Nitrogen Fertiliser Management for Yield and Fruit Quality

Transcription

1 Nitrogen Fertiliser Management for Yield and Fruit Quality P Jerie and F MacDonald Department of Natural Resources and Environment, Victoria Project Number: AP95024

2 AP95024 This report is published by Horticulture Australia Ltd to pass on information concerning horticultural research and development undertaken for Apple and Pear industry. The research contained in this report was funded by Horticulture Australia Ltd with the financial support of the apple and pear industry. All expressions of opinion are not to be regarded as expressing the opinion of Horticulture Australia Ltd or any authority of the Australian Government. The Company and the Australian Government accept no responsibility for any of the opinions or the accuracy of the information contained in this report and readers should rely upon their own enquiries in making decisions concerning their own interests. ISBN Published and distributed by: Horticultural Australia Ltd Level 1 50 Carrington Street Sydney W 2000 Telephone: (02) Fax: (02) horticulture@horticulture.com.au Copyright 2002 Horticulture Australia

3 Final Report Horticulture Australia Project Number AP95024 (2002) Nitrogen Fertiliser Management for Yield and Fruit Quality P. Jerie and F. MacDonald Department of Natural Resources and Environment, Victoria Institute of Sustainable Irrigated Agriculture Horticulture Australia Australian Apple & Pear Growers 'Association Inc State Government Victoria Department of Natural Resources and Environment Victoria The Place To Be

4 AP Nitrogen Fertiliser management for yield and fruit quality P. Jerie and F. MacDonald NRE Tatura Institute of Sustainable Irrigated Agriculture Private Bag 1, Ferguson Road Tatura Victoria 3616 Australia Note: Both authors resigned from NRE before this report was finalised. Inquiries should be directed to D. Williams at the above address. Purpose: This final report fulfills the requirements of milestone number 6 for HAL project AP Funding for Project AP95024 was provided by the NRE Horticulture Program Fruit and Nuts Key Project, Horticulture Australia Ltd and the Australian Apple and Pear Growers Association. Date of Report: January 2001 The State of Victoria, Department of Natural Resources and Environment, 2000 This publication is copyright. Apart from any fair dealing for the purposes of private study, research, criticism or review as permitted under the Copyright Act 1968, no part may be reproduced, copied, transmitted in any form or by any means (electronic, mechanical or graphic) without the prior written permission of the State of Victoria, Department of Natural Resources and Environment. All requests and inquiries should be directed to the Copyright Officer, Library Information Services, Department of Natural Resources and Environment, 5/250 Victoria Parade, East Melbourne, Victoria Disclaimers This publication may be of assistance to you but the State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes, and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication. Any recommendations contained in this publication do not necessarily represent current Horticulture Australia policy. No person should act on the basis of the contents of this publication, whether as to matters of fact or opinion or other content, without first obtaining specific, independent professional advice in respect of the matters set out in this publication.

5 AP95024: Nitrogen Fertiliser management for yield and fruit quality Media Summary Orchardists use nitrogen fertilisers to help manage tree vigour, fruitfulness, fruit colour and quality. This is difficult because mature trees, especially pears, respond slowly to changes in nitrogen management. Orchardists are also responding to environmental concerns by attempting to reduce the amount of nitrogen applied to pears while adopting improved application techniques. There is some uncertainty, however, on how to best monitor nitrogen status and how to identify the minimum sustainable quantity required. Research conducted at Tatura by NRE's Institute of Sustainable Irrigated Agriculture on behalf of Horticulture Australia and the Australian Apple and Pear Growers Association was aimed at improved monitoring of nitrogen status so that only the minimum amount of nitrogen needed for sustainable production would be applied. The project team set up an experiment using widely different levels of nitrogen on 50 year old Packham pear trees. They sampled a range of tissues from the trees at various timings, and also measured yield and fruit size at harvest. The only tissue analysis that detected a response to treatment was from spurs in autumn treated with Foliar Urea but the effect had disappeared by full bloom, when flower clusters of all treatments had similar nitrogen levels. None of the treatments affected yield, fruit size or fruit sugar levels. The team concluded that there is scope to reduce nitrogen applications in pear orchards provided that nitrogen status of the trees is monitored. This will have environmental benefits as well as reducing costs. Since none of the alternative tissue analyses were better than leaf analysis, and growers have some experience with this technique, leaf nitrogen levels are still considered the most appropriate indicator of nitrogen status and should be taken every 2-3 years. A best practice manual, "Fertiliser management for pears in the Goulburn-Murray valleys", has been published and is available from NRE Tatura.

