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Item Duration-controlled grazing of dairy cows : impacts on pasture production and losses of nutrients and faecal microbes to water : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand(Massey University, 2013) Christensen, Christine LynneMitigation strategies for improved environmental sustainability of the New Zealand dairy industry need to focus on reducing the transport of nitrogen (N) from urine patches and phosphorus (P) and faecal microbes from dung patches to waterways. One strategy is Duration-controlled grazing (DC grazing), a system based upon shorter grazing periods on pasture (4 hours) and removing cows to a stand-off facility for rumination and excretion. The stored effluent is applied to pasture as a slurry at an appropriate time when nutrients are required and soil conditions are suitable. A three year field study was established in the Manawatu to compare key features of DC grazing with a standard grazed (SG) system. This thesis explores the impact of a DC grazing system on the losses of N, P, potassium (K) and faecal microbes to water through drainage and surface runoff. It also investigates the effects of such a system on pasture production and intakes of pasture by cows. Pasture accumulation was the same for both treatments in the first year, but there was a 20% and 9% decline on the DC treatment in the subsequent two years. This was due to the way that slurry applications were managed. A large amount of slurry (212 kg N/ha) was applied in the first year, and no slurry was applied in the second year. In the third year slurry was applied four times at a total rate of 115 kg N/ha. The study indicates more frequent application of all nutrients captured in the effluent from standing cows off is required to maintain pasture production. Compared to the SG plots, the reductions in N losses from DC grazed plots were large, with an average 52% reduction in NO3- and 42% reduction in total N leached. Reducing urine deposition during autumn grazings appeared to have the largest impact on reducing NO3- leaching. Runoff losses of N were small and similar between treatments. The losses of P were small through both surface runoff and drainage. There was a large variation in runoff volume, which resulted in highly variable P runoff loads across plots and between treatments. The average 32% reduction in total P load from DC grazed plots was not significantly different from SG plots. Useful predictors of P load lost from all plots were runoff depth and the time cows spent grazing. Faecal microbe losses were also similar between treatments, with the useful predictors of faecal microbe concentration across all plots being the number of days since grazing and the climate after grazing. The amount of K applied in slurry and urine had a large influence on both soil and herbage K. It was determined that in a DC grazing situation, the K-rich liquid component must be included in the applied slurry to maintain soil K levels. The OVERSEER® nutrient budgeting software was able to simulate nutrient cycling in the DC grazing system reasonably well. The total N loss from the system was predicted accurately, although the relative proportion of N in drainage and runoff was not. Several opportunities for further work arise from this research. While DC grazing is a tool that could be implemented to significantly reduce N leaching losses, the management of collected excreta needs to be further developed to ensure pasture production gains are realised, or at least maintained. The combined effects of reducing treading damage and DC grazing should be investigated. Finally, a comprehensive economic analysis of standing cows off should be undertaken.Item Anion movement in a structured soil : a thesis for the degree of Doctor of Philosophy in Soil Science(Massey University, 1980) Kanchanasut, PimpanAnion movement in soil was studied both in the laboratory and in the field, using structured "undisturbed" soil and sieved aggregates. The movement of chloride, bromide and phosphorus was investigated. Chloride and bromide being non-reactive in soil, were used to indicate whether the flow was more uniform or preferential, while phosphorus was used to indicate the behaviour of strongly adsorbed anions. Experiments involving the movement of chloride and phosphorus through columns of 0.5-1 mm soil aggregates provided data on phosphate adsorption during miscible displacement. Chloride breakthrough curves were described well by conventional convective-dispersive theory. For phosphorus, linear adsorption isotherms were determined independently, using solution concentrations and equilibrium times similar to those pertaining in the aggregate columns. Conventional theory using these data predicted reasonably well the early part of the breakthrough curves, but did not predict the observed "tailing" of phosphorus breakthrough curves. The movement of anions through artificial soil channels and planar cracks was studied. The breakthrough curves showed the movement of both chloride and phosphorus was highly preferential through 0.5 mm diameter channels and 0.17 mm wide planar cracks. The results agreed quite well with model predictions. The movement of anions through 2.4 litre "undisturbed" soil cores was also studied. Under saturated conditions, both chloride and phosphorus moved preferentially. Dye studies indicated the major pathways were worm channels, root channels, and soil cracks. Under unsaturated conditions when