Yellowed grass, nitrogen burn and alkaline soil

(Question)

My lawn is yellow and I wonder if this is because I over-fertilized it in the fall (i.e., too much nitrogen?).  I replaced the soil and sod 2 years ago and the lawn looked OK for awhile, but then I fertilized it the next fall and it started to yellow.  Could I have over-fertilized it, and possibly there is too much nitrogen?  If so, can a “nitrogen burn” last over several years?  As well, I had the soil tested for alkalinity, and it is very alkaline.  How can I remedy this?

 

 

 

 

(Answer)

Fertilizer burn: Any type of fertilizer can cause fertilizer burn ( yellowing and browning dead grass usually caused by too much nitrogen)  if administered excessively. With soluble fertilizers the damage can be expected immediately. After that the fertilizer will be leached out with subsequent rain falls. Slow release fertilizers are less likely to cause fertilizer burn. An excess of slow release fertilizer in fall, however, might still have an effect the following spring as slow release fertilizers do not work well in cold soil and spring rains may increase the release of the fertilizer. An effect over several years is unlikely.

To repair damaged areas the dead patches have to be raked off and over seeded. For instructions please see the links at the bottom on how to maintain a healthy lawn.

High soil alkalinity: High soil alkalinity in urban soil can be caused if large amounts of cement have been used during construction, or if the top soil has been scraped away and the more calcareous soil is exposed. The grass used for sod in our climate is usually blue grass, which is tolerant of a wide pH range.

If the pH is 7.3 or higher it is not recommended to lower soil  pH with sulfur in the long run. The pH eventually increases again and excessive soluble salts might become a problem.

What is recommended though is adding organic matter. If you need to replace your entire lawn  you can take advantage to properly prepare the soil for sodding/seeding if this has not been done previously and ensure you have the necessary depth of top soil of 8-15 cm (4-6 inches) Please find the instructions for site preparation here. In addition each spring or fall add organic matter by adding good quality triple mix, consisting of loam, compost and peat moss, or compost. Adding the amount of 1/4-1/2 inch can be combined with over seeding if necessary. Please refer to the following references for additional information.

https://www.torontomastergardeners.ca/index.php/askagardener/spring-lawn-maintenance/

https://landscapeontario.com/how-to-maintain-a-healthy-lawn