6 AP95024: Nitrogen Fertiliser management for yield and fruit quality Industry Summary Nitrogen fertiliser applications in orchards are widely accepted as important for managing tree vigour, fruitfulness, fruit colour and quality. However, recent projects have shown that it was not possible to consistently relate nitrogen use in many mature orchards to yield and even to tree vigour. Pear orchards in particular respond very slowly to changes in nitrogen management. Fruit itself contains little nitrogen at harvest. Nitrogen contained in leaves and prunings is recycled. Nitrogen use efficiency in orchards is between 10% and 30% and is highly variable. This reduces the usefulness of standard fertiliser recommendations. Many growers are reducing the amount of nitrogen applied to pears while adopting improved application techniques. However, there is some uncertainty on how to best monitor nitrogen status and how to identify the minimum sustainable quantity required. The Department of Natural Resources and Environment, through the Institute of Sustainable Irrigated Agriculture (ISIA), has had a long-term program of research and extension to improve efficiency and sustainability of nitrogen fertiliser practices in orchards. The current project sought to improve monitoring of tree nitrogen in pear orchards so that growers could determine the minimum sustainable level of N application suited to a particular block. The project included two components. One was to produce a fertiliser management manual based on the experience of local extension and research projects and published data. The manual, "Fertiliser management for pears in the Goulburn-Murray valleys", was published in 1999 (Cook, 1999) and is available from ISIA. The second component was a trial on Packham pears using widely different levels of nitrogen and sampling different tree tissues at various times to see if it was possible to improve on traditional leaf sampling for monitoring orchard nitrogen status. The trial was set up in a high producing block of Packham pears that were 50 years old. The tissues sampled for nitrogen analysis were mid-shoot leaves taken at the traditional time and two later times, spurs that initiated flowers during autumn, bark and trunk storage tissues, flower clusters at full bloom and fruit in November, January and at harvest. Yield, fruit size and dry weight were taken at harvest and pruning weights in winter. The only tissue analysis that detected differences related to treatment was from spurs in autumn treated with Foliar Urea but the effect had disappeared by full bloom, when flower clusters of all treatments had similar nitrogen levels. None of the treatments affected yield, fruit size or fruit sugar levels as indicated by percent dry weight in the fruit. Soil nitrate levels in the root zone to a depth of 75cm were well related to treatments. A large amount of nitrate was found below 75cm and the concentration was not related to treatments. Similar quantities of nitrate have previously been found in other Goulburn Valley orchards. The results suggest that nitrate previously considered to be below the root zone may become available but the circumstances and timing of uptake are uncertain. In conclusion, reducing nitrogen applications in pear orchards is unlikely to reduce yield provided that tree nitrogen status is monitored, and will have environmental benefits as well as reducing costs. None of the other tissue analyses improved on leaf nitrogen levels for monitoring nitrogen status. Leaf analysis should be undertaken every 2-3 years.

