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    Water and solutes in soil : hydraulic characterisation, sustainable production, and environmental protection : application for the degree of Doctor of Science from Massey University, Palmerston North, New Zealand
    (Massey University, 2002) Clothier, Brent E
    The soil of the rootzone, the fragile and fertile interface between the atmosphere and the subterranean realm, is characterised by massive transfers of water and solutes. Our understanding of the biophysical transport processes into, and through, soil has been enhanced by the research endeavours of the applicant, Brent Euan Clothier. Dr Clothier, a 1977 Ph.D. graduate of Massey University, has developed tools and techniques that increased the acuity of our vision of transport processes of water and solutes in soil, as well it has sharpened our ability to hydraulically characterise those mechanisms for the purpose of modelling and risk assessment. His research has also enhanced our understanding of how these biophysical processes affect sustainable agriculture, environmental protection, and the bioremediation of contamination. These endeavours are grouped, in this thesis, into four overlapping areas of research: • Processes and properties of water movement into and through soil • Processes and properties of solute movement through soil • Root uptake processes and sustainable irrigation • Plants, groundwater protection and bioremediation of contaminated soil. The key elements of these four themes, and their contribution to knowledge, form Chapters 2-5 of this thesis. Dr Clothier's awards, honours, and impact are discussed in Chapter 6.
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    Soil water modelling in hill country, New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Earth Science at Massey University, Palmerston North, New Zealand
    (Massey University, 2019) Hajdu, Istvan
    As the importance of environmental sustainability and increasing market demands have expressed pressure on New Zealand’s hill country farming systems, the more effective use of available resources and additional inputs has become crucial. Pastoral hill country farms are critical components of New Zealand’s economy, and precision agriculture solutions have been increasingly utilised to improve the sectors’ financial stability and resilience, and to satisfy the elevated expectations in yield. Profitability is dependent on pasture productivity that is highly influenced by the availability of nutrients as well as the amount of soil moisture (θv, m³ m⁻³). However, high variability of soil and landscape factors that control productivity is the primary concept describing these diverse landscapes. Hence, a study was conducted on a 2600 ha dominantly beef and sheep farm in the southern east coast of the North Island of New Zealand representing typical hill country settings. Some of the specific concerns of this research were the examination of the role of accurate, calibrated θv measurements via a wireless sensor network (WSN) (1) and the spatiotemporal variability of θv (2). Furthermore, the study investigates the potential of remote sensing for the mapping of near surface θv in sloping lands (3) and the characterisation of pasture yield patterns induced by the topography (4). These primary points were addressed to better understand the complexity occurring behind the environmental factors governing pasture yield and to potentially achieve improvement in pasture growth simulations. Systematic θv measurements have been used increasingly to inform decisions regarding fertiliser applications, feed supply and stock management in non-irrigated farming systems. To assist near real time θv and soil temperature (Ts) monitoring, 400 mm capacitance-based AquaCheck (AquaCheck, South Africa) probes (four θv and four Ts sensors per probe) were installed at 20 locations (hereinafter microsites) in predominantly silt loam soils. The spatially distributed probes were arranged into a WSN to capture data from various topographical positions. The application of manufacturer-provided calibration formula resulted in a mean root mean square error (RMSE) of 0.106 m³ m⁻³, a mean bias error of -0.099 m³ m⁻³ (indicating underestimation), and a coefficient of determination (R²) of 0.58 when correlated to directly measured reference (θv values. A single custom formula, relevant to the local soils resulted in an improved RMSE of 0.039 m³ m⁻³, while microsite-specific calibrations achieved an RMSE of 0.029 m3 m−3 and R² of 0.77. The application of a sensor-specific calibration resulted in an RMSE of 0.019 m³ m⁻³ with R² = 0.9. Sensor performance and accuracy errors were observed to vary as a function of soil wetness, bulk density (ρb, gcm⁻³) clay and total organic carbon (TOC) content. These effects were significant (P value < 0.001) but eliminated by the sensor-specific custom calibration. Sensor specifically calibrated θv was utilised the examine the effect of highly variable terrain attributes such as aspect, slope angle and soil physical properties on the θv patterns, stability and distribution both spatiotemporally and along the soil profile. Non-normal θv distribution was observed in the study period. The statistical analysis confirmed that the temporal stability of θv was higher in the deeper sections in both dry and wet seasons, while the spatial variability of θv increased with decreasing mean θv, although the greatest was in the rewetting stages. The degree of temporal persistence of the θv patterns varied with soil wetness conditions and seasons. Based on the temporal stability assessment, a representative location was selected based on a north-facing and open slope with silt loam soils. The θv distribution patterns were influenced by the topographic attributes showing