Could forage peanut in low proportion replace N fertilizer in livestock systems?

Area of Science:

• Agronomy and Soil Science
• Plant and Animal Science
• Tropical Pasture Management

Background:

• Palisadegrass (Urochloa brizantha cv. Marandu) is a key forage in Brazil, often managed without nitrogen (N) fertilizer, leading to long-term pasture degradation.
• Economic factors (beef price vs. fertilizer cost) and limited legume success (<30% proportion) challenge sustainable N management in pastures.
• Alternative strategies like legume integration are explored to improve pasture productivity and N cycling without relying solely on synthetic N.

Purpose of the Study:

• To evaluate the impact of nitrogen (N) fertilization and pasture species composition on herbage responses under intermittent stocking.
• To compare the performance of fertilized palisadegrass, unfertilized palisadegrass, and a palisadegrass-forage peanut mixture.
• To assess the contribution of biological nitrogen fixation (BNF) and total aboveground N in forage peanut within the mixed system.

Main Methods:

• Experimental treatments included: fertilized palisadegrass (150 kg N ha⁻¹ yr⁻¹), unfertilized palisadegrass (control), and a palisadegrass-forage peanut mixture.
• Evaluations were conducted over two rainy seasons, with five growth cycle assessments per season, measuring herbage biomass, accumulation, and morphology.
• Total aboveground N of forage peanut and the contribution of biological N2 fixation (BNF) were quantified.

Main Results:

• Fertilized palisadegrass yielded significantly higher herbage biomass (5850 kg DM ha⁻¹) compared to the mixed pasture (3940 kg DM ha⁻¹).
• Nitrogen fertilizer increased palisadegrass leaf mass (2490 kg DM ha⁻¹) substantially more than in the control or mixed treatments.
• The forage peanut component remained below 10% in the mixed pasture, resulting in minimal benefits from biological N2 fixation (BNF).

Conclusions:

• Direct nitrogen fertilization is more effective in increasing palisadegrass herbage biomass than incorporating forage peanut under the tested conditions.
• The low proportion of forage peanut limited its contribution to nitrogen input and overall pasture productivity.
• Sustainable management of palisadegrass pastures in Brazil may require strategic N fertilization, considering current economic viability.