Abstract
Nitrogen (N) management affects herbage production and chemical composition; however, information on the impact of tropical herbage on N and carbohydrate fractions is scarce. A two-year study was conducted to investigate the potential use of pintoi peanut (Arachis pintoi) compared with N fertilization of palisade grass (Brachiariabrizantha cv. Marandu) by evaluating the herbage chemical composition (fractionation of protein and carbohydrate), herbage mass and accumulation rate, herbage disappearance rate, and stocking rate of pastures. The experiment was conducted in a completely randomized design with three treatments, and four replications (paddocks) were used with twenty-one non-lactating crossbred dairy heifers. Treatments consisted of pastures of palisade grass without a N source (control), fertilized with urea (150 kg/ha/year; fertilized), or mixed with pintoi peanut (mixed). Inclusion of the legume increased concentrations of fractions A (p = 0.009), which is the soluble N compound, and B3 (p < 0.001), which is slowly degraded true protein, compared with pastures fertilized with N and non-fertilized pastures. Nitrogen fertilization increased fraction B1 + B2 (p = 0.046), mainly true proteins, and decreased fraction C (p = 0.0007), indigestible protein, and neutral detergent fiber concentrations (p = 0.0003), contributing to increasing the nutritive value of the herbage. Additionally, N fertilization increased herbage mass (p = 0.004) and herbage allowance (p = 0.0001). Both N fertilization and biologically fixed N increased herbage allowance (p = 0.02) and accumulation rate (p = 0.02), as well as the crude protein content of herbage (p < 0.0001) compared with non-fertilized pastures. Nitrogen fertilization increased true protein and decreased indigestible protein of herbage and promoted a greater herbage mass production, while the inclusion of legumes increased soluble protein and decreased the slowly degraded true protein of herbage. Both N management strategies increased herbage allowance and accumulation rate.
Highlights
Interest is increasing in including legumes in grass pastures as an alternative to synthetic nitrogen (N) fertilization and to improve nutrient cycling [1]
total carbohydrate (TC) content was lower (p < 0.05) in fertilized pastures in relation to the control, and mixed pastures were similar to both (Table 1)
A quadratic effect of grazing cycle on total digestible nutrients (TDNs) content was found in the fertilized treatment
Summary
Interest is increasing in including legumes in grass pastures as an alternative to synthetic nitrogen (N) fertilization and to improve nutrient cycling [1]. Most beef and dairy cattle production is based on pastures, and N management is crucial to maintain the productivity and herbage protein levels required for satisfactory animal performance [3]. Nitrogen is the key nutrient involved in pasture degradation [4]. When the level of herbage N declines, herbage accumulation decreases, and performance per animal and per area declines [5]. Nitrogen from N fertilization can increase herbage accumulation and leaf proportion, facilitating greater dry matter intake (DMI) by grazing animals. Nitrogen application can increase the nutritive value of herbage by increasing
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