Maryland Department of Agriculture

Introduction

Nutrient management laws passed by the Maryland Legislature in 1998 require that turfgrass sod producers in Maryland participate in agriculture nutrient management programs. Major differences exist between the goals and practices of general agriculture and turfgrass production. The following information is intended to serve as a nutrient management guideline for the production of sod in Maryland in an efficient, timely, and environmentally sound manner.

The primary goal in most crops is to maximize yield in a manner that makes economic sense. The goals in sod production are substantially different. The primary goals in sod production are twofold: 1) producing turfgrass of sufficient quality that it is marketable, and 2) producing harvestable sod in the quickest manner possible.

Quality sod needs to be dense, relatively uniform, and free of weed, disease, and insect pests. Sod must also be harvestable, i.e., it must be sufficiently knit that it holds together when cut, can be rolled, can be transported, and can be unrolled and laid onsite without falling apart. A good nutrient management program is a major component of producing quality sod that is marketable.

For economic purposes, sod must also be produced in the most timely manner possible. The seasonal window for seeding cool season turfgrass species in Maryland to produce sod is relatively narrow. Seeding must be done from late summer through early fall if sod is to be harvestable before the prime seeding period is reached again the next year. Failure to produce harvestable sod within this timeframe means that sod production is on a two-year rather than a one-year cycle, which has serious economic consequences. Again, a good nutrient management program is critical in producing sod in an economically timely fashion.

Water Quality

Properly managed turfgrass has been shown to be an environmental asset. Water runoff is greatly reduced and water infiltration increased compared to most other

agriculture systems. Once turfgrass is established, soil loss is negligible. Runoff from established turf has compared favorably to forested land. Also, turfgrass is an organic matter producing system. Thus, little nitrogen (N) or phosphorus (P) is lost from turfgrass sites if sound nutrient management practices are followed.

Indeed, onsite monitoring and numerous research studies have shown that nutrient loss from turfgrass sites is very small. However, research has also shown that certain types of improper N applications on specific types of sites can result in excessive nitrate (NO3) leaching. This problem is very specific and has occurred as follows:

1. Very high rates of N were applied using soluble NO3-N containing fertilizers (such as ammonium nitrate [NH4NO3]),
2. The fertilizer was applied to dormant turf (such as bermudagrass during the winter),
3. Soils were predominantly sand, and
4. The sites had high water tables.

A sound turfgrass nutrient management plan shall take into consideration this set of conditions which can cause a potential problem.

Soil erosion from established turf is not a problem. However, from the time of soil preparation to the time seed has germinated and plants have become established, soil erosion can occur. Enhancing the rapidity of sod establishment, therefore, is an important factor in minimizing potential soil erosion. A sound nutrient management program is an important factor in enhancing rapid establishment and minimizing the potential for soil erosion.

Nitrogen Applications

Nitrogen fertility is of primary importance in producing quality sod in an economically timely fashion. Nitrogen has a major impact on both root and shoot growth rates. The density of sod, the ability to withstand the encroachment of weeds (thus also reducing the need for herbicide applications), the incidence of some diseases, the recovery from summer stress problems, and the length of time from seeding to harvestable sod are all highly dependent on adequate N.

Three major factors shall be considered in developing a N application plan:

1. What types of N should be applied,
2. How much N needs to be applied at seeding and during the year for production, and
3. When should N be applied.

Sources of N
A wide range of N-containing fertilizers are available to the sod producer. These fertilizers generally fall into one of two broad categories: 1) fertilizers that contain only soluble, quickly available N; and 2) fertilizers that contain some N in a slowly available form which is not immediately available for plant use.

Quickly available N-fertilizers contain NO3-N or NH4-N or both, which is soluble and readily available for uptake by turfgrass plants. Turfgrass uptake may occur within a few days with NO3-N fertilizer. Nitrogen uptake may begin within 7 10 days with NH4-N fertilizers, as NH4-N is converted to NO3-N in the soil. Nitrogen uptake by turfgrass roots is predominately in the NO3 form.

