Com o objetivo de propor um modelo para estimar a produtividade potencial (pastagem manejada sob condições ótimas e de forma intensiva) de fitomassa seca total de Brachiaria brizantha, variedades cultivadas Marandu e Xaraés, em função de radiação solar e temperatura do ar, bem como: (i) obter uma curva de resposta que represente a produtividade potencial de fitomassa seca de parte aérea e do sistema radicular em relação ao desenvolvimento relativo; (ii) caracterizar a produtividade de fitomassa seca de hastes, folhas e material senescente de parte aérea; (iii) identificar o momento adequado para o corte da pastagem; e (iv) caracterizar a variação temporal do índice de área foliar; foi conduzido experimento de campo na área experimental do Departamento de Produção Vegetal da Universidade de São Paulo, em Piracicaba, no período de 22 de novembro de 2003 a 26 de janeiro de 2004. Em função dos resultados obtidos, pode-se concluir que: (i) o modelo proposto simula satisfatoriamente a produtividade potencial de fitomassa seca total de Brachiaria brizantha, variedades cultivadas Marandu e Xaraés, em função do período do ano (a partir da data de corte), das variáveis climáticas (médias diárias de radiação solar global e temperatura do ar) e da latitude local; (ii) é possível obter a curva de resposta, através do trabalho conjunto de modelagem e experimentação de campo, que represente a produtividade potencial de fitomassa seca de parte aérea e do sistema radicular em relação ao desenvolvimento relativo, a partir dos valores observados de fitomassa seca de parte aérea e do sistema radicular, do índice de área foliar, da temperatura média do ar e da radiação solar global; (iii) as equações empíricas caracterizam de forma satisfatória a variação temporal de a produtividade de fitomassa seca de hastes, folhas e material senescente de parte aérea; (iv) o momento ótimo de utilização da pastagem (corte) é próximo a 64% do desenvolvimento relativo; visto que após esse instante, a produtividade de fitomassa seca de parte aérea é fortemente influenciada por haste e material senescente, em detrimento da folha, a qual diminui a taxa de acúmulo após esse momento; e (v) a variação temporal do índice de área foliar pode ser caracterizada pelo modelo exponencial. / With the main goal to purpose a model to estimate the total plant biomass (dry matter) potential productivity (forage removed under cutting management intensive system and optimal conditions) of Brachiaria brizantha, cultivars Marandu and Xaraés, as a function of global solar radiation and air temperature, besides the following goals: (i) acquiring a response curve that might show the shoot and root dried biomass potential productivity regarding to the relative development; (ii) characterizing the dry-matter productivity of leaves, stems and senescing structures of shoots; (iii) identifying the optimal time to pasture cutting; and (iv) characterizing the leaf area index temporal variation; field experiments were carried in Crop Production Department experimental area of Universidade de São Paulo (Piracicaba, SP, Brazil) from November 22nd of 2003 to January 26th of 2004. According to results acquired, it is possible to conclude: (i) the purposed model greatly simulates the total plant biomass (dry matter) potential productivity of Brachiaria brizantha, cultivars Marandu and Xaraés, as a function of year season (from cutting date), climatic variables (daily mean values of global solar radiation and air temperature) and local latitude; (ii) from modeling and field experiments taken together; it is possible to obtain a response-curve reporting the biomass potential productivity of shoot and root compartments as a function of relative development from observed shoot and root dry-matter values, leaf area index (LAI), air temperature and global solar radiation; (iii) the empirical equations greatly denote the productivity temporal variation of leaves, stems and senescing structures dry matter; (iv) the optimal time to both forage utilization (cutting) is around 64% of relative development due to after this moment the shoot dry-matter productivity is strongly affected by increases in stems and senescing structures productivities, otherwise leaf productivity rates decrease as much as relative development raises; and (v) the leaf area index temporal variation of both genotypes might be characterized as a exponential-growth response.

