Answer: Albizia (mimosa) can develop yellowing leaves during the season due to water stress or because the soil is too alkaline. While moisture is important to the roots, they need oxygen, as well. Depending upon the soil type and how quickly it drains, having your drip system deliver moisture 60 minutes a day might be excessive. Try checking the moisture content of your soil by digging down near the roots of your tree to see just how wet or dry the area is. If it's moist but not soggy wet, it should be okay; if the soil is soggy or there are dry pockets, you'll need to adjust the watering schedule. If you haven't had your soil tested, you should. If it is very alkaline, it could be binding up nutrients and making them unavailable to your tree's roots. You might also try applying some iron to combat chlorosis.
Best wishes with your tree!
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