that north-facing steep and moderately steep slopes were characterised with the highest variation, while east- and west-facing slopes showed similar trends. Due to the significant variability, near surface θv mapping at a spatial resolution that would be useful for describing within farm heterogeneity has been challenging for researchers. The near surface θv modelling performance of a Random Forest (RF) ensemble learning method and the synergetic use of various remote sensing data with terrain attributes were investigated at 20x 20 m pixel size. The RF model was trained using a two-year reference dataset containing Sentinel-1 SAR backscatter data (i), normalized difference vegetation index (NDVI derived from Sentinel-2, Landsat 7 and Landsat 8 images) (ii), a number of landscape parameters (iii) and in situ near surface θv values obtained by the WSN (iv) as ground truth. The RF algorithm captured a significant amount of the complex relationships and the model predicted θv with a mean RMSE of 0.047 m³ m⁻³ and adjusted R² of 0.76 at the point scale as given by the repeated cross validation. The fine-tuned RF regressor was trained using 15 microsites and a series of near surface θv maps was developed. The maps were validated using the five left out microsites resulting in 0.049 m³ m⁻³ RMSE and 0.76 adjusted R² indicating good agreement between modelled and observed θv values. The general annual trend of θv was closely reflected in the developed maps. The role of near surface and root zone θv, Ts, climatic variables and topographical attributes on the spatiotemporal pattern of pasture productivity was investigated at 13 selected microsites at which pasture herbage accumulation was monitored by the moveable exclusion cage method in 2016-2018. Considerable differences were found in the stored soil water response to significant rainfall events and climatic variables influencing pasture production. On the created multitable dataset, a multiple factor analysis was executed. As a result of this analysis, the role of various environmental parameters was defined highlighting the role of slope angle as the most significant determinant of pasture growth. The effect of landscape position was found to be more significant than aspect, which showed a seasonal dependence. Additionally, the contribution of terrain attributes was not consistent during the study period and changed from year to year. Ts and θv at a soil depth of 100 mm demonstrated the strongest governing effect on pasture production among the monitored parameters. In conclusion, the outcomes of this study imply that an extended and improved version of the proposed methods have the potential to be a basis of more accurate water balance simulations in complex landscapes at the regional scale. The presented quantification and isolation of the influencing topographic factors on pasture production may assist in hill country intensification by adding value to the generation of regulatory nutrient management plans. Ultimately, these advancements will enable the better characterisation of the dynamic hill country pastoral systems, which will lead towards helping hill country sheep and beef farmers to grow more pasture and increase returns while reducing the degrading effects of fertiliser applications on the environment.
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    Tillage and no-tillage effects on physical characteristics of a silt loam under 5 years of continuous oats-maize crop rotation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Applied Science in Agricultural Engineering, Institute of Technology and Engineering, Massey University
    (Massey University, 2000) Viegas, Edmundo da Silva Soares
    Conservation tillage is one of the conserving practices recognized worldwide despite its empirical benefits still largely undergoing continuous research. This research is part of a sequence of studies carried out at Massey University tillage trial. The soil type is Ohakea silt loam representing youngest yellow-grey earth with poor natural drainage on fine texture material, and topsoil moderately to strong acid enleached soils. Selected soil physical properties under different tillage systems i.e. no-tillage (NT), moldboard plough (MP) and permanent pasture (PP) (as control) were measured and compared. The important soil properties considered were soil aggregate stability, soil penetration resistance, water infiltration rate, soil bulk density, soil water content, crop dry matter, water runoff and leachate and soil pH (H2O), total C and N. Results from both the field and laboratory experiments suggested that 5 years of continuous no-tillage have improved soil characteristics relative to conventional tillage. Soil penetration resistance was significantly lower in the MP plots soon after cultivation and at the early oats growing season, compared to the NT and PP plots. However, this trend was reversed within six months, following winter grazing and spring fallow when soil was recompacted. Bulk density measured during early oats growing season indicated a remarkably higher density at the top 0-5 cm soil layer under the NT compared to the MP treatment suggesting that NT plots' soils were more compacted at the time of planting and had lower total porosity than soils in the MP plots. On the other hand, water infiltration rates measured over one year period indicated an average value significantly higher under the NT and PP treatments than the MP plots. These results suggest that macropore continuity, water-filled porosity and other hydraulic properties were improved under NT. A substantially higher level (11%) of water content was found in the NT plots compared to that in the MP plot. These suggested that although the NT soils were more resistant to penetration and had high levels of bulk density, these