the pressure potential was maintained at -0.02 bar (at which channels larger than 0.15 mm diameter and cracks wider than 0.07mm would be drained), the breakthrough curves for bromide were much less preferential than under saturated conditions. The experimental set-up for this experiment was designed so that the blockage of natural flow paths was minimized and the effects of porous plates at either end of the cores were avoided. Two field experiments were conducted at a mole-tile drained site on Tokomaru silt loam (a Fragiaqualf). One experiment investigated the movement of chloride and phosphorus solution ponded on the soil surface. The breakthrough curves for both chloride and phosphorus percolating from the surface to the mole-drains indicated the movement was very preferential, both anions reaching the mole-drains located at 400 mm depth within a minute of their application to the soil surface. Dye staining indicated the movement occurred mostly through worm channels and plant root channels associated with planar cracks. The other field experiment investigated the leaching of bromide under both ponded water and natural rainfall conditions. When the same amount of water was considered, leaching by rainfall was more effective than by ponding. However, under both water treatments, relatively large amounts of applied bromide remained unleached near the soil surface, while some bromide moved deep into the soil profile. Interception and stem flow appeared to be important factors causing non-uniform leaching under pasture by natural rainfall. Very considerable variation in bromide concentration between replicate soil samples was found, with a log-normal rather than normal distribution. Quite different leaching patterns were found in soil under pasture and in a soil which had been cultivated and cropped.Item The influence of phosphorus supply on below ground interferences between browntop and white clover : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1993) Pannell, Claire AstleyA low occurrence of white clover in pastures contributes to soil nitrogen (N) deficiency and a low quality feed for stock. There is evidence to suggest that competition for soil phosphorus (P) from roots of browntop plays an important role in determining the distribution of white clover in hill country swards. However, competition for soil P between roots of browntop and white clover has not been studied separately from other factors known to affect the growth and persistence of white clover (e.g., soil moisture, grazing management, shoot interferences (shading and physical impedance), and non-competitive root interferences). In hill country pastures, P level (phosphorus fertilisers), and defoliation (grazing management), are the main factors that can be changed by farmers to alter pasture botanical composition. The high cost of superphosphate has limited the potential of farmers to manipulate pastures using fertiliser applications. Therefore, it is important to know whether roots of browntop compete with roots of white clover for soil P, and whether a low supply of soil P will contribute to more severe competition from browntop roots. The possibility of non-competitive interferences occurring between roots of browntop and white clover must also be considered. How defoliation alters the balance of P acquisition between roots of browntop and white clover needs to be determined. Three techniques were employed to examine the nature of root interferences occurring between browntop and white clover: plant strategies; dual P isotope labelling; and a more traditional competitive settings trial using aerial partitions. Plant growth and root interferences were studied at a range of levels of soil P supply. Responses of growth and phosphorus uptake of browntop and white clover to increasing soil P supply were examined first, in the glasshouse, by growing monocultures of browntop and white clover in pots. Two mini-sward trials (one at deficient soil P supply, the other at adequate to luxury soil P supply) were carried out in the glasshouse to allow examination of root interactions (without shoot interactions). The basis of the experimental design was to determine the relative amounts of phosphorus-32 and -33 absorbed by a central row of plants (either browntop or white clover) from two adjacent soil spaces, one dominated by white clover roots, the other by browntop roots. 32P was injected into the soil on one side of the central row of plants, and 33P into the other side. 32p and 33p uptake was assessed by harvesting the shoots of the central plants, and counting the two isotopes. The competitive settings type trial compared the growth and P uptake of a single central plant in a small pot (no interference with other plants) with a central plant in a larger pot grown with roots associated with roots of plants of the same species (intraspecific association), or of the other species (interspecific association). Shoots of the central plant was separated from the shoots of outer plants by an aerial partition. The growth of browntop and white clover, and the nature of root interferences occurring within and between the two species was dependent on the level of soil P supply. However, the higher root density and specific root length (SRL) of browntop compared with white clover appeared to be the most important factor determining the success of browntop at all levels of soil P supply, regardless of whether or not browntop was grown with white clover. According to the plant strategy