No abstract available. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1984.

The work reported in this thesis was designed to develop a better understanding of the fate of fertiliser nitrogen applied to a tropical pasture under field conditions, with the eventual objective of improving the economy of livestock production off such pastures. This involved an examination of the concentrations of soil total nitrogen, ammonium nitrogen and nitrate nitrogen at different depths within the soil profile following the application of different levels of fertiliser nitrogen to a grazed kikuyu (Pennisetum clandestinum) pasture, as well as the influence of such applications on pasture yield and some elements of pasture quality. The trial was conducted over a two year period at Broadacres in the Natal Mistbelt. A labelled [15]NH[4]N0[3] fertiliser experiment was also conducted to ascertain how the labelled ammonium ion moved through the soil, roots and herbage after being applied in spring onto a kikuyu pasture. In the absence of fertiliser N, a total of 15.45 t/ha of soil N was recorded at an average concentration of 0.15%. More than 30% of the soil total N was, however, situated within the top 10cm of soil. organic matter (OM) content in the top 0-10cm of the profile was high (4.75%), reflecting an accumulation of organic matter in this zone. However, as organic C (and thus c: N ratios) declined with depth, so too did soil total N concentration. Not surprisingly, fertiliser measurably increase soil total N, N applications did not but indirectly may have affected soil N dynamics by increasing net mineralisation (due to its "priming" effect) thereby stimulating plant growth and thus increasing the size of the organic N pool through greater plant decay. Total soil N concentration did not change significantly from the first to the second season. This could be attributed to the fact that N gains and losses on the pastures, being over 15 years old, were probably in equilibrium. Generally similar trends in soil total N down the profile over both seasons was further confirmation of this. Before the application of any fertiliser, 331.9 kg NH[4]-N was measured in the soil to a depth of 1m, on average, over both seasons. This amount represented only 2.1% of the soil total N in the profile. The concentration of NH[4]-N followed a quadratic trend down the soil profile, irrespective of the amount of fertiliser N applied, with the largest concentrations accumulating, on average, in the 0-10cm and 75-100cm depth classes and lowest concentrations in the 50-75cm depth class. Laboratory wetting/drying experiments on soil samples collected from a depth of 75-100cm showed that NH[4]-N concentrations declined only marginally from their original concentrations. A high organic C content of 1.44% at this depth was also probable evidence of nitrification inhibition. Analysis of a similar Inanda soil form under a maize crop did not exhibit the properties eluded to above, suggesting that annual turn-over of the soil was causing mineralisation-immobilisation reactions to proceed normally. Addition of fertiliser N to the pasture significantly increased the amount of NH[4]-N over that of the control camps. Furthermore, the higher the application rate, the greater the increase in NH[4]-N accumulation within the soil profile. As N application rates increased, so the NH[4]-N:N0[3]-N ratio narrowed in the soil complex. This was probably due to NH[4]-N being applied ln excess of plant requirements at the high N application rates. On average, 66.7 kg more NH[4]-N was present in the soil in the first season than in the second after fertilisation. Although this amount did not differ significantly from spring through to autumn, during early spring and late summer/autumn concentrations were higher than in mid-summer. Observed soil NH4-N trends were also very similar to the soil total N trends within both seasons, suggesting that soil total N concentrations might well play an important role in determining soil NH4-N concentrations. Before fertilisation, only 45.6 kg N0[3]-N, representing 0.29% of the soil total N, was on average, found in the profile to a depth of 1m. The highest concentration of N0[3]-N was lodged in the top 10cm of the soil. Nitrate-N declined, on average, with depth down the profile. However, during the second season, even though the concentration of N03-N declined down the profile, it increased with depth during relative to that of the first season, suggesting the movement of N0[3]-N down the profile during this period. Fertilisation significantly increased the concentration of N0[3]-N above that of the control camps. Concentrations increased as fertiliser application rates increased, as did N0[3]-N concentrations with depth. This has important implications regarding potential leaching of N03-N into the groundwater, suggesting that once applications reach levels of 300 kg N/ha/season or more, applications should become smaller and more frequent over the season in order to remove this pollution potential. On average, 94.3 kg N0[3]-N/ha was present down to a depth of 1m over both seasons. However, significantly more N0[3]-N was present in the