soils retained more water. These further suggested that the water-filled porosity under the NT soil was higher, thus helped increase the water availability for plant growth. The results also demonstrated that the NT soil produced comparable winter oats and summer maize DM to those under MP treatment. Regression analysis results indicated, not unexpectedly, a strong linear relationship between bulk density and soil penetration resistance with R2 values of 0.97, 0.99, and 0.73 for the PP, MP, and NT treatments respectively. Similar analyses between soil water content and soil penetration resistance demonstrated a strong, moderate, and no correlations under the NT, MP and PP treatments respectively. The NT soils were substantially more stable than the MP soils but were similar to the PP soils. The surface soil (0-10 cm soil depth) water-stable aggregates remaining on sieve for the PP, MP, and NT were 75.2, 26.2 and 70.8% respectively. The macroaggregates (> 2 mm diameter) made up a large proportion of the pasture soil (54.7%) and the untilled soil (37.4%), whereas the ploughed soils had macroaggregates at 4.8%. The ploughed soil was consisted of 73.8% of 0.5 mm water-stable aggregates. Prolonged sieving for 60 minutes also confirmed the above results that the detachment of soils by water in the continuously ploughed land was much easier as compared to the NT and PP management. Thus making the MP soils most vulnerable to water erosion. Runoff and leachete experiments had produced rather inconclusive results as compared to the results on the same plots three years ago. However the trend was obvious that the MP treatment had caused more surface runoff than the other two treatments. By contrast, water runoff was lower in NT plots, which was also reflected by the occurrence of more water leaching under this treatment compared to the MP treatment. The NT soils were relatively more acidic (lower pH) both at 0-10 and 10-20 cm soil layers. Both the MP and NT had resulted in a marked decline in total C level compared to PP at the 0-10 cm soil layer. The decline of total C content after 5 years of continuous double cropping in the 0-20 cm soil layer was about 12% in the MP plots and 2.65% in the NT plots. At the 10-20 cm soil depth, total C and N showed no differences among all treatments. Total N at the 0-10 cm soil layer was significantly lower under MP treatment compared to the other two treatments.
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    Hydraulic properties of four soils from the Heretaunga Plains and prediction of their soil water behaviour during border-dyke irrigation : a thesis presented in partial fulfilment of the requirements for the degree of Master of Philosophy in Soil Science at Massey University
    (Massey University, 1980) Cook, Freeman John
    An irrigation scheme has been proposed for the Ngatarawa region of the Heretaunga Plains (Hawkes Bay). The method proposed for irrigation of these soils is the border-dyke method. It was felt that this method could be inefficient in the use of water and considerable amounts of water could be lost to drainage from some of the soils in this region. Thus experiments were performed on the four major soil types of this region – Poporangi sandy loam (Typic Durochrept), Ngatarawa sandy loam (Typic Ustorthent), Takapau sandy loam (Andri Ustochrept), and Pakowhai silt loam (Aquic Ustifluvent) – to determine their hydraulic properties. The instantaneous profile method was used to measure the drainage, and water storage behaviour of these soils, and their hydraulic conductivity. Hydraulic conductivity could not be calculated for the Poporangi sandy loam, due to the duripan causing lateral flow. This invalidated the assumption that the movement of water was only vertical. For one other soil, Ngatarawa sandy loam, the hydraulic conductivity data obtained were considered to be unreliable. Reliable hydraulic conductivity data were obtained for Takapau sandy loam and Pakowhai silt loam. From data obtained from "undisturbed cores" and the field experiments, the drainage behaviour and water storage properties were determined for all four soils. Using a numerical technique, vertical movement of water in Takapau sandy loam and Pakowhai silt loam,during and following ponded infiltration, was simulated using a CSMP computer model. These simulations indicate that the loss of water to through drainage from Takapau sandy loam would be at least 50% of that infiltrated, if the proposed residence time for ponding of water of 70 minutes is used. For Pakowhai silt loam the simulations indicate that little water is likely to be lost to drainage if a residence time of 120 minutes is used. As hysteresis in the volumetric water content/pressure potential relationship is likely to affect the validity of these simulations, the extent of hysteresis on this relationship in these soils was investigated. From all of these data it was concluded that only the Pakowhai silt loam would be suitable for irrigation by the border-dyke method. If this method was used on the other soils, large amounts of water could be lost to drainage. This would not only be a waste of a scarce resource, but as the Ngatarawa region lies over the unconfined part of the aquifer from which Napier and Hastings cities draw their water, it could also be a health hazard, as the drainage water from these soils could cause the nitrate level in the water in this aquifer to increase. Thus it would be better to irrigate the other three soils (Poporangi sandy loam, Ngatarawa sandy loam and Takapau sandy loam) using a sprinkler system. The application rate of the sprinkler system should be less than the saturated hydraulic conductivity of the A horizon of the soil, otherwise horizontal distribution of the amount of water infiltrating into the soil can be very uneven.
