Current Scenario and Perspectives for Nitrogen Fertilization Strategies on Tropical Perennial Grass Pastures: A Review

Abstract

Traditional Nitrogen (N) fertilization practices for tropical perennial grass are still based on annual amounts, following flat N rates instalments. This strategy does not consider variations in climatic conditions along the growing season, their impacts on the plant’s demand and the soil N availability. At regrowth cycles where the amount of soil N released from mineralization or through animal excreta surpass the plant’s demand, most of the N may be lost (as ammonia, nitrate, and nitrous oxide), increasing production costs and environmental pollution. This paper examines current N fertilization and discusses possible gaps in knowledge for the definition of more precise fertilization guidelines in pasture-based livestock systems based on tropical perennial grasses. More precise fertilization practices, based upon site and seasonal-specific recommendations, will substantially contribute to the establishment of best fertilization guidelines. Sustainable approaches can be defined by combining the identification of regrowth cycles where high N rates are required, with enhanced efficiency fertilizers, and/or using grass species with the potential for biological nitrification inhibition. The lack of information on tropical grasses requirements, and soil and climatic factors driving the N fate into the mineralization and immobilization processes and how these factors affect plant’s N demand, still prevents opportunities for tactical applications and the establishment of best management guidelines.

Canopy leaf area and leaf mass in the upper stratum of Urochloa hybrid ‘Mavuno’ grass subjected to nitrogen fertilisation

“…In this way, our results support evidence that N requirements of Mavuno grass pastures vary between regrowth cycles, from 30 to 45 kg N ha À1 and, within this range, a higher N requirement may be related to periods of intense tiller population renewal. These responses open new opportunities for an efficient management aiming at to conceive more sustainable grazing systems, highlighting the opportunity for a deeper understanding of the possibilities for using N fertilisation protocols based on variable rates along the growing season, which was previously pointed out inSmith et al (2018) andPereira et al (2022).Within the range of N fertilisation utilised in the present study, we partially accept our first hypothesis. The herbage mass and leaf mass were increased in the upper stratum with increasing N fertilisation rates in some specific regrowth cycles during Year II.…”