7 Introduction AP95024: Nitrogen Fertiliser management for yield and fruit quality Nitrogen fertiliser plays a major role in orchard management and is widely considered to affect tree vigour, yield, fruit size and quality. Pear orchards are typically fertilised with nitrogen in spring and autumn, with amounts ranging from less than 50 and up to 300 Units of N per hectare. In younger pear orchards high nitrogen is associated with high vigour, rapid tree growth and low fruit set. However, in comparing productivity across many orchards it was not possible to find a relationship between the amount of nitrogen applied and yield or even tree vigour (Schneider 2000). Other published research has stressed the importance of nitrogen uptake in autumn, to build up tree reserves and improve the early nutrition of fruitlets in the following spring. The Fertiliser Management manual ( Cook 1999) published as part of this project follows this approach. There is a general tendency in the industry for growers to use less nitrogen and to apply at least part in autumn. One particular difficulty is that while traditional leaf analysis may measure the longer-term nitrogen status in pear orchards, the results can not readily be related to recent changes in amounts or timing of nitrogen applications. It is not clear whether other types of tissue samples or times of sampling would give a better picture than the normal mid-summer leaf samples. Therefore, as growers trial reduced nitrogen rates they do not have a monitoring procedure that can be easily followed to record orchard nitrogen status or the impact of new application methods and timing. The complexity of nitrogen movement in the soil is one of the causes of variation that make it difficult to relate nitrogen application practices to tissue analysis. Trees absorb mainly nitrate and all organic or ammonium sources of nitrogen must be converted to nitrate by soil microbes in order to become available. Thus the effective timing of nitrogen depends on the rate at which nitrate forms in the soil, and that is strongly influenced by soil ph, temperature and moisture. Once formed in the soil, or if nitrate fertiliser is used, irrigation and rain will readily leach nitrate below the root zone (McNab et al 1994) where it appears in sub-soil, shallow water tables or in tile drains. Irrigation, soil conditions and how the nitrogen is applied in the first instance, can be more important in determining tree uptake than the actual amount applied. In one 4-year trial, half of the relatively low annual rate of 75 Units of nitrogen per hectare was lost in tile drainage over the following months while tree nutrition, vigour and yield were consistently good and not affected by treatments (Stork and Jerie 1999, McNab et al 1994). This illustrates the practical difficulty for orchardists in planning nitrogen management but also emphasizes the opportunity for reducing nitrogen application rates to reduce costs, possibly improve productivity, and to minimize environmental pollution (Schneider 1995). The Institute of Sustainable Irrigated Agriculture (ISIA) has had a long-term program of research and extension to improve efficiency and sustainability of nitrogen fertilizer practices in orchards. The objectives of the program were to minimize nitrogen use and improve the timing of applications in order to reduce environmental impacts of nitrogen

8 such as drainage pollution and soil acidification, and to provide a direct benefit to industry through reduced costs and improved productivity and fruit quality. If monitoring of tree nitrogen in pear orchards could be improved growers may be able to determine the minimum sustainable level of N application suited to a particular block. The aim of this project was to determine, in a mature Packham pear orchard, whether alternative types of tissue samples or sampling times may be better suited to monitoring the impact of changes in nitrogen management than the traditional mid-summer leaf sample. Also of interest was the rate of change of tree nitrogen status and, if developed, the capacity to detect the onset of low or deficient levels of nitrogen. For this purpose the treatments included nitrogen levels from nil to 160 Units per hectare and foliar applications in autumn. Materials and Methods Orchard site: A 50-year-old Packham pear orchard in the Goulburn Valley approximately 1km from ISIA Tatura was selected. The trees, spaced at 5.5x5.5m, were healthy and reasonably uniform. The soil type was Shepparton fine sandy loam in which the depth of the root zone was expected to be a maximum of 50-70cm. The trees were irrigated by two 180 microjets placed close to each side of the trunk. In two plot rows 12 uniform trees were selected with a minimum of two guard trees between each. Groups of four plot trees were treated as a block and treatments were randomized between them. Treatments were replicated six times. Apart from the nitrogen applications over the entire experimental rows and guards, the grower carried out all orchard management and irrigation according to normal commercial practice. The experiment was conducted over three seasons from September 1995 to winter in Treatments: Four treatments were randomized in six blocks. Adjacent guard trees received the same treatment as the plot tree. 1. Nil-N. No nitrogen was applied N. Ammonium nitrate was applied at the rate of 160 units per hectare, half in spring after full bloom and half after harvest in early March. Fertiliser was spread by hand on the tree line within the microjet wetting zone. To wash the fertilizer into the upper root zone it was applied either about 1 hour before the end of a normal irrigation or was spread dry and followed by a short irrigation of about 1 hour N. Ammonium nitrate at the rate of 80 Units per hectare was applied as described above. 4. Foliar-N. 40 Units per hectare were ground applied in spring as described above. After harvest three sprays of 2% low biuret urea were applied at 2-week intervals in March using about 101 per tree, totaling approximately 80 Units N/ha from urea. Tissue samples: All leaf, spur, flower and fruit samples were analysed separately for each plot. Leaf samples were taken in early January, mid-february and mid-march in each year. Thirty mid-shoot leaves were taken per tree. Spur samples consisted of the terminal

