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    Physiological effects of dietary moisture in cats (Felis catus) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science, Massey University, Palmerston North, New Zealand
    (Massey University, 2022) Hekman, Margreet
    There is no system in the mammalian body that does not depend on water. Water is an essential nutrient and comprises approximately two thirds of a domestic cat’s body weight. It is recommended that sufficient water is provided to domestic cats to allow self-regulation of intake, encompassing both voluntary drinking and intake of dietary moisture. Understanding the role of dietary moisture in health and disease in domestic cats, however, has thus far been neglected, and any physiological differences between cats consuming either high moisture (HM) or low moisture (LM) diets, have been assumed unimportant. Therefore, to fill this gap in the literature this thesis investigates the effects of consuming HM and LM diets in healthy cats and cats diagnosed with chronic kidney disease. By feeding cats diets which were created to differ in dietary moisture content only, this work aimed to determine if single or multiple meal feeding of a LM food influenced total water intake (TWI), urine concentration and pH, plasma osmolality (POsm), blood pressure (BP), water balance, and activity in cats when compared to free access HM food feeding (Chapters 2 and 3). Then the effect of a single meal and a single simulated meal on post-prandial BP and heart rate using the same diets was investigated (Chapter 4). Further, using these diets, the molecular weight distribution of urinary proteins was quantified and described (Chapter 6), and the effects of a meal on post-prandial vasopressin (VP) and copeptin concentrations were investigated (Chapter 7). Lastly the diets were used to compare the effects of consuming a HM and LM diet on urine concentration and pH, POsm, plasma VP, and BP, in cats recently diagnosed with chronic kidney disease (Chapter 8). Additionally, due to the difficult and inaccurate nature of VP hormone analysis, several alternative methods to quantitate the VP proxy copeptin were investigated, however these were unsuccessful (Chapter 5). It was found that TWI and output were significantly lower when healthy cats were fed LM diets compared to HM diets and increasing meal frequency of LM diets did not increase TWI. This difference in TWI did not result in a difference in BP or total urinary protein content. However, lower TWI did lead to a decrease in water turnover rate, and increased urine concentration, POsm, and plasma VP levels. Therefore, varying dietary moisture has meaningful physiological effects in the cat. In addition, the results may indicate increasing adverse effects on health when TWI is low, with particularly detrimental effects to the kidney. Furthermore, there were modest indications that additional adverse effects such as increasing urine protein to creatinine ratio appeared when older cats were fed LM diets. Therefore, it is proposed that the role of dietary moisture is significant for the health of domestic cats, especially as they age, and that primarily feeding a LM diet and allowing self-regulation of water intake through voluntary drinking does potentially not secure a high enough TWI for their long-term health. Feeding a HM diet ensures a high TWI, which may have clinical implications for rehydration of ill cats, especially in cats diagnosed with chronic kidney disease, and potentially may even prevent or delay progression of disease in healthy cats. Feeding a HM diet should primarily be considered when a greater water intake is required to counter dehydration, or in the treatment of diseases that benefit from an increase in water intake.