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    An analysis of the relationship of apparent electrical conductivity to soil moisture in alluvial recent soils, lower North Island, New Zealand : a thesis presented in partial fulfillment of the requirements for the degree of Masters of Philosophy (MPhil) in Soil Science at the Institute of Agriculture and Environment, Massey University, Palmerston North, New Zealand
    (Massey University, 2013) Killick, Michael
    Electromagnetic induction (EMI) sensors can be used in kinematic systems to provide rapid high-density measurement of apparent soil electrical conductivity (ECa) over large areas. In non-saline soils ECa has been used as a surrogate measurement for many soil properties including soil texture and moisture, critical properties in precision agriculture. However, complex interactions between soil properties and the irregular depth profiles of EMI measurements have prevented consistent interpretation of ECa in terms of soil properties. This study uses kinematic surveys and multi-height spot measurements of ECa with Geonics EM38 Mk2 and EM31 instruments together with field measurements of soil moisture and investigation of ECa theory to analyse the relationship of ECa to soil moisture in alluvial Recent Soils at two locations in the lower North Island, New Zealand. Soil samples from these locations were also analysed for bulk density, porosity, texture and the electrical conductivity (EC) of 1:1 soil pastes and extracts. Intact soil cores from one location were analysed for moisture retention properties. Results raise uncertainty about the function of EMI instruments, particularly the nature of temperature effects and the comparability of measurements by different instruments. Effects of soil solution conductivity on ECa were found to be significant though the soils studied were non-saline. Correlations of soil moisture with ECa in this study were varied and not in every case significant. The relationship of ECa to soil moisture in this study was too complex to allow simple use of ECa for measurement of soil moisture.
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    An investigation into repellency-induced runoff and its consequences in a New Zealand hill country pasture system : a thesis submitted in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science, Massey University
    (Massey University, 2012) Bretherton, Michael Robert
    Soil water repellency affects a wide range of soils within diverse environments. In agricultural systems, it has the potential to reduce infiltration of water into the soil and enhance surface runoff processes. Accordingly, soil water repellency may have significant consequences in hill country. In these landscapes, repellency-induced runoff has the potential to result in a marked reduction in the quantity of water available to pasture in summer and autumn, and to increase the impact of summer storm events on stream flow. The objective of this thesis is to examine repellency-induced runoff and to study its consequences in New Zealand hill country pasture systems, with a particular focus on the East Coast of the North Island as represented by the research area at Alfredton and a catchment near Waipawa. Detailed meteorological data, surface runoff measurements from small plots (1.0 x 2.0 m), and soil moisture values gathered over two years at the Alfredton catchment were used to determine the effect of soil water repellency on the infiltration rate of the soil and surface runoff, and to assess its importance as a hydrological process in that catchment. The persistence of repellency was further investigated on soil slabs in the laboratory. A soil water balance model, which incorporates the observed throttling effect of repellency in the top 50 mm of soil, was developed to help assess when this phenomenon was most likely to occur. Output from the model using 8 years of rainfall and stream flow data from the Waipawa catchment was used to help gauge the effect of repellency-induced runoff on peak stream flow and total stream flow. The effect of repellency on pasture production was also measured at the Alfredton site. The Alfredton soils had high intrinsic infiltrability (at least 2 mm min-1), but this property was compromised by water repellency under dry soil conditions. However, analysis of detailed meteorological, soil moisture, and surface runoff data at the Alfredton catchment indicated that plot-scale repellency-induced runoff events occurred less than 10 times a year and that over two years these events equated to less than 5 % of the mean annual rainfall of 1517 mm. Observations and modelling showed that repellency-induced runoff occurred whenever both the rainfall intensity exceeded 0.1 mm min-1 and the soil water content in the 0-50 mm topsoil was less than 0.28 m3 m-3. Although repellency reduced the infiltration rate of the Alfredton soils by a factor of 10, it disappeared less than 44 hours after significant rainfall, and only reappeared once the soils had again become sufficiently dry. The rapid disappearance of water repellency was confirmed by the laboratory study using large soil slabs. The implication is that repellency-induced runoff is not a significant hydrological process. The soil water balance model was used to predict repellency-induced runoff over 8 years in the Waipawa catchment. It predicted on average about 50 mm yr-1 of repellency-induced runoff from both the North catchment and South catchments over the 8 years, during which time the catchments received an average rainfall of 793 mm yr-1. This suggests that even in this drier climate, repellency-induced runoff plays a relatively minor role in the soil water balance of these hill country catchments. Examination of Waipawa stream flow data on those days when more than 10 mm of repellency-induced runoff was predicted, revealed a maximum stream flow of 1.1 mm and an average flow that was only 3.3 % of the modelled repellency-induced runoff. Additionally, on those days, peak stream flow was less than 3 % of peak rainfall intensity. These values suggest that at least 95 % of repellency-induced runoff infiltrated the soil before reaching the stream and thus contributed very little to both peak and total stream flow at Waipawa over the 8 years. Repellency-induced runoff appears to have had little effect on pasture production at the Alfredton site. Employment of the refined soil water balance model in combination with a pasture production model suggested that repellency-induced runoff would be responsible for less than 1 % reduction in pasture production per annum. Statistical analysis of production data over the 2010 and 2011 years showed that shallower (20o) slopes significantly out-produced steeper (30o) slopes by 2.7 t ha yr-1, with North and South aspect production being similar. In summary, repellency-induced runoff does not appear to play a major role in the soil water balance of the study catchment at Alfredton. Furthermore, repellency-induced runoff does not seem to have a marked impact on stream flow under the drier Waipawa climate.
