1a. Objectives (from AD-416)
One objective of this research project is to explore the use of arbuscular mycorrhizal [AM] fungi in crop production. The sources of AM fungi examined will be both indigenous fungi present in the soil and inoculum produced using on-farm technology developed as part of the parent CRIS project. The role of indigenous AM fungi in crop growth will be explored via creative use of tillage operations and an exclusion technique. The use of inoculum will be tested for crops in which seedlings are first grown in the greenhouse for later out planting to the field. Preliminary experiments will be conducted for the latter to optimize greenhouse culture regimes to produce seedlings that are well colonized by AM fungi and of satisfactory size and vigor via organic methods. A second objective of this project is to pursue modifications to the technology for the on-farm production of AM fungi to produce resultant inocula in a form amenable to mechanical application to the field. A third objective is to study the impact of the transition to no-till agriculture upon carbon sequestration and AM fungus populations in row crop agriculture.
1b. Approach (from AD-416)
The proper utilization of inoculum of AM fungi to produce vegetable seedlings for out planting to the field requires modification of routine greenhouse fertilization regimes. Too much fertilizer will inhibit colonization of plants, wasting the investment in inoculum. Conventional growers have a variety of chemical fertilizer preparations at their disposal. Organic growers are limited in this respect, and for the most part cannot manipulate the levels of individual mineral nutrients in fertility regimes. Since AM fungi are particularly useful in agricultural systems shunning chemical fertilizers and pesticides, it is important that organic growers have a greenhouse regime amenable to produce well colonized, healthy seedlings. Greenhouse potting media amendments such as compost, and high N low P fertilizers such as fish emulsion, will be studied for their effect upon AM fungus colonization of roots and overall plant growth. The role and use of AM fungi in crop production will be studied several ways. First, prior observations indicate that inoculation with AM fungi produces a significant growth response in the field when the soil has experienced disturbance, such as roto-tilling to control weeds prior to planting. This will be studied using a variety of repetitions of roto-tilling, at varying times before planting mycorrhizal and non-mycorrhizal leek (Allium porrum) seedlings. Leeks will be used because their mycorrhizal dependency makes them good test organisms. A second study of the use of AM fungi in crop production will utilize sweet corn. A recently adopted method for the production of sweet corn entails the production of seedling sin the greenhouse which are them later transplanted to the field. The use of AM fungi has not been examined in this production system. Uninoculated and pre-inoculated seedlings will be transplanted to the field and the effect of the inoculation upon plant growth and final yield will be quantified. The use of AM fungus inoculum produced on-the-farm is primarily limited to the production of seedlings in the greenhouse. Here, the inoculum can be efficiently and economically mixed into horticultural potting media. Application of inoculum to the field is labor intensive and limited to special, small-scale operations. The on-farm system of inoculum production produces AM fungi in a compost and vermiculite mixture. Other amendments to the system, such as porous biochar, will be tested for their use as carrier materials amenable to mechanical application to planting sites in the field. Work at the Rodale Institute’s Farming Systems Trial has shown greater carbon sequestration in organically than conventionally farmed soils. This result came from farming systems that incorporated conventional tillage at all points of the crop rotation. No-till has recently been incorporated as a treatment in the Farming Systems Trial, offering the opportunity to study the potential added benefits to carbon sequestration via reduced tillage.
3. Progress Report
The unique nutrient sources utilized in organic systems make it more difficult to obtain high arbuscular mycorrhizal (AM) fungus colonization of vegetable crop roots during the greenhouse growth phase. As opposed to conventional systems, organic systems rely heavily upon compost as a principal soil amendment. Due to the fact that composts can be high in phosphorus(P), their use in organic potting media is an obstacle to high levels of colonization. Peppers and tomatoes are moderately mycotrophic and AM fungus colonization of roots of these plants exhibits strong sensitivity to P levels. Therefore, greenhouse nutrient regimes must be properly formulated to ensure P concentrations are low enough to allow colonization, yet supply sufficient levels of other nutrients, notably Nitrogen(N), to support plant growth. Outplanting uncolonized seedlings due to over-fertilization in the greenhouse would confer no advantage, and result in money wasted on commercially-purchased inoculum. Research at The Rodale Institute with USDA-ARS sought to find an organic greenhouse production regime that will produce significant levels of AM fungus colonization while increasing plant health. As expected, leeks were well colonized in all treatments, with upwards of 65% root length colonized even in media containing 50% compost with no extra added N as blood meal. Colonization of pepper cv. Lafayette was greater than for cv. Colossal. The 0.5 level of N addition as blood meal resulted in colonization levels that were greater than those produced using the low P conventional fertilizer. Colonization of tomato cv. Mountain Fresh plus was greater than that found in cv. Brandywine. The organic treatments produced plants of greater shoot weight, but colonization varied with N addition according to a pattern that differed for the media with 50% compost vs. that with 20% compost. These experiments will have to be repeated in 2012 to verify the results. Progress is monitored by site visits and conference calls.