second season than in the first. This result is in contrast to that of the NH[4]-N, wherein lower concentrations were found in the second season than in the first. No specific trends in N0[3]-N concentration were observed within each season. Rather, N0[3]-N concentrations tended to vary inconsistently at each sampling period. Nitrate N and ammonium N concentrations within each month followed a near mirror image. A DM yield of 12.7 t/ha, averaged over all treatments, was measured over the two seasons. A progressive increase in DM yield was obtained with successive increments of N fertiliser. The response of the kikuyu to the N applied did, however, decline as N applications increased. A higher yield of 1.8 t DM/ha in the first season over that of the second was difficult to explain since rainfall amount and distribution was similar over both seasons. On average, 2.84% protein N was measured in the herbage over both seasons. In general, protein N concentrations increased as N application rates increased. On average, higher concentrations of protein-N were measured within the upper (>5cm) than in the lower <5cm) herbage stratum, irrespective of the amount of N applied. Similar bi-modal trends over time in protein-N concentration were measured for all N treatments and within both herbage strata over both seasons, with concentrations tending to be highest during early summer (Dec), and in early autumn (Feb), and lowest during spring (Oct), mid-summer (Jan) and autumn (March). spring and autumn peaks seemed to correspond with periods of slower growth, whilst low mid-summer concentrations coincided with periods of high DM yields and TNC concentrations. The range of N0[3]-N observed in the DM on the Broadacres trial was 0.12% to 0.43%. As applications of fertiliser N to the pasture increased, N0[3]-N concentrations within the herbage increased in a near-linear fashion. On average, higher concentrations of N0[3]-N, irrespective of the amount of fertiliser N applied, were measured wi thin the upper (>5cm) than the lower <5cm) herbage stratum. A similar bi-modal trend to that measured with protein-N concentrations was observed in both seasons for N0[3]-N in the herbage. High concentrations of N0[3]-N were measured during spring (Nov) and autumn (Feb), and lower concentrations in midsummer (Dec & Jan), very early spring (Oct) and early autumn (March). During summer, declining N0[3]-N concentrations were associated with a corresponding increase in herbage DM yields. A lack of any distinctive trend emerged on these trials in the response of TNC to increased fertilisation with N suggests that, in kikuyu, applied N alone would not materially alter TNC concentrations. Higher concentrations of TNC were determined in the lower <5cm) height stratum, on average, than in the corresponding upper (>5cm) stratum. This may be ascribed to the fact that TNCs tend to be found in higher concentrations where plant protein-N and N0[3]-N concentrations are low. A P concentration of 0.248% before N fertilisation, is such that it should preclude any necessity for P supplementation, at least to beef animals. Herbage P concentrations did, however, drop as N fertiliser application rates were increased on the pasture, but were still high enough to preclude supplementation. Even though no significant difference in P concentration was measured between the two herbage strata, a higher P content prevailed within the lower <5cm) herbage stratum. On average, 2.96% K was present within the herbage material in this trial. The norm for pastures ranges between 0.7 and 4.0%. On these trials, applications of fertiliser N to the camps did not significantly affect K concentrations within the herbage. The lower <5cm) herbage stratum, comprising most of the older herbage fraction, was found to contain the highest K concentration in the pasture. The presence of significantly (although probably biologically non-significantly) less K within the herbage in the second season than in the first may be linked to depletion of reserves of · this element in the soil by the plant and/ or elemental interactions between K and other macro-nutrients. An average Ca content of 0.35% within the herbage falls within the range of 0.14 to 1.5% specified by the NRC (1976) as being adequate for all except high-producing dairy animals. Increasing N application rates to the pasture increased the Ca content within the herbage . No significant differences in Ca concentration were found between the upper (>5cm) and lower <5cm) herbage strata over both seasons, even though the lower stratum had a slightly higher Ca concentration, on average, than the upper stratum. Calcium concentrations did not vary between seasons, probably because concentrations tend rather to vary according to stage of plant maturity, season or soil condition. However, higher concentrations of the element were measured in the second season than in the first. The reason for this is unknown. On average, 0.377% Mg was present within the herbage over both seasons. This compares favourably with published data wherein Mg concentrations varied from 0 . 