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    New sensing methods for scheduling variable rate irrigation to improve water use efficiency and reduce the environmental footprint : 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, 2020) El-Naggar, Ahmed
    Irrigation is the largest user of allocated freshwater, so conservation of water use should begin with improving the efficiency of crop irrigation. Improved irrigation management is necessary for humid areas such as New Zealand in order to produce greater yields, overcome excessive irrigation and eliminate nitrogen losses due to accelerated leaching and/or denitrification. The impact of two different climatic regimes (Hawkes Bay, Manawatū) and soils (free and imperfect drainage) on irrigated pea (Pisum sativum., cv. ‘Ashton’) and barley (Hordeum vulgare., cv. ‘Carfields CKS1’) production was investigated. These experiments were conducted to determine whether variable-rate irrigation (VRI) was warranted. The results showed that both weather conditions and within-field soil variability had a significant effect on the irrigated pea and barley crops (pea yield - 4.15 and 1.75 t/ha; barley yield - 4.0 and 10.3 t/ha for freely and imperfectly drained soils, respectively). Given these results, soil spatial variability was characterised at precision scales using proximal sensor survey systems: to inform precision irrigation practice. Apparent soil electrical conductivity (ECa) data were collected by a Dualem-421S electromagnetic (EM) survey, and the data were kriged into a map and modelled to predict ECa to depth. The ECa depth models were related to soil moisture (θv), and the intrinsic soil differences. The method was used to guide the placement of soil moisture sensors. After quantifying precision irrigation management zones using EM technology, dynamic irrigation scheduling for a VRI system was used to efficiently irrigate a pea crop (Pisum sativum., cv. ‘Massey’) and a French bean crop (Phaseolus vulgaris., cv. ‘Contender’) over one season at the Manawatū site. The effects of two VRI scheduling methods using (i) a soil water balance model and (ii) sensors, were compared. The sensor-based technique irrigated 23–45% less water because the model-based approach overestimated drainage for the slower draining soil. There were no significant crop growth and yield differences between the two approaches, and water use efficiency (WUE) was higher under the scheduling regime based on sensors. ii To further investigate the use of sensor-based scheduling, a new method was developed to assess crop height and biomass for pea, bean and barley crops at high field resolution (0.01 m) using ground-based LiDAR (Light Detection and Ranging) data. The LiDAR multi-temporal, crop height maps can usefully improve crop coefficient estimates in soil water balance models. The results were validated against manually measured plant parameters. A critical component of soil water balance models, and of major importance for irrigation scheduling, is the estimation of crop evapotranspiration (ETc) which traditionally relies on regional climate data and default crop factors based on the day of planting. Therefore, the potential of a simpler, site-specific method for estimation of ETc using in-field crop sensors was investigated. Crop indices (NDVI, and canopy surface temperature, Tc) together with site-specific climate data were used to estimate daily crop water use at the Manawatū and Hawkes Bay sites (2017-2019). These site-specific estimates of daily crop water use were then used to evaluate a calibrated FAO-56 Penman-Monteith algorithm to estimate ETc from barley, pea and bean crops. The modified ETc–model showed a high linear correlation between measured and modelled daily ETc for barley, pea, and bean crops. This indicates the potential value of in-field crop sensing for estimating site-specific values of ETc. A model-based, decision support software system (VRI–DSS) that automates irrigation scheduling to variable soils and multiple crops was then tested at both the Manawatū and Hawkes Bay farm sites. The results showed that the virtual climate forecast models used for this study provided an adequate prediction of evapotranspiration but over predicted rainfall. However, when local data was used with the VRI–DSS system to simulate results, the soil moisture deficit showed good agreement with weekly neutron probe readings. The use of model system-based irrigation scheduling allowed two-thirds of the irrigation water to be saved for the high available water content (AWC) soil. During the season 2018 – 2019, the VRI–DSS was again used to evaluate the level of available soil water (threshold) at which irrigation should be applied to increase WUE and crop water productivity (WP) for spring wheat (Triticum aestivum L., cv. ‘Sensas’) on the sandy loam and silt loam soil zones at the Manawatū site. Two irrigation thresholds (40% and 60% AWC), were investigated in each soil zone along with a rainfed control. Soil water uptake pattern was affected mainly by the soil type rather than irrigation. The soil iii water uptake decreased with soil depth for the sandy loam whereas water was taken up uniformly from all depths of the silt loam. The 60% AWC treatments had greater irrigation water use efficiency (IWUE) than the 40% AWC treatments, indicating that irrigation scheduling using a 60% AWC trigger could be recommended for this soil-crop scenario. Overall, in this study, we have developed new sensor-based methods that can support improved spatial irrigation water management. The findings from this study led to a more beneficial use of agricultural water.