theory of Grime, browntop was found to be a stress tolerant plant. At low levels of P supply, the lower growth rate of browntop compared with white clover would be an important factor contributing to the dominance of browntop in hill country pastures. At adequate to luxury levels of soil P supply, shoot growth of browntop was more responsive than white clover, and browntop was capable of luxury consumption of P. The high growth rate and large demand for P contributed to the competitiveness of browntop at high P supply. However, the lower demand for P by white clover, and the high P supply may have enabled white clover to avoid competition with browntop. On unamended subsoil, browntop reduced P acquisition by white clover roots, and had a greater P uptake in the presence of roots of white clover than with roots of other browntop plants. Therefore, evidence of root competition for soil P from browntop with white clover was found. The competitive effect of browntop appeared to be due to browntop decreasing the availability of P in the soil, explained by browntop's ability to acquire more radioactive P from the soil than white clover. At low P supply (subsoil), P application, but not defoliation of browntop, reduced the competitiveness of browntop. At adequate P supply, the ability of browntop to acquire P was reduced by defoliation. The effect of defoliation was rapid (four days), and browntop was able to acquire P isotope to higher concentrations in the shoots than when undefoliated. Possibly the reduction of root competitiveness of browntop may be short-lived. Some interference, other than root competition, was occurring at intermediate to luxury levels of soil P supply, and may have masked the competitive effects of browntop. White clover appeared to benefit for P acquisition from growing with browntop, due to greater local root density compared with when growing with other white clover plants. Therefore, browntop and white clover appeared to gain mutual benefit for P acquisition from the presence of roots of the other species, and the competitive effects of browntop were not of overriding importance. The possibility of autotoxicity of white clover on its own root growth was discussed in relation to rhizosphere acidity effects on the toxicity of phenolics. At adequate to luxury levels of soil P supply, neither undefoliated browntop nor undefoliated white clover benefited from defoliation of adjacently growing white clover plants. However, at lower P supply, defoliation of white clover led to an increased P isotope acquisition by nearby browntop plants. Therefore, defoliation reduced the demand for soil P by white clover. Roots of browntop were not as tolerant of defoliation as white clover. In the field, the mat forming behaviour of browntop, physically impeding the growth of white clover and shading white clover stolons, would reduce the severity of competition for soil P between roots of browntop and white clover. Overall, root competition for P from browntop with white clover was found not to be as important as previously thought. The use of several experimental techniques allowed a clearer picture of the interferences that occur between browntop and white clover to be obtained. The nature of root interference changed with increasing P supply. The responses of browntop and white clover to increasing P supply was found to be enlightening when the plant strategy theory of Grime was used to compare browntop and white clover. However, the dual P isotope technique found plant interferences that were not detected by the other methods used (P response and competitive settings trial), and allowed interferences that were occurring simultaneously to be elucidated.Item The reactions and mechanisms of inorganic phosphate sorption by soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1975) Ryden, John ChristopherA review of the literature relating to the reactions and mechanisms involved in the sorption of inorganic phosphate (P) by soils and soil components suggested several topics for further research, the results and interpretations of which are presented in this thesis. Soils which contracted in components and properties considered to be important in P sorption sorbed between 210 and 3350 μg P/g during 40 hr from 0.1M NaCl at a final P concentration of 10 μg P/ml. Contrasting soils provided a more reliable basis for the interpretation of data obtained in investigations of the reactions and mechanisms of P sorption by soils. Sorption of P was described by four first-order reactions for each soil. The rate constant for a particular reaction was also similar for each soil, implying that the same series of reactions were involved in P sorption. The decrease in extractability and isotopic exchangeability of sorbed P with increasing time, following P addition, coupled with increased recovery of P by citrate-dithionite-bicarbonate extraction indicated that adsorption was followed by absorption. Elimination of the differences between the amounts of P sorbed from various support media during 40 hr, when an estimate of the equilibrium condition was made, pointed to the implications of time-dependent sorption in the interpretation of P sorption data. Virtually complete replaceability by K of Ca removed from solution in response to P sorption was obtained. Retention of Ca to balance the increased negative charge arising from P sorption, and not the precipitation of a calcium phosphate, is indicated. Time-dependent sorption affected significantly