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The management and sustainable use of Central Australian rangelands for livestock production and conservation requires improved knowledge of the temporal and spatial distribution of primary production in this region. To provide such information, this thesis investigated methods that could rapidly and efficiently estimate regional herbage biomass production in these arid landscapes. Two different approaches were examined, using (1) ground-based or (2) satellite-based data sources. Soil moisture and herbage growth data were collected over several growth seasons and five landscape types in Central Australia, and the data used to develop a model of soil moisture balance and herbage production for the region. The model has few parameters and only requires inputs of rainfall and potential evaporation to predict daily soil moisture and plant growth. Moisture loss in the 0-500 mm soil profile was modelled using a negative exponential function that depends on available soil moisture and is driven by potential evaporation. The growth of herbage, whilst soil moisture is above wilting point, is a linear function of actual evapotranspiration, with the decay of plant material represented by a logistic curve through time. Soil moisture, herbage biomass and species composition assessments made at hectare and square kilometre scales at four locations within Central Australia were examined to determine if a small sample area could be used to accurately describe the soil and plant conditions at a landscape scale. Moisture levels of the 0-200 and 0-500 mm soil profiles from nine samples were analysed for the beginning and conclusion of a growth season, whilst herbage biomass and species composition from 50 samples were compared at the end of the growth season. Results suggest that mean soil moisture levels determined in a 1 ha area are comparable with mean values in the surrounding 1 km2 area. Herbage biomass and species richness for a square kilometre can be assessed at a hectare site for some landscape types, but a larger sampling area (> 1 ha) is recommended for most rangeland assessments. Satellite data (NOAA-11) were examined for their potential application in assessing primary productivity in Central Australia. Several image correction techniques were tested to minimise the adverse effects of atmospheric contamination and illumination. Two measures of atmospheric moisture: (1) radiosonde data and (2) temperature differences between bands 4 and 5 of the NOAA satellite (split-window) were used to explain variations in NOAA-11 normalised difference vegetation index (NDVI) on inert desert sites. The splitwindow approach provided the best single factor relationship (r2=0.63) and, when combined with scattering angle (illumination) effects, up to 81% of the variation in NDVI data could be explained. Field measurements of herbage biomass were correlated with four growth indices derived from NOAA-11 NDVI data. The influence of preflight and sensor degradation calibrations of Bands 1 and 2, and atmospheric correction techniques were also tested. Correlations between temporal sums of NDVI and herbage biomass data were relatively poor (r2<0.42) and unsuitable for herbage assessment in Central Australia. However, correlations between atmospherically corrected and background-adjusted maximum NDVI data and observed herbage biomass were strong (r2=0.91), that will allow primary production in the arid rangelands of Central Australia to be assessed rapidly and efficiently using remotely-sensed information.

Pasture-based dairies have become more prevalent in recent years due to a higher proportion of organic milk demand and production. Organic certification requires that animals must graze at least 120 days in each growing season. However, dry matter intake is often limited when dairy animals receive most of their herbage from pasture, resulting in lower animal performance and milk production. The purpose of this study was to analyze the complimentary effect of high energy grasses with birdsfoot trefoil (BFT) tannins to improve intake of dairy heifers. Jersey heifers were rotationally grazed for 105 days in 2017 and 2018 on eight different pasture treatments, which included monocultures of perennial ryegrass (PR), orchardgrass (OG), meadow bromegrass (MB), and tall fescue (TF), with each respective grass also planted in mixture with BFT. Intake was measured by sampling herbage before and after each seven-day grazing period and was from greatest to least as follows: MB+BFT, OG+BFT, OG, MB, PR+BFT, TF+BFT, PR, TF. Physical characteristics such as pasture bulk density, herbage height, herbage allowance, leaf pubescence, leaf softness, and birdsfoot trefoil content as well as nutritional properties such as fat, non-fibrous carbohydrates, fiber, and energy were all associated with intake. Crude protein and ash were also associated with intake. While PR+BFT did not have the greatest overall intake, it was the only treatment that consistently had greater intake than its respective grass monoculture (PR). Since it had more energy and tannins than all other grasses, a complimentary effect between energy and tannins to increase intake was likely. The fact that both physical and chemical herbage characteristics were associated with intake shows the importance of planting the right species in pasture as well as making proper management decisions to maximize nutritive value and herbage intake.

