Nitrogen Requirement of a Tropical Grass Hybrid Determined by Model Identity Analysis

Methods capable of inferring the nutritional requirements of forage cultivars from related genotypes may help generate preliminary fertilization recommendations when experimental information is limited. This study evaluated whether model identity analysis can be used to infer the nitrogen requirement of Mulato II hybrid grass from the response patterns of its progenitor species, Urochloa brizantha cv. Marandu and Urochloa decumbens cv. Basilisk. A greenhouse experiment using pots filled with an Oxisol was conducted using a completely randomized design in a 3 × 5 factorial arrangement, with three grasses and five nitrogen doses (0, 100, 200, 300, and 400 mg dm−3). Forage production, tiller density, and nutritive value were evaluated during establishment and regrowth phases. Linear and quadratic regressions were fitted, and significant models were compared using model identity tests. When model differences were detected, intercepts and parameters were further compared using F-tests. In both establishment and regrowth phases, Mulato II showed response patterns similar to Urochloa brizantha for most evaluated variables, with model identity observed except for tiller number and crude protein concentration. In contrast, Mulato II differed from Urochloa decumbens for all measured traits. Therefore, under the greenhouse conditions evaluated, the nitrogen requirement of Mulato II is more closely related to that of Urochloa brizantha, demonstrating the potential of model identity analysis as a tool for generating preliminary fertilization recommendations for forage cultivars from related genotypes before field validation.