Orientador: Jose Eduardo Cora / Banca: Carolina Fernandes / Banca: Maria Helena Moraes / Resumo: Os sistemas de manejo alteram a qualidade dos solos, devido à influência da quantidade e da qualidade da matéria orgânica do solo, as quais podem afetar a agregação do solo. O objetivo do presente trabalho foi avaliar a influência de usos do solo no teor de carbono total, substâncias húmicas e na estabilidade de agregados do solo. Os sistemas de uso do solo foram: pastagem, sistema convencional de preparo do solo (PC) e dois sistemas em semeadura direta (SSD), um com sucessão milho/milho (SDMM) e outro com a sucessão soja/milho (SDSM), utilizando como referência de qualidade do solo uma mata nativa (MN). A área de estudo localizou-se em Jaboticabal, SP, em um Latossolo Vermelho eutroférrico. Amostras de solo foram coletadas na camada de 0-0,1 m, as quais foram analisadas quando ao diâmetro médio ponderado (DMP) e ao índice de estabilidade (IEA) dos agregados, teores de C orgânico total (COT), ácidos fúlvicos (AF), ácidos húmicos (AH) e humina (HUM) do solo. O solo sob pastagem apresentou teores de COT e C-AH semelhantes àqueles do solo sob MN. O solo sob pastagem apresentou maiores teores de C-HUM do que o solo sob MN, porém, observou-se resultado contrário nos teores de C-AF. O solo sob pastagem apresentou maiores teores de COT, C-HUM, C-AH e C-AF em relação aos sistemas de uso com SSD e PC. O solo sob pastagem apresentou agregados com tamanhos semelhantes àqueles observados no solo sob MN; porém superiores aos solos sob SDMM e SDSM. O solo sob PC apresentou os menores valores de DMP e IEA e teores de COT e C nas substâncias húmicas. Correlações significativas e positivas foram obtidas entre COT e os índices de agregação (IEA e DMP) em todos os manejos avaliados. Portanto, nesse estudo, a agregação do solo foi governada principalmente pelo COT do solo / Abstract: The soil management systems change the soil quality, due to the amounts and quality of soil organic matter, which may affect the soil aggregation. The aim of this study was to assess the influence of soil use on organic C content in total soil and in humic substances and the soil aggregation stability. The soil uses assessed were a pasture, conventional soil tillage (CT) and two systems under no-tillage (NT), one with maize/maize succession (NTMM) and other with soybean/maize succession (NTSM). A native forest (natural ecosystem) was used as reference of soil quality. The sites were located at Jaboticabal, Sao Paulo, Brazil, within the same soil, an Eutroferric Red Latosol (Oxisol). The soil samples were collected at 0-0.1 m depth layer and analyzed for aggregates mean-weight diameter (MWD), aggregates stability index (ASI), total organic C (TOC), fulvic acid (C-FA), humic acid (C-HA) and humin (C-HUM). The soil under pasture showed similar TOC and C-HA contents when compared with those from the soil under native forest. The C-HUM content of the soil under pasture was higher than that from the soil under native forest, however, an opposite result was observed in C-FA. The soil under pasture showed higher TOC, C-HUM, C-HA and C-FA when compared with the soils under NT and CT. The soils under pasture and MN were similar within the aggregate sizes (MWD), however, higher than the soils under NTMM and NTSM. The soil under CT showed the lowest MWD and ASI values and organic C contents in TOC and in humic substances. Positive correlations were observed between the COT contents and ASI and MWD values in all sites. Therefore, in this study, the soil aggregation was governed by TOC / Mestre

Pasture is considered one of our most important agricultural crops, contributing more than one third of all feed consumed by livestock in the United States. High quality pasture has been recognized to be highly important in efficient milk production. It has been shown, however, that good pasture must be supplemented by concentrates if' milk production is to be maintained at a high level.

