Where a range of recommended rates is given, use the higher rate if available K from the soil test is in the lower end of its respective range. The addition of organic matter to soil, at the time of lawn establishment, is the best way to enhance structure, as well as water and nutrient retention capabilities. It is important that the source of organic matter be free of pathogens and weed seeds and that it be low in soluble salt content. Soil organic matter and nutrient content can also be increased by leaving clippings on your lawn and mowing tree leaves back into your lawn in the fall instead of raking and collecting. Best results occur with the use of a mulching mower.
Soils generally contain large amounts of nitrogen, but it is mostly present in soil organic matter.
Nitrogen is released from organic matter relatively slowly, but the amount is generally insufficient to supply the needs of a medium to high quality lawn. Several soil and weather variables affect the release of soil nitrogen and what happens to the nitrogen in the soil following release. Also, nitrogen can be easily leached from the soil when it is in nitrate form. Thus it is not a stable element in the soil and is not normally tested by soil testing labs. Rather, yearly nitrogen applications, based on field experiments, have been developed by turfgrass scientists.