Incremental gains in productivity from new forages are likely to be very small in developed countries like the USA where forage research is highly advanced, thus animals must be used in determining their value. Three experiments were conducted. Experiment I evaluated grazing preference of cattle and its relationship with morphological and chemical characteristics. Treatments were two diploid cultivars ‘Marshall’ and ‘Gulf’ and two tetraploid cultivars ‘Maximus’ and ‘Nelson’ arranged in a 4 × 4 Latin square design experiment. Animal preference was based on herbage disappearance, the Chesson-Manly index, and animal grazing time. Both herbage disappearance (1400 vs. 890 kg ha-1) and Chesson-Manly index (8.1 vs. 5.8%) were greater for tetraploid than diploid cultivars. Experiment II quantified forage and animal response of a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass. Three stocking rates (SR), 3.75, 5, or 7.5 animals ha-1, were imposed on the two cultivars in a 3 × 2 factorial of a CRD experiment with two replications. Angus cross-bred heifers (initial BW = 240 kg) were used. There was no cultivar effect or any interactions on ADG or herbage mass (HM). Both ADG (1.22 kg d-1 at low SR to 0.98 kg d-1 at high SR) and HM (3.8 Mg ha-1 at low SR to 2.5 Mg ha-1 at high SR) had a linear response to SR. Experiment III quantified forage production, morphological characteristics, and nutritive value between a tetraploid (Maximus) vs. a diploid (Marshall) annual ryegrass cultivar harvested at three different leaf stages 2-, 3-, and 4-leaves tiller-1 and two stubble heights 5 and 10 cm. Treatments were arranged in a 3 × 2 × 2 factorial of a RCBD experiment with four replications. In 2011, there was a linear increase in forage harvested from 2-leaf (7.3 Mg DM ha-1) to 4-leaf stage (8.8 Mg DM ha-1) and in 2012 the response was quadratic with the highest forage harvested at 2- and 4-leaf stages (7.6 Mg DM ha-1). These results indicate that cultivars of annual ryegrass varied in their responses to grazing preference, grazing management, and defoliation management based on leaf stage.

A presente linha de pesquisa objetivou caracterizar a distribuição dos bolos fecais de bovinos depositados em uma pastagem de capim-braquiarão [(Brachiaria brizantha (Hochst ex A. Rich.) Stapf cv. Marandu], sob lotação rotacionada e intensidades de pastejo e verificar as alterações na fertilidade do solo e no acúmulo de foragem. O experimento foi conduzido na Faculdade de Zootecnia e Engenharia de Alimentos - FZEA/USP em pastagem com 25,2 ha, dividida em 80 piquetes de 3150 m&sup2;. O ciclo de pastejo foi de 35 dias, sendo a ocupação de 7 dias e o período de descanso de 28 dias durante o verão. Os piquetes avaliados eram aqueles utilizados com ofertas de forragem de 5 e 10 % (5 kg de massa de forragem para cada 100 kg de peso animal dia-1). Assim, foram dois tratamentos com quatro blocos (repetições). Em cada piquete avaliado houve a demarcação de três círculos de 12,5 metros de raio. Cada círculo recebeu uma letra (A, B, C) para identificação. Após o período de ocupação de 7 dias houve a contagem dos bolos fecais e o registro do respectivo circulo de ocorrência. Houve a amostragem de fezes para análise da composição em matéria seca, matéria orgânica, matéria mineral, macro e micronutrientes, além da coleta dos dados de peso e da área ocupada pelo bolo fecal. Houve a marcação de áreas em cada piquete, ao lado do bolo fecal, para avaliação de acúmulo de forragem, da fertilidade solo quanto aos nutrientes que retornam ao solo nas profundidades de 0-5, 5-10, 10-15,15-20, 20-25 cm abaixo do bolo fecal. As porcentagens de bolos fecais presentes nas áreas de descanso foram de 33,5 e 18,9% para 5 e 10% OF e de 4,2 e 13,8% para as áreas de rejeição. As áreas cobertas pelos bolos fecais por dia para cada unidade animal nos tratamentos de 5 e 10% OF foram 0,248 e 0,214 m&sup2; respectivamente, e que uma unidade animal defeca em média 5,63 e 4,84 vezes ao dia para as OF de 5 e 10%. Os valores de densidade de bolos fecais presentes na pastagem foram de 0,100 e 0,065 bolos fecais por m&sup2;, nos tratamentos 5 e 10% de OF. Sendo que os