9 3-4cm and any bourse swelling from well developed two or three year old fruiting spurs. Attached leaves were removed. Spur samples were taken in mid-march, late May and late June. Ten flower clusters per tree were taken near full bloom, selecting clusters in which the first flower to open had dehisced anthers. Fruit, 5-10 per tree, were sampled after fruit shedding finished in mid-november, in early January, and at harvest in late February. All samples were dried in an oven at 80 C and ground for analysis. Analyses for total Keldahl nitrogen were carried out in the analytical laboratory at ISIA. Bark and wood samples were taken approximately 4 weeks before full bloom. A 3cm square of bark was removed to the depth of the xylem with a chisel. The outer dead layer was trimmed off. The wood sample was obtained by drilling into the exposed xylem from under the bark sample to a depth of 1cm with a 15mm drill. For bark and wood samples, tissue from all six replicates was combined to make one composite sample for each. The samples were dried and ground for analysis as above. Soil Samples: Soil samples were taken in the tree line in the center of the microjet wetting pattern, 1-1.5m from the trunk over depth intervals of 0-25, 25-50, and cm. Soil was air dried, ground and extracted with distilled water using log of soil and 20ml of water. Nitrate was determined using Merck Nitrochek nitrate test strips and meter to read strip colour after 1 minute. Harvest and pruning measurements: All plot trees were strip picked at the same time by two commercial pickers. The fruit was put into 8-12 boxes per tree and weighed, a subsample of approximately 10% was removed, weighed and the diameter of individual fruit was measured. Average fruit size, fruit weight and total fruit number per tree were estimated. A further subsample of 5 fruit was taken for chemical analysis. All fruit were then delivered to the grower. Two orchard staff pruned all plot trees several days before the remaining trees were pruned to avoid confusion of samples from plot and guard trees. Prunings were picked up and weighed within 2 days. In year 1 the grower wanted to make some heavier cuts. As pruning weight would not reflect the annual growth under these circumstances the weights were not taken in that year. Statistical analysis: Data was compared in analysis of variance ANOVA using Genstat 542, Laws Agricultural Trust (Rothamstead Experimental Station). Treatment means were compared using Fisher's unrestricted LSD 5 o /o. The data was log transformed to stabilize variances where appropriate. Arithmetic means of treatments are shown in all tables for ease of understanding and comparison with other published or existing data. The level of significance shown in the tables was obtained by analysis of the transformed data. Results and Discussion Old pear orchards have previously been found to respond very slowly to changes in nitrogen management (Selimi and Keatley 1969) and, in recent work, no relationship was

10 found between the amount of nitrogen applied in a number of commercial orchards and leaf nitrogen levels or yield (Schneider 2000). In the present trial, storage tissues and developing fruit were analysed for nitrogen to determine whether these tissues could provide samples that would better reflect the range of nitrogen treatments or fruit growth and nitrogen content. If such a relationship could be found it would possibly lead to an improved approach for monitoring nitrogen in pears and provide a sound basis for growers to minimize their nitrogen use. Recommending general rates for annual fertilizer application, as had been practiced in the past, is not really valid in any individual orchard as soil type, irrigation and fertilizer application methods create at least 2-3 fold differences in the uptake of nitrogen. Effect of treatments on yield and tree growth The experiment was located in a high yielding orchard that had crops of tonnes per hectare in the first two years. In the 1997/98 season there was a light fruit set and yields were reduced by about one-third across all treatments. In any one year during the three years of the trial, there were no significant treatment effects on yield, fruit size or percent fruit dry weight (Table 1). However, in each year the Nil-N treatment showed a strong trend towards a higher yield and this became statistically significant (P 0.05) when the data was analysed over all years. The higher yield was due to a greater fruit number on Nil-N trees and was considered a surprising result given the circumstances of the experiment, particularly in year one. The final fruit number on Packham pear trees is determined by early November when natural fruit shedding is completed. In the first year, 1995/96, nitrogen treatments were not applied until about 3 weeks before the fruit number stabilised. The results in table 1 imply that, during the next 2-3 weeks, the nitrogen applied to the 160-N, 80-N and Foliar- N treatments increased fruit drop relative to the Nil-N treatment. High vegetative vigour resulting from high levels of nitrogen can reduce fruit number but such a mechanism was thought most unlikely to explain the differences in this instance, given the short time available for nitrogen uptake and action within the tree. The greater level of fruit set in Nil-N compared to other treatments remained very consistent over the next two seasons. Pruning weights could not be obtained in the first season but higher pruning weights in Nil-N trees over the following two years indicated that it was the Nil-N trees that made significantly more shoot growth than the other treatments (Table 2). It appeared that, despite their random selection, the Nil-N trees were stronger or possibly larger than trees in the other treatments. Randomisation is used to reduce the chances of such an occurrence but cannot completely eliminate it. There is no reason to believe that a nil nitrogen treatment could have increased tree growth. This raises the possibility that the higher yield of the Nil-N treatment resulted from the original randomisation rather than treatment effects. The question could not be resolved within the present experiment because there was insufficient time available, after the effect was noticed, to obtain another site. It was also too late to re-randomise the existing site. On the evidence available, it should not be concluded that spring nitrogen applications as low as 40 Units per hectare caused rapid fruit drop in pears. More work is required to resolve this question.