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    An investigation into the techniques of direct drilling seeds into undisturbed, sprayed pasture : a thesis presented in partial fulfillment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 1976) Baker, Christopher John
    Methods of evaluating the techniques and equipment used for direct drilling of seeds into untilled soils were reviewed and developed. Field tests were used to highlight seedling establishment problems and were complimented by a tillage bin technique which sought to isolate variables such as climate, soil type and soil moisture regime. The tillage bin technique involved collecting half-tonne undisturbed blocks of turf in open ended steel bins using a special turf cutting machine. These tillage bins were subjected to a common climate and moisture supply by placing them beneath transparent rain canopies and applying water artificially. Drilling utilized a support bed on which several bins were placed end to end and which was straddled by a moving gantry and tool testing apparatus operating on rails alongside. This facility allowed close visual appraisal to be made of the action of coulters and seed deposition and was operated at speeds which were infinitely variable, within limits. Seed metering was precisely controlled and selected coulter forces and soil physical properties were measured with the apparatus. Turf blocks, in their tillage bins, were returned to the rain protection canopies after drilling for plant response studies. Soil cover over the seed appeared to be important in promoting seedling emergence. Field covering devices were evaluated and a bar harrow was developed and adopted as a standard covering procedure. The importance of covering the seed appeared to be more pronounced with large seeds such as maize and barley than with smaller seeds such as lucerne. A strong relationship between visual scoring of the amount and type of cover, and seedling emergence data was established. This favoured covering media with a predominance of unbroken dead pasture mulch, compared with loose soil and rubble. The performances of a range of drill coulters operating at slow speeds in association with the bar harrow, were compared in terms of plant responses under soil moisture stress. An experimental chisel coulter was developed to obviate the noted shortcomings of some of these existing coulters. In contrast to the "V" shaped grooves left by most coulters, the chisel confined most of its soil disturbance to sub surface layers, with a narrow opening at the surface. With all coulters, seed germination appeared to be less affected by coulter design than seedling emergence because of sub surface mortality of seedlings. In this respect clear seedling emergence responses favoured the chisel coulter. Maximum wheat seedling emergence with the chisel coulter assembly was 77%, which was significantly greater than hoe and triple disc coulters with 27% and 26% respectively. As the initial soil moisture level was raised in other experiments the magnitude of these differences decreased but the order of ranking remained. A 22% comparative decrease in initial soil moisture content was necessary to reduce the performance of the chisel coulter to a similar level to that of the hoe and triple disc coulters. Difficulty was experienced in accurately monitoring in-groove soil moisture regimes, but irrigation responses and gravimetric determinations of sub samples suggested that the ability of grooves to retain available soil moisture was a critical factor in the plant emergence responses. Soil temperatures appeared not to be greatly affected by coulter type in these experiments although the in-groove minimum temperature with the chisel coulter was significantly higher than the hoe and triple disc coulters in one experiment. Observation of the modes of action of coulters showed that the chisel and hoe coulters produced some upward soil heaving while the triple disc appeared to operate with a downward and outward wedging action in the soil. An increase in soil density under the groove resulted from passage of the triple disc coulter but no effect on density was seen with the chisel or hoe coulters. The down forces required for 38 mm penetration of all coulters tested, appeared also to be closely related to their modes of action and relatively insensitive to soil moisture content in the stress range. In this respect the triple disc required 1.4 times more force than the dished disc coulter and from 2.3 to 4.6 times more force than a range of 4 other coulters. Field tests of the wear rates of chisel coulters constructed of various steel based materials, with and without hardening treatments, suggested a number of preferred treatments but could not establish any difference in wear rate from coulters operating in the tractor wheel marks compared with those operating in unmarked soil.
