Rootzone Amendments for Germination and Establishment.

seedlings

Turfgrass Establishment

Cool-season turfgrasses, such as bentgrass, fescue, and perennial rye, thrive when planted as fall arrives and summer temperatures cool down. This period, with soil temperatures ranging from 45 to 68 degrees F, is an optimal time for robust root development and healthy leaf growth.  

Sometimes it’s necessary to establish turfgrass earlier in the year in Spring or early Summer. While this period may have lower than optimum soil temperatures, late April/early May, with long and warm days before the excessive peak of summer heat can provide good opportunities for turfgrass establishment. 

Proper site preparation is essential for a successful turfgrass establishment. This involves activities like site clearing, removing debris, rocks, gravel, tree stumps, and undesirable grasses, as well as cultivation and soil modification. Site grading is crucial for drainage, and it involves cutting high areas and filling low areas to achieve the desired grade. 

Selecting the right turfgrass for a site is also important. Different grass species have specific adaptabilities to environmental conditions like temperature, shade, and soil type. Factors like management practices and intended use of the turf also influence grass selection. Each turfgrass has its unique characteristics and requirements, making it essential to choose wisely based on the site’s conditions.

Establishment of turfgrass involves either seeding, sprigging, plugging, or sodding. The method chosen depends on various factors such as grass type, time available for development, and budget. Proper seed quality, rate, and planting time are crucial for seeding success. Sprigging involves planting stem or rhizome segments, while plugging and sodding provide instant turf but require more planting materials. 

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Turfgrass Establishment For Golf Greens

Modern golf course greens often consist of high sand content rootzones, with sand making up over 90% by volume. Sand is preferred for its ability to prevent compaction, maintain good drainage, and be cost-effective. A major challenge however with this system is preventing nutrient loss, especially as these porous rootzones have high percolation rates and low Cation Exchange Capacity (CEC). Young turfgrass on newly established sand rootzones is particularly prone to nutrient leaching due to this poor retention. Nitrogen, commonly applied in highly soluble forms, can leach easily in these conditions. Mature-dense turfgrass on sandy soils is better at capturing nitrogen due to its extensive root network, but this efficiency is lacking in young turfgrass on new sand rootzones. To address this, newly sown developing turfgrass needs regular light nutritional inputs and regular irrigation or precipitation to compensate for its shallow root system and inefficient nutrient absorption.

Rootzone Amendments for Establishment

Historically, construction of sand-based golf greens have traditionally involved amending sand with stable organic matter like peat to improve water and nutrient retention. In recent years, various inorganic soil amendments, including porous ceramics, diatomaceous earth, and clinoptilolite zeolites, have been investigated and advocated as viable alternatives to peat. Porous ceramics and zeolites integrated into sandy growing media have shown benefits for turf establishment and growth. These inorganic amendments offer potential advantages for sand rootzones because they do not undergo biological degradation and are able to preserve the physical properties of the rootzone for a longer period than peat. Further advantages of their use is partly due to the primary mineral content of most porous ceramics, which is clay, and the high Cation Exchange Capacities (CEC) of many clays and zeolites which can exceed the typical CEC of sand. 

Studies consistently demonstrate that unamended sands have high nitrogen leaching rates, especially in the absence of mature turfgrass, with over 95% of applied nitrogen leaching out. Incorporating specific inorganic amendments can significantly reduce nitrogen leaching by providing sufficient CEC to retain nitrogen molecules. 

There is extensive research available on several types of zeolites, showing consistently enhanced establishment and early leaf growth, and better moisture and nutrient retention compared to a sand/ peat rootzone. 

Points to Consider When Using Rootzone Amendments:

  • Is using a higher quantity of rootzone amendment necessarily more effective? The answer varies depending on the specific environmental conditions and the desired outcome. Higher quantities might improve nutrient retention but could also alter physical properties such as drainage and aeration. 
  • Should amendments be used from the outset in new construction projects? Incorporating amendments during construction can be advantageous as they integrate seamlessly into the rootzone from the beginning, enhancing its function right from establishment. 
  • The cost of inorganic amendments like porous ceramics, diatomaceous earth, and clinoptilolite zeolites, can be substantially higher than peat. While they may be more effective in certain aspects, this cost difference can limit their wider adoption unless their long-term benefits justify the initial investment. 
  • How do these inorganic amendments affect the rootzone’s physical properties? Research indicates that while they do contribute to water retention due to their porosity, they may not perform as effectively as peat under conditions of extreme drought, especially when used with various sizes of sand. This suggests that their  effectiveness can be context-dependent, with their benefits more pronounced in less extreme conditions. 
  • The best method to incorporate these inorganic amendments into an existing putting green rootzone is often during routine aeration operations. Since these amendments are available in dry, flowable forms, they can be easily applied into the aeration holes. This method of application allows for gradual incorporation of the  amendments over time, potentially reducing costs and enhancing the utilization efficiency of applied fertilizers by slowly building up a beneficial volume of  amendments. 

Conclusion:

Successful turfgrass establishment involves proper site preparation and choosing the right species or cultivar of turfgrass for the specific environmental conditions and intended use. For golf greens with high-sand-content rootzones, maintaining nutrient retention and managing leaching are significant challenges. This is particularly true with young turfgrass on new sand rootzones, requiring frequent, light irrigation that can increase the risk of nutrient loss. To combat these issues, various amendments like peat and inorganic options such as porous ceramics and zeolites can enhance water and nutrient retention. Best management practices to further mitigate nutrient leaching include using optimally sized sand, incorporating amendments early in construction, and using controlled-release or  ammonium-based fertilizers.

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