11 We do not consider results from tissue analyses in the following section to be affected by the difficulty in evaluating yield data. The major purpose of tissue analysis was for monitoring nitrogen levels across the range of treatments and determining how well a particular tissue sample could be related to treatment. Table 1. Average yield per treatment (kg of fruit per tree) and estimated fruit size (mm, average diameter of fruit) for each season. Statistical analysis: indicates treatment differences were not significant (P<0.05) in that year. Analysis of data for all years showed that in fruit yield (kg/tree) the mean of Nil-N was significantly greater than 160- N and Foliar-N (PO.05). Treatment Nil-N 160-N 80-N Foliar Kg/tree /96 Size, mm Kg/tree /97 Size, mm Kg/tree /98 Size, mm Table 2. Average pruning weights per treatment (kg fresh weight per tree) for the second and third season of the trial. Statistical analysis: Means with the same superscript are not significantly different (P<0.05). indicates treatment differences were not significant (P<0.05) in that year. Treatment Nil-N 160-N 80-N Foliar June 1997 Kg/tree June 1998 Kg/tree All Years Kg/tree 21.4 a 15.6 b 16.2 b 17.2 b Tissue samples for monitoring tree nitrogen status Leaf nitrogen levels were not influenced by fertilizer treatments as shown by the results of the samples taken in the normal time in January (Table 3). The February results were unchanged showing that in pears, leaf nitrogen levels were not affected by the rapid fruit growth over that period, even with a heavy crop of 70 tonnes/ha. The exact time of leaf sampling is therefore not critical. An unexpected result was that the March sample from the Foliar-N treatment did not show a higher nitrogen level except in 1997/98. At the time of sampling the trees had been sprayed two times with 2% urea. Approximately Units of nitrogen per ha were applied in each spray. It was not possible to determine the amount of urea actually taken up by the leaves. Some uptake must have occurred because the Foliar-N treatment did significantly increase nitrogen levels in spur tissue.

12 Any urea taken up by the leaves must have been rapidly mobilised into the tree. The soil nitrogen data (Table 8) indicates that there was considerable runoff. The nitrogen level in fruiting spurs, including the swollen tissue that develops after the first flowering, increased over autumn as would be expected in a tissue that acts as a nutrient storage site for flower and leaf bud development in spring (Table 4). The sample in late July was taken before there was any visible bud development. Spur nitrogen levels were not affected by ground applied nitrogen treatments and were similar for Nil and 180-N treatments. Urea sprays in the Foliar-N treatment significantly increased spur nitrogen in each year. However, by full bloom (Table 5) the effect had been lost and the nitrogen level was similar in flower clusters of all treatments. Some seasonal effects were observed (Tables 4 and 5). Spur nitrogen levels were generally lower in July 1996 than in July 1997 but in both years, nitrogen in the flower clusters did not reflect the difference and were similar at 3.3 to 3.5%. Subsequently fruit set and yield from the 1997 flowering was 30% smaller than in the previous year. By contrast, flower clusters in September of 1995 had a relatively low nitrogen level ( %) but fruit set and yield were as high as in the 1996/97 season. Table 3. Arithmetic means of total leaf nitrogen (% of dry weight) in mid shoot leaf samples taken each season on 8th of January and again just before harvest in mid February and in mid March. February sample in 1997/98 were lost. Fertiliser treatments started in October Statistical analysis: Means with the same superscript are not significantly different (PO.05). indicates treatment differences were not significant (P<0.05) at that sampling date. Treatment Nil-N 160-N 80-N Foliar-N Jan %N, 1995/96 Season Feb March Jan %N, 1996/97 Season Feb March Jan %N, 1997/98 Season Feb March 2.10 ab 2.27 ab 2.06 b 3.31 a Table 4. Arithmetic means of total nitrogen (% of dry weight) in spurs and associated buds from 2 year old or older fruiting spurs sampled in mid March, late May and late July in each season. The first urea spray had been applied in the Foliar treatment about 10 days before the March sample. Fertiliser treatments started in September Statistical analysis: Means with the same superscript are not significantly different (PO.05). indicates treatment differences were not significant (P<0.05) at that sampling date. Treatment Nil-N 160-N 80-N Foliar-N %N, 1996 season May March July 1.32b 1.32 b 1.28 b 1.52 a %N, 1997 season May 1.36" 1.32 b 1.31 b 1.80 a March July 1.61" 1.65 b 1.51 b 1.91 a %N, 1998 season May 1.56 b 1.56 b 1.59 b 2.02 a March July 1.58 b 1.63 b 1.72 b 2.09 a