Leaching and runoff potential is much higher for NO3-N. Thus, where conditions exist that are conducive to leaching or runoff, fertilizers that contain significant amounts of NO3-N should not be used. These conditions include sandy sites (sands and loamy sands) with high water tables when turf is not actively growing, and sites that are highly sloped. Fertilizers high in NO3-N include NH4NO3, potassium nitrate, and calcium nitrate.

Slow release fertilizers contain significant amounts of N that is not immediately available for plant uptake. Examples of fertilizer sources that contain various amounts of slow release N include: sulfur coated ureas, polymer coated ureas, methylene ureas, ureaformaldehydes, IBDU, natural organics, and various types of sludge. Slow release fertilizers, while varying considerably in individual characteristics, typically provide more even turfgrass response, provide N over a longer period of time, and are less prone to N leaching and runoff as compared to soluble N fertilizers. The expense of slow release fertilizers makes their widespread use in sod production limited. Their use, however, should be considered on the aforementioned sites that are prone to leaching or runoff, and when N applications need to be made to turfgrass that is not in prime growing conditions.

Total N Requirements
Establishment - Whereas the annual N requirements vary somewhat with turfgrass species, particularly after the first year of growth, the N requirements at the time of seeding are rather uniform. It is recommended that up to 45 lbs. of readily available (soluble) N per acre be applied prior to seeding if fertilizer is broadcast. If fertilizer is incorporated deeper than 2 inches, then up to 90 lbs. of readily available N per acre may be applied and incorporated into the soil. Research would indicate, however, that there is no great advantage in sod production with the incorporation of N deeper than the surface 2 inches of soil.

If fertilizers are applied containing slow release N (water insoluble N [WIN]), no more shall be applied than that which provides the aforementioned rates of readily available N. For example, if a slow release fertilizer contains 50% WIN and the recommended application rate is 45 lbs. N per acre, then no more than 90 lbs. N per acre of this fertilizer should be applied. Also, the slow release N applied to the seedbed shall be factored into the first year's production applications of N.

Production Maintenance fertilizer applications for growing sod generally begin 4 8 weeks after turfgrass seed has germinated. The total annual N requirements for growing quality sod in a timely manner is dependent on many factors, including: turfgrass species, length of growing season, soil type, field fertility history, and the need for recovery from stresses caused by unusual weather or pest problems. However, the annual N requirements for the most common turfgrass species grown for sod in Maryland generally fall into the ranges listed in Table 1. If fertilizer containing slow release N was applied to the seedbed at or prior to seeding, the slow release fraction (WIN) shall be included in calculating the total N applied for production of the sod in the first year.

Timing of N Applications
The primary potential for N loss from turfgrass sites is when excessive rates of NO3- N is applied to turf that is not actively growing. Thus, most of the annual fertilizer requirement should be applied during periods of active shoot (leaf blades, rhizomes, stolons) or root growth.

The primary period for growth of warm season grass species (zoysiagrass, bermudagrass, buffalograss) is from mid-spring, after dormancy has broken, through mid- fall, when the first killing frost is experienced. Thus, N applications should generally be restricted to these periods; however, fertilizer that contains primarily NH4-N can be applied up to a month before dormancy is typically broken in the spring so that N is available for plant uptake at this time. Applications after September 1 are not generally recommended, due to the possible enhancement of winter-kill, particularly with bermudagrass. However, if bermudagrass has been overseeded with a cool season species, such as perennial ryegrass, up to 45 lbs. N/acre may be applied after September 1 to enhance its performance.

Cool season grasses have a much longer growth period. They can exhibit growth at virtually anytime during the year if moisture and temperature conditions are conducive. The prime periods for growth are typically from late winter through early summer, and from late summer through early winter. Research would indicate that 2/3 to of the total annual N should be applied during the latter period to maximize turfgrass performance and quality.

Under extended hot and dry periods during mid-summer, cool season grasses may experience a period of dormancy until rainfall occurs. If irrigation is available, or if rainfall is adequate throughout the summer, little dormancy will occur and N uptake will continue.

