Here are a few issues that I've always had with 'synthetic' turfgrass ferts.
- Explosive growth (due to fast-acting Urea present as a %)
- The explosive growth requires more cutting
- Soluble Salts.
- The evolutionary biology of turfgrasses doesn't really support huge amounts of N/P/K/etc. (Hence excessive thatch accumulation, turf diseases, etc)
- Leeching of high % of N/P/K (your soil is not a closed ecosystem). Do you want to throw money away if you have crappy soil? At least try and improve the soil chemistry overall.
- Harmful Thatch accumulation
The longer version about Thatch - In my opinion is the greatest problems with some turfs (Zoysia, Cool Season Grasses, some Bermudas?)
The formation of a thatch layer on turfgrasses (especially golf greens) is accelerated when organic matter production exceeds the degradation rate (Beard, 1973). This means that when you feed a turf synthetic with %/% of fast/slow release Nitrogen, the organic matter production surges (more cutting required)
Now, with that being said, the thatch layer is more or less highly organic matter that accumulates between the soil and green turfgrass; it consists of dead and living stolon, rhizome, root, crown, leaf sheath, and blade tissues (Engel, 1954; Roberts and Bredakis, 1960). A mat layer is generally below the thatch layer, where soil or sand is intermingled (depending on your turf maintenance/topsoil) with thatch as a result of earthworm activity or cultural practices, such as core aeration and topdressing (McCarty, 2005). A thatch layer is often desirable to increase resilience and wear tolerance of the turfgrass surface, reduce surface hardness, and moderate soil temperature extremes (Beard, 1973). However, an excessive thatch or mat layer is undesirable in turfgrass because it leads to decreased saturated hydraulic conductivity (SHC), decreased movement of oxygen through the thatch or mat zone, low oxygen levels within the thatch/mat layer during wet periods, and increased water retention (Carrow, 2003; Hartwiger, 2004; McCarty et al., 2007).
More negative physical and biological effects on the soil profile relating to Excessive Thatch; increased localized dry spots (Cornman, 1952), reduced tolerance to cold temperatures (White, 1962; Thompson, 1967), increased disease and insect problems (Musser, 1960; Mascaro, 1961; Thompson, 1967; Sprague, 1970), and reduced pesticide effectiveness (Cornman, 1952; Latham, 1955; Musser, 1960).
The rate of microbial decomposition of thatch is partially dependent on the lignin content of organic matter. Lignin degradation can act as the rate-limiting step in organic matter decomposition (Taylor et al., 1989). Sinsabaugh et al. (1993) conducted a plant litter decomposition study and reported a close relationship between lignocellulose-degrading enzymes and plant litter mass loss.
Lima et al. (2009) performed a study showing increases in lignin content in the soil when using organic ferts (See "Effects of organic and inorganic amendments on soil organic matter properties" Lima et al (2009))
Li et al (2020) performed a comparison of synthetic/organic (30-year application) fertilizers and noted with a synthetic application, increased microbial biomass (161%) and amino sugar production (19.7%), but did not alter lignin phenol and SOC concentrations despite the increased plant input.
Comparatively, long term organic (manure) applications increased the concentration of SOC (30.8-70.9%), as well as that of amino sugars (82.9-107%) and lignin (96.8-212%) in soil.
"Differential accumulation of microbial necromass and plant lignin in synthetic versus organic fertilizer-amended soil" Li et al (2020)
The tl;dr: Organic applications are better for your soil health/turfgrass than Synthetics in the long run.