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    Some effects of water stress and environment on soybean plants : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Botany at Massey University
    (Massey University, 1970) Beardsell, Michael Fletcher
    Although a great deal of research has been carried out on the effects of water stress on plant processes, the influence of environmental conditions on plant response to water stress has received comparatively little attention. In this study the rates of CO2 exchange and transpiration and the leaf water status of whole soybean plants (Glycine max (L.) Merr. cv. Merit) were measured under contrasting sets of environmental conditions when (a) the plants were maintained under conditions of adequate soil water supply. (b) water stress was imposed by withholding water and, (c) when water stress was imposed and then relieved by rewatering. Light intensity and quality, atmospheric CO2 concentration, wind speed and daylength were all constant; the between-treatment variables were air temperature and vapour pressure deficit (VPD). Plants were grown under one of four environmental treatments in a growth cabinet and the experiments carried out under very similar conditions in a plant chamber with facilities for measuring CO2 exchange and transpiration. Details of this equipment are given. Under conditions of adequate soil water supply rates of photosynthesis were lower under low VPD than under high VPD conditions at the same temperature. The effect was particularly marked at low temperature (22.5°C). Between-treatment differences in photosynthetic rate appeared to be mainly attributable to differences in the magnitude of the mesophyll resistance to CO2 transfer. Transpiration rates were largely determined by the VPD, plants under high VPD treatments having the higher rates. At low VPD temperature had little effect on the rate of transpiration, but at high VPD plants under low temperature had lower rates of transpiration than plants under high temperature (27.5°C). Possible mechanisms whereby low temperatures may reduce transpiration under conditions of high VPD are discussed. When water stress was imposed the rates of photosynthesis and transpiration declined in parallel under all treatments at soil moisture tensions in excess of 0.2 atm. This suggested that both plant processes were subject to a common controlling mechanism, probably stomatal diffusion resistance. At soil moisture tensions below 0.2 atm. the rates of photosynthesis and transpiration were independent of the soil moisture status. Between 0.2 and 0.4 atm. tension they appeared to be determined by plant, soil and atmospheric factors. The relative rates of photosynthesis and transpiration were reduced to a greater extent at any tension between 0.2 and 0.4 atm. under high VPD than under low VPD conditions. Above 0.4 atm. soil moisture tension the rates of photosynthesis and transpiration became independent of the atmospheric conditions and it is suggested that transpiration was limited chiefly by the rate of movement of water into the root zone from the surrounding soil. Photosynthesis may have been limited by direct effects of dehydration on the biochemical components of the process at these severe stress levels. It was thus possible to distinguish three stages in the development of water stress, the significance and possible general application of which are discussed. Under high temperature/high VPD conditions the rates of photosynthesis and transpiration recovered simultaneously and to a very similar extent when stress was relieved by rewatering, the degree of recovery being inversely proportional to the soil moisture tension at the time of rewatering. Possible causes of the failure of the rates of photosynthesis and transpiration to recover to their original prestressed values are discussed. These results are discussed in relation to the findings of other workers, and suggestions for further research in this field made.
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    A study of the effects of water and cutting on seed production of Verano stylo (Stylosanthes hamata) and Siratro (Macroptilium atropurpureum) : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy at Massey University, Palmerston North, New Zealand
    (Massey University, 1983) Waikakul, Phanna
    Tropical pasture legume seed production in the North-east of Thailand first began in the early 1970's. Stylosanthes hamata cv. Verano and Macroptilium atropurpureum cv. Siratro were two of the forage legumes proposed to fill the requirement for improved pastures in this region of Thailand. This study was initiated to provide information on the effects of water stress, stage of plant development at the time of cutting and cutting intensity on seed production of these two tropical forage legumes, in the field at Khon Kaen, Thailand. A second and more intensive study on the reaction of Verano stylo to water stress, and stage and intensity of cutting was carried out to provide a better understanding of possible plant adaptation and the contribution of plant components to seed yield of this species under controlled environment conditions at the D.S.I.R., Palmerston North, New Zealand. Initially, field experiments were carried out in two different seasons, (dry season and wet season). The dry season experiment studied the effects of irrigation, non-irrigation, and cutting on seed yield. In the wet season field experiment only the effect of cutting was studied in both Verano stylo and Siratro. The results from the dry season study showed that species are responsive to irrigation. Irrigated plants produced about 25% more seed yield than non-irrigated plants in Verano stylo