Com o objetivo de propor um modelo para estimar a produtividade potencial (pastagem manejada sob condições ótimas e de forma intensiva) de fitomassa seca total de Brachiaria brizantha, variedades cultivadas Marandu e Xaraés, em função de radiação solar e temperatura do ar, bem como: (i) obter uma curva de resposta que represente a produtividade potencial de fitomassa seca de parte aérea e do sistema radicular em relação ao desenvolvimento relativo; (ii) caracterizar a produtividade de fitomassa seca de hastes, folhas e material senescente de parte aérea; (iii) identificar o momento adequado para o corte da pastagem; e (iv) caracterizar a variação temporal do índice de área foliar; foi conduzido experimento de campo na área experimental do Departamento de Produção Vegetal da Universidade de São Paulo, em Piracicaba, no período de 22 de novembro de 2003 a 26 de janeiro de 2004. Em função dos resultados obtidos, pode-se concluir que: (i) o modelo proposto simula satisfatoriamente a produtividade potencial de fitomassa seca total de Brachiaria brizantha, variedades cultivadas Marandu e Xaraés, em função do período do ano (a partir da data de corte), das variáveis climáticas (médias diárias de radiação solar global e temperatura do ar) e da latitude local; (ii) é possível obter a curva de resposta, através do trabalho conjunto de modelagem e experimentação de campo, que represente a produtividade potencial de fitomassa seca de parte aérea e do sistema radicular em relação ao desenvolvimento relativo, a partir dos valores observados de fitomassa seca de parte aérea e do sistema radicular, do índice de área foliar, da temperatura média do ar e da radiação solar global; (iii) as equações empíricas caracterizam de forma satisfatória a variação temporal de a produtividade de fitomassa seca de hastes, folhas e material senescente de parte aérea; (iv) o momento ótimo de utilização da pastagem (corte) é próximo a 64% do desenvolvimento relativo; visto que após esse instante, a produtividade de fitomassa seca de parte aérea é fortemente influenciada por haste e material senescente, em detrimento da folha, a qual diminui a taxa de acúmulo após esse momento; e (v) a variação temporal do índice de área foliar pode ser caracterizada pelo modelo exponencial. / With the main goal to purpose a model to estimate the total plant biomass (dry matter) potential productivity (forage removed under cutting management intensive system and optimal conditions) of Brachiaria brizantha, cultivars Marandu and Xaraés, as a function of global solar radiation and air temperature, besides the following goals: (i) acquiring a response curve that might show the shoot and root dried biomass potential productivity regarding to the relative development; (ii) characterizing the dry-matter productivity of leaves, stems and senescing structures of shoots; (iii) identifying the optimal time to pasture cutting; and (iv) characterizing the leaf area index temporal variation; field experiments were carried in Crop Production Department experimental area of Universidade de São Paulo (Piracicaba, SP, Brazil) from November 22nd of 2003 to January 26th of 2004. According to results acquired, it is possible to conclude: (i) the purposed model greatly simulates the total plant biomass (dry matter) potential productivity of Brachiaria brizantha, cultivars Marandu and Xaraés, as a function of year season (from cutting date), climatic variables (daily mean values of global solar radiation and air temperature) and local latitude; (ii) from modeling and field experiments taken together; it is possible to obtain a response-curve reporting the biomass potential productivity of shoot and root compartments as a function of relative development from observed shoot and root dry-matter values, leaf area index (LAI), air temperature and global solar radiation; (iii) the empirical equations greatly denote the productivity temporal variation of leaves, stems and senescing structures dry matter; (iv) the optimal time to both forage utilization (cutting) is around 64% of relative development due to after this moment the shoot dry-matter productivity is strongly affected by increases in stems and senescing structures productivities, otherwise leaf productivity rates decrease as much as relative development raises; and (v) the leaf area index temporal variation of both genotypes might be characterized as a exponential-growth response.