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    Interrelationships between performance of direct drilled seeds, soil micro-environment and drilling equipment : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University
    (Massey University, 1979) Choudhary, Mohammed Ashraf
    Stand establishment of crops by direct drilling is a function of seed germination and seedling emergence efficacy and their interactions with the soil physical micro-environment created by direct drill coulters. Experiments conducted in two contrasting controlled climates using 0.5 tonne undisturbed turf blocks suggested that the three coulter types compared (viz. an experimental chisel coulter, a hoe and a triple disc coulter) performed significantly differently, in terms of wheat seedling emergence, when the seed was direct drilled into a fine sandy loam soil. Overall the chisel coulter promoted highest seedling emergence (63.5%) followed by the hoe coulter (50.6%) and the triple disc coulter (27.0%). When the initial soil moisture potential was close to permanent wilting point, seedling emergence counts between these three coulters were highly significant with the difference between the chisel and triple disc coulters being almost six-fold. When the initial soil moisture level was adequate, seedling emergence counts from the triple disc grooves, were Still significantly lower than from the chisel and hoe coulters which themselves performed equally. When the controlled relative humidity was increased from 60% to 90%, seedling emergence increased but this difference was significant only at a lower level of probability of P = 0.10. Application of pressures (using press wheels) up to 70 kPa over the covered seeds after bar harrowing had no significant effect on seedling emergence at either the low or adequate initial soil moisture levels. When similar pressures were applied directly over the uncovered seeds, seedling emergence significantly increased to 60% in the hoe coulter grooves and to 28% in the triple disc coulter grooves compared to the impressed seeds. No significant increase was observed from the chisel coulter groove as a result of these pressures because it had already promoted a high seedling emergence count of 58%. Further experiments, using small undisturbed turf blocks, to examine more closely the poor performance of the triple disc coulter, indicated that smearing had not been the main cause of seedling emergence failure. When the triple disc coulter grooves were modified using combinations of pressure applications and seed covering techniques, seedling emergence was significantly improved. It appeared that this improvement in seedling emergence was a function of a modified soil physical micro-environment at the seed-soil interface. Based on these results two hypotheses were evolved. The first hypothesis suggested that the transfer of liquid soil moisture to the seed for germination (and perhaps away from the unprotected seedling after germination but prior to emergence) could be altered by the shape of the seed groove and placement and covering of the seed. This was described as "soil moisture diffusion" The second hypothesis suggested that after the germination, subterranean seedling survival depended on the availability of vapour phase moisture which was also a function of the groove shape and covering medium. This was described as "soil moisture captivity". A thermo-electric dew point hygrometer was used to measure the in-groove vapour moisture potential within the drilled grooves in the larger turf blocks, in a controlled environment. Significant and repeatable differences in the drying rates of the grooves created by the three coulter types were measured and promised to at least partly explain the underlying causes of their abilities (or lack of abilities in some cases) to promote seedling emergence. Combined counts of seedling emergence and sub-surface seedling survival were moderately correlated (r = 0.71) with the corresponding rates of loss of in-groove soil vapour moisture. It appeared from the data that the important design characteristics for direct drilling coulters were that they must have the ability to both exploit the limited supply of sub-surface liquid moisture for germination and also retain soil moisture in the vapour form for seedling emergence and/or survival. The latter function appeared to be aided by the creation of minimum surface shattering and maintenance of a high incidence of surface mulch in the form of sod or organic matter. Field experiments suggested that when the only measured soil moisture data available was at or prior to drilling, the present state of knowledge would not permit accurate seedling emergence data to be predicted for any given coulter and covering technique. If however, soil moisture data was available for the period between drilling and seedling emergence, reasonable predictions of seedling emergence could be made, given the characteristics of the coulter types and covering techniques used. Examples of mathematical models were constructed for each of the three coulter types used, to predict seedling emergence as a function of these soil moisture data. The field experiments also confirmed that higher seedling emergence counts could be expected when the chisel coulter was used in dry soils compared with the hoe or triple disc coulters. During a typical spring-summer-autumn period in the Manawatu, when wheat seed was direct-drilled at fortnightly intervals into a "Tokomaru silt loam soil"; from 16% of the drillings the chisel coulter promoted significantly higher seedling emergence counts than either the hoe or triple disc coulters.
