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Research Report Contents
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A project facilitated by the Research and Development Group of the Bio Dynamic Farming and Gardening Association 4 Organic Fruit Production in New Zealand – A Review of Understorey and Soil Management Literature A decade ago very little attention was given to research on organic fruit production in New Zealand or internationally. In this regard, the work of Daly and colleagues at the Winchmore apple orchard could be regarded as pioneering. This is reflected by the fact that their work is one of the principal sources of published literature on understorey and soil management for organic apple production. Other research is being conducted, at the Louis Bolk Institute in the Netherlands, but much of this material has not been published in English. There is relatively little, if any, literature on organic systems of other temperate and sub-tropical fruit crops. Because of this, this review is far from comprehensive and does not solely rely on findings from organic research programmes. Within the scope of this study as wide a net as possible has been cast to draw together relevant literature, not all of which has been peer reviewed. As a starting point, a review of what is already known in New Zealand is provided. This is followed by a review of literature from international sources, sourced primarily from abstracting databases and the internet. It is hoped that as this material is read, a reasonable picture of what is known about organic soil management in orchard environments will emerge for the reader, and questions may begin to arise about what is not known. A final section is provided in which the various threads are drawn together to develop a clearer picture of important gaps in knowledge that need to be addressed in a New Zealand context.
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New Zealand Literature on Understorey and Soil Management There is very little published literature on orchard understorey and soil management in New Zealand. The most relevant material is from the Winchmore apple orchard study, which began in 1989. Key papers are Daly, (1994) and Marsh et al., (1996). Other useful papers are Goh et al., (1994) and Marsh et al., (1994). Daly (1994) indicated that an important reason for choosing the Winchmore site was that it was an existing 3-year old orchard, (containing Royal Gala, Red Delicious, Braeburn and Fuji), and thus changes through the organic conversion process were able to be examined. While conversion is a more difficult option than designing an organic system from the outset, it is the most common scenario faced by potential organic producers. Three separate herbage understorey treatments were examined. The red clover understorey led to the best tree growth and highest tree nitrogen in the early years of conversion, but showed lack of persistence after 3 years (Daly, 1994). With its persistence, positive tree growth and nutrition effects, the herb ley was found to be the most promising. Mowing management and mulching also had very positive effects. No decline of soil nutrient reserves was observed over the initial 4 years, which was attributed to enhanced microbial activity and increased earthworm numbers. Fruit quality was good with all understorey treatments, with no nutrition or storage disorders. Marsh et al., (1996) examined the effects of understorey treatments in more detail, and concluded that tree nutrition will be affected by choice of understorey species and management (e.g., mowing vs mulching), but the overall effects on tree growth, yield and storage disorders showed minimal differences after 3 years. Mulching (with mown herbage and pea straw) showed a number of benefits, including increased soil nutrients (C, N, K, Mg, Ca), increased leaf N and K, increased pH, and increased tree growth and fruit yields. The greatest difficulty faced at the Winchmore site, and still prevalent with organic apple production in New Zealand, was vulnerability to disease infection. In a separate study, at Appleby, Marsh et al., (1994) examined the effects on the quality of Fuji apples of managing nitrogen levels with different understorey management. They found more highly coloured fruit and advanced fruit maturity with a grassed understorey, which compensated for lower yields under this regime through a higher export pack-out. Of interest is a mulching trial in a Hawke’s Bay apple orchard by Hartley et al., (1994), who found that straw mulch, in particular, was beneficial in terms of weed control and reducing diurnal fluctuations in soil temperature. Goh et al., (1999) evaluated the effects of different production systems (organic, integrated and conventional) on the quality and quantity of soil organic matter in the soil, and identified sensitive indicators. They found no significant differences between commercial and experimental orchards. Sensitive indicators of differences between different production systems included the microbial biomass C (BC) and the ratio of BC to total carbon (TC). With a shift to integrated fruit production (IFP) by the pipfruit industry and an increasing number of organic producers, there is an increased interest in understorey management. A Sustainable Farming Fund project, being implemented through the Focus Orchard programme, aims to develop an understorey management strategy for the pipfruit industry, including: selection of appropriate species, soil health implications, information on likely effects on tree growth and fruit development. As a precursor to this project, a survey of current understorey management practices was made (NZ Pipfruit Ltd, 2001). Tree strip