the interpretation of P sorption data using the Langmuir equation. For equilibrium data, the P sorption isothern for each soil was described by three distinct Langmuir equations, each corresponding to a particular P concentration range or region ( 0 to 0.02, 0.08 to 0.80, and 1.0 to > 20 μg P/ml ). The sorption energy constant of a Langmuir equation corresponding to a particular region was very similar for each soil and suggested similar sorption mechanisms for each soil. Charge and pH relationships of P sorption by two soils and Fe gel demonstrated that three distinct P sorption mechanisms caused the deviation of P sorption data from a single Langmuir equation. The same mechanisms were involved in P sorption by soils and Fe gel. Data suggested that the mechanisms involved the ligand exchange reactions -OH2+; H2PO4-, -OH; H2PO4-, and -OH; HPO42- at the hydrous-oxide surface. These mechanisms are in accord with the three Langmuir sorption energy constants obtained for each soil. The reactions and mechanisms of P sorption established have important implications to the plant availability of soil and fertilizer P, and provide a basis for the interpretation of other P sorption data.Item Phosphorus cycling in grazed, steep hill country : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1978) Gillingham, Allan GilbertMeasurements of P uptake by pasture and P return in posture litter and dung were made on two intensively grazed, north- and south-facing paddocks in steep hill country with soils of moderate to high P status. Both P uptake and more particularly the return of P in dung by grazing sheep, was high on the relatively level campsite areas but decreased sharply as ground surface slope increased. A high grazing pressure ensured that P return via litter was low relative to plant uptake. A net P balance derived for differing paddock strata showed a large net annual gain of P on campsites (50.1 and 119.8 kg ha-1 on north and south aspects, respectively) but a considerable net P loss from both 25° slopes (19.5 and 10.0 kg ha-1 on north and south aspects, respectively) and 45° slopes (15.3 and 13.8 kg ha-1 on north and south aspects, respectively). Differences between aspects in the net P balance could be explained by the overall difference in the topography of the two paddocks as it affected relative camping and grazing pressure on each stratum. Subsequent simulation studies were conducted using a mathematical model based on field data from the north-aspect paddock and validated against results from the south-aspect paddock. Results obtained from the model indicated that the quantity of P transfer from slopes increased at a greater than directly proportionate rate as stocking rate increased and was also directly related to pasture P content. Determination of relative root activity using 32P showed that approximately 90% of P uptake by pasture in spring occurred from within 7cm of the soil surface. The greater proportion of this occurred within the 0-3cm soil depth. No significant P uptake occurred from depths greater than 30cm. Although the extent of P uptake front 0-3cm depth soil was similar both upslope and downslope from a P source, the direction of predominant root activity at greater depths was affected by the steepness of slope, tending to be at an angle between vertical and that normal to the soil surface. A technique was developed to characterize short term plant-available P, using both 32P and 33P. Results indicated that the 32P/33P ratio of the water-extractable P fraction more closely resembled that in the plant than was the case for the Olsen P extract. Both ryegrass (Lolium perenne) and white clover (Trifolium repens) apparently utilized P from the same soil pool, the measured higher P content of ryegrass in this study being due only to a more extensive and rapidly developing root system than that of clover. The addition to soil of P extracted by water from litter, dung, and superphosphate sources showed that all forms had similar effects in increasing the water-extractable and Olsen P levels in the soil. Thus it could be expected that P from these three sources would have a similar availability to plants. The results of these and also P desorption experiments were qualitatively similar to those derived from a simple Langmuir model, suggesting that sorption and desorption of P in the soil from the field area occurred at sites on the solid phase with predominantly uniform sorption characteristics. Marked and largely unexplained variations in several soil parameters monitored over a year obscured the effects of P addition as a maintenance fertilizer application and also the net P transfer by grazing animals. In this and related situations, soil P analysis may not provide a sensitive measure of P status, except in the longer term. A more detailed examination is required to assess the usefulness of routine soil P analysis of hill soils for advisory purposes. The significant net P transfer from slopes by grazing animals suggests that the complementary roles of grazing management and fertilizer requirements in hill country should also be examined further.Item Field and laboratory studies of the movement and reactions of phosphorus in soils : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1978) Rennes, Alexander Marinus DickLow and stable concentrations of phosphorus (P) forms and sediment were obtained in stream flow from two small, adjacent, scrub-covered, and minimally-disturbed catchments near Palmerston North, New Zealand. In