International Journal of Fruit Science, 9:257–281, 2009 Copyright © Taylor & Francis Group, LLC ISSN: 1553-8362 print/1553-8621 online DOI: 10.1080/15538360903245212 vbWSFR1553-83621553-8621International JournalResearch of Fruit Science,Science Vol. 9, No. 3, Aug 2009: pp. 0–0 Knowledge and Needs for Orchard Floor Management in Organic Tree Fruit Systems OrganicD. Granatstein Orchard and Floor E. Sánchez Management DAVID GRANATSTEIN1 and ENRIQUE SÁNCHEZ2 1Center for Sustaining Agriculture and Natural Resources, Washington State University, Wenatchee, Washington, USA 2INTA EEA Alto Valle, General Roca, Patagonia, Argentina While pest management and tree horticulture dominate the research agenda for temperate tree fruits, organic production requires more attention to weed control and nutrient manage- ment because of the limited options growers have. Weed control and tree nutrition are interlinked and can have impacts on other parts of the system such as rodent pests, beneficial insect habitat, water use, and soil quality. Trade-offs commonly occur when trying to solve weed control and nutrient management in organic orchards. This article reviews numerous orchard-floor manage- ment studies relevant to finding solutions for organic systems and suggests areas for further research. Alternatives to soil tillage are needed, as it can degrade soil and tree performance. Conversely, mulching frequently leads to improved tree performance and increased soil quality but can be a costly practice relative to other options. Currently effective organic analogues to the herbicide strip-grass alley system are lacking. A plant-based solution would be ideal from a sustainability standpoint, but no satisfactory solu- tion has been developed for widespread use. KEYWORDS apple, compost, cover crop, mulch, nitrogen, pear, tillage Address correspondence to David Granatstein, Center for Sustaining Agriculture and Natural Resources, Washington State University, Wenatchee, WA 98810, USA. E-mail: granats @wsu.edu 257 258 D. Granatstein and E. Sánchez INTRODUCTION The orchard floor represents a substantial portion of the orchard agroeco- system, but it has generally received less research and management atten- tion than tree horticulture and pest management. Yet opportunities exist to improve orchard sustainability through manipulation of the orchard floor. Enhanced pest control and greater internal nutrient supply are two possible improvements that can be achieved, and these would improve the performance and lower the cost of organic tree fruit production. The desired outcomes of orchard-floor management are foremost focused on good tree performance (e.g., tree growth) and a high, consistent yield of quality fruit. Other outcomes are now receiving increased attention, such as biodiversity and soil carbon sequestration. The role of the orchard floor is arguably more important in organic tree-fruit systems than in conventional orchards (Granatstein, 2003; Weibel and Häseli, 2003). Both weed control and tree fertilization can be achieved quite easily and with relatively low cost in conventional production using herbicides and synthetic fertilizers. This is not the case in organic systems, where poorly controlled weeds can compete with the trees for slowly released and expensive nutrient inputs. Organic systems generally substitute tillage for herbicides as part of the weed control program, but tillage is known to negatively impact tree growth and potentially degrade soil qual- ity. Organic tree-fruit producers would welcome increased research on orchard-floor management that resulted in individual practices and their combinations that provided multiple benefits (e.g., weed control, fertility, carbon sequestration, insect biocontrol) to the orchard at lower overall cost. Most orchard-floor management studies have been carried out in con- ventional orchards, but many of them have examined practices that would also be used by organic growers, such as tillage, mulching, and cover crops, and therefore are useful to consider. No single practice or set of practices is likely to perform equally well across the wide range of climatic, soil, and orchard conditions found where organic tree fruit is produced. Even the presence or absence of a single pest such as voles (Microtus pennsylvanicus) can dramatically shape organic orchard-floor management. Therefore, exist- ing knowledge from the diverse growing regions needs to be examined for widely applicable practices as well as practices best suited to a more local set of conditions. The review presented here focuses on temperate tree-fruit experience and attempts to identify key considerations for organic orchard- floor management and suggest priority topics for future research. Extent of Organic Tree Fruit