Some Experimental Field Work Studies on Compost Tea

Some Experimental Field Work Studies on Compost Tea

Overview

I examine two studies, after which I make some comments and conclusions. The studies are from 2003 and 2005 and if anyone has any later scientific studies I would be interested in looking at them in a future blog.

I’m interested in studies which use randomized block design over a large enough homogonous area, as blocking allows for statistical control of experimental results. It is the simplest design for comparative experiments using all three basic principles of experimental designs: randomization, replication, and local control.

The importance of an academic approach can be seen in this anecdote, from a very honest farmer, about a two field trial of compost tea:

“It is impossible to say with any certainty how much of a role the compost tea played in the checking of this potato blight infection. The potatoes may have fought the infection off themselves. The improved airflow and reduced humidity created by a drastic pruning of the leaves may have been responsible, or contributed. I also couldn’t let a control crop go to ruin without intervening. Unlike an academic researcher, this is my food.”

That is precisely the problem which the studies described here are designed to avoid, because in a real life farming situation there are commercial pressures against running an experiment to completion. Moreover such situations again have to be modified to the commercial process of planting and production, and randomized block design rarely fits well with these.

Randomized block experimental designs have been widely used in agricultural and industrial research for many decades. With the right experimental design and statistical analysis, it is possible can identify and isolate the effects of natural variation and determine whether the differences between treatments are “real,” within certain levels of probability.

Field Study: Rodale Institute

In 2003, the Rodale Institute (TRI) conducted trials on compost teas which was reported on by Laura Sayre. Extracts from her report are given below.

Background:

Undertaken in collaboration with three area farmers and Pennsylvania State University plant pathologist Dr. James Travis, the field segment of TRI's compost tea study is focused on three crops: wine grapes, potatoes, and pumpkins. These crops were chosen for their profitability, susceptibility to fungal diseases, and consequent high use of fungicides under conventional management.

Lead TRI investigators Matt Ryan and Dave Wilson explain that the goals of the project are twofold: to gather hard data on the compost tea's effectiveness for stimulating plant growth and suppressing disease, and to educate farmers and extension agents about its potential benefits--and hazards--as an organic material.

"There's a lot of excitement right now about compost tea--more and more growers are using it, and there's a lot of anecdotal evidence about its ability to suppress plant diseases," says Ryan. "But there's a real lack of independent scientific evidence. Our hope is to start filling that void."

Study 1: Compost tea shows potential for disease management in grapes

The vineyard experiments include three treatments: a weekly, foliar application of compost tea beginning in mid-May, a pesticide control, and a no-spray control. In 2003, results here were the most dramatic out of the three crops, with compost tea suppressing powdery mildew (Uncinula necator) by approximately 50 percent on Chardonnay grapes.

The tea also appeared to help control the spread of gray mold (Botrytis cineria), but this result was not statistically significant. Trials showed no detectable effect, finally, on black rot (Guignardia bidwellii) or Phomopsis (Phomopsis viticola), and use of compost tea actually seemed to encourage infection by downy mildew (Plasmopara viticola). (Vineyard managers resorted to fungicides to control the latter diseases in late June and early July.)

Study 2: Pumpkins and potatoes react very differently

The vegetable crop trials were based on a half-acre, randomized complete block design plot located at The Rodale Institute Experimental Farm, and also included three treatments: compost tea applied once at planting as a soil drench and then weekly as a foliar spray; a non-compost tea application containing the nutrient ingredients but not the compost found in the tea; and a no-spray control.

Results in the vegetables contrasted starkly with those found in the grapes. Powdery mildew in pumpkins is caused by a different fungus (in fact, by two fungal species, Erysiphe cichoracearum and Sphaerotheca fuliginea) than powdery mildew in grapes, and the compost tea applications showed no effectiveness here, with high levels of infection across all treatments.

In the potato plots, on the other hand, disease levels were so low overall that no significant differences could be found between the three treatments.

The spuds did show a yield response to compost tea applications, however. Plants receiving regular doses of compost tea produced larger, better potatoes than both the nutrient-ingredient-only and the untreated control plants. Marketable yields in the compost tea plots were between 18 and 19 percent higher than in the untreated plots and about 15 percent higher than in the nutrient-only plots. Compost tea-treated plants also produced tubers that tested higher for a range of nutrients, including iron, boron, potassium, and manganese. Iron showed the biggest response, with levels an astonishing 1700 percent higher in plants receiving compost tea than in untreated plants.

The widely divergent results in the three crops studied here suggest that it is difficult, if not impossible, to generalize about the efficacy of compost tea for disease suppression across all crop species--different crops have different leaf architecture, which means they will receive sprays differently, not to mention the differences in physiology and phylogeny.

Field Study: ADAS: Potato Blight (Phytophthora infestans) and Planting Density Field Demonstrations, 2005

Compost Tea: Mixed Results from Scientific Trials

The results are presented of a trial of 28 potato varieties, including 19 blight-resistant Sarpo varieties The effects of compost tea preparations in protecting against blight are also studied.

ADAS is a Leading agricultural and environmental consultancy (Agricultural Development Advisory Service)

The trial was conducted under the oversight of David Frost, Study Director for ADAS Wales

Strategies to combat blight

As the Late Blight pathogen Phytophthora infestans is able to evolve and diversify, the British Potato Council acknowledges that the problems of controlling it are increasing year on year.

