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Response of a permanent pasture sod to rates of nitrogen and to nitrogen combined with phosphorus and potassium fertilizersLlambias, Carlos J. J. January 1962 (has links)
Thesis (M.S.)--University of Wisconsin--Madison, 1962. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 58-63).
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Effects of certain fertilizer and lime treatments on yield, chemical composition, and vegetative population of a pasture and on certain properties of Coeburn silt loamHenry, Charles William January 1946 (has links)
Fertilizer and lime investigations to determine their effect upon crops and soils have been carried out at many experiment stations. The correlation of the yield, the type and the chemical composition of vegetation and changes taking place in chemical properties of soil will contribute to a better understanding of soil fertility problems.
Since 1940 the Virginia Agricultural Experiment Station, in cooperation with the Tennessee Valley Authority has conducted a pasture experiment on Coeburn Silt Loam in Wise County, Virginia. Several different fertilizer treatments with and without lime, were used to evaluate their effect upon pasture vegetation.
The purpose of this study is to determine the extent of and nature of the effects of certain fertilizers and lime treatments on pasture vegetation and on the soil.
The experiment was conducted on Coeburn Silt Loam, a soil derived from interbedded shale and arkosic sandstone. This soil is well drained, occurs on rolling to hilly relief, is low in inherent fertility and is fairly well adapted to agricultural uses. / Master of Science
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The influence of fertiliser nitrogen on soil nitrogen and on the herbage of a grazed kikuyu pasture in Natal.Hefer, Graham Daniel. January 1994 (has links)
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.
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Nitrogen utilization in tall fescue (Festuca arundinacea Schreb.) pastures fertilized with nitrogen or grown with alfalfa (Medicago sativa L.) or red clover (Trifolium pratense L.)Absher, Karen Lynne 01 August 2012 (has links)
Use of legumes as an alternative to nitrogen (N) fertilization in pasture management improves forage quality and animal performance and has been suggested to reduce the potential for environmental pollution. "Kentucky 3l" tall fescue fertilized with 160 kg N ha-1 yr-1 (split application) was compared to tall fescue grown with alfalfa or red clover in a 5-yr pasture experiment on a mixed Typic Hapludult. During yr 6, effects of N fertilization or the legume on soil N, forage N concentration, yield, botanical composition, N intake by esophageally fistulated steers grazing the pastures and N utilization by wethers fed the harvested forages were investigated. Soil ammonium was higher (P ≤ .01) in the A and B horizons in the tall fescue-red clover pastures compared to the other treatments and nitrate was lower (P ≤ .05) in the A horizon, but concentrations differed (P ≤ .01) by date. Nitrate in the A horizon averaged 2.65, 1.38 and 2.21 ppm for tall fescue-N, tall fescue-red clover and tall fescue-alfalfa, respectively. In the B horizon, average soil NO3 was .43, .23 and .53 ppm for tall fescueâ N, tall fescue-red clover and tall fescue-alfalfa, respectively. Tall fescue-alfalfa pastures were higher (P ≤ .01) in percentage legume than tall fescue-red clover, overall, but differed by date (P ≤ .01). Alfalfa was generally higher (P ≤ .05) in N concentration than red clover. Total kg N accumulated ha⁻¹ in above-ground herbage was higher (P≤ .05) for the grass-legume mixtures than N-fertilized tall fescue. Esophageally fistulated steers grazing stockpiled tall fescue-alfalfa selected forage higher (P ≤ .05) in N concentration than steers grazing the other pastures. Stockpiled tall fescue-alfalfa fed to wethers in a metabolism trial was higher (P ≤ .01) in N concentration, dry matter digestibility (DMD), apparent N absorption, and N retention than the other treatments. All treatments differed, with wethers fed tall fescue-red clover having the lowest DMD, apparent N absorption and N retention. Wethers fed tall fescue-alfalfa and tall fescue-red clover had higher blood urea N then those fed tall fescue-N. Results of this research demonstrate that soil NO₃ concentrations were low for all three forage treatments and would not contribute to ground water contamination. Legumes supplied adequate N to achieve yields similar to tall fescue fertilized with N and increased N production ha⁻¹ in the above ground biomass. Digestibility and utilization of the N in stockpiled tall fescue were improved by inclusion of alfalfa but not red clover. / Master of Science
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Adubação de sistemas: antecipação de adubação nitrogenada para a cultura do milho em integração lavoura-pecuária / Fertilization systems: anticipation of corn nitrogen fertilization inintegrated crop-livestock systemsBortolli, Marcos Antonio de 17 February 2016 (has links)