Kikuyu pasture was fertilized at low and high levels of nitrogen (N), namely 50 and 200 kg N/ha, after mowing and clearing the plots, to induce low and high levels of N in the herbage. The subsequent growth was harvested at 20-, 30- and 40-d re-growth. These treatments were conducted in spring, summer and autumn. Treatments included level of N, stage of re-growth and season as variables in digestion trials using sheep and voluntary feed intake (VFI) trials using long yearling heifers in pens equipped with Calan gates. Nitrogen fertilization level had no impact on herbage dry matter digestibility (DMD). Stage of re-growth influenced digestibility in the spring and summer, the highest values recorded in the 30-d treatment. However, in the autumn, the 20-d re-growth recorded the greatest digestibility. Digestibility declined as the season progressed. Digestibility was not correlated to any of the chemical fractions measured in the herbage, including in vitro DM digestibility (IVDMD). Voluntary feed intake (VFI) followed a similar trend to digestibility, with peak values recorded for the 30-d treatment in the spring and summer, while the 20-d material induced the greatest intake in the autumn. Nitrogen fertilization had a negative impact on VFI over all seasons. Similarly to digestibility, VFI was not correlated to any of the chemical fractions measured, but was correlated to digestibility and moisture concentration of the herbage. Nitrogen degradability was determined using the in situ bag technique. Differences (p<0.05) were recorded for the quickly degradable N (a) and potentially degradable N (b) fractions within season, but not for the degradation rate of the slowly degraded fraction (c) per hour. The effective degradability (dg) was not influenced by N fertilization level in the spring, while N fertilization increased the dg values in the summer and autumn. Stage of re-growth exerted a positive effect (P<0.05) on the dg values. Rumen pH, rumen ammonia and blood urea nitrogen (BUN) levels were measured in rumen fistulated sheep. Rumen pH increased also with increasing level of N fertilization and declined with advancing stage of herbage re-growth in the autumn. Rumen ammonia increased with time of sampling post feeding to 4 hrs and then tended to decline by 6 hrs. Nitrogen fertilization level influenced rumen ammonia levels (p<0.05), with the low N level producing the lowest rumen ammonia levels. Rumen ammonia levels were highest at 20-d re-growth stage in summer and at the 40-d re-growth stage in autumn. DM concentration of the herbage had an inverse relationship with rumen ammonia. BUN levels were increased by high N fertilization and were positively correlated to rumen ammonia levels. Five years of digestibility data (82 digestion trials) and three years of intake trials (38 trials) data was pooled. These data, chemical composition of the herbage and the daily maximum temperatures, rainfall and evaporation recorded at and prior to the digestion and intake trials at Cedara were analysed using multiple regression techniques. Rainfall and temperature in the period of cutting and fertilization had a negative effect on digestibility, irrespective of the stage of re-growth at harvesting, 20, 30 or 40 days later, and a combination of the two proved significant, accounting for the most variance in DDM. Temperature depressed DMD by 11.4 g/kg DM per degree rise in temperature (Degrees C). Temperatures recorded during the cutting and fertilization phase were highly negatively correlated to VFI, irrespective of stage of re-growth. The DM concentration of the herbage as fed accounting for 32% of the variance in DMD, the NPN content of the herbage accounting for only 12.2% of the variance and the ash concentration of the herbage accounting for 15.9% of the variance in digestibility. Non-protein nitrogen was negatively correlated to VFI. Both DMD and VFI were highly negatively influenced by the moisture concentration of the herbage. Overall, the results of these trials demonstrated that environmental factors such as rainfall and temperature had a far greater impact on the digestibility of kikuyu herbage than the chemical composition, which had a minimal effect. Nitrogen fertilization did not influence herbage digestibility overall, but exerted a highly negative impact on voluntary intake. / Thesis (Ph.D.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2011.

Univ., Diss.--Wuppertal, 2005. / Literaturverz. S. 280 - 294.

