Nitrogen fertilization time affects the root reserves of tropical grasses

ABSTRACT Grass regrowth can reduce root mass, delaying reestablishment and grazing periods by reducing the nutrient absorption from the soil by plants. This study aimed to determine the optimal intervals for harvest and nitrogen fertilization in Urochloa brizantha cv. BRS Piatã and Megathyrsus maximus cv. BRS Quênia, as well as to investigate whether the flexibility of the fertilization time is related to the accumulation of water-soluble carbohydrates (WSC) and nitrogen in the roots. The experiment was conducted in a greenhouse, using a completely randomized design, with five treatments (nitrogen fertilization after harvest: 0, 2, 4, 6 and 8 days) and ten replicates. The nitrogen fertilization time linearly reduced the forage and root mass for the BRS Piatã, but had no effect on the BRS Quênia guinea grass. For the BRS Piatã, the WSC and starch concentrations in the roots showed a quadratic response, decreasing from harvest to day 2 and increasing until the day 8. However, the delayed fertilization led to a linear reduction in the root nitrogen content. The nitrogen fertilization time had a quadratic effect on the WSC concentration for the BRS Quênia roots. For the BRS Piatã, the nitrogen fertilization immediately after harvest improves the forage and root masses, WSC and nitrogen reserves. In contrast, the BRS Quênia exhibited a greater flexibility, concerning the nitrogen fertilization time. The interval between harvest and nitrogen fertilization is primarily depended on root mass, which influences the nitrogen accumulation in the roots.