contrast, higher and irregular concentrations and loadings were obtained following land clearing, P fertilizer application, and the establishment of grazed pasture. The need for intensive stream sampling, as well as complete hydrograph data in order to obtain reliable information on stream loadings, is emphasised. High and fluctuating concentrations of P forms and sediment were obtained following the change in land use. A high proportion of the P and sediment loss occurred in the storm runoff component of stream flow. The estimated losses of fertilizer P in stream flow (approximately 1% of that added) were very small from an agronomic standpoint but they represent large proportional increases in the loadings of P forms in stream flow. The high amounts of water-extractable P present in the soils of the catchment (field soils), immediately following the aerial application of fertiliser P, declined rapidly to lower, more stable values. This pattern of decline for field soils was replicated using small pots established in the field (pot soils) and containing fertilized soil representative of the catchments. Close correlations were obtained between water-extractable P in the upper 1cm of field and pot soils, and mean dissolved inorganic P (DIP) concentrations in the surface runoff component of stream flow in closely-following storms. The possibility of predicting DIP losses in surface runoff from soils using a water-extraction technique is thus indicated. The decrease with time in the amounts of water-extractable P observed after superphosphate addition to field and pot soils was reproduced in the laboratory. This relationship validated the use of laboratory studies to examine the rate and extent of interaction of fertilizer P occurring in field soils and to predict the potential movement of fertilizer P from soils to waters. The decline in water-extractable P closely paralleled the decrease in plant uptake of P with time following fertilizer P addition to two constrasting soils. This suggested that water extraction may be a useful soil-testing procedure for predicting P availability to plants, as well as the movement of P in surface runoff from soils. The rate of decline in water-extractable P in a given soil was proportional to both the amount of P added and the amount initially extractable immediately following P addition. This suggests that the rate and extent of P sorption in a soil is directly related to soil solution P concentration. Differences were obtained, however, between three contrasting soils in the relative rate and extent of P sorption. A kinetic model based on the Langmuir equation was developed to simulate the decline in water-extractability of P added to three soils. Three populations of sites were assumed and the appropriate sorption maxima and binding energy constants were derived from sorption isotherm studies. The model provided a satisfactory prediction of the fate of different amounts of fertilizer P. It is probable that the further development of this model would provide a useful basis for predicting the fate of P added to soils and the potential movement of added P in surface-runoff waters.Item Phosphate cycling in grazed hill-country pasture : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1987) Rowarth, Jacqueline SaraA detailed study of the "above-" and "below-ground" components of the phosphorus (P) cycle was carried out in the North Island hill country of New Zealand. The effect of P fertiliser rate and degree of land-slope on pasture P uptake, faecal P return and changes in soil P fractions was examined over a three year period. Plant P uptake was found to decrease with increasing slope and increase with increasing rate of P fertiliser. The changes in plant P uptake were a function of changes in both dry matter yield and pasture P concentration. Pasture on campsites which initially had a high Olsen P status (>30) showed an unexpected apparent P response in both dry matter yield and plant P uptake. This response results from an artefact of the trial design whereby P fertiliser was applied to whole paddocks. The resulting improved nitrogen status of slopes at high rates of P fertiliser created abnormally high soil nitrogen levels on campsites, leading to very high levels of production. These findings are of significance in relation to soil fertility field trials conducted on individual slopes in hill country. Over the three year period of the trial seasonal plant P uptake followed the order: spring ≥ summer > autumn > winter, irrespective of slope category, fertiliser rate or grazing regime. The distribution of faecal material was found to be markedly affected by slope and approximately 60% of the material deposited in each paddock was returned to campsites. In the remainder of the paddock, faecal P return decreased by at least 50% with each 10° increase in slope. Paddock faecal P concentration (FP%) was predicted from the pre-grazed pasture P concentration (PP%) (calculated on a paddock basis) using the relationship: FP% = 3.19 PP% - 0.09 (r = 0.94). Net P balance calculations for various slope group categories showed that deficits between plant P uptake and faecal P return increased with increasing slope but were little affected by increasing P fertiliser rate and consequent increase in stocking rate. This finding verifies the use of a single animal loss factor for a given topography, irrespective of sheep stocking rate, in the Ministry of Agriculture's (MAF's) Computerised Fertiliser Advisory Scheme (CFAS) for P. Measurements of faecal distribution in this trial suggested the use of a lower animal loss factor (0.5 kg su-1 of P) for "Easy" hill country than that used currently (0.7 kg su-1 of P) in the CFAS model. Independent studies on the rate of P cycling from faeces were conducted. The study investigating breakdown of faecal material revealed that physical disintegration of faecal material is likely to occur before chemical decomposition. In winter conditions faecal material disintegrated within a month; in summer conditions disintegration took approximately three months. In both seasons material on campsites disintegrated more rapidly than that on steeper slopes. A further study using radioisotopes in the field found that the shortterm plant availability of inorganic faecal P was approximately half that of monocalcium phosphate fertiliser over a two month period in the spring. In a study on the "below-ground" components of the P cycle total soil P was found to increase with increasing rate of P fertiliser. The magnitude of these increases decreased with increasing slope and depth. Increases in organic P were found to be higher on campsites than steeper slopes. On campsites, the extent of increase in organic P decreased with increasing rate of P fertiliser. Inorganic P increased with increasing rate of P fertiliser on all slopes; the magnitude of the increase decreased with increasing slope. At low rates of P fertiliser a decrease in inorganic P was measured on steep-slopes over time indicating that P inputs were not balancing P outputs. A change in the non-occluded P fraction accounted for the greatest proportion of the change in inorganic P on most slopes. The fact that calcium-bound P accumulated on all slopes, and that large increases were evident at high rates of P fertiliser suggested that this fraction was not playing an active part in the P cycle but was accumulating as an insoluble residue from superphosphate. The plant availability of soil P fractions was investigated in a glasshouse study. Total plant P uptake was found to be highly correlated with initial levels of total P (r = 0.92),non-occluded P (r = 0.82), inorganic P (r = 0.91), Olsen P (r = 0.93) and water-extractable P (r = 0.97). Levels of organic P, occluded P and calcium-bound P were found to be essentially unchanged by plant growth over the eleven month trial period. Changes in the size of the cycling soil P pool were examined by combining results from the field trial with those from the glasshouse study. At low rates of P fertiliser (10 kg ha-1), increases in occluded P and calcium-bound P (i.e., unavailable inorganic P) in the 0-15 cm depth were occurring at the expense of available P. At a high rate of P fertiliser (100 kg ha-1) approximately two thirds of the P applied remained in the available form. On an annual basis, Olsen P increased with an increasing rate of P fertiliser and decreased with increasing soil depth and slope. Over the period of the trial Olsen P decreased significantly at the lowest rate of P fertiliser (10 kg ha-1) and increased significantly at the highest rate (100 kg ha-1) on the two slope groups studied. This indicated that these areas were not at "equilibrium" as defined by a stable Olsen P. At moderate rates of P fertiliser (20 and 30 kg ha-1) it was not possible to determine whether or not equilibrium conditions existed as the annual variability in Olsen P was too high. An attempt was made to determine soil P losses (as defined by the CFAS model) at the trial site. Despite intensive and careful soil sampling Olsen P could not be used to determine "equilibrium" conditions which are a pre-requisite for measurement of soil P loss. This finding prevented validation of soil loss factors on this hill-country site. Data generated from the large field trial for "above-" and "below-ground" components of the P cycle enabled recommendations to be made on the location of suitable soil sampling sites and also on the location of priority areas for application of P fertiliser in grazed hill country.Item Assessment of the biological availability of particulate-phase phosphorus : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1978) Hedley, Michael JamesA bioassay procedure for particulate-phase phosphorus (P), using Anabaena subcylindrica was developed and evaluated. Measurements of chlorophyll concentration and whole cell alkaline phosphatase activity were established as reliable indices of biomass and algal P status, respectively. Algal P content was found to be dependent on external P availability and was directly related to biomass, only when P availability was constant. The availability of P to Anabaena was controlled by culturing Anabaena in systems containing P sorbed on hydrous ferric oxide gel, saturated to varying proportions of the sorption maximum. By manipulating the amounts of P and gel, algae of similar P status to those grown in soil systems were produced. The combined bioassay-chemical fractionation procedure developed was used to chemically characterize the amounts and forms of biologically-available particulate inorganic P (IP) and organic P (OP) in potential surface runoff fractions from a wide range of soils. The simultaneous fractionation of Anabaena of similar P status to those in the bioassay systems, enabled a correction to be made for the algal-P contribution to extractable soil + algal P. In this way, the depletion of particulate IP and OP could be monitored. Algal growth depleted P from the 0.1M NaOH-soil-P