04 to 0.9% in the DM, with a mean of 0.36%. All camps with N applied to them contained significantly more Mg in their herbage than did the material of the control camps. On these trials, the Ca :Mg ratio is 0.92: 1, which 1S considered to be near the optimum for livestock and thus the potential for tetany to arise is minimal. Magnesium concentrations remained essentially similar within both herbage strata, regardless of the rate of fertiliser N applied. As in the case of Ca, Mg concentrations within the herbage were significantly higher in the second season than in the first. Calcium:phosphate ratios increased, on average in the herbage, as N application rates increased. This ratio was high in spring, dropped off in summer and increased again into autumn, suggesting that the two ions were following the growth pattern of the kikuyu over the season. The K/Mg+Ca ratios were nearly double that of the norm, suggesting that the pasture was experiencing luxury K uptake which may be conducive to tetany in animals grazing the pasture. This ratio narrowed as N application rates were increased, probably as a result of ion dilution as the herbage yields increased in response to these N applications. The ratio was low in spring (October), but increased to a peak in December, before declining again to a low in March. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

The seasonal production of 11 pastures was evaluated in dryland and irrigated trials at eight sites in the Winter Rainfall Region. These data were related to climatic conditions using the Growth Index concept to produce a model for pasture growth. Under dryland at Tygerhoek, the animal production potential of lucerne and medic was compared in grazing trials. Lucerne was found to be the higher producing of the two. At this site also, the influence of chemical control of volunteer grasses in dryland pastures on animal production potential was tested. Weed control had a positive influence on animal production at low, but not at high stocking rates. Under irrigation at complex grass/legume Tygerhoek, the grazing capacity of a mixture was established under continuous and rotational grazing. While rotationally grazed pastures produced the highest yields, the clover component of these pastures proved to be most productive under continuous grazing. As a result, rotationally grazed pastures, could carry more animals, but animal production was generally highest under continuous grazing. Under irrigation at Outeniqua, seven grass and grass/legume mixtures were compared in grazing trials. Pastures based on fescue generally had the highest grazing capacity, but those based on white clover the highest animal production potential. These data were used to produce a climate:pasture:animal which was validated using independent This model was used to predict animal production model, grazing trial data. performance of two-species mixtures at a number of sites. These results suggested that while grass pastures allowed more animals to be carried than did mixtures, both animal performance and gross returns were highest in grass/legume mixtures. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.

Lolium perenne L. (perennial ryegrass) generally fails to persist under the sub-tropical cpnditions of South Africa. Furthermore, little research data are available on how to manage this species locally. This study was designed to identify the management options, particularly with r espect to grazing defoliation, which would help enhance the longevity of perennial ryegrass pastures. This was addressed by: 1) reviewing on-farm management practices of perennial ryegrass in KwaZulu-Natal; 2) conducting a detailed two-year field study of the effects of grazing frequency (HF, MF and LF = high, medium and low frequency, respectively) and intensity (HI, MI and LI = high, medium and low intensity, respectively), rotationally applied with the addition of a continuous grazing treatment (CG), on parameters linked to persistency. tiller population dynamics, dry matter These included: (DM) yield and quality, perennial ryegrass vigour, weed invasion and root development; and 3) examining effects of different levels of applied nitrogen (N) during the establishment year on various parameters linked to persistency. These included: tiller population densities, DM yield and quality, perennial ryegrass vigour, weed invasion and root development. The review of on-farm management practices of perennial ryegrass growers in KwaZulu-Natal revealed that reasonably high rates of N application (e.g. 350 and 250 kg N ha¯¹ a¯¹ to perennial ryegrass as pure and clover-based stands, respectively) are important for pasture survival. However, a consistent distribution of the applied N is even more important (i. e. at least seven split applications of N onto pure stands of perennial ryegrass and five onto perennial ryegrass-clover). In terms of grazing management, the period of absence of animals from the pasture during summer was identified as the most important grazing variable affecting pasture survival (i.e. ≥ 21 days). Also, the length of the period of occupation by animals should be as short as possible, particularly during summer (i. e. ≤ 3 days). Paying careful attention to summer irrigation is also