but only about 10% more in Siratro. The response of the plants to cutting was variable depending on the stage and intensity of cutting. Light cutting at either the vegetative or floral initiation stages gave higher seed yields than uncut plants in Verano stylo, while in Siratro all cut plants gave higher seed yields than uncut plants. Planting Verano stylo or Siratro in the wet season resulted in plants taking longer to reach the reproductive stage than in the dry season. This protracted vegetative stage resulted in bigger plants and more sites for seedheads. In stylo both cut and uncut plants gave higher seed yields than those obtained in the dry season planting, while in Siratro plants heavily cut at the vegetative stage gave the highest seed yield. Siratro plants grown in the wet season tended to produce strong vegetative growth and good inflorescence development. However, seed yield was lower because of poor pod development and low numbers of seeds per pod. The second experiment on verano stylo was carried out under controlled environment conditions designed to simulate as closely as possible the different growing seasons previously used in the field. The results confirmed that water plays an important role in increasing seed yield in both cut and uncut plants, and especially in cut plants provided they received high water levels throughout the growing period. Water stress appeared to change plant structure, both vegetative and reproductive growth being greatly reduced during the stress period. Water also had an effect on the number of sites for seedhead formation and the contribution to seed yield. In plants which were water stressed from about 30 days after sowing (vegetative stage) both cut and uncut plants remained small resulting in low branch numbers, shorter branches and fewer sites for seedhead development. Water stress applied following peak flowering (55 days after sowing) also reduced seed yield, compared with the yield from plants receiving water throughout the period of seed development. The maximum yield obtained varied from 1.2-9.3 grams per plant between the three water treatments. Studies on the contribution to seed yield from each branch order and seedhead position indicated that in both cut and uncut plants most of the seed yield came from secondary branches (60-75%). The contribution to seed yield, however, was different between water treatments. In early stressed plants seed yield was apportioned almost equally between primary and secondary branches. However in plants which had been placed under water stress at peak flowering, the seed yield obtained from primary branches was only half that produced from secondary branches. In non-stressed plants 70% of total seed yield came from seedheads produced on secondary branches and only 20% from primary branches. The position of seedhead formation on each branch was also important. The results showed that about 75-90% of total seed yield came from seedheads formed at nodal sites. The number of seedheads formed at terminal sites was low. In later stressed plants and in well watered plants the contribution of nodal sites to seed yield was higher than in early stressed plants. The results of the field study on Verano stylo and Siratro, and the second experiment on stylo grown under controlled environment conditions were incorporated into practical recommendations which lead to conclusions on the most economically, socially and agriculturally acceptable management system for the seed production of Verano stylo and Siratro by Thai farmers.
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    A study of the combined effects of irrigation frequency and phosphorus fertility on summer pasture production : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy (PhD) in Soil Science, Institute of Natural Resources, Massey University, Palmerston North, New Zealand
    (Massey University, 2003) Hewana Arachchige Sumanasena
    During the last five years, there has been an increase in both the area of irrigated pasture in New Zealand and the intensity of this irrigation. Research has failed to keep pace with this change: the benefits of irrigation to pasture production have not been studied in a sustained manner since the 1980s. Since then a number of factors have changed including; a change in the type of irrigation system commonly employed, the productive potential of new pasture cultivars, an appreciation of the importance of relationships between water and nutrient uptakes by plants, and a heightened awareness of the environmental implication of irrigation. It is claimed that the ability of irrigation systems such as centre pivot and long lateral systems to increase irrigation frequency affords a major advantage to pasture production. As yet, these claims are largely unsubstantiated in New Zealand. In addition, there has been no research of the mechanisms or processes that might account for this phenomenon. The study described here set out to quantify the benefits of more frequent irrigation (in the readily available water range) to ryegrass and white clover production, including the relationship with increased nutrient status, and to elucidate the mechanism(s) that might explain this response. The responses of ryegrass and white clover to irrigation frequency (within the readily available water range) and nutrient addition, particularly phosphorus (P) were investigated with a pot experiment using Ramiha silt loam. The rate of fertiliser addition to the pots had a significant and consistent effect on a number of indicators of ryegrass and clover performance including total yield. In contrast, irrigation frequency did not significantly or consistently affect total pasture production. It