Phosphorus in Soils, Strawberries in June, Beneficials in Media

by Dr. Eric Sideman, MOFGA’s Director of Technical Services

The New England Vegetable and Berry Conference and Trade Show is sort of the opposite of the MOFGA Farmer to Farmer Conference. Rather than accentuating farmer to farmer interaction through a small number of long and detailed discussions, the NEVBC houses an enormous number of half hour talks that at best have time for one or two questions. However, it is great and its format works for what it is: an opportunity for growers to learn some basic crop production information in introductory sessions and to get breaking information from new research reports.

The Conference, which began in 1979, is held in December every other year in Sturbridge, Massachusetts, and attracts well over a thousand farmers. I have been attending since 1986, and about six years ago I was invited to be on the planning team along with Extension personnel and farmers from the New England states and eastern New York. We do our best to put together a broad range of educational sessions on new and basic production and marketing techniques. One MOFGA farmer once said to me, when asked whether the Conference was worth the time and money, that he did not think growers could afford to miss it.

You may have missed it this December, but I hope to see you there in 2001.

For those of you who did miss it, I have summarized a few of the talks that I thought were very important for us. If you would like a copy of the proceedings, which has abstracts for most of the talks, send $10 to MOFGA, P.O. Box 2176, Augusta, ME 04338.

Optimizing Phosphorus Management

by Tom Morris, Soil Specialist, University of Connecticut

Tom did a great job of integrating environmental and agronomic concerns. When I was in college and until recently, the only environmental concern related to phosphorus amended soil was thought to result from soil erosion. This was not an unreasonable belief, as phosphorus is quickly bound to soil particles in chemical compounds and does not become mobile. In fact, from an agronomic view, it is very important when supplying phosphorus to crops that it be put within reach of roots because it moves so little--as opposed to nitrogen, which moves readily in soil solution. But Tom pointed out that annual phosphorus applications over many years can accumulate vast reservoirs of phosphorus. Even though only a small proportion of it will become soluble at one time, if the accumulation is very large, a significant amount may eventually become soluble. This soluble phosphorus could end up in surface water, even without soil erosion.

The environmental concern about phosphorus applications is that plant growth in fresh water bodies is generally limited by phosphorus concentrations. If the phosphorus concentrations increase, plant growth increases. A little phosphorus can cause a lot of plant growth, and when that plant growth decomposes, that decomposition uses the oxygen dissolved in the water. With extensive decomposition, the water body become anoxic and the animal life suffers. I can remember driving by Lake Erie in 1972 and seeing the shore covered with dead fish. The fish kill was caused by the excessive use of phosphorus in the Midwest.

Crops actually remove very little phosphorus from the field. For example, tomatoes, which are heavy phosphorus feeders, remove only about 29 lbs./A, and harvesting broccoli heads removes only 5 lbs./A. So, why do farmers add so much phosphorus and why do soil reports recommend so much--often 50 to 100 lbs./A? Plants need high concentrations of phosphorus in solution for good growth, and since phosphorus quickly becomes bound up, recommended levels are high in order to keep a lot in solution. Recommendations are based on plant yield response curves, and plants yield more with higher concentrations. Since there is no risk of crop damage from phosphorus, labs generally suggest high concentrations to assure rapid crop growth. But, soil tests measure only available phosphorus.

They do not take into account what will become available from organic matter during the growing season. This can be a problem, because repeated, annual applications of phosphorus result in high concentrations of bound phosphorus in the soil and in accumulating organic matter.

Even organic growers run the risk of accumulating excessive levels of phosphorus in their soil. For example, 20 tons of dairy manure can accumulate 1200 lbs./A of phosphorus over 20 years, even taking into account crop removal. Poultry manure is much worse.

The first step in environmentally conscious phosphorus management is to take into account what is there. Levels of 20 to 40 lbs./A are sufficient for good crop growth with no additional amendment. If your soil tests higher than 40 lbs./A, eliminate phosphorus applications, or band fertilizers in small amounts for early season starts.

I am part of a grant proposal that Tom has submitted to SARE to study phosphorus accumulation and management on organic farms. We will be looking for a few farms to include in the study.

Environmentally Modified Growing Systems for Strawberry in the Northeast

William Lord, University of New Hampshire

The matted row system of strawberry production is the primary production system used in the Northeast. In this system bare rooted plantlets are set out in the early spring, and the field is kept clean cultivated while daughter plants fill in the rows. The year of planting is an establishment year and no crop is harvested until the following June. In contrast, the system Bill Lord has been modifying for the Northeast is an adaptation of the annual hill system of culture that has been used in California, Florida, and recently as far north on the east coast as New Jersey. In the annual hill system, plug plants are set into plastic covered, raised beds in late summer or early autumn. These plants will fruit the following spring.

The advantages of this system include cropping use of the field the season before strawberry harvest, weed control made easier with black plastic, and earlier harvest (around June 1). The disadvantages are a higher cost for plants because they are set at the final density (setting no daughter plants), and the earlier harvest means an earlier frost sensitive bloom period. If you are willing to deal with frost protection, I think this culture system deserves a close look by organic growers because the greatest deterrent to success with strawberries for organic growers is the weed problem.

‘Chandler’ is the cultivar most often used and so far shows the best results of all tested. This is the cultivar of most of the California and Florida strawberries you see in the supermarket. Believe it or not, it tastes great if it is harvested when ripe. The schedule used in the studies at UNH is to set out the plugs on September 1. (If you are growing your own plug plants, collect tips of the runners in late July and root them in a greenhouse.) Irrigation is usually needed for planting out. Around October 1, cover the rows with a floating row cover. The floating row cover is taken off at bloom the following spring for pollination. The Univ. of N.H. is now experimenting with leaving the plants in for a second year of harvest.

Biological Fungicides for Transplant Production

Charles Vavrina, University of Florida

At the University of Florida, Dr. Vavrina and coworkers are studying a number of different products on the market that put an active biological fungicide into the media for raising transplants. Vavrina explained the mode of activity and assessed the efficacy of each. The organisms in these products are beneficial bacteria (Bacillus pumilus) or beneficial fungi (Gliocladium sp. or Trichoderma sp.). The organisms make the soil suppressive to pathogenic fungi, such as Fusarium and Pythium. The beneficial organism may exude antibiotics, compete for sites or resources, or induce the plant to develop its own defenses.

The most exciting part for me was what Vavrina called Systemic Acquired Resistance Responses. The recorded growth enhancement occurred not only at the transplant level but was carried over into the field long into the growing season. Dramatic results were recorded with products such as Rootshield, SoilGard and ActiGard, but Vavrina warned growers to test the materials themselves because some problems occurred with some products on some crops sometimes.

I asked what their control in the experiments was and it turned out to be a sterile medium. I suggested that these experiments be tried with a compost-based medium as another treatment, because these beneficial organisms are common inhabitants of good compost, and thus you may not have to buy a product to attain similar results. Of course, the manufactures claim to have their own selected strains of these beneficial organisms that are much more effective than the common strains. I don't know, but I do recommend buying as few farm inputs as possible. Still this is exciting research, and to see it happening in Florida at a University laboratory is good news.

  I always leave these conferences with a great hope and a million plans for the next growing season. Try for yourself next year.

  About the author: Eric is MOFGA’s "extension agent." You can direct questions to him at the MOFGA office in Augusta (622-3118; esideman@mofga.org)