Call number: LD2668 .T4 1962 G36

Invasive species drive ecosystem changes throughout the world. Introduced grasses in dryland ecosystems have driven a grass-fire cycle that transforms ecosystems into homogenized grasslands (Brooks et al. 2004; D'Antonio & Vitousek 1992). Little is known about the spread rates of these grasses, effects on native ecosystems or how climate modulates spread, yet these uncertainties may be the difference between success and failure. Equally important is a quantitative assessment of the current states of invasion, yet mapping efforts have been lacking and remote sensing assessments have been inadequate for regional and local assessments. This research examines these uncertainties in the context of buffelgrass (Pennisetum ciliare Link (L.)), a C₄ grass introduced into the Sonoran Desert. These are presented as three distinct but related studies. The first study documents changes in diversity and dominance at 11 sites in the Sonoran Desert with respect to time since infestation by buffelgrass. Dominant and rare species alike declined rapidly following infestation, although the longer-lived shrubs showed no signs until after five years. This calls into question basic assumptions about the grass-fire cycle. The second study assesses constraints to successful operational identification of buffelgrass via remote sensing. We combined ground-based spectral measurements with cover estimates and found that Landsat TM-based classification will result in high commission/omission errors regardless of timing. We also identified several spectral characteristics that distinguish buffelgrass that are only available using hyperspectral imagery. The third study reconstructs spread of buffelgrass using historical aerial photography dating from 1979. Populations grew from small colonizing patches to 66 ha in 2008, doubling every 2-3 years since 1988. Although spread closely fit a logistic growth curve between 1989 and 2008, we found evidence that the 1980s were a period of rapid expansion. Thus, we may presently be in a period of slower spread in which treatment efforts will be more effective than the long-term average. This research documents grass-led ecosystem transformation without changes in the fire regime and constant spread rates over multiple decades. Along with suggested methods derived from our remote sensing study, this provides managers with critical information for managing buffelgrass in the long-term.

2 pp. / The most difficult part of conversion from a lawn to a low water (xeriscape) landscape is the removal of a lawn. By removing a Bermuda grass lawn, it is estimated that water savings of 50 -75% is possible. Potential water savings comes from the fact that water is applied to a limited amount of total yard space, compared to the greater water needs of a continuous grass-covered area. Also, by planting low water use plants, less maintenance is required and substantial cost savings can be realized. Turf removal and subsequent weed suppression is achievable using readily available herbicides.

Cattle grazing patterns on Lehmann lovegrass rangelands often create heavily-grazed (HG) areas surrounded by lightly-grazed (LG) or ungrazed patches. The purpose of this study was to characterize the forage resource and ingestive behavior of cattle grazing Lehmann lovegrass plants in both LG and HG patches on the Santa Rita Experimental Range. The general hypothesis was that residual bunchgrass vegetation resulted in sward characteristics which physically inhibited the efficiency of cattle grazing by increasing the manipulative activity per harvested bite. The overall heights of residual stems and green tillers averaged 70 and 49 cm for LG, 8 and 9 cm for HG patches. Biomass of total standing crop (SC), residual vegetation (RV) and green herbage (GH) averaged 4159, 3395 and 764 kg/ha for LG, 345, 185 and 160 kg/ha for HG patches, respectively. Bulk density of SC, RV and GH of LG and HG patches averaged 58, 48, and 19 [(gm/cm³) X 10⁻⁵] for LG, 38, 23 and 20 [(gm/cm³) X 10⁻⁵] for HG patches, respectively. The ratio of green herbage to residual vegetation averaged 0.22 for LG and 0.86 for HG patches. The different sward structure of LG and HG patches affected the ingestive behavior of the grazing cows. Overall handling time for each grazing bite averaged 1.5 and 1.2 sec/bite in LG and HG patches, respectively. Cows employed different foraging tactics in response to the dynamic changes of the sward conditions. Cows employed top biting extensively to harvest the seed-head and other green herbage at the top of the sward surface. As the height of residual stems increased and dominated the upper strata of the sward, side and low biting were mainly used by the cows as grazing methods to bite the plants to reduce the manipulative activity. Avoidance of LG patches or preference for HG patches was related to the sward structure and largely shaped by the build-up of residual vegetation. Removal of residual vegetation through fire, mowing or heavy utilization for short periods late in the growing season to allow for more accessible green herbage could improve both animal and pasture utilization of the range resource.

