Nitrogen use of Panicum and brachiaria cultivars vary with nitrogen supply: I. differences in plant growth

Abstract

Tropical grass pastures are broadly split between those that use high N fertilizer rates and those that use little or none. Maximizing the efficiency of N application in pastures requires understanding which features and adaptations species utilize to take advantage. This study was designed to determine the variation in growth of Brachiaria cultivars (Basilisk, Marandu, Piatã and Xaraés) and Panicum cultivars (Aruana, Massai, Mombaça and Tanzania) under two N supply rates (low and high) in order to understanding forage-grass species adaptive mechanisms for high and low N supply. Changes in growth were determined based on the following characteristics: number of leaves and tillers, leaf area (LA), shoot dry matter (SDM) production, root surface area (RSA), root length (RL) and root dry matter(RDM) production. The experimental design consisted of 8 forage-grass cultivars x 2 N rates (30 and 300 mg dm-3) in a randomized block design with four replications. At low N supply, Marandu, Xaraés, Piatã, Basilisk and Mombaça cultivars maintained a constant number of tillers but showed a decrease in the number of leaves and LA compared to high N. Tanzania cultivar maintained a constant number of tillers and LA but showed a decrease in the number of leaves under low N. In contrast, cultivars Aruana and Massai showed an increased number of tillers and a reduced LA. At low N rate, Brachiaria cultivars prioritized roots growth but with high N supply increased leaf and tiller growth. Brachiaria cultivars demonstrated high plasticity of reserve allocation, suggesting that these cultivars may better withstand N stress, ensuring their persistence. Panicum cultivars exhibited vigorous roots growth which may improve the capture of soil N and reduce losses from leaching and volatilization, and also can contribute to reduce environment contamination.