Responses of grasses to N fertilization are affected by cutting intensity although little is known regarding the interactions of these factors in warm‐season grasses. Pre‐cutting canopy height, herbage accumulation and changes in the nutritive value of warm‐season grasses in response to four different management strategies were assessed from October 2011 to September 2014. Treatments included two cutting intensities (70 vs. 50% depletion of canopy height set by 95% light interception), two N fertilization levels (zero vs. 300 kg N ha−1 year−1) and six perennial C4 grass species (Axonopus catharinensis; Cynodon spp. hybrid Tifton 85; Hemarthria altissima cv. Flórida; Megathyrsus maximus cv. Aruana; Paspalum notatum cv. Pensacola; and Urochloa brizantha cv. Marandu) grown in monoculture in a factorial experimental design. Canopy height varied among grass species, cutting intensity and N treatments, mainly among seasons, indicating that more than one management target (i.e. canopy height) existed throughout the plant growth cycle for each species. The largest herbage accumulation occurred in the N fertilization treatments for most species, regardless of cutting intensity. Nitrogen fertilization and 50% depletion of canopy height increased the leaf proportion and decreased the neutral detergent fibre content. Overall, N fertilization had a stronger positive impact than cutting intensity on the acid detergent fibre content, dry‐matter digestibility and crude protein content, but the magnitudes of the responses were species‐specific.

Sward height (SH) is an important management variable for both continuous and intermittent stocking, since it is easily measured and highly correlated to herbage mass (HM). However, in systems with trees, tree shading can alter the relationship between SH and HM by changes in the sward structure. Understanding these relationships under shading could help identify and design management practices for swards in association with trees. The aim of this study was to investigate the SH and HM relationship for a continuously stocked mixed black oat (Avena strigosa Schreb.) + annual ryegrass (Lolium multiflorum Lam.) pasture in two systems, i.e. with and without trees, with two levels of nitrogen (N) (90 vs. 180 kg N ha−1), three replicates and over 2 years (2014/2015). Comparison of regression lines was performed between SH (x‐variable) and HM (y‐variable), showing mainly a system effect. Shading altered the relationship between SH and HM in order of magnitude (i.e. different intercepts), but not in the rate of change (i.e. equal slopes). Regardless the SH, oat + ryegrass mixture under trees produced 698 kg of dry matter (DM) ha−1 less than those without trees. Therefore, a target SH used at full sun systems as an index for management (e.g. 20 cm) might not apply under trees with >50% shade, since HM may be limiting to ensure intake of grazing animals (e.g. <1200 kg DM ha−1). The shade level must be controlled to optimize the yield of these forage species and to maintain the necessary HM to ensure the sustainability of no‐till silvopastoral systems.

Plant adaptations to cope with shade may vary according to the degree of shade tolerance and nutrient availability for each species. Studies of different understory species and their responses to combined shade and N effects are important to identify ways to optimize the quantity and quality of forage production. Our objective was to measure the dry matter yield (DMY) and nutritive value of six C4 grasses grown in two systems (full sunlight [FS] vs. a naturally shaded system composed of Eucalyptus dunnii Maiden trees) with two N levels (0 vs. 300 kg N ha−1yr−1) using the same target sward conditions (i.e., 50% depletion of the canopy height set by 95% light interception). Over 3 yr, the decreases in DMY under shade compared with FS ranged from 7% [Urochloa brizantha (Hochst. ex A. Rich) R.D. Webster] to 56% (Cynodon spp.) in fertilized treatments and between 11% (Paspalum notatum Fluegge) to 46% (Cynodon spp.) in treatments without N. The N effect was more important to the nutritive value of the forage than the shade effect, particularly for crude protein (CP, +46 g kg−1 with N supply), acid detergent fiber (ADF, –46 g kg−1) and leaf proportion (+11.2%). However, most of the species displayed higher leaf digestibility under shade due to decreases in ADF. Even with intense shading (light approximately 48% of unshaded), the digestible DMY and CP yield under trees were, on average, 70 and 71% of the 6.8 and 1.4 t ha−1 recorded in FS, respectively.Core Ideas The study identifies C4 species for the optimization of forage production under trees. Nitrogen and shade have combined effects on forage production and nutritive value. Limitations and benefits of integrated crop–livestock systems with trees. Shade effects on nutritive value occur at the leaf level and of the total biomass harvested.

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Changes in grazing intensity affect forage production and performance of animal on C4 grass pastures; however, these relationships are not well defined for cattle grazing on limpograss (Hemarthria altissima (Poir) Stapf &amp; C.E. Hubb. cv. Flórida) under continuous stocking. The objective of this study was to quantify plant and animal production from Flórida limpograss pastures, managed at different grazing intensities by beef heifers (i.e. different sward heights) in order to define pasture management outcomes that maximise plant and animal responses. For a 3-year period, the influence exerted by the sward height (10, 20, 30 and 40 cm) was assessed. Greater total herbage accumulation and herbage accumulation rate were observed for the more lenient grazing heights (30 and 40 cm). The 20-, 30- and 40-cm heights revealed similar heifer average daily gain of 0.49 kg liveweight (LW) animal–1 day–1, reducing at the rate of 0.04 kg LW animal–1 day–1, for each cm decrease below 19 cm, according to a segmented equation. LW gain per area showed a quadratic response to the sward height, with optimum values (i.e. 2.1 kg LW ha–1 day–1) achieved at a pasture height of around 21 cm. Therefore, to optimise cattle performance on continuously stocked Flórida limpograss pastures, a sward height of ~20 cm should be maintained.