an important variable contributing to pasture survival. Grazing intensity was not highlighted as an important contributor to pasture survival. In terms of tillering potential, DM yield and quality (cellulose dry matter disappearance and herbage N) and perennial ryegrass vigour, perennial ryegrass followed definite seasonal trends. These were highest during autumn and spring and were lowest during the mid to late summer period. Perennial ryegrass was most susceptible to general sward degradation through poor management during the mid to late summer period when the danger from weed invasion is greatest and its growth potential, vigour and tillering abilities are lowest within these seasonal periods, grazing defoliation produced marked effects. In terms of tiller survival, DM yield, plant vigour, reduced weed invasion and root production, treatments incorporating low frequency grazing (e.g. LFLI and LFHI) generally out-performed (P≤0.05) those incorporating high frequency grazing, irrespective of the intensity (e.g. HFHI, HFLI, and continuous grazing (CG)). The defoliation treatment incorporating medium frequency and intensity (MFMI) (currently the recommended defoliation strategy for perennial ryegrass) was also out-performed in many instances (P~0.05) by the low frequency treatments (e.g. LFHI and LFLI) . During the establishment year, increasing levels of applied N increased (P≤O. 05) perennial ryegrass DM yields and herbage quality. Models predicting the response of DM yield and quality to applied N suggest linear responses up to 720 kg N ha¯¹ a¯¹. Further refinement of such models and the inclusion of animal production parameters is recommended. Maximum (P≤0.05) tiller population densities occurred at applied N levels of 480 kg ha¯¹ a¯¹. Perennial ryegrass vigour increased (P≤O. 05) with increasing levels of applied N up to 480 kg h¯¹ a¯¹, but individual tiller vigour decreased. Increasing levels of applied N up to 360 kg ha¯¹ a¯¹ suppressed (P≤O. 05) weed tiller densities. Increasing levels of applied N (up to 600 kg h¯¹) increased (P≤O. 05) the root organic matter (OM) per unit volume of soil in the top 5 cm of the soil and decreased root OM per unit volume in the 10 - 20 cm soil depth category. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1994.

La invasió de pastures per arbustos és un fenomen global. Als Pirineus, el bàlec (Cytisus balansae ssp europaeus) és un dels arbustos que més freqüentment envaeix pastures de muntanya. La presència de bàlec comporta alguns efectes negatius, com poden ser la reducció de la productivitat de pastures, homogeneïtat d’hàbitats, pèrdua d’hàbitat per a algunes espècies animals amb interès de conservació o increment del risc d’incendis. Degut als efectes negatius, la invasió de pastures per bàlec s’ha gestionat freqüentment amb foc prescrit o desbrossament mecànic, juntament amb pasturatge per reduir la capacitat de colonització de les pastures per bàlec. Tot i que es creu que la disminució de l’activitat agrària ha afavorit la invasió de pastures per bàlec, les causes d’aquesta invasió són incertes i podrien ser degudes a la combinació de múltiples factors que interaccionen i que per tant, són difícils de considerar de forma aïllada. A escala regional, el canvi climàtic podria contribuir a la invasió de pastures per bàlec. A escala local, les pertorbacions (com el pasturatge i el foc) podrien ser claus per entendre la dinàmica de la vegetació en aquests sistemes. A la mateixa escala, també les interaccions entre plantes (competència i facilitació) podrien determinar la dinàmica de la vegetació en les pastures. A la tesi, s’intenten analitzar les causes de la invasió de pastures per bàlec a escala local, considerant les pertorbacions amb foc, el pasturatge i les interaccions entre plantes en diferents comunitats de pastures com a determinants de la invasibilitat d’aquestes. Entre els efectes de la invasió de pastures per arbustos, s’ha observat una reducció en la capacitat de segrest de carboni dels sòls que podria contribuir de forma decisiva al canvi climàtic, tenint en compte la gran superfície de pastures del planeta que estan sent envaïdes per arbustos. A la tesis s’intenten detectar els efectes de la invasió de pastures per bàlec sobre el segrest de carboni, així com detectar els principals mecanismes que explicarien aquests canvis. Sobre les causes de la invasió de pastures per bàlec es conclou que els processos a petita escala com la competència i la facilitació poden ser claus per entendre la dinàmica de la invasió de pastures per arbustos. Pastures amb diferent palatabilitat van mostrar diferent invasibilitat. Així, el bàlec apareixia amb més freqüència en pastures amb espècies palatables, i en menor freqüència en pastures no palatables, malgrat que en aquestes últimes podria existir una menor mortalitat dels arbusts juvenils degut a una menor pressió de pasturatge. Diferents pertorbacions amb foc també van demostrar tenir efectes diferents sobre la cobertura de bàlec després de la pertorbació, amb els focs prescrits repetits mostrant un efecte similar al dels incendis. Sobre els efectes de la invasió de pastures per arbustos sobre el segrest de carboni, es