13 Table 5. Arithmetic means of total nitrogen (% of dry weight) in flower clusters sampled at full bloom. Clusters were selected when anthers in the first flower to open had dehisced. In 1995 the spring fertilizer treatments were applied about 2 weeks after the flower sample had been taken. Statistical analysis: indicates treatment differences were not significant (P<0.05) at that sampling date. Date Treatment Nil-N 160-N 80-N Foliar-N 26 Sept %N Sept %N Sept 1997 %N Bark and wood also act as storage tissue. These samples were not statistically analysable because only a composite sample had been taken for each treatment due to difficulties in the procedure. Bark tissue had the same nitrogen level in each year for all treatments (Table 6). Wood samples contained less nitrogen than bark and were also unaffected by fertilizer treatment but did vary in 1996 and 1997 in a similar way to spur samples (Table 6). Table 6. Total nitrogen (% of dry weight) in bark and wood samples taken from the trunk approximately 4 weeks before flowering in each year. Samples from all trees in each treatment were combined into composite samples of bark and wood. Date Treatment Nil-N 160-N 80-N Foliar-N 4/09/ % N, Bark 5/09/ /09/ /09/ % N, Wood 5/09/ /09/ Packham fruit growth follows a regular curve (Mitchell 1986) apart from small season to season variations. Fruit growth was not monitored in this experiment but, based on the above data, the fruit sampling dates in November, January and February were chosen to represent fruit development of 15-18%, 40% and 95% respectively of the final fruit fresh and dry weight present at harvest. Natural fruit drop finished just before the November sampling date so that fruit number was essentially constant after that time. There were no significant treatment effects on the level of nitrogen in the fruit in November in both years (Table 7), as with nitrogen in flower clusters in those years. The decline in nitrogen levels until harvest was also similar in both years and between treatments. While procedures in this experiment were not primarily designed to follow nitrogen accumulation in developing flowers or fruit, it is interesting to note that all the nitrogen in