was concluded that when soil, nutrients and plants roots constitute a relatively homogenous mix (i.e. the pot environment), more frequent watering is not significantly advantageous to plant growth and, therefore, all of the readily available water is equally available. Although there was no response in pasture production to irrigation frequency in the pot experiment, it was hypothesised that irrigation frequency (in the readily available range) in the field, where P values vary with depth in the soil profile, would affect pasture production. The response of swards of ryegrass and white clover growing in Manawatu fine sandy loam to irrigation frequency and P status was measured in a field experiment during the summer of 2000/01. Three irrigation frequencies within the readily available water range (irrigation triggered at soil water deficits of 20 mm (I-20), 40 mm (I-40) or 60 mm (I-60)) were combined with two P fertility treatments (no P fertiliser added or 40 kg P ha-1 applied). For comparative purposes, there were also 4 non-irrigated, non-P fertilised plots outside the main trial block. Plant production, nutrient content of plant material, soil moisture content, soil N and P contents, and nitrate-N, ammonium-N and phosphorus concentrations of soil water samples were measured. The herbage on the plots was cut and removed i.e. there was no grazing. In the field, irrigation frequency had a significant effect on ryegrass and clover production. Irrigation of ryegrass and white clover at I-20, over the summer period resulted in the greatest pasture production and was associated with the most efficient water use (defined as k with units kg DM ha-1) of the irrigated treatments, I-60 gave the smallest production and water use efficiency. Application of the recommended quantity of P fertiliser (40 kg ha-1) significantly enhanced total pasture production and hence water use efficiency. Soil P and N was most concentrated in the surface soil. The results of the field trial support the hypothesis that ryegrass and white clover production is greatest when the plant is taking most of the water it requires from the surface soil where nutrients are most concentrated i.e. the frequent (I-20) irrigation case. Production is smaller when the plant is extracting large quantities of water from depth where nutrient concentrations are smaller i.e. the less frequent irrigation (I-60) case. The effects of irrigation frequency and P fertility on root re-growth activity of ryegrass and white clover swards were evaluated using a modified refilled core method. Root growth of both species decreased with depth. Fertiliser P application significantly increased root growth of both species in two of the three sampling depths at the December and February harvests. In only one root harvest did irrigation frequency significantly affect root activity. At the April harvest, the greatest root growth in the surface soil was observed for I-60, P-0 plots. It is suggested that in addition to encouraging more moisture uptake from nutrient-rich surface soil, an additional benefit of frequent irrigation is that in soils that are consistently moist, plants need to produce fewer roots. A simple water balance model was developed to simulate volumetric soil water contents in the three depths of the Manawatu fine sandy loam that are most closely related to the three irrigation frequencies i.e. 0-150 mm, 0-300 mm, and 0-450 mm. The model illustrates how initially the plants extract most of their water requirement from the surface soil and then as the profile dries they remove more water from lower depths. Accordingly, it highlighted differences in soil water contents between the irrigation frequencies particularly in the surface soil (0 - 150 mm). Soil water sampling was conducted using ceramic suction cups. Estimated total nitrate-N losses until 31 July, 2001 indicated that irrigation frequency of ryegrass during the previous summer did not have a major effect on the overall nitrate-N leaching losses during the late autumn/early winter period but nitrate-N losses under clover tended to be lower under less frequent irrigation. P and ammonium-N leaching losses were negligible. Using the understanding developed in the pot and field trials, a model was constructed to predict ryegrass and clover production on Manawatu fine sandy loam under the different irrigation frequency and P fertility regimes. The model relates pasture production (G) to evaporation from a series of soil water deficit ranges (Ei) according to G = k1E1 + k2E2 +...+ knEn (where kiEi is the pasture production when soil water is in the ith soil water deficit range, and ki is the water use efficiency when soil water is in the ith soil moisture deficit). The ki values were derived using the production data from the field trial. The model was used to simulate the effect of irrigation frequency and P fertility on seasonal (1 November to 30 April) pasture production for a range of climate conditions using the past 26 years weather data. The simulation illustrates how pasture production under irrigation varies markedly with climate, irrigation frequency, P fertility status and the ryegrass:clover composition of the sward. Increasing irrigation frequency from I-60 to I-20 increased pasture production, on average, by 1473 kg DM ha-1 (23%) and 1105 kg DM ha-1 (19%) for P-0 and P-40, respectively. For the farmer contemplating the adoption of irrigation, the purchase of a system that allows more frequent irrigation is as significant a consideration as the decision to adopt irrigation itself. On a cautionary note, the model suggests that I-20 irrigation typically increases drainage losses by about 40 mm (42%) compared to I-60 irrigation.