va observar que no disminuïa el contingut de carboni del sòl. Fins i tot, en els primers centímetres de sòl existia un lleuger increment del carboni sota els arbustos, respecte del carboni sota les pastures. La baixa qualitat de la fullaraca dels arbustos s’apunta com la causa de l’augment de carboni en els primers centímetres de sòl sota els arbustos. Un increment de temperatura com a conseqüència del canvi climàtic podria causar una pèrdua de carboni del sòl tant en les pastures com en els arbustos. Tot i així, la fracció més recalcitrant del carboni dels sòls sota bàlec semblava ser més sensible a increments de temperatura que la fracció de carboni total. / Land use changes are one of the main components of the global change and they have important effects on ecosystems. Woody plant encroachment into grasslands is a worldwide phenomenon. In the Pyrenees, the most abundant shrubs encroaching into mountain grasslands are a legume shrub (Cytisus balansae ssp europaeus) and a conifer shrub (Juniperus communis ssp alpina). This thesis focuses on the understanding of the causes and consequences of shrub encroachment into mountain grasslands in the Pyrenees. The main objectives of the thesis are: (i) understanding the role of different grassland communities and different fire disturbances on grassland invasibility by shrubs, and thus on shrub proliferation dynamics; (ii) understanding how shrub encroachment into grasslands affects carbon (C) sequestration, in order to know if shrub encroachment may contribute to increase global warming. Our results show that fine-scale spatial heterogeneity in grasslands is crucial to understand shrub encroachment into grasslands. Shrubs established more often close to palatable grasses, but the associational resistance mechanism may contribute to decrease shrub mortality rates close to unpalatable grasses. The effects of repeated prescribed burning were similar to those of wildfire on reducing shrub cover and shrub patch size. Contrary to previous works, our results show that shrub encroachment into mesic grasslands increased sequestered C between 4 and 5 kg m-2 with respect to grasslands, mainly due aboveground and belowground biomass and litter. In addition, shrub encroachment increased soil organic C in the top 15 cm of soil with an accretion rate of 28-42 g C m-2 year-1. Shrub encroachment caused changes in the quantity and quality of organic matter and microclimate, although changes in aboveground quality may be the main mechanism to increase soil organic C after shrub encroachment. Increases in temperature, as a consequence of climate change, may reduce C stored in soils both under grasslands and shrublands. However, plant functional type (legume vs. conifer shrub) may have a different effect on C sequestration, and soil C under legume shrubs may be more vulnerable to climate change than soil C under conifer shrubs or grasslands.

Bibliography : leaves 150-158. / viii, 158 leaves, [7] leaves of plates : ill. (some col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.)--University of Adelaide, Dept. of Crop Protection, 1996?

[Truncated abstract] With the rapid development of multiple herbicide resistant weeds in crops, it is likely that an important role now exists for new grazing management strategies in farming systems to provide an integrated approach to weed management. In this thesis we examined the general hypothesis that sowing a legume of low preference by sheep relative to the target weeds of crops would improve the control of those weeds in a grazed pasture. To test this general hypothesis, legumes of low preference by Merino sheep were identified and a series of experiments conducted to determine the effect on pasture composition when these less preferred legumes were incorporated into a grazed pasture. We found a learned response that altered forage preference by sheep was important in determining the effectiveness of grazing to reduce seed set by weeds of crops. Investigations on this aspect of the grazing behaviour of sheep were a key part of this thesis. The short-term relative preference of Merino hoggets among 15 pasture legumes, 4 grain legumes and annual ryegrass was determined by offering adjacent monocultures of each of the forage genotypes to the sheep. The relative preference of the hoggets for each of the 20 forages was determined at three phases of plant growth from estimates of the amount of forage consumed. Sheep showed a low selective preference for Vetch (Vicia sativa L.), chickpea (Cicer arietinum L.), biserrula (Biserrula pelecinus L.), lotus (Lotus ornithopodioides L.) and snail medic (Medicago scutellata L.) cvs. Kelson and Sava at the vegetative phase of plant growth. An indoor method was also developed to test the relative preference of sheep among forages growing in pots. Using this method chickpea and snail medic, but not biserrula, were found to have a low relative preference by sheep at the vegetative phase.

Diss. (sammanfattning) Alnarp : Sveriges lantbruksuniv. / Härtill 5 uppsatser och 1 bildbil.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2003. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2007. / Härtill 4 uppsatser.