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.