fraction only; in several bioassays, 0.1M NaOH-soil-OP constituted the larger part of the P depleted. For most of the materials studied, except allophanic material, 0.1M NaOH-soil-P was depleted by 70 to 100% during the growth of Anabaena. Extractability in 0.1M NaOH suggests that biologically-available IP is present as surface-sorbed IP. A similar origin is probable for particulate-phase OP. The amounts of particulate P extracted by persulphate digestion, a commonly-used extraction procedure, were greater than those of biologically-available particulate P. Conversely, the amounts of isotopically-exchangeable P underestimated those of biologically-available particulate IP, as determined by the developed procedure. Algal-soil contact was an important factor influencing the depletion of soil P. Soluble, algal-extracellular products, acting in isolation from the algae, had little influence on particulate IP desorptlon. Also, the simple desorption of particulate IP was unable to account for the release of large amounts of P to the algae. The initial solution P concentration maintained by a particulate P source material considerably influenced the amount of algal growth and the extent to which particulate P was subsequently depleted. Biologically-available OP in two soil materials was extracted with 0.1M NaOH and the extracts were separated into humic and fulvic material, which were fractionated by agar gel and Sephadex gel chromatography, respectively. Most of the OP in the humic extract was present as high molecular weight organic matter-Fe-P complexes. In the fulvic extract, both high and low molecular weight organic matter-Fe-P complexes were identified. Inositol polyphosphates, both free and complexed, were identified by ion-exchange chromatography in the fulvic material. A major objective of the present study was the development of a chemical test for estimating the amount of biologically-available P in stream sediment-source materials. Except for samples containing allophanic material, the extraction of a water sample with 0.1M NaOH is proposed as a rapid and simple test for estimating the maximum amount of biologically-available P present in the sample.Item Investigating and modelling the dependency of pasture growth on soil sulphur and phosphorus availability : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University(Massey University, 1997) Faulalo, KenetiA study was conducted in the lower North Island of New Zealand to evaluate new soil testing methods for diagnosis of sulphur (S) deficiency against pasture growth responses to applied S fertiliser, in the presence and absence of phosphorus (P) and nitrogen (N). Field trials were conducted on eight sites at the AgResearch Hill Country Research Station at Ballantrae. The amounts of total soil S, P, and N at each site varied widely, caused by different superphosphate (SSP) fertiliser histories (low fertiliser input [LF] to high fertiliser input [HF]) and differences in grazing animal excreta return. Pasture growth on all of the eight plot trial sites chosen to represent a range of fertility levels, did not increase significantly to applications of S fertiliser alone (+S) (3 x 50kg S/ha as gypsum) over two years. Three LF sites did show significant increases in yields to application of S together with P (+SP, equivalent to SSP) (2 x 50kg P/ha as MCP). The +SP treatment was the most effective at promoting legume growth. A suite of soil tests were designed and tested for their ability to extract sulphate S and labile organic S from soils. The amount of S extracted by a mixture of 4%H2O2 and 0.5M KCl [4%H2O2/KCl(16hr)] (ranged from 50.7 - 105.3mg S/kg at a LF to a HF site) was found to be as good as the Olsen P test (ranged from 14.4 - 39.2mg P/kg soil) at predicting actual yields on unfertilised control plots (R2 > 63% using several mathematical expressions). The 4%H2O2/KC1(16hr) and the Olsen P tests were also strongly correlated (R2 = 77%). However, the 4%H2O2/KCl(16hr) was found to be better than the Olsen P test at predicting relative yield (RY) due to the application of a +SP treatment (R2 = 60% and 19% respectively) probably because it has the ability to predict any S deficiencies that applied P would have induced. Only after basal S fertiliser was applied to the control did the Olsen P explain a similar percentage of the variation in RY (R2 = 58%). As pasture growth was not singularly responsive to S, the ability of the 4%H2O2/KCl(16hr) test to predict S deficiency without P could not be tested. The 4%H2O2/KCl(16hr) test was examined on a series of short-term trials established at nine locations in the lower North Island on different soil types and different climatic conditions. The fertiliser treatments on these trials included an S treatment (50kg S/ha as gypsum) with and without N (50kg N/ha as urea). A basal application of P at a rate of 40kg P/ha as MCP was also applied. Similar to Ballantrae, application of S on top of P (+SP) was the most effective at promoting legume growth (17 - 400%). Application of N caused detrimental effect on legume growth but did increase total pasture yield at all sites (14 - 83%). Although the amounts of S extracted ranged from 59 to 156mg S/kg soil, this variation did not explain the variations in RY response to S at these sites, neither did the more traditional phosphate extractable S test (ranged from 4.1 - 10.5mg S/kg soil). The large range in RY suggest that basal P induced S deficiency on the control plots subsequent to soil