The objective was to evaluate water‐soluble carbohydrate (WSC) and crude protein (CP) concentration of perennial ryegrass (PRG) cultivars with different genetic potential for producing WSC under two contrasting agronomic managements in temperate climate (southern Chile). A 4 × 2 factorial design was randomly allocated to 24 plots (31 m2 each, three blocks): four PRG cultivars (diploid standard cultivar, “2nSt”; tetraploid standard cultivar, “4nSt”; diploid high sugar cultivar developed in New Zealand, “2nHSNZ”; and tetraploid high sugar cultivar developed in Europe, “4nHSEU”) and two agronomic managements (“favourable,” defoliations at three leaves per tiller and nitrogen (N) fertilization rate of 83.3 kg N ha−1 year−1; “unfavourable,” defoliations at two leaves per tiller and N fertilization rate of 250 kg N ha−1 year−1). Herbage samples were collected in early spring, spring, summer and autumn. Concentration of WSC did not differ among cultivars in spring and summer, averaging 194 and 251 g/kg DM, respectively. The cultivar 4nHSEU had the greatest WSC concentration in early spring and autumn (187 and 266 g/kg DM, respectively) and the greatest CP concentration across samplings (average 230 g/kg DM). Favourable management improved WSC concentrations in early spring and summer and decreased CP in spring, summer and autumn. Annual DM yield did not vary with cultivar or management, averaging 8.43 t/ha. Within a 12‐month study at one site in a temperate environment in southern Chile, PRG cultivars have not shown a consistent expression of the “high sugar” trait, where a genetic × environment interaction might be operating.

I. Lobos, C.J. Moscoso, and P. Pavez. 2019. Calibration models for the nutritional quality of fresh pastures by near-infrared reflectance spectroscopy. Cien. Inv. Agr. 46(3):234-242.High levels of animal performance and health depend on high-quality nutrition. Determining forage quality both reliably and quickly is essential for improving animal production. The present study describes the use of near infrared reflectance spectroscopy (NIRS) for the quantification of nutritional quality (dry matter (DM), water-soluble carbohydrates (WSC), crude protein (CP), in vitro dry matter digestibility (DMD), organic matter digestibility (OMD), neutral detergent fiber (NDF) and the WSC/CP ratio) in samples from fresh pastures in southern Chile (39° to 40° S). Calibration models were developed with wet chemistry and NIRS spectral data using partial least squares regression (PLSR). The coefficients of determination in the validation set ranged between 0.69 and 0.93, and the error of prediction varied from 0.064 to 2.89. The evaluation of the model confirmed the high predictive ability of NIRS for DM and CP and its low predictive ability for DMD, OMD, NDF and the WSC/CP ratio. It was not possible to obtain a model for WSC because it would have required an increased number of samples to improve the spectral variability and the R 2 value (> 80%).

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One of the challenges of modern grassland systems is to minimize nitrogen (N) fertilization without negatively affecting the forage yield. Therefore, critical N dilution curves (Nc = ac W−b) have been developed in different species to improve N fertilization management. The aim of this study was to validate a critical N dilution curve for hybrid ryegrasses. Two field experiments were conducted in southern Chile. Treatments were the factorial combination of two hybrid ryegrasses (Shogun and Trojan cultivars) and seven N fertilization rates (0, 50, 100, 200, 350, 525 and 700 kg N/ha). Factors were arranged in a split‐plot design, where forage species were assigned to main plots and N rates to subplots that were randomized into four blocks. A wide range in forage yield and plant N concentration was observed (yield: 0.16 and 3.9 Mg DM/ha and N: 1.6% and 5.1%). The variations in these traits were principally explained by the N levels and harvest times. Relative yield responses of both cultivars were significantly (p < 0.001, R2 = 0.81–0.87) related to the nitrogen nutrition index (NNI) calculated with different critical N dilution curves. However, the NNI calculated with N dilution curves from annual ryegrass best described the relative yield response of hybrid ryegrass. Therefore, this validated critical N dilution curve (%Nc = 4.1W−0.38) will serve as a useful diagnosis tool for improving the N fertilization management of grazing systems for hybrid ryegrasses.