14 the fruit appears to have been imported by the November sampling date. At that stage the total amount of nitrogen in one fruit was approximately 20 times the amount in one flower cluster. After November, nitrogen levels reduced approximately in proportion to fruit growth. For example, assuming a fruit at 16% of final size and 1.8% nitrogen in November, it would be expected to have a nitrogen level of 0.26% just before harvest if no net import of nitrogen occurred during the remaining fruit growing season. This closely matches the data in Table 7. The total amount of nitrogen contained in a 70 tonne per hectare crop would be less than 30 Units. Table 7. Arithmetic means of total nitrogen (% of dry weight) in fruit sampled in November after the completion of natural drop, in early January at the start of rapid fruit growth and in February just before harvest in the 1996/97 and 1997/98 seasons. Statistical analysis: indicates treatment differences were not significant (P<0.05) at that sampling date. Treatments Nil-N 160-N 80-N Foliar-N Nov %N, 1996/97 Jan. Feb Nov %N, 1997/98 Jan. Feb Soil nitrate concentrations Nitrate was analysed by a non-conventional method using 2:1 water-soil extracts and determining nitrate concentration in a small pool of unfiltered water with Merck Nitrochek strips and meter to read the strip colour. Concentrations below 1 Oppm could only be estimated in the range of 1-5 or 6-9 ppm. In earlier comparisons at Tatura, this method had been shown to be suitable for semi quantitative comparisons giving results within 10-20% of conventional laboratory methods. It is estimated that a result of looppm would correspond to 65 Units of nitrogen for a layer of soil 10cm deep over one hectare. Analysis of soil nitrate showed that in the upper 50cm, where most of the tree roots are located, and in the next layer of 50-75cm, nitrate concentrations closely reflected fertilizer treatments (Table 8). The Nil-N treatment had very low levels, generally below 10 ppm, the 160-N had the highest level and 80-N was low to intermediate. The Foliar-N treatment had received no soil application in autumn and the relatively high nitrate levels in winter were not expected. A possible explanation is that runoff from urea sprays could have added up to 60 Units of nitrogen per hectare. With a slow formation of nitrate from urea/ammonium at that time of the year, a relatively high proportion of the sprayed nitrogen may have persisted at the time of sampling. In the subsoil it is generally considered from soil pit observations that the root density rapidly declines below 50cm and is extremely low below 70cm. Nitrate levels below

15 75cm were high in both years and particularly in 1997 showed no influence of treatment. There is no clear explanation for the lower nitrate levels in 1998 but it appears to be the result of an overall environmental influence rather than a cumulative effect of treatments. For example, the nitrate level was reduced by 48% and 40% in the Nil-N and 160-N treatments respectively. Table 8. Nitrate concentrations in mg per kg dry soil. Concentrations below loppm could not be accurately measured and are indicated as (a) between l-5ppm and (b) 6-9ppm. Figures shown are the treatment means from individual samples analysed for each plot. The data was not statistically analysed. Treatment Nil-N 160-N 80-N Foliar June 1997, Soil depth cm (a) (a) June 1998, Soil depth cm (b) 52 (b) Conclusions It was not possible from the results of the experiment to determine an improved sampling approach for monitoring tree nitrogen status. This objective was made more difficult because the ground applied fertilizer treatments did not produce any measurable differences in nitrogen nutrition, yield, fruit size or fruit dry weight. Treatment differences or nitrogen deficient trees would have been expected to help identify and demonstrate the usefulness of alternative sampling approaches. Possible causes of the lack of treatment effects are discussed below. However, given this situation, it appears that the types of samples taken are not likely to be suitable as predictors of tree nitrogen status or to allow a prediction of yield. For example, autumn urea sprays increased the nitrogen level in fruiting spurs significantly but this had no measurable impact at full bloom or on subsequent fruit development. There were also significant seasonal differences with nitrogen in wood being high in 1997 and low in flower clusters in 1995 and in spurs in 1996 without any effect on yield. None of these differences were reflected in January leaf analyses, the results of which remained constant over the three years. Similarly none of the results could be related to the low fruit set and yield in It appears that in this orchard, and possibly in many other pear orchards in the Goulburn Valley, nitrogen is not a limiting factor in determining yield or tree growth In another nitrogen trial, in a Nashi pear orchard with tile drains (McNab et al 1994, Stork and Jerie 1999), yield, fruit size and leaf nitrogen levels also showed no response during four years of treatments of 75 and 200 Units of nitrogen per hectare. At that site it was clearly demonstrated that nitrate was leached very efficiently by irrigation or rain and left the orchard in tile drainage. Over a whole year the leaching fraction with respect