Production Organic tree-fruit production has been expanding in many commercial tree- fruit production regions in response to the continued increase in demand Organic Orchard Floor Management 259 for organic fruit by consumers. Organic food sales have increased at 20% per year for over 10 years in the United States (Haumann, 2008; Sahota, 2008), with similar trends in Europe. Fruits and vegetables represent about half of organic food sales (OTA, 2008). Market penetration for organic fruit ranged from 5–7% of all fruit purchases in Switzerland, Austria, and Germany, according to recent data from BioAustria, AC Nielsen/ZMP/ BOELW, and Bio Suisse. Over 70,000 hectares of temperate organic tree fruit were identified in 2006 that were located in all fruit-producing regions of the world (Granatstein et al., 2009a). Leading producers of selected organic tree fruit are listed in Table 1. Orchard Floor Components The orchard floor can be viewed as a combination of five elements (soil, hydrologic cycle, nutrient cycle, flora and fauna, and energy) that interact with management. These elements have numerous intersections with orchard sustainability issues and the parts interact with one another: • Soil – erosion control, compaction, nutrient cycling, gas exchange, soil- borne disease control, carbon storage, pesticide decomposition • Water and nutrients – intake and storage, minimal nitrate and chemical leaching, water conservation • Biodiversity – potential to control pests, legumes to fix N, alternative crops • Energy—frost protection, reduced energy inputs TABLE 1 Estimated World Area of Selected Organic Tree Fruits Hectares Apple Pear Cherry Plum Data year Italy 2863 1420 2907 759 2006 Turkey 4278 2627 574 2471 2006 U.S. 7566 970 863 1195 2006 China 1600 1200 — 200 2005 Other N. Hemisphere 10,118 868 248 815 Argentina 1069 1354 — 400 2006 Chile 755 — 113 — 2006 Australia 150 120 50 75 2005 New Zealand 947 22 5 — 2007 TOTAL 29,356 8,581 4,760 5,915 Includes both certified and transition hectares. Transition area represents roughly 30% of the hectares reported in major producing countries of Italy, Turkey, and the United States. Adapted from Granatstein et al. (2009a). 260 D. Granatstein and E. Sánchez The orchard floor generally consists of two zones with often distinct functions and management: the tree row, generally a 1–2 m strip in which competing vegetation is controlled, with the tree trunks in a line down the center; and the drive alley, typically planted to a perennial grass that is rou- tinely mowed. The orchard floor performs several important functions for an orchard system. These include: • Physical support for tree growth, machinery operation • Water intake/storage/transfer • Nutrient cycling/storage (including litter decomposition) • Gas exchange for roots • Habitat (micro- and macrofauna) • Microclimate (e.g., heat exchange) These functions are impacted by various management practices, such as choice of understory species, tree architecture, irrigation system, nutrient inputs, spray drip, and weed control. In looking to design orchard-floor management systems for improved sustainability, trade-offs routinely occur. For example, while a vegetative cover under the trees might maximize soil quality, it will negatively affect tree performance. Therefore, continued research and grower experimentation are needed to test combinations of orchard-floor management practices that can optimize the system. Limiting Competition with the Trees A primary objective of orchard-floor management is to maximize tree growth and fruit yield by controlling the competition trees face from other vegetation. Competition for water and nutrients can come from weeds or planted cover crops. Fruit trees are relatively poor competitors with other vegetation, largely because of their low root density per unit of soil (Merwin, 2003). Apple (Malus x domestica) trees have 1–10 cm root per cm−2 of soil surface, compared to 103 cm/cm−2 for grasses (Neilsen and Neilsen, 2003). Hogue and Neilsen (1987) identified four major orchard-floor man- agement systems: permanent vegetation, mulching, cultivation, and herbi- cides. The standard system in high-density orchards is a vegetation-free strip (∼1.5 m wide) in the tree row managed with herbicides, and a perennial grass drive alley that is occasionally mowed. The “herbicide strip” or “weed strip” in the tree row eliminates competition while also reducing rodent habitat and maintaining water distribution by under-tree sprinklers. Merwin and Ray (1997) found that a 60–90 day weed-free period from May to July provided the best growth in apples. In their New York setting, a 2 m2 weed- free area per tree, or a 0.7 m wide weed strip were the minimum needed. Weed growth influenced cumulative yield more than