My lawn has been turning yellow over the past few weeks, even though I water it every night. I've already tried adding NPK fertilizer but it didn't help. Could it be a nutrient deficiency or some kind of disease? I live in São Paulo and the heat has been absolutely crazy.
When I'm on the road far from home, I see a lot of this in the lawns at gas stations and rest areas, especially with that São Paulo heat.
The problem could be a combination of extreme heat with nighttime watering - the grass is suffering thermal stress and watering at night leaves the lawn humid during the hottest hours of the day, which promotes fungi and even salt burn from salt concentration. Try watering early in the morning, really deep but less often per week (like 2-3 times), and check if there's no white fungus or dark spots - if there is, you might need a specific fungicide before adding more nutrients.
NPK will only help if the soil has aerated space, so if the soil is compacted from use, aerating the lawn makes a difference.
Don't water at night, because prolonged moisture promotes fungi and diseases! With that ridiculous heat in São Paulo, watering at night leaves the grass wet during the coolest hours and it's a wide-open invitation for root rot. Try watering early in the morning, really early, so the water soaks in but the surface dries quickly as the sun rises.
Another thing that a lot of people don't realize is that in extreme heat NPK alone won't fix it if the soil doesn't have organic matter! Yellow grass under these conditions usually means the soil is compacted or poor in humus, so the chemical fertilizer just sits there without doing much good. Consider adding a surface layer of compost or a good fertilizer with organic matter, and if you can manage it, do a soil aeration to loosen it up. It makes all the difference!
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