sampling. For evaluation of the soil S test, an unfertilised control plot should have been included in the trial design. Failing to incorporate the interaction of S and P into the design of field experiments appear to be the main weakness in using RY as the pasture yield parameter for regression against soil test values. While efforts into improving soil tests for S are still required, it was concluded that the RY device is inadequate to normalise yields across sites because i) differences in yield potential caused by the interactions of soil fertility with climate could not be eliminated, and ii) estimates of yield potential vary with experimental designs. To overcome these problems with RY, a mechanistic pasture growth model was developed to incorporate the effects of actual evapotranspiration (ETa) on the relationships between pasture yields and soil fertility. It is assumed that climate can adequately be represented by rainfall, average temperature, and sunshine hours. A soil water balance model developed at Ballantrae, predicted daily soil water contents, drainage, and ETa. Pasture growth dependency on ETa and existing harvestable pasture mass were then modelled on a daily basis. The model was developed from pasture yields derived from 2 and 4 weekly harvesting regimes throughout 1993. The ceiling yield (Y ceiling) and ceiling growth rate (g ceiling) values for each site that were estimated from these data, ranged from 662 - 2526 kg/ha and 7.1 - 30.3 kg/ha/mm respectively from LF to HF sites. Soil fertility as indicated by the Olsen P test explained much of the variation in Y ceiling (R2 = 69%) and g ceiling (R2 = 77%). The estimated maximum yield (Y max) and maximum growth rate (g max) values unconstrained by soil fertility were 3125kg DM/ha (R2 = 69%) and 38.4 kg/ha/mm (R2 = 77%). These values were considered too low because the 2 and 4 weekly data did not represent the full range of pasture growth normally represented in sigmoid curves. Nevertheless, the structural strength of the model was shown by both Y ceiling and g ceiling approaching Y max and g max at the same rate, controlled by f1/2, the fertility level at which 50% of Y max (f1/2 = 23.0 mg P/kg soil, Olsen P) and 50% of g max (f1/2 = 22.5 mg P/kg soil, Olsen P) are obtained. A better estimate of Y max (8923 kg/ha) was obtained when yields harvested after a 9 week summer growth period was used to represent the ceiling yields at each site. As the dependency on soil fertility was the same, a g max of 70 kg/ha/mm was estimated. These estimates were used to simulate pasture growth over variable harvest intervals from autumn 1990 to autumn 1992. The same parameter values were transferred to simulate pasture growth on sites in the east coast of the North Island. The seasonal variations in predicted harvested yields, closely resembled the patterns of yields measured through time. However, the actual yields predicted were generally lower than measured. The model therefore has structural strength but need extensive data for better estimates of initial parameter values. This new approach, although require further development, emerges as a far better basis for understanding the relationship between pasture yields and nutrient supplies than regressions of soil tests against RY.Item Rhizosphere processes influencing soil and fertilizer phosphorus availability to Pinus radiata : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University, Palmerston North, New Zealand(Massey University, 2005) Liu, QianheProduction of Pinus radiata is a major contributor to New Zealand's economy and new plantings are a valuable carbon sink. Phosphorus (P) deficiency and high P fixing capacity of some volcanic ash soils (e.g. Allophanic Soil) may constrain radiata productivity. This thesis investigates the role of ectomycorrhizal (ECM) root processes in the acquisition of P by P. radiata fiom native soil and soil fertilised with two reactive phosphate rock (RPR) fertilisers. The application of finely-divided RPRs to a P deficient Allophanic Soil significantly increased P. radiata seedling growth and P uptake in 10 month pot trials. RPR dissolution was high in this soil, and it was further enhanced by the radiata rhizosphere processes. The development and formation of ECM in radiata seedlings was stimulated by low rates of RPR application but was hindered in unfertilised soils and high rates of RPR application. The P. radiata ECM roots induced acidification and increased oxalate concentration and phosphatase activities in the rhizosphere soil. These changes in rhizosphere biochemical properties were associated with enhanced solubilisation of fertiliser and soil inorganic P and increased mineralisation of organic P, leading to increased P bioavailability in the rhizosphere. ECM inoculation of P. radiata roots with Rhizopogen rubescens and Suillus luteus stimulated production of phosphatase enzymes and oxalate and induced acidification in the rhizosphere. The extent of root-induced changes in the rhizosphere soils was associated with ECM hyphae length density. A technique using pulse labelling of radiata shoots with 14CO2 showed promise in estimating the active ECM hyphae density. The 14C activity was highly correlated with ECM hyphae density measured by an agar film technique. Overall, observations made in this thesis indicate that sparingly soluble forms of organic and inorganic P in soils low in plant-available P are readily solubilised and utilised for P. radiata growth through ECM rhizosphere processes.