Excessive phosphorus (P) excreted by animals can affect water quality and cause eutrophication. Better understanding of factors that influence P utilization and excretion in horses may reduce the environmental impact of P. Two animal experiments were conducted that examined P excretion by horses. The efficacy of titanium dioxide as an external marker to calculate digestibility was studied concurrently with both animal experiments. Additionally, pasture P concentrations were evaluated over the growing season using near-infrared spectroscopy (NIRS). Experiment 1 examined P excretion by post-lactational mares fed a low P diet immediately prior to weaning compared to non-lactating controls fed an adequate P diet. Post-lactational mares excreted more P compared to controls. Experiment 2 compared P excretion in horses fed to lose, maintain, or gain weight. Horses fed to lose weight tended to excrete more fecal P compared to horses fed to gain weight and had increased markers of bone turnover. The efficacy of titanium dioxide for estimating fecal output from limited fecal grab samples was variable. Titanium dioxide may be useful in situations where many fecal samples are collected over 5 d, but may not be as accurate if one fecal grab sample is expected to be representative of fecal output. Experiment 3 focused on examining the changes in pasture mineral concentration over the season using NIRS. A discussion of how these results may inform equine P supplementation programs is included. Overall, the work in this dissertation suggests that factors that influence P excretion in the horse include the dietary availability of P, physiological status, and active weight change. These variables can be incorporated into feeding programs to meet horses’ needs more closely while minimizing P excretion in the environment.

Typewritten copy Includes bibliographical references

This thesis is about the dynamics of eastern grey kangaroo (Macropus giganteus) populations and their food supplies in temperate grasslands of south-eastern Australia. It is based on the study of three populations of eastern grey kangaroos inhabiting �warm dry�, �cold dry�, and �warm wet� sites within the Southern Tablelands climatic region. After a pilot survey and methods trial in early 2001, the main period of study was from August 2001 to July 2003. The study populations were found to have the highest densities of any kangaroo populations, 450 to 510 km-2. Their density was the same at the end of the two year study period as at the beginning, in spite of a strong decline in herbage availability due to drought. The eastern grey kangaroo populations were limited according to the predation-sensitive food hypothesis. Fecundity, as the observed proportion of females with late pouch young in spring, was high, in spite of the high kangaroo density and restricted food availability. Age-specific fecundity of a kangaroo sample shot on one of the sites in 1997 to avert starvation was the highest reported for kangaroos. Thus, limitation acted through mortality rather than fecundity. Population growth rate was most sensitive to adult survival but the demographic rate that had the greatest effect in practice was mortality of juveniles, most likely sub-adults. The combination of high fecundity with high mortality of immatures would provide resilience to low levels of imposed mortality and to fertility control. The normal pattern of spring pasture growth was not observed in the drought conditions and few of the recorded increments of growth were of the magnitude considered typical for sites on the southern and central tablelands. Temperature was necessary to predict pasture growth, as well as rainfall, over the previous two months. The best model of pasture growth (lowest AICc) included negative terms for herbage mass, rainfall over the previous two months, and temperature, and a positive term for the interaction between rainfall and temperature. It accounted for 13% more of the variation in the data than did the simpler model of the type used by Robertson (1987a), Caughley (1987) and Choquenot et al. (1998). However this was only 63% of total variation. Re-evaluation of the model based on measurements of pasture growth in more typical (non-drought) conditions is recommended. Grazing had a powerful influence on the biomass of pasture due to the high density of kangaroos. This is a marked difference to many other studies of the type which have been conducted in semi-arid environments where rainfall dominates. The offtake of pasture by kangaroos, as estimated on the research sites by the cage method, was linear on herbage mass. It was of greater magnitude than the more exact estimate of the (curved) functional response from grazedowns in high�quality and low�quality pastures. The widespread recognition of three forms of functional response is inadequate. Both the theoretical basis, and supporting data, have been published for domed, inaccessible residue, and power forms as well (Holling 1966; Noy-Meir 1975; Hassell et al. 1976, 1977; Short 1986; Sabelis 1992). Eastern grey kangaroos had approximately the same Type 2 functional response when consuming either a high quality artificial pasture (Phalaris aquatica), or dry native pasture (Themeda australis) in autumn. Their functional response rose more gradually than those published for red kangaroos and western grey kangaroos in the semi-arid rangelands, and did not satiate at the levels of pasture available. This gradual behaviour of the functional response contributes to continuous stability of the consumer-resource system, as opposed to discontinuous stability. The numerical response was estimated using the ratio equation, assuming an intrinsic rate of increase for eastern grey kangaroos in temperate grasslands of 0.55. There is indirect evidence of effects of predation in the dynamics of the kangaroo populations. This is demonstrated by the positive relationship between r and kangaroo density. Such a relationship can be generated by predation. A desirable future task is to compile estimates of population growth rate and simultaneous estimates of pasture, in the absence of predation, where kangaroo population density is changing, so that the numerical response can be estimated empirically. The management implications arising from this study are numerous and a full account would require a separate report. As one example, kangaroos in these temperate grasslands are on average smaller, eat less, are more numerous, and are more fecund, than would be predicted from other studies (e.g. Caughley et al. 1987). Thus the benefit of shooting each kangaroo, in terms of grass production, is less, or, in other words, more kangaroos have to be shot to achieve a certain level of impact reduction, and the population will recover more quickly, than would have been predicted prior to this study. Secondly, of much importance to managers, the interactive model which can readily be assembled from the products of Chapters 4, 5 and 8, can be used to test a range of management options, and the effect of variation in weather conditions, such as increased or decreased rainfall. For example, the model indicates that commercial harvesting (currently under trial in the region), at the maximum level allowed, results in a sustainable harvest of kangaroos, but does not increase the herbage mass, and only slightly reduces the frequency of crashes when herbage mass falls to low levels. (To demonstrate this with an ecological experiment would require an extremely large investment of research effort.) However, an alternative �national park damage mitigation� formula, which holds kangaroo density to about 1 ha-1, is predicted to increase herbage mass considerably and to reduce the frequency of crashes in herbage mass, but these effects would be achieved at the cost of having to shoot large numbers of kangaroos. Thus, aside from many specific details of kangaroo ecology, the knowledge gained in this study appears to have useful potential to illustrate to managers the dynamic properties of a resource-consumer system, the probabilistic nature of management outcomes, and the consequences of particular kangaroo management proposals.