16 to applied nitrogen was above 90%. In the Packham orchard the nitrogen accumulated in the subsoil though we did not establish to what depth below 100cm. The results of the two trials raise doubts regarding previous assumptions about the rate, timing and location of nitrogen uptake in the pear root zone and the efficiency with which nitrogen can be applied and limited to the upper root zone. The results also indicate that, because of storage in the total root environment and possibly because of the small amount needed to be taken up annually, the amount of nitrogen applied to pear orchards in the Goulburn Valley could be reduced to between zero and 30 Units annually. Eventually this should result in nitrogen deficiency. It is not possible to say how well the onset of deficiency will be monitored by leaf analysis but at present there is no other alternative. Lowering rates of nitrogen application will reduce costs and soil acidification. High subsoil nitrogen levels have been found in several other orchards in the Goulburn Valley and may occur fairly generally. In soil pits and using soil moisture probes, roots or root activity are rarely observed below 70cm in these soils. Once nitrate moved below 70cm it was considered to be lost to the orchard and that it would eventually be leached to the water table. This occurred in the tile drained Nashi orchard mentioned above. However, results from a Partial Rootzone Drying (PRD) experiment in a different Packham orchard (Loveys et al 1999 and unpublished data) suggest a more complicated movement of water and possibly nitrate. In PRD irrigation, alternate rows of the orchard are not irrigated at all. In the dry rows detailed soil moisture measurements showed drying of the previously wet soil between 70 and 110cm. It is not known whether the drying was due to uptake from a very small number of roots at that depth or to upward capillary movement of water into the much dryer soil above 70cm. A similar situation could occur in any orchard that was being dried out in autumn. Nitrate would move into low roots or, with the capillary water, to roots higher in the profile and would be taken up by the tree. During wet periods, either irrigation or winter rain, the subsoil nitrate store is replenished by leaching. This could explain how the Nil-N trees maintained nitrogen levels in leaf and other tissues when the amount of nitrate above 50cm was very low. Subsoil nitrate could also result in an undesirable high nitrogen status in, for example, apple orchards and result in excessive vigour and reduce colour and fruit quality even when fertilizer application were at a low level. Acknowledgments Permission to locate the trial in a commercial orchard near the Institute and helpful cooperation from the management is gratefully acknowledged. The project was financially supported by the NRE Horticulture Program and an HRDC research grant (AP95024) with matching industry funds from AAPGA. Dr L. Callinan conducted statistical analysis. Chemical analyses were carried out in the ISIA analytical laboratory.

17 References Cook, H. (1999). Fertiliser management for pears in the Goulburn-Murray valleys. Manual published by Department of Natural Resources and Environment, Victoria, Australia. Loveys, B., Dry, P., Hutton, R. and Jerie, P. (1999) Improving the water use efficiency of horticultural crops. Final Report, NPIRD project number CDH1. McNab, S., Jerie, P., O'Connor, R and MacDonald, P. (1994). Efficient fertilizer application techniques and nutrient losses in irrigated horticulture. In: Nutrient and fertilizer management in perennial horticulture, Proceedings of workshop, Land and Water Resources Research and Development Corporation, Occasional Paper 07/94. Mitchell, P.D. (1986). Pear fruit growth and the use of diameter to estimate fruit volume and weight. Hortscience, 23, Selimi, A and Keatley, J.C. (1969). Effect of soil management, pollination, and nitrogen fertilisers on Williams' pear trees. Australian Journal of Experimental Agriculture and Animal Husbandry 9:553 Schneider, H.G. (2000). Develop orchard fertiliser strategies using successive leaf analyses and focussed discussion groups. Final report, Horticultural research and Development Corporation, Project number FR Schneider, H.G. (1995). Soil acidity management by technology transfer of improved fertiliser and irrigation management techniques. Final Report, Horticultural research and Development Corporation, Project number FR333. Stork, P. and Jerie, P. (1999). Developing and evaluating best management fertilizer practices for irrigated horticulture. Final Report, Project NRMS 16062, Murray Darling Basin Commission, Canberra, Australia.

18 AP95024: Nitrogen Fertiliser management for yield and fruit quality Technology Transfer Technology transfer for this project was delivered via project FR96010 Develop orchard fertiliser strategies using successive annual leaf analyses andfoe us groups, conducted by Henry Schneider from NRE Cobram. Information from the project was incorporated into discussions with grower groups in Cobram, Tatura, Harcourt over the 3 years of FR The pear manual, produced by Heather Cook as part of AP95024, was also used by the grower groups as a resource. Over 100 copies of the pear manual have been sold and have also been distributed to Fruitcheque staff for use in industry training programs and focus groups. The pear manual is being used as a template for the development of similar manuals for apples and stone fruit. The findings from this project, and their implications for other crops have been presented to growers and other industry personnel at meetings of Nashi growers (June 2001), W Apple growers (1999) and growers in Southern Victoria (2 meetings in 2000).