management by surveyed organic growers and some IFP growers includes mulching (with mown grass, bark, straw) or use of herb leys and rye/clover. Orchard sward practices included use of herb leys, clover, spread of mulched prunings, leaving the sward to grow. Surprisingly, it appears that there has been no research done on organic soil and understorey management for kiwifruit in New Zealand. A thorough search of the HortNet web site, which contains comprehensive information from a diversity of sources, yielded one reference (Stowell, 2000), which related to maintenance of soil fertility and yields for organic kiwifruit production. There is no published literature on organic soil and understorey management of citrus in New Zealand, although there has been some work done on nitrogen nutrition (Mooney et al., 1997). For mature trees (5 years or older) a strong spring flush is desirable for commercial production. This is best managed by autumn applications of nitrogen, with a recommended application rate of 3–4 tonnes per hectare from organic sources. No relevant New Zealand literature was found for avocados or stonefruit. The New Zealand Avocado Industry Council is in the process of implementing an understorey management project, supported by Agmardt, although this is not specifically focussed on organic production. There is also a mulching trial in place at an organic orchard in the Bay of Plenty, established by Dr Ben Faber, a farm advisor from California, USA. A principal focus for this work is phytophthora control. Summary The Winchmore study established a valuable knowledge base for organic understorey and soil management in New Zealand apple orchards. The pipfruit industry currently has a strong impetus towards organic production, and there is increased research taking place that is of relevance to organic pipfruit growers. Much of the current research is focussed on disease problems, particularly blackspot. An understanding of the link between organic soil management, nutrient dynamics, and pest and disease management has yet to be developed. Aside from the research on pipfruit, there has been no significant research of relevance to organic systems under other fruit production systems. Useful New Zealand websites include:
International Literature on Understorey and Soil Management The principal sources of international literature were the internet and searchable databases. Two important sources of information are the Henry Doubleday Research Association (HDRA) in the UK and the Louis Bolk Institute (LBI) in the Netherlands. For a more practical and relatively generalised focus, the Appropriate Technology Transfer for Rural Areas (ATTRA) programme, in the USA, is a good source of information. Much of the available literature focuses on apple production. Material from HDRA and LBI is strongly focussed on apples, and is reviewed separately. The remainder of the literature, including relevant information gleaned from ATTRA publications, is organised thematically, rather than by crop, as there are common principals and practices relevant to a variety of perennial fruit crops. Apart from apples, literature relating to avocados, citrus, kiwifruit and stonefruit was reviewed. In some cases, such as with information relevant to phytophthera control in avocados, separate sections are justified. The Henry Doubleday Research Association (HDRA) and Louis Bolk Institute (LBI) The HDRA received funding from the Ministry of Agriculture, Fisheries and Food for a year-long study on organic fruit production (Bevan & Lennartsson, 1999). The main aim of this project was "to collect existing information on organic fruit production from growers, researchers and advisors from both the UK and overseas." The 128-page report produced is focussed principally on apples and strawberry production, largely because there was more information for these crops, and to a lesser degree on pears, raspberry, currant and gooseberry production. The principal sources of information for the literature review of apples were the work of Daly, Marsh and colleagues in New Zealand, and the work of Bloksma and colleagues at the Louis Bolk Institute (LBI) in the Netherlands. A strong theme in this review is the issue of providing adequate and balanced nutrition to apple trees. Successful organic soil management is related to understanding and managing the soil processes. The management of the understorey for nutrient supply to the trees also has to be balanced against competition in the treeline for nutrients and water. Under temperate European conditions the availability of adequate nitrogen in spring, when soil temperatures and microbial activity are low, is very important for good fruit set and yield. The mineralization and immobilization of nutrients by microbial activity in the soil, the principal source of nutrient supply in a well-balanced organic system, is a principal focus of a detailed report on "Soil management in organic fruit cultivation" by Bloksma (1996). The LBI agriculture department was established in 1987. Their research is conducted on-farm, and the research focus is developed in a participatory manner with growers. A significant amount of research on organic apple production has been carried out over the last decade but the bulk of the research findings have been published in Dutch, with relatively little available in English. The above-mentioned report (Bloksma, 1996), which has recently been updated and revised, has not been translated to English although it contains valuable information. Recent annual reports (Bloksma & Jansonius, 1999, 2000) in English are available from the LBI website and provide a useful overview of current research, including recent research findings. While the specific questions being addressed by LBI may not be directly relevant to New Zealand conditions, their holistic research approach is. The LBI organic systems programme aims to design "a coherent package of measures, which integrates weed control, fertilisation, cover crops, growth regulation and ripening" (Bloksma & Jansonius, 1999). A current research focus is on various ground-cover treatments at the tree strip. They have examined four different strategies:
From a nutrient management point of view, a principal aim of these strategies is to optimise nutrient availability to the tree, particularly nitrogen. For example, the sowing of late summer cover crop is seen as a good strategy for transferring soil nitrogen from late summer/autumn to the following spring. Understorey management Ames & Kuepper (2000) provide an overview of issues relevant to organic production of temperate zone fruits. Amongst other things they provide an overview of orchard floor management and mulching. The benefits of ground covers to soil and tree nutrition and for pest control, are discussed. General guidelines for mulching are also provided, with established benefits including: weed control; enhanced soil aggregation and water availability; moderation of soil temperatures; reduction of plant stress; and greater availability of major nutrients. These authors also mention the benefits of improved soil organic matter in reduced susceptibility to disease. Mitham, (1999) reports on a presentation by David Granatstein, coordinator of the Center for Sustaining Agriculture and Natural Resources at Washington State University who talked about the importance of shifting from the trading of inputs, which often characterises orchards and farms in the early years of conversion to organics, to the need to change management practices. The rest of the article discusses the merits of using cover crops in the orchard environment, to replenish soil nutrients and manage tree vigour, control weeds and orchard pests, and reduce erosion. The importance of matching a particular cover crop to needs, aimed at achieving best practices for a particular farm, is discussed. Warner, (1998) reports on a presentation by Dr Robert Stevens, a soil scientist with Washington State University. Stevens talks about the importance of allowing soil to develop a balance over time. In the context of balancing nutrients, he comments that there is a very small pool of nutrients being balanced, and thus even small doses of fertilizer can cause big swings. The comment is made that "growers should be concerned about movement of nutrients and whether the orchard contributes to leaching into groundwater". It is significant that these comments were not specifically directed at organic production, indicating that there is an increasing awareness of the importance of developing a balanced, healthy, environment for sustainable fruit production. Use of cover crops and nutrient management Earles et al., (1999) provide several grower case studies, including a Maryland organic apple grower who uses a variety of products to boost soil fertility, including: green sand; rock phosphate; compost from beef manure and leaf litter, fish meal and pelletized poultry litter. He uses a cover crop of clover and Companion grass (a cross between dwarf fescue and rye). Schenk and Veijer (1996) experimented with different cover crops for apples and found turnips (sown in mid summer) gave highest soil N reserves, followed by a mixture of summer cabbage and Phacelia. Mulching with organic materials in a young apple orchard had a number of benefits, including well-balanced temperatures, and low nitrate levels during the growing period. A late summer cover crop, sown in the cultivated strips, reduced nitrate concentrations in soil water (Himmelsbach et al., 1995). In a 14-year trial, frequent cutting and mulching of a grass-legume cover crop gave the highest yield, increased soil organic matter and nutrients and moderated upper soil temperature during the summer (Shabanova, 1985). Heller & Weibel, (1997) provide an account of plant nutrition and fertilization needs in IFP and organic apple production systems in Switzerland. Ben-Ya, (1995) found higher avocado yields with organic manure, compared with N fertilizer, while Garcia et al. (1989) examined the soil and plant nutrition status of a biodynamic avocado plantation (compared with a conventional system), where they found higher levels of pH, OM, available P, Ca, Mg and K in the biodynamic system. Jaime et al. (1994) found that greater tree size and fruit yield was realised with mulching in an avocado orchard, but soil cultivation and permanent swards were preferred because of smaller tree size, which made them more manageable. Dou & Alva, (1998) found that citrus leaf litter makes an important contribution to available N in the soil. In another study on citrus nutrient management, Calabrese, (1992) found that N application (based on leaf analysis) was being overemphasized and that low soil organic matter was becoming a problem. Celano et al., (1997, 1998) recommended sowing crops in autumn to take up residual N from soil and incorporating them into the soil in spring at the time of peach bloom, ensuring sufficient supply when demand from trees was greatest (1 month after full bloom). Green manured soil showed higher microbial and soluble C. Vitanova (1999) found winter fodder peas and pea-rye mixtures to be suitable for green manuring on Stanley plum trees. Pre-plant compost application and mulching of the soil surface had very positive effects on cumulative yields in an apricot orchard. Compost increased cation exchange and water holding capacity of the soil (Kotze & Joubert, 1992). Different cover crops in a 9-year old vineyard (cv Merlot) were found to reduce excessive growth and cropping, and also the incidence of Botrytis infection (Sicher et al., 1995). In a tropical environment, use of nitrogen-fixing species for hedgerows and mulching is a common technique for soil improvement, particularly in degraded sloping land environments. Trials with Jackfruit in Hawaii showed improvements in soil K, N and pH (Elevitch et al., 1998). Mulching The benefits of mulching are now widely recognised. A large number of studies have evaluated a range of mulching practices. Key findings from these are summarised:
Phytophthora control in avocados With respect to the benefits of various organic soil treatments for phytophthora, most studies showed benefits from mulching or use of ground covers. Mans and Hattingh (1992) experimented with three permanent ground covers (Arachis glabrata, Polygonum capitatum, Lippia canescens [Phyla nodiflora]) in an avocado orchard. While the latter species showed the greatest potential because of relatively rapid growth rate, it competed for N. A. glabrata increased N content of leaves. There was no incidence of Phytophthora at time of planting or 1 year later. Cow manure, alone or in combination with lucerne straw-resulted in better control of P. cinnamoni and higher root growth and yield (Cortes-Flores et al., 1993). Duvenhage et al., (1993) applied various organic soil amendments to Fuerte trees recovering from root rot. Condition declined during the 3rd and 4th years of the trial, attributed to drought stress, but improved with use of a leguminous cover crop or a lucerne straw mulch. Rosas-Romero et al., (1986) found best phytophthora control with lucerne straw alone or in combination with cow dung. Ames and Kuepper, (2000) use the example of phytophthora control of avocado, citing work from Australia where liming and cover crops are used in combination with applications of chicken manure, cereal straw, weed residues and other materials. Dr Ben Faber, made available a detailed report of a California study on use of yard trimmings and compost for phytophthora control on citrus and avocado (Menge et al., 1999). Their findings indicated significant benefits to avocados from the use of mulch. Benefits included increased root growth, and in two out of four groves they observed improved growth, yield, or appearance as a result of mulch application. Microbial numbers were found to increase in the vicinity of the mulch, including two enzymes, cellulase and laminarinase, which dissolve the hyphae of Phytophthora cinnamomi. These effects were only noted in the surface soil layers, not deeper, but were beneficial because of the predominantly surface rooting habit of avocados. Plant nutrition and disease In the case of a Maryland organic apple grower, discussed by Earles et al., (1999), the grower’s experience is that there is a correlation between high nitrogen availability and high disease pressure. As a result, the grower deliberately under-uses nitrogen and has noticed an increase in yield. Earles et al., (1999) also discuss briefly the disease-suppressing effects of composts, which are discussed in more detail by Granatstein (1998). Warner, (1996) reports on a University of California study that found that excess nitrogen can make peach trees more susceptible to pests and diseases, reduce red colour on the fruit, and increase nitrate leaching to ground water. Ground-cover management is very important for N regulation in vines, e.g., excess N during berry maturation can lead to greater incidence of Botrytis and greater must acidity (Maigre & Murisier, 1991). Fruit quality Grass cover gives lower fruit yields (Hornig & Bunemann, 1995; Mage & Skogerbo, 1992) and improved fruit colour and acid content (Hornig & Bunemann, 1995). Soil quality indicators Swezey et al., (1998) examined changes during conversion of an apple orchard to certified organic management. Soil bulk density and water-holding capacity were good indicators of physical soil changes. Sensitive indicators of soil biological changes were the potentially mineralizable nitrogen and microbial biomass-C. Increased earthworm biomass and abundance were observed in the third year. System design Ingels, (1992) outlines a range of factors important for development of sustainable grape growing, including site and cultivar selection, crop diversity, soil and nutrient management, reduction of off-farm inputs. Granatstein, (2001) provides a useful review of orchard understorey management. In his introduction he discusses what is meant by sustainable as a concept, which in his view encompasses three parts: economically viable; environmentally sound; and socially responsible. He then extends this to highlight changes in orchard management, which are increasingly encompass these three parts. The discussion is further developed to highlight the need for conscious design and management of systems, citing the work of Stuart Hill (in MacRae et al., 1990), who identified three strategies that represent degrees of sustainability. The first can be equated to the introduction of IPM strategies, focussed on improving efficiency of existing systems. The second involves input substitution, which normally occurs in the early stages of conversion to organics. The third involves conscious design, or re-design, of the agro-ecosystem. Redesign of the orchard understorey is placed in the last category. The various functions of the understorey and design issues are discussed, and topics covered include: cover crops; weed control and mulches; soil fertility; soil health. Granatstein, (2001) concludes that "more research is needed on both the biology of individual components and the ecology of the system so components can be