Studies were conducted at three different sites in Saskatchewan, Canada (Colonsay, Vanscoy and Rosthern) over two years (2005 and 2006) to determine the effect of dribble banded and coulter injected liquid fertilizer applied in the spring of 2005 at 56, 112 and 224 kg N ha-1 with and without P at 28 kg P2O5 ha-1. A similar study was conducted in 2006 at one site in Mongolia to determine the effect of granular N and P fertilizer application on dry matter yield, and N and P concentration in plant biomass in the year of application (2006) only. The three Saskatchewan sites were unfertilized, 7-8 year old stands of mainly meadow bromegrass (<i>Bromus riparius</i>) dominated haylands, while the Mongolia site was mixed species of native rangeland.<p>All fertilization treatments produced significantly (p≤0.05) higher dry matter yield than the control in the year of application at the three Saskatchewan sites. The addition of 28 kg P2O5 ha-1 P fertilizer along with the N fertilizer did not have a significant effect on yield in most cases. In the year of application, increasing N rates above 56 kg N ha-1 did not significantly increase yield over the 56 kg N ha-1 rate in most cases but did increase N concentration, N uptake and protein content. A significant residual effect was found in the high N rate treatments in 2006, with significantly higher yield and N uptake. In 2005, the forage N and P uptake were in all cases significantly higher than the control in the fertilized treatments. The N uptake at the three Saskatchewan sites increased with increasing N rate up to the high rate of 224 kg N ha-1, although the percent recovery decreased with increasing rate. The P fertilization with 28 kg P2O5 ha-1 also increased P uptake at the three Saskatchewan sites. The site in Mongolia was less responsive to fertilization than the three Saskatchewan sites, with only a significant response in yield, N uptake and no significant effect of P fertilization. <p>For incubation soil cores collected in the fall of 2006, mean respiration rates were similar among the fertilized treatments at all the sites and the pattern of CO2 and N2O evolution measured over a two-week period showed similar trend at the three sites, with no significant difference between treatments. However a significant increase in gas production occured as the soils were wetted during the incubation. By the fall of 2005, the fertilization effect had likely diminished along with available substrate for the soil microbial biomass.<p>Overall, rates of fertilizer of approximately 50 kg N ha-1 appear to be sufficient to produce nearly maximum yield and protein concentration of the grass in the year of application for the Saskatchewan and Mongolia sites. Surface banding placement was as effective as in soil placement and there was limited response to P fertilization. A small amount of N fertilizer that is surface-placed on these grass dominated forage systems appears to be an effective means of increasing production in the year of application. Higher rates are needed to sustain the rejuvenation beyond one year.