The abundance of Lehmann lovegrass (Eragrostis lehmanniana, Nees.) on Arizona ranges prompted this research to evaluate the animal production and winter palatability of this species. Sulfurcoated urea (SCU) was applied to desert grassland range to minimize the risks of fertilization that are brought about by drought and unseasonable rainfall. Tebuthiuron (TEB) was also applied to pasture to document any beneficial effects on forage production and palatability. During the 2 years of this project, two experiments were conducted. A preference study examined forage and animal responses to one-time applications of fertilizer or herbicide treatments and combinations. The second experiment compared the potentials for improved animal production from SCU and SCU + TEB with untreated range. Results indicated that the fertilizer and combination treatments produced more forage than the untreated plots. Tebuthiuron improved forage production by 200 percent in the first year but reduced yields in the second year. The high rate of TEB was detrimental in both years. Forage utilization was improved by all treatments. Nitrogen increased the crude protein content of the grasses proportional to the rate applied. Tebuthiuron also enhanced the protein content of the forage. Total available carbohydrates were lowest in TEB treated forages, but digestibility was increased. Only the 31 lb SCU appeared to be economically profitable. However, excellent carry-over by the 60 SCU treatment suggested profitability after 3 years. Results from the grazing study indicated that production was significantly improved by both treatments. Although forage production was similar for the treatments, the SCU-only pasture provided superior animal gains and greater carrying capacity than the SCU + TEB pasture, even though forage digestibility and apparent disappearance were greater on the combination pasture. The difference in animal performance was attributed to low levels of carbohydrates available from the combination pasture. Treatment of Lehmann lovegrass/blue grama range with 40 SCU/acre appeared profitable for raising growing beef animals, but not for maintenance of a breeding cow herd.

Field and laboratory experiments to determine the effect of the quality of irrigation water and the combination effects of the quality of water and chemical amendments (Gypsum and H ₂SO₄) on growth and yields of sudangrass, total soluble salt and ionic distribution and the infiltration rates of a Pima soil were conducted. Pima soil was classified as calcareous saline-sodic soil. A field experiment was conducted on the University of Arizona Experimental Farm at Safford, Arizona, for a period of five years. During the first three years, three qualities of water as supplied by well, river and city were used. During the last two years, these waters were coupled with two chemical amendments, gypsum and sulfuric acid. The experiment was a randomized split plot design with nine main plots and 27 subplots and three replications. The rates of the amendments were arbitrarily chosen 1 and 1.72 ton/acre of H ₂SO₄ and gypsum respectively. Four harvests were made over the two-year period and city water treatment gave the best growth and yield of sudangrass as compared to well and river water treatments. H ₂SO₄ and gypsum increased the yield significantly in comparison to the control in 1975. No significant effects of the chemical amendments on the growth and yield of sudangrass were obtained in 1976. Significant negative correlations between the EC and ESP of the first two feet of soil and yield of sudangrass were obtained. Soil analysis indicated that significant decrease in the pH and ESP of the soil resulted from H ₂SO₄ application with the three water treatments. Gypsum reduced pH and ESP significantly just with well water treatment. Due to the stratified texture of soil profile, ions and salts accumulated in the center of the sampled profile. Infiltration rates were higher for well water treatments than for city water treatments. H ₂SO₄ increased the infiltration rates significantly with all water treatments; gypsum increased infiltration only with well water treatment. Infiltration was further studied in the laboratory using soil columns. Two rates of acid and two rates of gypsum were used (1 or 5 and 1.72 or 8.6 ton/acre H ₂SO₄ and gypsum respectively). The higher rate of H ₂SO₄ gave the highest infiltration rate and the lowest infiltration rates were obtained with control with all water treatments. The low rate of H ₂SO₄ and the high rate of gypsum gave similar infiltration rates with the three water treatments. Gypsum treated soil columns required more water to be leached to a specific EC than H ₂SO₄ treated and control columns. More salt can be removed from the soil per unit volume of water with H ₂SO₄ treatment than gypsum or untreated soil. The poorest quality of irrigation water required the least time and amount of water needed to reach equilibrium between the solid and solution phases of soil. The EC of effluent was found to be an index to predict the presence of gypsum and lime in the soil under very low water penetration. Regression equations were developed to predict the time and depth of water required to leach one foot of Pima soil column to a specific EC with a given quality of water and a given type and rate of chemical amendments (H ₂SO₄ and gypsum). A regression equation was developed to estimate the EC of the saturation extract from that of 1:1 soil :water ratio for Pima soil.