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    An investigation of water repellency in a range of New Zealand soils : a thesis presented in partial fulfilment of the requirement for the degree of Doctor of Philosophy in Soil Science at Massey University, New Zealand
    (Massey University, 1991) Wallis, Murray Gordon
    The severity of water repellency was investigated on a wide range of agricultural, horticultural and turf soils in New Zealand. All the soils studied had some degree of repellency, regardless of texture or land use. Techniques for repellency measurement and amelioration were evaluated and the organic component responsible for repellency development investigated. The temporal and extreme spatial variability of repellency expression was quantified using geostatistics. The 'repellency index' (RI) based upon soil intrinsic sorptivity was developed and evaluated on 14 New Zealand soils. The RI measured undisturbed cores of all the soils water repellent at field moisture conditions and was more sensitive than the MED or water drop penetration time (WDPT) tests. The RI was used to demonstrate that repellency reduced the short-time infiltration rate, i of all the soils by approximately an order of magnitude, including those which appeared to wet normally (i.e. low WDPT). Calculations identified that the reduction in i would be hydrologically significant under intense rainfall and many irrigation systems. Investigation of a development sequence of yellow-brown sands (Aquic Udipsamments) revealed maximum repellency in < 130 y old Waitarere sand, which had the lowest level of organic carbon. Repellency was also severe in the Motuiti and Himatangi sands (c. 500 y) but declined in the Foxton (1600 - 6000 y) and Koputaroa (10000 - 25000 y) soils. While water repellency (measured with the Molarity of Ethanol Droplet, MED test) of the Himatangi sand profile was correlated with organic carbon content, this was not the case with the other soils. Organic matter composition is a more likely determinant of the degree of repellency than organic matter quantity per se. Spectroscopic examination of extracts removed from Himatangi sand by an isopropanol/ammonia mixture using a soxhlet apparatus indicated a range of long chain organic compounds comprising esters and fatty acids as the cause of repellency. The spatial variability of volumetric soil water content (θ) to 200 mm depth at two adjacent sites (A and B) of Himatangi sand, each c. 860 m2, was studied with geostatistical techniques. At both sites θ varied isotropically and generally followed a normal distribution. Variograms of θ changed over time and were not transferable between the two sites, although there was evidence of drift in the mean at site B. At site A, compared to an October analysis, in summer the coefficient of variation (C.V.) of θ increased and the range of θ spatial dependence, a decreased. Irrigation of both site A and B with a travelling boom slightly increased C.V.(θ), markedly increased the semivariance and slightly decreased a(θ) at site A. When a wetting agent was applied prior to irrigation of site A the C.V.(θ) halved, a(θ) increased and the θ increase was improved by 63 % over irrigation of site A and 206 % over irrigation of site B. Agitation of soil samples reduced repellency significantly, however the effect was somewhat reversible and field cultivation could be precluded by the degree and depth of the repellent topsoil. Soil wetting agents increased grass establishment and growth in both glasshouse and field experiments. In the glasshouse, wetting agent performance was not affected by delayed initial irrigation, however short irrigation return intervals improved plant growth in both untreated and wetting agent treated soil. A survey of golf courses throughout New Zealand found that repellency was a major management problem. Soil cores were removed from areas of greens displaying repellency symptoms ('dry patch') and from areas of compatatively healthy turf. No significant difference was found between the MED profile or the thatch content of the dry patch and non-dry patch cores. Dry patch areas were found to match the poorly irrigated areas of a green using a simple 'catch-can' test, which indicated that irrigation uniformity affected repellency expression in turf.
