Show simple item record

dc.contributor.authorCastle, Maria L.
dc.date.accessioned2010-10-12T00:37:51Z
dc.date.issued2000
dc.identifier.urihttps://hdl.handle.net/10182/2664
dc.description.abstractWhite clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) are often grown in conjunction with each other, and occupy more than 6.4 million hectares of improved pasture land in New Zealand. In order to increase production from this land increasing amounts of nitrogen (N) fertilisers are being applied, particularly at low temperatures. However, reduced plant N demand at low temperatures, combined with increased rainfall, can result in leaching losses causing groundwater contamination. Hence, many economic, environmental and social concerns associated with N use have arisen. This research was done to identify the differences in losses and uptake of N in white clover and ryegrass by examining the different agronomic and physiological processes associated with N losses and uptake. A lysimeter study was done to determine the extent to which differences in agronomic features between white clover and ryegrass would affect the losses and subsequent uptake of N. In the autumn of 1998, twenty four lysimeters consisting of a templeton silt loam were extracted from pasture land in Lincoln, Canterbury, New Zealand. Twelve were sown with white clover (Trifolium repens L.) cv. Grasslands Huia and twelve with ryegrass (Lolium perenne L.) cv. Grasslands Nui. ¹⁵N labelled urea was applied (23 kgN/ha) on 4th May 1998 or the 13th August 1998. The lysimeters were destructively harvested in September 1998. Dry matter, of shoots and roots and total N and ¹⁴N/¹⁵N ratios in the shoots, roots and soil were measured. The leaching losses of total N were significantly (P<0.05) greater under white clover than ryegrass and the uptake of ¹⁵N in white clover was significantly (P<0.05) less than ryegrass. When N was applied in August, 65 % and 43 % of ¹⁵N was located in the top 100 mm of the soil profile under white clover and ryegrass respectively; 65 % of white clover and ryegrass roots were located in the top 100 mm of the soil profile, suggesting that N was available in the rooting zone for subsequent uptake and growth. In order to confirm the agronomic differences and to investigate the physiological reasons for the differences in N uptake between white clover and ryegrass, a further field study was established in March, 1999. Eighty eight plastic tubes were filled with silica sand and buried in a randomised design; forty four were sown with white clover (Trifolium repens L.) cv. Grasslands Huia and forty four with ryegrass (Lolium perenne L.) cv. Grasslands Nui. N was applied in three treatment regimes: 0.5 molar N for the whole of the growing period; 0.5 molar N before 5th May 1999 and high 5.0 molar N from 5th May 1999 onwards, or 0.5 molar N before 13th August 1999 or high 5.0 molar N from the 13th of August 1999 onwards. The plants were destructively harvested six times during the growing period (33, 58, 88, 123, 157 or 185 days after sowing). Photosynthesis was measured on both white clover and ryegrass plants two days prior to each harvest date. Shoot and root dry matter production, leaf area, root length, and shoot and root in vitro and in vivo NRA were measured at each harvest date. Total N concentration and sap nitrate were analysed. Root to shoot ratios, specific leaf area, specific root length and the expression of NRA were then calculated. This study provided further support for the agronomic differences exhibited between white clover and ryegrass during the lysimeter investigation. Increasing N concentration in the nutrient solution from Mayor August onwards had no affect on dry matter production in white clover. In comparison, applying extra N to ryegrass from May onwards resulted in a significant (P<0.05) increase in dry matter production from 157 days after sowing onwards. The rooting morphologies of the two species differed; the white clover plant roots were predominantly fine (associated with soil exploitation), whereas ryegrass roots consisted of fine and thick roots (associated with exploration). The photosynthetic rate of white clover was significantly (P<0.05) less than ryegrass, except at the last harvest when shading may have resulted in a decrease in photosynthetic rate of ryegrass. There was no effect of temperature on in vitro and in vivo nitrate reductase activity (NRA), hence NRA did not appear to limit N assimilation. This study identified some physiological differences between white clover and ryegrass, e.g., photosynthesis, which may have contributed to the difference in growth between the two species over the low temperature months. In order to provide further information