combined for optimal benefit". In many developing countries, diverse agroecosystems are an integral part of traditional agricultural practices. There systems provide multiple benefits — to the environment, people and local economies. For example, studies by Grewal et al., (1992) and Neugebauer, (1990) focussed on the benefits of two different agroforestry systems, one in northern India, the other in Mexico. These ecologically diverse systems, which included citrus and other fruit trees, showed considerable benefits to the environment and local economies. While such systems are not directly transferable to New Zealand, they do provide important information on the benefits of ecological complexity in agroecosystem design. Summary The preceding review was drawn from international literature with a specific focus on soil-plant-animal systems research relating to perennial fruit production. As with the New Zealand situation, overseas research has predominantly focused on organic apple production. Important issues emerging from this review are: the importance of understanding and managing nutrient flows in the orchard system; linkages between nutrient management and disease pressure; and the importance of developing a more holistic approach to research on organic soil and understorey management in orchard systems. Useful international websites:
Other useful links can be found in the reference list. What Are the Gaps in Knowledge that Need to be Addressed in New Zealand? In his introduction, Daly (1994) explained that conversion rather than system design is likely to be the most common situation faced by growers. This was an important rationale for using an already established orchard for their research. Many of the benefits of this research are now being realised, with significant numbers of apple growers successfully converting to organic production in New Zealand. However, those who have converted face on-going challenges, particularly with disease control. There is evidence to suggest that good organic soil management can lead to a reduction in disease problems as indicated, for example, by the observed link between overuse of nitrogen and disease problems. The greatest difficulty is that specific soil management solutions to widespread problems, such as blackspot or phytophthora, cannot necessarily be prescribed and do not wholly lie with the soil. Many factors play a role, not least the design of the orchard. This is where the greatest challenge lies, as identified by Hill (cited by Granatstein, 2001) to move towards re-thinking the orchard system in a holistic framework. Very little of the material provided in the preceding sections has been gathered from such a framework, and for this reason provides only fragments of a complete picture. What, therefore, are some important gaps that need to be addressed?
These three general areas of research lead to increasing levels of complexity, and it is unlikely that answers will readily be found through short-term research programmes. In organic systems the solutions to problems are ultimately site and producer based. Many important changes in the system are likely to occur over longer-term ecological time horizons. This suggests the need for research that has the active involvement of producers, involves quantitative and qualitative approaches, and is focussed on understanding the dynamic and evolving nature of organic orchard systems, of which soil and understorey management is a very important component.
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Weed control with organic mulches in apple orchards: effects on yield, fruit quality, and dynamics of nitrogen in soil solution. Gartenbauwissenschaft 54(5): 224-232. NZ Pipfruit Limited (2001). Pipfruit Solutions 1(5): 5-6. Rosas-Romero, M, Teliz-Ortiz, D, Garcia-Espinosa, R, Salazar-Garcia, S (1986). Effect of cowdung, lucerne and metalaxyl on the population dynamics of Phytophthora cinnamoni Rands, causal agent of avocado (Persia americana Mill.) root rot. Revista Mexicana de Fitopatologia 4(2): 114-123. Schenk, A, Veijer, H (1996). FPO-research on nitrogen regulation via cover crops and biological fertilizers. Fruit setting difficult to improve with extra nitrogen in the soil. Fruitteelt Den Haag 86(34): 20-21. Shabanova, LS (1985). Sod-mulch system in irrigated orchards. Sadovodstvo 2. Sicher, L, Dorigoni, A, Stringari, G, Tagliavini, M, Neilsen, GH, Millard, P (1995). Soil management effects on nutritional status and grapevine performance. Mineral nutrition of deciduous fruit plants. Proceedings of the second international symposium on diagnosis of nutritional status of deciduous fruit orchards, Trento, Italy, 13-15 September 1993. Acta Horticulturae 383: 73-82. Spring, JL (1993). Trials on soil management along the line of trees: intermediate results. Revue Suisse de Viticulture d’Arboriculture et d’Horticulture 25(6): 353-361. Stowell, B (2000). Organic kiwifruit production – maintaining soil fertility and yields. Kiwifruit 139: 18-21. Swezey, SL, Werner, MR, Buchanan, M, Allison, J (1998). Comparison of conventional and organic apple production systems during three years of conversion to organic management in coastal California. American Journal of Alternative Agriculture 13(4): 162-180. Vitanova, I (1999). Green fertilization of plum trees by applying winter fodder pea and pea-and-rye mixture. Pochvoznanie Agrokhimiya I Ekologiya 34(1): 38-40. Warner, G (1996). Study shows the drawbacks of overfertilizing. Good Fruit Grower 9 July. Warner, G (1998). Balancing soil nutrients takes time and attention. Good Fruit Grower 1 May. Go to top of Chapter Five Return to top of Chapter Four Return to Table of Contents
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