B. C. e Pedreira

Acúmulo de forragem durante a rebrotação de capim-xaraés submetido a três estratégias de desfolhação

The objective of this research was to describe comparatively the dynamics of herbage accumulation in Xaraes palisadegrass pastures [Brachiaria brizantha (A. Rich.) Stapf cv. Xaraes] submitted to rotational stocking managements, defined either by pre-graze light interception (LI) by the canopy (95% or 100% LI) or calendar days (28d). Pre-graze forage mass (FM) was higher for 100% LI pastures. Pastures grazed at 95% LI and 28-d resulted in similar pre-graze FM in the spring, both lower than that of the 100%-LI treatment. Grazing at 95% LI resulted in higher leaf percentage in pre-graze forage, although total pre-graze FM was lower. Forage produced in paddocks grazed at 100% LI had lower pre-graze leaf percentage, indicating that the higher forage accumulation in that treatment was a result of higher stem elongation, likely due to light competition within the canopy. Rest periods beyond the point where swards achieved 95% LI (100% LI or 28-d during the summer) resulted in higher accumulation and higher pre-graze FM, although this corresponded mainly to large amounts of stem and dead material, which could negatively affect the nutritive value of the forage produced and animal performance.

Fotossíntese foliar do capim-xaraés [Brachiaria brizantha (A. Rich.) Stapf. cv. Xaraés] e modelagem da assimilação potencial de dosséis sob estratégias de pastejo rotativo

The objective of this research was to quantify leaf photosynthetic rates during the regrowth period and to model canopy photosynthesis of vegetative swards of Xaraes palisadegrass [Brachiaria brizantha (A. Rich.) Stapf.] under contrasting management strategies of rotational stocking. Early regrowth was characterized by low photosynthetic potential (10.4 µmol CO2 m-2 s-1) and for paddocks under the 100% LI treatment, leaf photosynthesis was 3.3 µmol CO2 m-2 s-1, which may require plants to draw on organic reserves during the early phases of the process. Half way through regrowth, leaf photosynthetic rates increased to 26 µmol CO2 m-2 s-1 in all treatments. Paddocks under the 95% LI treatment (shortest mean regrowth periods; 22 days), sustained pre-graze photosynthetic rates at 26.1 µmol CO2 m-2 s-1. The longer regrowth intervals (28 and 32 days on average, for the 28 d and for the 100% LI paddocks, respectively), resulted in lower rates of 21.3 and 24.5 µmol CO2 m-2 s-1, respectively. Under the highest grazing frequency (95% LI), the short rest period and the low mean LAI (2.08) allowed for more light penetration into the canopy. Optimum management practices for Xaraes palisadegrass should include grazing intervals shorter than 28 days, so that higher photosynthetic rates are achieved during the regrowth period.

METABOLIC CHANGE, TILLERING AND ROOT SYSTEM OF BRACHIARIA BRIZANTHA IN RESPONSE TO PHOSPHORUS AND ZINC NUTRITION

Phosphorus (P) and zinc (Zn) availabilities are important to the nutrition of tropical forage grasses. In this manner, this study aimed to identify and quantify changes in metabolism, tillering, and root system of Brachiaria brizantha cv. ‘Marandu’ related to P and Zn availabilities. Plants of B. brizantha cv. ‘Marandu’ were grown in nutrient solution under five rates of P (0.1, 0.6, 1.1, 1.6, and 2.1 mmol L−1) and five rates of Zn (0.00, 0.75, 1.5, 2.25, and 3.00 μmol L−1), in a fractionated factorial. The interaction P x Zn rates and the Zn supply were not significant for the activity of acid phosphatase enzyme, P-use index, number of tillers, and root parameters. P-use index and enzyme activity decreased as P availability increased. The high efficiency in P use was a result of high acid phosphatase activity and P supply was essential to the development of ‘Marandu’ palisadegrass root system.

Photosynthesis and Leaf Area of Brachiaria brizantha in Response to Phosphorus and Zinc Nutrition

Phosphorus (P) and zinc (Zn) are important determinants of plant productivity, particularly in the tropical grasslands of Brazil. Nutrient deficiency is one of the most important factors limiting plant productivity, decreasing photosynthesis efficiency and plant development. The present study investigates in Brachiaria brizantha (Hochst. ex A. Rich.) Stapf. cv. ‘Marandu’: 1) the gas exchange measurements; 2) the total leaf area development; and 3) the dry matter production due to P and Zn nutrition. Plants of B. brizantha cv. ‘Marandu’ were grown in nutrient solution under five rates of P (0.1, 0.6, 1.1, 1.6, and 2.1 mmol L−1) and five rates of Zn (0.00, 0.75, 1.5, 2.25, and 3.00 μmol L−1), in a fractioned factorial. Plants were harvested two times. Phosphorus supply increased carbon dioxide (CO2) assimilation and stomatal conductance, and decreased intercellular CO2. The interaction P rates x Zn rates were significant for the total leaf area variables and shoot dry matter in the second growth period. The nutrition of P and Zn interfered in the B. brizantha productivity by changing the grass photosynthesis and leaf area.

Aveia preta e azevém anual colhidos por interceptação de luz ou intervalo fixo de tempo em sistemas integrados de agricultura e pecuária no Estado de São Paulo

The objective in this study was to characterize the productive potential, monthly yield distribution, and forage plant-part and botanical composition of black oats and annual ryegrass under harvest strategies in Sao Paulo. The experimental design was completely randomized with treatments corresponding to the combination among stand composition (exclusive oats, exclusive annual ryegrass, or oats + ryegrass, O+R) and harvest strategies (at 95% LI or every 30 days of regrowth, FIXED), in a factorial arrangement with three replications. Stands managed by LI accumulated 1580kg DM ha-1 harvest-1, and those managed by FIXED 2020kg DM ha-1 harvest-1. Leaf proportion was higher in ryegrass (70%), followed by O+R (64%) and oat (52%). Swards managed by LI had higher proportion of leaves and less stem than those harvested at FIXED intervals. The proportion of ryegrass was higher under the LI management (64%), than under the FIXED (70%). Over time there was the replacement of oats by ryegrass in the mixed canopy composition. Exclusive ryegrass stands are recommended. Both harvest strategies can be adopted for these winter forages in integrated systems of agriculture and livestock.