Studies were conducted at three different sites in Saskatchewan, Canada (Colonsay, Vanscoy and Rosthern) over two years (2005 and 2006) to determine the effect of dribble banded and coulter injected liquid fertilizer applied in the spring of 2005 at 56, 112 and 224 kg N ha-1 with and without P at 28 kg P2O5 ha-1. A similar study was conducted in 2006 at one site in Mongolia to determine the effect of granular N and P fertilizer application on dry matter yield, and N and P concentration in plant biomass in the year of application (2006) only. The three Saskatchewan sites were unfertilized, 7-8 year old stands of mainly meadow bromegrass (<i>Bromus riparius</i>) dominated haylands, while the Mongolia site was mixed species of native rangeland.<p>All fertilization treatments produced significantly (p≤0.05) higher dry matter yield than the control in the year of application at the three Saskatchewan sites. The addition of 28 kg P2O5 ha-1 P fertilizer along with the N fertilizer did not have a significant effect on yield in most cases. In the year of application, increasing N rates above 56 kg N ha-1 did not significantly increase yield over the 56 kg N ha-1 rate in most cases but did increase N concentration, N uptake and protein content. A significant residual effect was found in the high N rate treatments in 2006, with significantly higher yield and N uptake. In 2005, the forage N and P uptake were in all cases significantly higher than the control in the fertilized treatments. The N uptake at the three Saskatchewan sites increased with increasing N rate up to the high rate of 224 kg N ha-1, although the percent recovery decreased with increasing rate. The P fertilization with 28 kg P2O5 ha-1 also increased P uptake at the three Saskatchewan sites. The site in Mongolia was less responsive to fertilization than the three Saskatchewan sites, with only a significant response in yield, N uptake and no significant effect of P fertilization. <p>For incubation soil cores collected in the fall of 2006, mean respiration rates were similar among the fertilized treatments at all the sites and the pattern of CO2 and N2O evolution measured over a two-week period showed similar trend at the three sites, with no significant difference between treatments. However a significant increase in gas production occured as the soils were wetted during the incubation. By the fall of 2005, the fertilization effect had likely diminished along with available substrate for the soil microbial biomass.<p>Overall, rates of fertilizer of approximately 50 kg N ha-1 appear to be sufficient to produce nearly maximum yield and protein concentration of the grass in the year of application for the Saskatchewan and Mongolia sites. Surface banding placement was as effective as in soil placement and there was limited response to P fertilization. A small amount of N fertilizer that is surface-placed on these grass dominated forage systems appears to be an effective means of increasing production in the year of application. Higher rates are needed to sustain the rejuvenation beyond one year.

No description available.

Pastures established using buffelgrass (Cenchrus ciliaris L.) have shown heterogeneous responses in terms of forage production and permanence. A good alternative for determining establishment sites and predict trends in buffelgrass conditions is the use of simulation models. The objectives of this research were to determine the factors that regulate successfulness in buffelgrass pastures and to develop a model to determine suitability in areas managed for buffelgrass pastures, based on environmental, ecological, and management variables. Above ground biomass production was considered to determine suitability in sites with buffelgrass. Eight ranches with different geographic locations, environmental situations, and management conditions were sampled as preliminary study sites to measure and model plant production. The resulting model was used to estimate plant production in the 37 sampling sites of the study areas. Results of the study indicate that basal area is a good modeling parameter to estimate production in buffelgrass plants. I also found that plant production in buffelgrass is negatively affected by population density. I concluded that there exist a positive correlation between pasture management and buffelgrass plant production. Correlation analyses demonstrate that there exist significant correlations between Pasture Condition Index (PCI) and mean annual temperatures, aspect, pasture age, nitrogen and sodium content. However, after performing stepwise regressions, only three variables were significant: pasture age (PA), nitrogen content (N2), and mean annual temperature (MAT); the last two, produce a negative response on PCI.

Sequestering atmospheric carbon in soil is an attractive option for mitigation of rising atmospheric carbon dioxide concentrations through agriculture. Perennial crops are more likely to gain carbon while annual crops are more likely to lose carbon. A pair of eddy covariance towers were set up near Winnipeg Manitoba, Canada to measure carbon flux over adjacent fertilized long-term perennial grass hay fields with high soil organic carbon. In 2009 the forage stand of one field (Treatment) was sprayed with herbicide, cut and bailed; following which cattle manure was applied and the land was tilled. The forage stand in the other field (Control) continued to be cut and bailed. Differences between net ecosystem productivity of the fields were mainly due to gross primary productivity; ecosystem respiration was similar for both fields. When biomass removals and manure applications are included in the carbon balance, the Treatment conversion lost 149 g C m^(-2) and whereas the Control sequestered 96 g C m^(-2), for a net loss of 245 g C m^(-2) over the June to December period (210 days). This suggests that perennial grass converted for annual cropping can lose more carbon than perennial grasses can sequester in a season.