on the differences observed between the photosynthetic rates of white clover and ryegrass a further study was conducted in July 1999. Sixteen plastic tubes were filled with silica sand and buried in a randomised design; eight were sown with white clover (Trifolium repens L.) cv. Grasslands Huia and eight with ryegrass (Lolium perenne L.) cv. Grasslands Nui in March 1999. One hundred and twenty three days after sowing, photosynthesis was measured over a diurnal (10.00h to 16.00h) period. Both white clover and ryegrass reached maximum photosynthetic rates at 13.00h. There were, however, significant (P<0.05) differences III the maximum rate achieved: white clover reached 55 % of the maximum photosynthetic rate achieved by ryegrass. The effects of temperature on the rate of photosynthesis and NRA were determined using white clover and ryegrass in sand culture. Nitrogenase activity was determined in white clover over a diurnal period or at different measurement temperatures. The plants were kept in a glasshouse where day/night temperatures averaged 15/5°C for eight weeks. At 63 days after sowing, photosynthesis was measured at 15, 20, 25 or 30°C. Temperature had a significant (P<0.05) effect on the photosynthetic rates of both white clover and ryegrass. Maximum photosynthetic rates occurred at 15°C; at this temperature, white clover's photosynthetic rate was half that of ryegrass. The incubation temperature for NRA in vitro and in vivo on both roots and shoots was done at 5, 10, 15, 20, 25 or 30°C. There was no consistent effect of temperature on either in vitro or in vivo NRA. There was a trend towards increased expression of activity in white clover occurring at 15°C and 30°C. In ryegrass maximum expression occurred at 30°C. In contrast, there was a significant effect of temperature on nitrogenase activity in white clover. Furthermore, the temperature to which white clover roots were exposed at the beginning of the day significantly (P<0.05) affected N₂ fixation (hydrogen production) rates for the remainder of the day. The results from this research suggest that (1) photosynthesis was the primary controlling factor for the yield differences exhibited by white clover compared with ryegrass at low temperatures and (2) nitrogenase activity in white clover was determined by soil/root temperature. Applying N to white clover increased dry matter production only in the lysimeter study. This may have been a consequence of the trial protocol. In the lysimeter trial, the single application of N may have temporarily inhibited N₂ fixation, allowing carbohydrates to be partitioned predominately to the shoots. In subsequent trials, plants were fed with nutrient solution, and there were no apparent differences in carbohydrate partitioning in the white clover. In contrast applying high N in May to ryegrass resulted in a significant (P<0.05) dry matter increase. From this research, it was concluded that white clover produced significantly less dry matter than ryegrass between autumn and winter, due to a lower photosynthetic rate; with in a species photosynthesis could be a process identified as a major growth limiting step. The balance between respiration and both gross and net photosynthesis may account for the differences seen between the species, particularly as white clover has the added cost of nodule respiration. Therefore, to improve the competitiveness of white clover at low temperatures compared with ryegrass, research on breeding and selection are required to increase net photosynthesis and efficiency of N₂ fixation. By increasing white clover growth at low temperatures, and hence increasing pasture quantity and quality, requirements for fertiliser N should decrease, hence maintaining sustainability of pasture ecosystems.en
dc.language.isoen
dc.publisherLincoln University
dc.subjectdry matteren
dc.subjectnitrogenaseen
dc.subjectnitrateen
dc.subjectphotosynthesisen
dc.subjectryegrassen
dc.subjectwhite cloveren
dc.subjectleachingen
dc.subjectlysimetersen
dc.titleThe losses and uptake of N in white clover (Trifolium repens L.) and ryegrass (Lolium perenne L.) at low temperatures : agronomic and physiological aspectsen
dc.typeThesis
thesis.degree.grantorLincoln Universityen
thesis.degree.levelMastersen
thesis.degree.nameMaster of Applied Scienceen
lu.contributor.unitLincoln University
dc.rights.accessRightsDigital thesis can be viewed by current staff and students of Lincoln University only. If you are the author of this item, please contact us if you wish to discuss making the full text publicly available.en
pubs.organisational-group/LU
pubs.publication-statusPublisheden


Files in this item

Default Thumbnail

This item appears in the following Collection(s)

Show simple item record