Tradicionalmente, em cultivo sob sistema de plantio direto, a adubação é feita para a cultura produtora de grãos e durante o cultivo de pastagens, poucos são os casos em que se utiliza algum tipo de fertilização. A demanda por nutrientes de uma cultura pode ser atendida pela ciclagem de nutrientes do sistema e pelas entradas ou adições oriundas da adubação mineral, porém de forma geral a ciclagem não tem sido tratada como uma ferramenta importante no processo de fornecimento de nutrientes para as plantas. O tipo e a condição em que se encontra o resíduo vegetal em decomposição sobre o solo pode afetar a eficiência da ciclagem de nutrientes principalmente o momento em que o nutriente da palhada vai ser liberado. Deste modo, faz-se importante um estudo dos efeitos da adubação nitrogenada e o manejo de altura do pasto sobre a produtividade de grãos de milho, os níveis de nitrogênio (N) mineral do solo bem como sobre a dinâmica da decomposição dos resíduos produzidos em um sistema de integração lavoura-pecuária. Foi realizado um experimento dividido em três fases: 1- cultivo e manejo de sorgo forrageiro sob pastejo; 2- cultivo de aveia preta sob pastejo e 3- cultivo de milho para produção de grãos Nas fases 1 e 2 o experimento foi conduzido em um fatorial 2 x 2 sendo o primeiro fator duas alturas de de manejo do pasto, alta e baixa altura do pasto (AAP e BAP) e o segundo fator foi a aplicação de 200 kg ha-1nitrogênio na pastagem ou na cultura de grãos (NP e NG). Na fase 3 que era composta pela produção de grãos de milho o experimento foi um tri-fatorial com parcela dividida sendo que os tratamentos são os mesmos das fases anteriores, porém as parcelas foram divididas e a elas incluido um terceiro fator: doses de nitrogênio aplicadas em cobertura na cultura do milho (0, 100, 200 e 300 Kg ha-1). O experimento foi realizado em delineamento blocos ao acaso com três repetições e foi instalado no município de Abelardo Luz – SC no período de outubro de 2012 a agosto de 2014. Avaliou-se a velocidade de decomposição dos resíduos das culturas implantadas, bem como a liberação de nutrientes destes resíduos, o efeito dos tratamentos sobre o N-mineral do solo e a produtividade de grãos de milho e seus componentes principais. Os resultados demonstraram quea antecipação da adubação nitrogenada a qual é aplicada na fase de pastagens em sistemas de integração lavoura-pecuária mostrou-se uma tecnologia eficiente podendo vir a substituir a adubação de cobertura de plantas de milho cultivadas na sequencia. O potássio componente dos residuos vegetais apresentou elevada taxa de liberação sendo liberado em grande quantidade já nos primeiros dias após a secagem dos resíduos culturais. Apesar de consideravelmente alta a dose de nitrogênio utilizada tanto na pastagem quanto na cultura de grãos não apresentou riscos de lixiviação de nitrato no período avaliado. / Traditionally in no-tillage systems, fertilization is done to the catch crop. In general nutrient cycling in crop systems has not been treated as an important tool in the process of nutrient supplying for plants. The type and the condition in which vegetable residuesis decomposed can affect the efficiency of nutrient cycling.This study assessed the effect of anticipated nitrogen fertilization in crop-livestock systems on cultivated cornproduction, rate ofnutrient release from plant residue, and theN-minerallevels of soil. The study was carried out in the city Abelardo Luz (SC) in a Clayey Oxisol. The experimental design was a randomized block design with three replications. The treatments were arranged in a 2 x 2 factorial arrangement. The first factor was N Fertilization Time: in the N-Pasture level, nitrogen (200 kg ha-1 N) and N-Grains level, no nitrogen was applied. The second factor was the Grazing Height, characterized by two sward heights of oat at 15 cm (Low Height Pasture) and at 30 cm (High Height Pasture). Corn hybrid ‘Máximus’ was sowed in 10thOctober, 31 days after the removal of animals. In the twelve resulting plots from the combination of treatments on pasture phase (N Fertilization Time x Grazing Height) rates of N-fertilizer (0, 100, 200 e 300 Kg ha-1 of N) as urea were allocated in the split plot.We conclude that anticipated N fertilization of winter cover crop pasture to provide high-quality forage and carry-over N to the subsequent corn crop and may eventually replace side drees nitrogen fertilization on corn and can improve overall N fertilizer efficiency use in integrated crop-livestock systems.The rate of K release from plant residues is very fast, releasing large quantities in the first days after plant desiccation.Despite of considerably high nitrogen dose used in both the pasture and at the grain crop it was not observed nitrate leaching risks during the study period.
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Nitrogen management strategies on perennial ryegrass-white clover pastures in the Western Cape ProvinceLabuschagne, Johan 03 1900 (has links)
Thesis (PhD(Agric) (Agronomy))--University of Stellenbosch, 2005. / The response of perennial ryegrass and white clover, grown under controlled conditions, to
fertiliser N rates applied under variable soil temperature (6, 12 and 18 °C), soil water potential
(-10, -20, -25 and -35 kPa) and seasonal growing (June/July and October/November)
conditions as well as field conditions, were evaluated. Primary- (PDM), residual- (RDM) and
total dry matter (TDM) production (g pot-1) were recorded over the first- and second regrowth
cycles as well as the accumulative DM production over the two regrowth cycles, respectively.
