Additional MSU Organic Fruit Research Projects with special reference to Soil Biology
Report by George Bird, Entomology.
At least eight tree fruit research projects with organic components have been conducted by various researchers at Michigan State University. These include: i) a certified organic apple orchard at the Clarksville Horticulture Research Station, ii) an established commercial tart cherry orchard ground cover research site in Northwest Michigan, iii) a new tart cherry orchard designed to study the functional diversity of permaculture at the Northwest Horticultural Research Station, iv) a comparative survey of soil food webs associated with four organic and four conventional commercial tart cherry orchards, v) an organic apple pest management project at the Kellogg Biological Station, vi) an organic pear pest management trial in a commercial orchard in Northwest Michigan, vii) Roberto Zoppolo's on-going Ph.D. dissertation research on the relationship to organic apple production practices and soil nutrition and viii) Dario Stefanelli's on-going Ph.D. dissertation research on the dynamics of apple root growth in relation to organic production practices. The majority of theses projects are truly interdisciplinary. Although relatively little is known about the comparative soil quality and its associated biology of organic and conventional systems, the dynamics among soil-borne organisms and the resulting nutrient cycling is one of the most important keys to successful organic agriculture. The objectives of this report are to describe the above initiatives and summarize the soil biology results from projects i-iv.
Vertical Distribution of Soil Organisms Associated with Organic and Conventional Tart Cherry Orchards
Four Michigan commercial organic and four conventional tart cherry orchards are part of an on-going project to evaluate the influence of management systems on soil biology. The project was started in 2002 with soil samples taken from the little layer (duff, 0-horizon), 0-6-inch depth and 6-12 inch depth. Analysis of the soil food webs of the eight orchards indicated that significantly more flagellates, amoebae and ciliates were present in the little layer than at either of the soil depths. (Fig. 1) Similar results were obtained for bacterial feeding nematodes (Fig. 2). Highest population densities of plant feeding nematodes, however, were presented at a 0-6 inch soil depth. When the organic and conventional orchards were partitioned, there were approximately 10-fold more flagellates associated with the organic, compared to the conventional orchards (Fig. 3). One organic orchard was only at the end of its first year of transition. One conventional and one organic site had never previously been used for agricultural purposes other that cattle grazing.
Soil Dynamics Associated with the Transition of a Conventional Corn Production Site to an Organic Apple Orchard
Soil quality indicators associated with the organic apple orchard site at the Clarksville Horticultural Research Station have been monitored since May 1999. The trees were planted in 2000, and the orchard received its OCIA Certification in 2003. The project has both marketing and educational components.
In 1999, the mean active bacterial biomass associated with the site was low, 13.2 ug/g soil. During the transition period this increased to a high level of 71 ug/g at a 0 to 6 inch soil depth. The active fungal biomass however started low, 9.1-ug/g soil and did not show an increase until 2003. Population densities of flagellates and amoebae remain low in a number of areas. While densities of ciliates are high, this may be an indication of soil compaction. The vertical distribution of soil-borne organisms is the same as reported for the eight tart cherry orchards.
Initial 1999 population densities of both bacterial and fungal nematodes were directly related to the biomass of their food source (Bird, 2000). Bacterial feeding nematodes population densities were low, 381/100 cm^3 soil. By fall 2002, they had increased to a close to optimal level of 1,452 per 100 cm^3 soil. Similar increases have not been observed for fungal feeding nematodes. The initial population density was 55/100 cm^3 . Population densities were 19.1 and 48.9/100 cm^3 soil in the fall 2002 and spring 2003, respectively. Current fungal feeding nematodes population densities are much higher at a commercial organic farm in Barry County that received its certification eighteen years ago.
Initial 1999 data from a modified Reams Test (Bio-Test) indicated that the conventional soybean-corn site was very high in potash, very low in calcium, had a CEC of 3.5 and SOM of 1.2. The nitrate and phosphorus levels were very low and the soil was not considered very active from the Bio-Test energy analysis (electrical conductivity). These and subsequent soil monitoring data were used for soil quality management decisions. Today, the soil is very high in potash, very high in phosphate with medium levels of calcium and appropriate levels of nitrate. The pH is about 6.9 and the Bio-Test energy levels are very good.
Tart Cherry Ground Cover Trial
Results from the project that compared 13 management systems at a commercial tart cherry sire in northwest Michigan have been published in Amer. J. Hort. Sci. (Sanchez et al., 2003) and summarized in Fruit Ecology and Management (Landis et al., 2002). Highest population densities of bacterial feeding nematodes, active nitrogen were associated with the organic system. High population densities of non-plant parasitic nematodes (bacterivores, fungivores, carnivores, omnivores) were associated with low population densities of plant parasites (Fig. 4). The greatest amount of nitrate-N leaching was associated with one of the conventional systems, and the highest cherry yield with a rye straw and hay mulch ground cover. The project was started in 1995 and concluded in 2002.
Tart Cherry Permaculture Orchard
A new cherry orchard was established at the NWHRS to evaluate functional diversity in relation to several management systems. The permaculture portion of this site consists of six management systems, ranging from the least diverse (herbicide strip beneath the trees, conventional nitrogen, conventional IPM and clean tillage alley-ways) to the most diverse (straw mulch beneath the trees, dairy compost, native legume sandwich, organic pest management, native species mixture alley-way and Siberian pea and sea buckthorn interplanted with the cherry trees.) The management systems form a gradient of soil signatures, as indicated by bacterial feeding nematodes, mycorrhizal fungi and micro-oligocheates. The soil biology indicator within the tree rows differs from those in the alleyways.
First MSU Organic Apple Orchard Project
The first organic tree fruit research project was at the Kellogg Biological Station under the leadership of Dr. Stuart Gage. A scab resistant variety was used and both insects and weeds were successfully managed using geese. The project had a highly successful marketing component. The project was funded with SARE resources, but done at a time when there was significantly less interest in organic production among the MSU tree fruit researchers than currently.
Organic Pear Research
An organic pear project was initiated under the leadership on Gary Thornton, in a northwest Michigan commercial pear orchard. The initiative was funded through MSU GREEEN resources. Thornton was able to demonstrate that it was possible to manage Michigan pear pests with organic practices, and two Michigan pear growers currently have contracts for organic pears for processing.
Ph.D. Dissertation Research in Organic Apple Production
Both Roberto Zoppolo and Dario Stefanelli are using the Clarksville Organic Apple site for a major portion of their Ph.D. dissertation research. Zoppolo is working on the relationship of organic practices to soil nutrients and Stefanelli is researching the dynamics of root growth under organic management systems.