AAFC gets to the root of organic fruit crops in BC

Organic Agriculture Centre of Canada

For any crop plant, healthy roots are the foundation for sustainable, high quality yield.  Healthy roots are dependent on healthy soils that are biologically active, have a porous, stable structure, and high water-holding capacity. 

In organic perennial fruit crops, soil health can be manipulated through irrigation and the application of organic materials and organisms.  At Agriculture and Agri-Food Canada (AAFC) in Summerland and Agassiz, B.C., researchers Dr. Gerry Neilsen, Dr. Denise Neilsen, and Dr. Tom Forge are examining the use of these strategies to improve soil and root health of four important fruit crops: apples, grapes, blueberries, and raspberries.

Mulches serve many purposes in organic production systems: they control weeds, alter soil properties, and influence soil biology.  The team of B.C. researchers explored the use of mulches of shredded paper, composts, alfalfa hay, and polyethylene fabric under apple trees and compared them to conventional weed-free bare soil.  Their findings suggest that the abundance of protozoa and beneficial nematodes, and the consequent cycling of nutrients, were greater under organic mulches when compared to bare soil or plastic mulch.  Additionally, root growth was increased under mulches, and populations of the damaging root lesion nematode appeared to decrease under some organic mulches and increase under plastic mulch.

In a study on apples led by Denise Neilsen, the effects of reduced irrigation and crop load on root growth and parasitic nematode populations are being examined. Root growth is being studied with minirhizotrons:  clear acrylic tubes inserted in the ground through which a special camera photographs root growth.  With climate change expected to reduce water availability, using less water is important for both organic and conventional fruit growers.  Reducing irrigation may also result in healthier root systems and more resilient crops.

Replant disorders can result in poor establishment of new orchard plantings and subsequent yield reductions, and are a particular problem for organic growers, who are unable to fumigate the soil and apply chemical fertilizers at planting.  Dr. Louise Nelson and Molly Thurston of UBC Okanagan, in collaboration with Gerry Neilsen, are exploring the use of composts in the planting holes of trees and the application of bacteria to the roots to improve orchard establishment.   Some bacteria can improve plant growth by increasing nutrient availability, producing plant hormones, or reducing the effects of plant pathogens.  The current focus is on phosphate-solubilizing bacteria.

Replant disorder is also a concern for raspberry growers in the Fraser Valley, where pathogen buildup necessitates frequent replanting. Current practices of fumigation and leaving the soil bare over the winter may be contributing to nitrate leaching into groundwater.  Forge is looking at organic alternatives to fumigation, with the goal of improving overall soil health.  Trials compare the use of a fall cover crop and spring applications of manure and compost to fumigation.  He is evaluating crop growth and the buildup of plant pathogens, particularly root lesion nematode, and monitoring nitrate leaching.  Preliminary results indicate that the cover crop reduces leaching.  The fumigated plots have the best growth and fewest nematodes, indicating that pathogens are truly a problem, but compost and manure also reduced nematodes and increased growth.  Forge says the next step is to look at a combination of a fall cover crop, spring application of compost at planting, and immediate seeding of a between-row cover crop to take up any extra nitrogen.
The AAFC team is also comparing different rates of fertilization and irrigation, manure applications, and the use of annual and perennial between-row cover crops in an established raspberry crop.  They are looking at nitrate leaching and soil health factors including fungal and nematode pathogens, earthworm numbers, and soil structure.  Although little data is yet available, the cover crops do not appear to reduce yield, a concern that has kept them from being widely adopted.

Nematode pests of blueberry and grape are of increasing concern in BC.  Forge has discovered a new nematode pest, Paratrichodorus renifer, on blueberries in the Fraser Valley.  In microplot studies, populations of the nematode increased rapidly and caused a 30% drop in growth and yield.  Forge and the Neilsens are also looking at the effects of irrigation and nitrogen inputs on ring nematode, a nematode they have demonstrated to be damaging to grapes.  Higher nitrogen and greater irrigation tend to increase populations.

While agricultural practices are usually aimed at optimizing short-term yield, research is needed to determine if these techniques are conducive to maintaining long-term crop health and productivity.  Sustainable soil and root health continues to be a goal of the research conducted on perennial fruit crops at AAFC.

This article was written by Andrea Muehlchen on behalf of the OACC with funding provided by Canada’s Organic Science Cluster (a part of the Canadian Agri-Science Clusters Initiative of Agriculture and Agri-Food Canada's Growing Forward Policy Framework).  The Organic Science Cluster is a collaborative effort led jointly by the OACC, the Organic Federation of Canada and industry partners. For more information: oacc@dal.ca or 902-893-7256.

Posted January 2012