The Official Blog of Agresource, Inc.

Compost, in contrast to common fertilizers, contains nutrients that are part of the organic matter and therefore not readily leached from the soil. Nutrients in compost are made available slowly as the organic matter breaks down in the soil. As they are slowly released, the plant root will absorb the nutrients and risks of nutrients, primarily nitrogen, entering ground water are eliminated. In contrast, commercial fertilizers contain water-soluble forms of nitrogen. Although this nitrogen is readily available to the plants, it is also easily leached into the ground water during heavy rain or irrigation.

Compost test results indicate that Agresoil Compost has about 1% total nitrogen and that most of this is in the organic form. Only about 1% of the total nitrogen is in the water-soluble forms of ammonium-N and nitrate-N. Testing performed on Agresoil Compost also indicates that about 20 % of the compost nutrients will be released in the first year after application thus the amount of plant available nitrogen (the amount that will be made soluble) is about 2.0 lbs of nitrogen per 1,000 square feet of turf when the compost is used at the suggested application rate. Most of this is in the organic form (90%) and will be released slowly as the compost is broken down over the summer.

Soil testing labs typically recommend that 1 lb. Per 1,000 square feet of available nitrogen be applied in the spring and then again in June and late August. This is consistent with the general recommendation for 4 lbs of nitrogen fertilizer per 1,000 square feet of turf.   

Thus, topdressing with Agresoil Compost will provide water-soluble nitrogen well within the recommendations issued by labs and is highly unlikely to result in any excess nitrogen that would have the potential to leach to ground water. In order to meet the full recommendation for nitrogen a second top-dressing application should also be considered in the late fall. Compost applied at this time to cool soils will decompose very slowly and nutrients will be released at a rate to optimize plant uptake. In the late fall roots continue to grow and absorb nutrients although top growth is not apparent.

Agresoil Compost will also reduce, if not eliminate, the need to apply lime or other nutrients (P2O5 and K20) as recommended by the soil testing. Compost topdressing will increase the soil organic matter levels and thus also increase the ability of the soil to hold nutrients and water promoting better root penetration in the soil which further reduces risks that nutrients will leach into the ground water.

In conclusion, compost topdressing is an excellent alternative to fertilizer applications and will improve the turf condition with no risk to groundwater resources when performed at the recommended rates.