brushing isn’t practical, it is still recommended that ureaform and phosphate fertilizers be applied after coring. Apply the higher rate of ureaform (5 pounds per 1,000 square feet) prior to the beginning of sports activity. This will help hasten recovery of damaged turf.

Potassium important for sports turf

Intensively managed turfgrass requires potassium at levels equal to or exceeding that of nitrogen. Potassium is vital in maintaining leaf and stem strength, and helps the plant defend itself against many causes of stress. Apply 6 to 8 pounds of actual K2O per 1,000 square feet on an annual basis. Use an NPK turf-grade fertilizer or any potassium fertilizer. Potassium sulfate has a lower salt index than muriate, KCl (potassium chloride), and is safer to apply in warm weather. Since potassium fertilizer is more soluble than phosphorous or ureaform, there is no advantage in soil incorporation. Bimonthly applications during the growing season will assist sports turf in recovery from wear and tear.

Sod and sodding

At certain times, all turf professionals need to push the panic button. Having a ready source of good sod has rescued many grounds managers from agony and despair. Consider allocating an acre or more of turf in a lesser-used area for emergency repairs to sports fields. Ureaform 38-0-0 will encourage rapid establishment of all varieties of turf from seed. Applied to the sod bed prior to laying sod, ureaform helps promote fast knitting and rooting.

When growing your own sod from seed, apply ureaform with phosphorus in a 2-to-1 ratio of N to P2O5 at the rate of 400 pounds ureaform per acre (150 pounds. N) for bluegrass and/or ryegrasses and bermudagrasses. Use half this rate for turf-type tall fescues. A solid cover will be established quickly, and additional nitrogen should not be necessary for 12 months.

In sod beds for all turf except tall fescue, apply 130 pounds ureaform per acre or 3 pounds per 1,000 square feet (1.14 pounds N per 1,000 square feet) in a 2-to-1 ratio of N to P2O5. Note: Phosphorus may be derived from DAP (diammonium phosphate), MAP (monammonium phosphate) or a straight super phosphate fertilizer. For tall fescue, use half this rate of ureaform nitrogen in a 1-to-1 N to P2O5 ratio.


For superior sports turf, grounds management practices can be economically and easily adjusted for maximum rooting. An enriched microbial population will encourage vigorous root activity and regeneration of vegetative cover in damaged areas. Again, why do we stress improved root systems? Roots have basically three functions: to anchor the plant, provide water and nutrient uptake and provide for carbohydrate storage.

Any improvement of the root system improves its functionality. Better roots equal better turf. Other points to consider include:

• Ureaform or methyleneurea fertilizers provide both nitrogen and energy-rich carbon for microbial utilization.

• Core cultivation improves air movement and water percolation in compacted soils.

• Apply ureaform and phosphorus following core cultivation to place nutrients directly in the rootzone where they will nourish both plants and microorganisms.

• Use ureaform and phosphorus in sod beds to hasten establishment and encourage rapid knitting and rooting.

• Make generous use of potassium to strengthen turf tissue and promote vigor.

Note: The rates for nutrients contained in this article are not recommendations. Consult your extension agent, turf specialist, university or other turf consultant prior to use of any fertilizer. Climate, turf type and intended use of the field will all vary the nutritional program. It is not possible to address every situation in these guidelines.

Residual release (feeding) for Nitroform or Nutralene are average times. No guarantee is implied.

B.J. Bilas is marketing manager/manager, field development for Nu-Gro Technologies, Inc., based in DeWitt, Mich. He has 31 years of experience in the agricultural and turf industries.