valores da porção da pastagem coberta sem e com a sobreposição da pastagem indicando que ao final de um ano a pastagem pode ser coberta de 5,7 a 10,6%. O acúmulo de forragem na pastagem, para os pontos com a presença do bolo fecal, foi da ordem de 685,62 kg de MS/ha e de 242,87kg de MS/ha sem a presença do bolo fecal, portanto, cerca de 2,8 vezes superiores. O número de bolos fecais presentes nas áreas de avaliação é determinado pela taxa de lotação. A sua deposição na área de descanso e de rejeição foi de maneira inversa. Nas ofertas de forragem estudadas durante os anos de 2003-2004, o modelo de distribuição espacial dos bolos fecais foi o agregado e sua contribuição para a fertilidade é concentrada em pequenas áreas. O bolo fecal na oferta de forragem de 5% apresenta maior contato com o solo, portanto teve participação significativa no aumento de pH em superfície, o que contribuiu com a disponibilidade de macro e micronutrientes e com a indisponibilidade de Al. Os macronutrientes primários fósforo e potássio apresentaram-se mais disponíveis no tempo e nas camadas superficiais do solo devido às alterações de pH pela presença do bolo fecal. A área de influência do bolo fecal (fertilidade) teve papel importante para melhorar o acúmulo de forragem na pastagem. No entanto, essa área é concentrada e pontual. / The objective of research was characterize the distribution of bovines dung pats deposited in a palisadegrass pasture [(Brachiaria brizantha (Hochst ex A. Rich.) Stapf cv. Marandu], under rotational stocking and grazing intensities and the influence of dung pats in fertility of soil and the herbage accumulation. The experiment was carried out at Faculdade de Zootecnia e Engenharia de Alimentos - FZEA/USP in a pasture with 25,2 ha, divided in 80 plots with 3150 m&sup2;. In the grazing cycle of 35 days, 7 days of grazing and 28 days of rest, during the summer. The evaluated plots was the used two levels of herbage allowance 5 and 10% (5 kg of dry matter per 100 kg live weight per day). Them, two treatments with four blocks (repetitions). Each evaluated plots, the ground was located three circles of 12.5 meters of ray. Each circle received a letter (A, B, C) for identification. After 7 days of occupation, dung pats was counting and register in the respective circulate of occurrence. Samples of feces was collected to analysis to determine the dry matter, organic matter, mineral matter, macro and microminerals and data of weight and the area covered by dung pats. Each plots, areas was located the side of the dung pats, to evaluation of the herbage accumulation, and the fertility of soil and nutrients that return in the depths of 0-5; 5-10; 10-15;15-20; 20-25 cm under of the dung pats. The dung pats percentage in resting areas was 33.5 and 18.9% to 5 end 10% HA and the 4.2 and 13.8% to reject areas. Covered areas by animal unit dung pats by day was 0.248 and 0.214 m&sup2; to treatments of 5 and 10% HA respectively, a animal unit deposit feces 5.63 and 4.84 times by day to the HA of 5 and 10%. The values of density in the pasture was 0.100 and 0.065 dung pats by m&sup2;, in the treatments of 5 e 10% of HA. And the portion of pasture covered in one year can be 5.7 to 10.6%. The herbage accumulation in the pasture, in area with the dung pats was 685.62 de DM/ha and the 242.87 kg DM/ha without the dung pats. The number of dung pats presents in areas of evaluation is determinates by stocking rate. Its deposition in resting areas and the reject areas are different. In the herbage allowance studded during the years 2003-2004, the spatial model distribution of dung pats was aggregate, and contribution to the soil fertility is concentrated in small areas. The dung pats in herbage allowance of 5% had more contact with the soil, had participation in the increase of pH in surface, change the available of micro and macronutrients. The primary macronutrients phosphorus and potassium more available in the time and the layer of the soil due the alteration of the pH. The influence area to the dung pats (fertility) had important contribution to the herbage accumulation in the pasture, but this area is concentrated and small.