During the winter months, although top growth may have virtually ceased, root growth and N uptake may still occur during the periods when the ground is not actually frozen, particularly with Kentucky bluegrass. Research has shown that applications of N during this period can enhance root growth and spring performance of turf. Also, it is often difficult to fertilize sod fields in late winter to early spring due to excessive soil moisture, and there is potential for significant damage to the sod from equipment used for fertilization under those conditions. There is little risk of runoff or leaching problems from winter application of N if certain guidelines are followed. No more than 45 lbs. N per acre shall be applied, fertilizers containing significant amounts of NO3-N shall not be used, and applications shall not be made to frozen ground if significant rainfall is in the immediate forecast.

Phosphorus and Potassium

Phosphorus (P) is critical in the establishment of turfgrass. Inadequate soil P will result in very poor seedling vigor, slow establishment of grass, and a stand with very poor density and root growth. Not only will sod be unharvestable, but soil will be more susceptible to erosion. Weed encroachment will also be much more severe due to the lack of competition from the thin turfgrass stand. Thus, it is essential that sufficient P be added to the soil at the time of seeding, if harvestable sod is to be obtained.

Potassium (K) is not as critical as N or P during the initial establishment phase of sod. However, K plays an important role in mature sod regarding rhizome production and tolerances to heat, drought, and cold. Thus, sufficient K needs to be available for turfgrass use, to ensure that quality sod will be obtained after summer or winter stresses, or both. Severe deficiencies of K will result in thin, chlorotic, and unvigorous turf.

Whereas N application recommendations cannot currently be obtained from soil tests, recommendations for application of P and K can be obtained from them. Any field that is going into sod production for the first time should be sampled. For fields that have previously been in production, sampling every 3 years is generally sufficient to monitor soil P and K levels. However, it is advisable to sample soil prior to any new seeding. Fields having different soil types, fields with different cropping or management histories, or fields having substantially different fertility levels, as determined by previous soil tests, should be sampled separately. Conversely, fields having similar soil types, having similar cropping and management histories, and having similar fertility levels, as determined by past soil tests, may be lumped together into one sample.

Current P and K recommendations based on soil test results for the establishment and production of sod are listed in Table 2 and Table 3.

Table 2. Phosphorus Recommendations for Sod Production Based on Soil Test Results from University of Maryland.

	Low	Medium	Optimum -- Excessive
Establishment
Broadcast*	90 - 175	45 - 90	0 - 90
Incorporated**	130 - 220	45 - 90	0 - 90
Production	90 -130	45 - 90	0 - 90

* or incorporated up to 2 inches
** incorporated over a 2 inch depth

Table 3. Potassium Recommendations for Sod Production Based on Soil Test Results from University of Maryland.

	Low	Medium	Optimum -- Excessive
Establishment
Broadcast*	90 - 175	45 - 135	0 - 90
Incorporated**	130 - 220	45 - 135	0 - 90
Production	90 -175	45 - 135	0 - 90

* or incorporated up to 2 inches
** incorporated over a 2 inch depth

Soil Reaction
Maintaining soil pH in an optimum range is important for maximizing the efficiency of nutrient use, and can be important in reducing weed and disease problems. Turfgrass can withstand a rather broad range of soil pH, but 5.8 to 6.4 is generally considered ideal. Wide deviations from this range can result in reduced P and micronutrient availability, and can interfere with soil N metabolism and availability. Depending on turfgrass species, problems in turf may start to occur at soil pH above 7.8 and below 5.4 Thus, to maximize efficiency of nutrient availability and use, soil tests should be taken as recommended previously for soil P and K to determine soil pH.

Recommended limestone applications to achieve a soil pH of about 6.4 are shown in Table 4. If diseases such as: take-all patch of bentgrass, summer patch of Kentucky bluegrass, or spring dead spot of bermudagrass are of concern, maintaining lower soil pH (5.4 - 5.7) may be desirable, and reduced or no limestone shall be applied to achieve this level. Also, it is recommended, when practical, that limestone be applied approximately 1 month or more before seeding to minimize potential P availability problems and minimize the potential for volatilization loss of applied N.

* These rates are for limestone that is tilled into the soil to a 4 to 6 inch depth. Use maintenance rates if not tilled in.

**Divide the above rates by 2 to obtain maintenance limestone recommendations for turfgrass.

NOTES :
Do not apply more than 2,000 pounds per acre for any one maintenance application to turfgrass.

Divide the listed rate by 43.5 to obtain rate in pounds per 1000 square feet.