Defoliation frequency affects litter responses and nitrogen excretion by heifers in palisadegrass–forage peanut pastures

Abstract

Legumes can contribute significantly to nitrogen (N) input in grazing systems. Grazing management is a critical factor affecting N cycling in mixed pastures, altering the legume N input as a result. This study assessed how defoliation frequency affects N cycling in rotationally stocked palisadegrass (Brachiaria brizantha) and forage peanut (Arachis pintoi) pastures. Treatments included four grazing management strategies, defined by the rest period interruption when the canopy reached 90 (90LI), 95 (95LI), and 100% (100LI) of photosynthetically active radiation interception (LI), and a fixed rest period of 42 d (42D). A 2‐yr experimental period was adopted. Existing litter was greater at 100LI (2208 vs. 1964 kg ha−1; average of 42D, 90LI, and 95LI, respectively). Greater defoliation frequency (42D and 90LI) resulted in increase of litter legume proportion, resulting in greater decomposition rate, lower litter half‐life (p < .001, and p = .015, respectively), and greater N cycling (91 vs. 64 kg ha−1 season−1). Less frequent defoliation (100LI) resulted in reduced total forage intake, proportion of legume intake, and lower N intake compared with other treatments (p = .007, p = .081, and p < .001, respectively). Greater defoliation frequency increased N cycling via litter, but did not affect excretion due to compensation with stocking rate. Defoliation frequency between 90 and 95% LI optimizes N cycling in palisadegrass‐forage peanut mixed pastures.

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

“…The litter mass reflects the net balance between litter deposition and decomposition rates and, for a given grass species, varies between seasons due to the prevailing climatic conditions [60,66], pasture management [69] and stocking rates [17,63], as well as previous fertilization practices [67]. Litter deposition is expected to be increased on pastures subjected to high N fertilization rates, particularly when subjected to low stocking rates, light grazing intensities under continuous stocking, or in pastures maintained under long regrowth periods with intermittent stocking [60,67,69].…”

“…Moreover, once grazing management strategies significantly impact the nutritive value [13] and stocking rates [72] in tropical perennial grasses, direct effects on nutrient cycling are also expected. Both [69,73] showed that defoliation frequency is an important management parameter for maximizing leaf mass, growth rates, nutritive value, and stocking rates, allowing for a greater total N intake as well as the highest fecal and urinary N excretions.…”

“…Grazing strategies that ensure fast leaf turnover, such as moderate grazing intensities under continuous stocking, frequent defoliation under rotational stocking and N fertilization, increase the N concentration of herbage mass [79], improve N intake by grazing animals but may also result in higher urinary and fecal N excretion [17,69]. According to [82], peaks of soil NH 4 + normally occur in the first few days after urine deposition, but only from 10 to 14 days after dung deposition.…”

Palisadegrass pastures with or without nitrogen or mixed with forage peanut grazed to a similar target canopy height. 2. Effects on animal performance, forage intake and digestion, and nitrogen metabolism

“…An attractive alternative would be the establishment of a mixed grass–legume pasture. Some studies have highlighted the effects of mixed pastures on canopy structure, nutrient cycling, and animal productivity (Gomes et al., 2018, 2020; Muir et al., ,2011, 2014; Pereira et al., 2020). Legumes can establish symbioses with rhizobia, which induce the formation of root nodules with the capacity of biological fixation of atmospheric nitrogen, which will increase the forage production.…”

Litter mass and nitrogen disappearance in year‐round nitrogen‐fertilized grass and legume–grass forage systems

“…Gomes et al. (2020) evaluated palisadegrass–forage perennial peanut mixtures managed under three frequencies of grazing and reported greater litter decomposition rate and N release with more frequent defoliation due to a greater proportion of legume in litter of that treatment.…”