Leaf N content (%) was recorded at the end of first and second regrowth cycles. Tiller/stolon
numbers and root dry mass (g pot-1) were recorded at the end of the second regrowth cycle.
Soil ammonium-N and nitrate-N (mg kg-1) content was monitored after fertiliser N
application.
Decreasing soil temperatures resulted in decreased TDM production in both crops. Only
perennial ryegrass was influenced by fertiliser N rate, with a general increase in dry matter
production as fertiliser N rate was increased. Ryegrass TDM production did not differ
between the 100 and 150 kg N ha-1 rates but were both higher (P=0.05) if compared to the 0
and 50 kg N ha-1 treatments. Soil nitrate levels 31 days after application of 150 kg N ha–1 were
still sufficient to stimulate ryegrass RDM production. The 173.8% increase in ryegrass TDM
production measured at 6 °C where 150 kg N ha-1 was applied compared to the 0 kg N ha-1
treatment illustrated the ability of ryegrass to respond to fertiliser N at low soil temperatures.
Soil water potential of -20 kPa resulted in higher ryegrass PDM and TDM production
compared to the -25 and -35 kPa levels. White clover PDM and TDM production were
however not influenced by soil water potential or fertiliser N rate. Ryegrass TDM production
increased (P=0.05) as fertiliser N rates were increased. The most favourable soil water level
for both ryegrass and clover root development was found to be -35 kPa.
Perennial ryegrass and white clover PDM, RDM and TDM production were higher during the
October/November season compared to the June/July season. Increased fertiliser N rates
resulted in increased (P=0.05) ryegrass PDM and TDM production. White clover dry matter
production was not influenced by fertiliser N rates. In the field study the effect of 0, 50, 100 and 150 kg N ha-1 applied as a single application
either in autumn, early winter, late winter, early spring or late spring on pasture dry matter
production, clover content and selected quality parameters of a perennial ryegrass-white
clover pasture were investigated. Soil nitrogen dynamics in the 0-100, 200-300 and 400-500
mm soil layers were studied for 49 days following fertiliser N application.
The effect of 50 kg N ha-1 on soil N dynamics was generally the same as found at the 0 kg N
ha-1 applications and may therefore be regarded as a low risk treatment. The application of
150 kg N ha-1 especially in autumn and early winter showed a tendency to exceed the
absorption capacity of the pasture and thereby expose fertiliser N to possible leaching and
contamination of natural resources.
Increased fertiliser N rate resulted in a general increase in pasture dry matter production with
the highest yields recorded where N was applied in early and late spring and the lowest in
early winter. The application of 150 kg N ha-1 in early and late spring resulted in the highest
TDM production, however, the 50 kg N ha-1 resulted in a more efficient conversion of N
applied to additional DM produced. In contrast to DM production, the clover percentage
generally decreased as fertiliser N rate was increased. The effect of season of application was
inconsistent. Annual trends show that the clover percentage eventually recovered to the same
levels as the 0 kg N ha-1 treatments. Due to the above minimum levels recorded for most
mineral and quality parameters tested it is envisaged that treatment combinations as used in
this study will not be at any disadvantage to pasture and animal productivity.
The study has shown that the use of fertiliser N to boost perennial ryegrass-white clover
productivity and thereby minimising the negative effect of the winter gap on fodder flow
management during the cool season in the Western Cape Province, may be an important
management tool. Except for late spring applications, all seasons of application reduced the
negative impact of the winter gap on fodder availability. It is concluded that regression lines
as summarised in Tables 7.2 and 8.2 show great potential to be instrumental in developing
regression models, accurately predicting the effect of fertiliser N rate on pasture performance.
Other factors to be considered includes the productivity of the pasture, initial clover content,
expected clover content at the end of the first regrowth cycle after fertiliser N application and
the quantity of additional fodder required. Additional requirements will be to maintain and 150 kg N ha-1) in winter, as the N uptake capacity of the pasture could be exceeded and
thereby increasing the risk of N leaching, resulting in environmental pollution. The N
response efficiency of the pasture is also the lowest at the 150 kg N ha-1 rates, thereby
reducing the profitability of these treatments.
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The effect of nitrogen fertilization and stage of re-growth on the nutrititive value of kikuyu in the Midlands of KwaZulu-Natal.Dugmore, Trevor John. January 2011 (has links)
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.
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Pasture responses to lime and phosphorus on acid soils in Natal.Miles, Neil. January 1986 (has links)
No abstract available. / Thesis (Ph.D.)-University of Natal, Pietermaritzburg, 1986.
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