Browsing by Author "Miles, Neil."

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Effect of potassium, nitrogen and silicon fertilisation on sugarcane growth and quality, nutrient uptake dynamics and soil chemistry in two contrasting soils of KwaZulu-Natal, South Africa.
(2020) Rhodes, Ruth.; Hughes, Jeffrey Charles.; Miles, Neil.
Abstract available in pdf.
Factors affecting phosphorus requirements for the soils of South African Sugar Industry.
(2016) Poswa, Lwazi Zukisa.; Muchaonyerwa, Pardon.; Miles, Neil.; Manson, Alan David.
Abstract available in PDF file.
The influence of fertiliser nitrogen on soil nitrogen and on the herbage of a grazed kikuyu pasture in Natal.
(1994) Hefer, Graham Daniel.; Tainton, Neil M.; Miles, Neil.
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.
An investigation of factors contributing to soil degradation under dairy farming in the Tsitsikamma.
(2002) Milne, Ryan McKinlay.; Haynes, Richard John.; Miles, Neil.
Pasture-based dairy farming is the major land use in the Tsitsikamma region of the Eastern Cape. Permanent kikuyu grass (Pennisetum clandestinum) dominates pastures in the region. Kikuyu pastures do not, however, provide adequate year-round quality feed for dairy cows. This has led to the use of annually sown pastures with perennial ryegrass (Lolium perenne) to provide winter forage. Soil degradation under this management has, however, become recognised as a major limitation. Soil quality and degradation under annual and permanent pasture in the region were evaluated in three separate studies. These were (i) an investigation of the extent of loss of soil organic matter and related soil microbial properties and aggregate stability under annual pastures, (ii) a comparison of soil physical properties under annual and permanent pastures and (iii) a survey of the nutrient status of soils and pasture herbage in the region. In the first study, four commercial dairy farms, situated on sites which represented the three main soil groups in the region were sampled, were taken from under permanent kikuyu pastures, annual ryegrass pastures and undisturbed native vegetation nearby. In comparison with undisturbed, native vegetation, soils under both annually cultivated and permanent pasture had gained soil organic matter on the sandy, low rainfall eastern end of the Tsitsikamma. By contrast, at the higher rainfall, finer-textured, western end, where the native vegetation consists of coastal forest, there was a loss of soil organic matter under both types of pasture. Despite this, soil organic C content was lower under annual ryegrass than permanent kikuyu pasture at all the sites reflecting the degrading effect of annual cultivation on soil organic matter. As a consequence, labile, K(2)S0(4) - extractable C, microbial biomass C, basal respiration, arginine ammonification, flourescein diacetate hydrolysis rates and aggregate stability were all less under annual ryegrass than permanent kikuyu pastures at all the sites. The effects of annual ryegrass and permanent kikuyu pastures on soil physical properties and root length density were compared with those of undisturbed native vegetation on the four experimental sites. Root density and the depth of rooting were much less under annual ryegrass than under kikuyu pastures or native vegetation. There was no consistent effect of improved pastures or pasture type on bulk density and total porosity or penetrometer resistance, although annual pasture soils generally had higher bulk densities and lower total porosities than those under native vegetation. There was a tendency for smaller saturated hydraulic conductivity and air permeability under ryegrass than kikuyu pastures, regardless of whether total porosity was higher or lower under ryegrass. This was attributed to annual cultivation and subsequent natural consolidation causing a decrease in pore continuity under ryegrass pastures. Penetrometer resistance values confirmed the presence of subsoil compacted layers at two annual ryegrass pasture sites. At one such site, subsoil tillage was effective in reducing penetrometer resistance and bulk density, increasing pore continuity (as evaluated by hydraulic conductivity and air permeability) and greatly increasing root density and rooting depth. The nutrient status of soil and herbage from annual ryegrass and permanent kikuyu pastures sampled from 40 dairy farms in the Tsitsikamma region were evaluated. Along with the decreased organic matter content, there was a decrease in soil pH and a loss of exchangeable cations under annual pastures. Large concentrations of extractable P and sometimes exchangeable K were measured in soils under both ryegrass and kikuyu pastures and it was concluded that the rates of applied P, and sometimes K, were often excessive (particularly under kikuyu). Various nutritional problems were also identified. These included the need for Ca supplementation, particularly under kikuyu, due to the low herbage Ca concentrations. The low Ca : P ratio measured in annual ryegrass pastures, and more particularly in kikuyu herbage, highlighted the low Ca content of herbage and also the tendency of kikuyu grass to accumulate large concentrations of P. The large K concentrations and high K : Ca +Mg ratios identified in pasture herbage suggest the potential for animal nutritional problems such as hypomagnesaemia. It was concluded that although kikuyu is an excellent pasture in terms of dry matter production it tends to be deficient in Ca (and sometimes Na) and can contain prohibitively high K levels, which are likely to induce Mg deficiencies in grazing animals. The micronutrient concentrations in herbage were generally adequate, although copper concentrations tended to be low suggesting that fertilizer applications and/or feed supplementation is required. It was concluded that annual conventional tillage results in a substantial loss of soil organic matter, soil microbial activity and aggregate stability under annual ryegrass pastures when compared to those under permanent kikuyu grass. This loss of soil organic matter can result in natural consolidation of the soil in the cultivated layer and exasperated through treading by the grazing cows. The annual cultivation can also lead to the formation of a subsoil compacted layer. Nonetheless, compaction can also occur under permanent pasture presumably due to treading damage. Careful management to avoid treading damage to pastures should be practised. In order to protect the organic matter status of annual pastures, direct drilling of such pastures should be seriously considered. In some cases, annual fertilizer P rates (and to lesser extent those of K) could be reduced considerably since the levels accumulated in the soils are excessive.
Pasture responses to lime and phosphorus on acid soils in Natal.
(1986) Miles, Neil.; De Villiers, John Matthew.
No abstract available.
Potassium reserves and fixation capacity in soils of the South African sugar industry and potential for their inclusion in soil testing and fertilizer recommendations.
(2018) Elephant, Dimpho Elvis.; Muchaonyerwa, Pardon.; Miles, Neil.
Abstract available in PDF file.