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    A description of the soil potassium fertility of steepland pastures in the southern North Island of New Zealand : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Soil Science at Massey University
    (Massey University, 1999) Officer, Sally Jane; Officer, Sally Jane
    The pattern of soil K fertility was investigated in two typical steepland pastures, located in the southern North Island of New Zealand. The parent materials of soils in this area are predominantly derived from sedimentary rocks. The soils have medium to high K reserves, and K fertilisers are not normally applied to the areas of steepland pasture. The study sites are part of well-established mixed stock grazing farms and have received regular aerial topdressing with superphosphate for at least 30 years. Grazing animals in steepland tend to favour the flatter areas, which are mainly on the crests of the ridges, and to spend relatively short periods of time grazing the steep slopes. Concerns have arisen as to the development of K deficiencies on the steep slopes, as stock are expected to graze these areas, and then to excrete most of the K ingested in the herbage onto the flatter areas. Two surveys were made of the K fertility patterns in two steepland paddocks. The first study was made over one paddock, by collecting soil samples along vectors of random direction, from points that were between 0.25 m and 25 m apart. The second survey targeted the main trends, sampling at regular intervals along the ridge crests and down the transects of the main slopes, at two paddocks The tests on the soil samples included exchangeable K (Quick test K), acid extractable K and the difference between the two factors, which was thought to provide a measure of plant available nonexchangeable K (Step K). The Quick test K values in one pasture alone ranged from 0.07 to 1.34 mg K/g soil, which was a range between very low and extremely high values for New Zealand soils. There was a similar wide range of values for other parameters. The frequency distributions of the soil test values were skewed, so that the arithmetic mean of the results was higher than 60-70% of the values. Spatial variability was at a maximum at a sampling distance of 0.25 m. The results indicated that the bulking of soil samples was a poor practise when sampling for exchangeable and plant available nonexchangeable K at these sites. Some relationships could be discerned between the soil K fertility patterns and the position of the topsoil in a steepland landscape, despite the high spatial variability. On the steep slopes, the Step K value of a soil was related to the soil moisture pattern, as determined by aspect and water seeps, and also to the pattern of the soil parent materials. Quick test K had no similar relationship to position in the landscape on the steep slopes. The spatial variability of both tests increased as the ground slope decreased. The mean and variability of Quick test K increased sharply on both well drained shoulder slopes and ridge-tops that were animal campsites. In contrast, the mean and variability of Step K increased markedly only on the well drained ridge-top campsites The different behaviour of cattle and sheep, the relatively large amounts of K deposited in excreta compared to P, and the slower rate of breakdown and dispersal of excreta in drier conditions, were all thought to contribute to these effects. The mineralogy of the topsoils at the two sites was also investigated. The clay mineralogy was dominated by a complex of 2:1 layer silicates, accompanied by lesser quantities of quartz, feldspars and kandites. The topsoils formed a sequence, which ranged from a 2:1 layer silicate clay complex that was dominated by mica and interlayered mica smectite (MS), to a 2:1 layer silicate clay complex that was dominated by vermiculite and hydroxy interlayered vermiculite (HIV). There was a very strong relationship between the Step K value and the mica content of a soil on the steep slopes. The relationship indicated that the dominance of either mica and MS, or vermiculite and HIV, in the clay fraction of a soil on the steep slopes depended on the original composition of the soil parent materials, the age of the soil profile, and the soil moisture conditions. On the shoulder slope and ridge-tops, there was a similar range of clay mineralogy, but Step K value now had a poor relationship to the mica content. This effect was mainly associated with soils under the well drained animal campsites, which had a distinctive mica and irregularly interstratified MS dominated clay mineralogy. The results were consistent with a reversal of the 2:1 layer silicate weathering processes under well drained animal campsites. Concentrations of total K and P were investigated in the topsoils of the two steepland pastures. The average difference between the total P of slope and ridge-top samples was about 200 kg P/ha, indicating a relatively small accumulation of P on the ridge-tops after many years of aerial topdressing and grazing. The expected accompanying increase in total K was not found. The marked effect of animal transfer processes on the plant available chemistry and mineralogy of the well drained ridge-top soils was thought to be a disproportionate indicator of the relatively small extent of total nutrient accumulation that appeared to have occurred on the ridge-top campsites. The plant response to K fertiliser was measured at the two steepland pastures sites. No K uptake response or growth response was identified at either site, despite low exchangeable K values in some areas and a low K content in some of the pasture samples, even after fertiliser was applied. In contrast, an exhaustive pot trial, using a selection of soils from the two sites, revealed a considerable range in the ability of the soils to supply K. Cation and anion concentrations were measured in the leachates of "stove pipe" soil cores collected from the ridge-tops and steep slopes. K concentration in the leachates of soil from the steep slopes were relatively low and reasonably consistent over time, compared to the Ca and Mg concentrations that were more sensitive to changes in the ionic strength. K concentration in the leachate of soils from different ridge-top locations varied markedly between the different locations. The increased leaching of K under animal campsites was identified as a significant loss mechanism for the K that is transferred to these areas. However, it was thought that an exact quantification of this process would be difficult, because the spatial variability of the concentration of K leaching from the topsoil into the subsoil under campsites was expected to be even higher than the spatial variability of exchangeable K in these soils. In conclusion, animal transfer losses of K from the steep slopes to the flatter areas at these sites appeared to be in the low range for New Zealand steepland pastures. No significant depletion of the K fertility appeared to have developed on the steep slopes, although the measurements were confounded by the very high degree of spatial variability found in all aspects of the K fertility patterns. The current conventional practice of not applying K fertiliser to these and similar sites was thought to be sustainable.