School of Agriculture, Food and Ecosystem Sciences - Theses
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ItemThe interactive effects of soil water and nitrogen supply on grapevine vigour and juice quality in a cool climate vineyard in North East Victoria(University of Melbourne, 2006)Excess vigour due to abundant N supply is a major problem in cool climate vineyards resulting in poor fruit and wine quality. A study was undertaken to investigate the relationship between grapevine vigour and inherent N-fertility of soil in cool climate vineyards. The study included a laboratory experiment in which the relationship between grapevine vigour and N-mineralization potential of soils from selected cool climate vineyards (Whitlands vineyard in King Valley, Hoddles Creek vineyard in Yana Valley and T' Gallant vineyard in Mornington Peninsula) was determined. The soil at the main site (Whitlands) was a Red Ferrosol. The study showed that the potentially mineralizable-N (No) from soil organic matter (SOM) was high in the selected cool climate regions. Internode length of vines showed reasonable agreement with vine vigour of respective high and low vigour blocks. The positive relationship (R2 = 0.61) observed between No and soil total N indicated the possibility of using No values to interpret mineral-N availability to grapevines in these cool climate regions. Production of mineral-N was highest in the first 10 cm of these deep fertile soils and the correlation between No and soil total N was better in the 0-10 cm layer than the 10-20 cm layer. A field experiment was undertaken to investigate the interactive effects of soil water and soil mineral-N, manipulated through irrigation and inter-row management, on vegetative growth and juice quality of grapevines. There were two main treatments. In one treatment irrigation was applied to keep the surface soil layer close to field capacity (FC) during the growing season. The other treatment was the non-irrigated treatment, where the surface layer was allowed to dry-out during the growing season. There were four inter-row treatments (Control, Ryegrass, Clover and Dead mulch). During the three seasons of the experiment, rainfall, heat degree days and vine water use varied showing the seasonal variability that might occur in a cool climate vineyard. In all three seasons, irrigation resulted in a smaller soil water deficit (SWD) in the irrigated treatment than the non-irrigated treatment during berry development, but the largest difference in SWD between the irrigated and non-irrigated treatments was observed in the last season of the experiment (2003/2004 season). Leaf water potential values (?leaf) observed in vines from irrigated and non-irrigated treatments were well above the stress limit for wine grapes (> -1.5 MPa), which indicated that vines were not stressed even under nonirrigated conditions in this deep clay loam. Seasonal water balance showed that considerable drainage (from 133-148 mm for a comparatively dry year and 302-316 mm in an average year) occurred during winter and early spring when vine water uptake was negligible or very small. This shows the potential for groundwater pollution through leaching of excess NO3- produced during summer months in these viticultural soils. Soil mineral-N contents varied with time due to seasonal changes or due to grapevine or grass uptake and to leaching. High levels were due to increased mineralization and/ or low N uptake by the vines. Even during the period, when the demand for N by grapevines is greatest, there was plenty of soil mineral-N mostly in the form NO3- (250- 294 kg N ha-1). In the comparatively dry year of 2002/2003 there was a significant decline in mineral-N under ryegrass at flowering under both irrigated and non-irrigated treatments. The vigour-inducing effect of irrigation through increased soil water and mineral-N availability was observed as increased internode lengths, summer trimmings and winter prunings. These effects were prominent during the second and third seasons of the experiment. Irrigation increased yield in the first two seasons of the experiment, but the large amount of irrigation applied during the third season had a negative impact on the yield of irrigated vines. Grapevine N status was affected by seasonal variability and irrigation, or as a result of both. Irrigation affected all juice quality parameters in a fairly dry year, when juice from irrigated vines had significantly lower pH, higher titratable acidity (TA) (p < 0.01), lower �Brix and �Baume contents (p < 0.01) than non-irrigated vines. In all three seasons, juice from irrigated vines had lower pH and higher TA than non-irrigated vines indicating that they are the mostly affected juice quality parameters due to increased soil water and mineral-N availability. Use of highly enriched (15NH4)2SO4 (98%15N) as a tracer enabled the depth of mineral- N uptake of vines under irrigated and non-irrigated conditions to be determined. Cumulative mineral-N uptake was four times greater in the irrigated vines than the nonirrigated vines. This may be due to increased N availability and accessibility due to applied irrigation. The differences in SWD (indicating water extraction) in different depth layers suggested that drip irrigation induced more feeder roots in the surface 15 cm of soil. As a result more mineral-N was taken up from 0-15 cm depth layer under irrigation than without irrigation. The results of this experiment confirmed the potential to use irrigation practices as a tool to enhance or lessen N uptake from different soil depths in a deep fertile soil. The 15N natural abundance method was used to assess the contribution of biologically fixed N (BFN) from clover to the vineyard soil. However, the fact that both ryegrass and clover samples from the inter-rows were depleted in 15N and lack of a suitable B value meant that this technique was not effective. The distribution of ?15N values down the soil profile in soil total N and mineral-N fraction indicated that leaching of NO3- was a major mineral-N loss in this highly permeable soil.