Traditional control methods relied on copper-based fungicides such as Bordeaux mixture (copper sulphate and calcium oxide). Copper (Cu) is a broad-spectrum fungicide which acts as a protectant – it needs to be applied to prevent disease – and is potentially phytotoxic. As the use of copper as a fungicide is being withdrawn1 and as the drive to reduce the use of agri-chemicals such as fungicides increases, alternative strategies require evaluation. These include:

• Agronomic strategies - control of volunteers, manipulation of planting dates, presprouting, seed spacing, irrigation and defoliation.
• Prophylactic strategies - compost teas & herbal preparations
• Use of resistant varieties

Compost Teas

Although ranking of blight resistant varieties and evaluation of compost extracts were included in the MOP project; the use of compost teas from Controlled Microbial Composting systems as a prophylactic (preventative) against blight was not assessed.

The microbial activity of these preparations provides a potential alternative to chemical pesticides and fungicides such as sulphur and copper (Hutchinson, 2003; Hutchinson, 2004), but to date few trials have been undertaken. A limited trial of compost tea preparations was undertaken by ADAS Wales in 2004 and further trials were undertaken in 2005.

1.1 Primary Objectives

• To examine the level of resistance to Phytophthora infestans in selected Sarpo potato clones in a high risk blight area
• To undertake potato variety trials, including assessment of yield, on an established certified organic holding
• To evaluate the cultivar Axona for yield potential under different seed rates

1.2 Secondary Objectives

• To evaluate the use of compost tea in the control of potato blight in Wales
• To undertake evaluations of the eating quality of varieties selected from the trials

Compost Tea Evaluations

For the compost tea evaluations, two varieties were used, Charlotte and Cosmos. The nationally listed cultivar Axona was evaluated in the planting density trial. The blight prone variety King Edward was planted in guide rows to spread infection throughout the site.

Compost tea was made in a microbrewer using material from a Controlled Microbial Composting system. All sprays were applied using an Oxford Precision Sprayer

Layout of Trial

In order to evaluate the vigour and growth of Sarpo cultivars under organic husbandry, the trial was undertaken on certified organic land.

4.1.2 Layout of trials to assess the use of compost tea against foliar blight

The plots were arranged in a fully randomised complete block design with four replicates (2 replicates on Charlotte and 2 replicates on Cosmos). Plots were four rows wide (3.0 m) and measuring 9 m in length.

Results

AUDPC analysis shows that foliar blight developed most rapidly on cultivar Orla, followed by Desiree. Cara was comparable with the Sarpo variety Dawn. Sarpo varieties Quentin and Harri were slightly susceptible to foliar blight, while Carrie and Rob were unaffected by foliar blight

Foliage blight on compost tea treatment plots

There was little difference in disease progression between treated and untreated plots. Although the progression of foliar blight in the untreated plots compared to the two treatment plots was slighlty more advanced during July this was not maintained during August. Furthermore, when subject to Analysis of Variance, the differences were not found to be significant.

Looking at the progression of foliar blight in the two varieites in the compost tea trial - the progression was more rapid in cultivar Charlotte than in Cosmos, but when subject to Analysis of Variance the differences were not found to be significant except for one assessment undertaken on 30 July 2005.

Conclusions

The trials undertaken in 2005 found that Sarpo cultivars showed high foliar blight resistance with the exception of Sarpo Dawn, Sarpo Harri and Sarpo Quentin. Blight resistance in Sarpo cultivars was greater than in commercially available varieties in the trial with the exception of Sarpo Dawn. Sarpo Dawn showed no significantly higher degree of blight resistance than the highest scoring commercial cultivar, Cara.

Compost tea treatments did not significantly delay the onset of foliar blight on either of the varieties in the trial. This experiment was a major blight challenge to the treatments because as the epidemic progressed the site became heavily infected. Overall, there was no statistically significant prophylactic effect of the compost tea treatments.

My Comments

Experimental Design

Both studies in fields employed the statistical technique known as a randomized block design.With a randomized block design, the experimenter divides subjects into subgroups called blocks, such that the variability within blocks is less than the variability between blocks. Then, subjects within each block are randomly assigned to treatment conditions. Compared to a completely randomized design, this design reduces variability within treatment conditions and potential confounding, producing a better estimate of treatment effects.

There are a large number of anecdotal studies of compound teas being used, and while the tea may appear to be effective, and may in fact be effective, that is not a scientific test. Claims need proper scientific testing, and that means creating randomised block design within the same field so that the initial conditions have minimal divergence.

Darwinian Strategy for Testing

The Rodale Institute took the blight on its crops as and when it occurred. The ADAS field study, however, encouraged infection- the blight prone variety King Edward was planted in guide rows to spread infection throughout the site.

This is closer to James Torbitt’s experimental design (commended by Charles Darwin), and seeks to see how resistant strains are, and whether applications of compost tea are as effective as fungicides by deliberately making sure that the worst blight conditions - but best for the experiment – can be created.

Why that is so important is because many factors can affect the onset and severity of blight, so by looking at the worst scenario that can be obtained, the results would be more significant than just allowing natural conditions to prevail which might by chance be milder.

Variety of Effect

While chemical methods of control use relatively simple compounds, compost teas are complex, organic and living. It is therefore not surprising that how they work varies, and the Rodale Institute results show that while they are effective for grapes against some pathogens, they can actually encourage others.

There is no statistical evidence from either trial that they are effective against potato blight. This agrees with other studies reviewed by me so far, which show there has been success in some crops, but there is not conclusive demonstration of effectiveness against blight under field conditions.


References http://newfarm.rodaleinstitute.org/depts/NFfield_trials/0404/tea.shtml
http://orgprints.org/10843/1/Potato_blight_field_demonstrations_2004.pdf

On Randomised Block Design, see:
http://www.stat.yale.edu/Courses/1997-98/101/expdes.htm
http://pbgworks.org/node/1534
https://academic.oup.com/ilarjournal/article/55/3/472/645707
https://www.sare.org/Learning-Center/Bulletins/How-to-Conduct-Research-on-Your-Farm-or-Ranch/Text-Version/Basics-of-Experimental-Design/Common-Research-Designs-for-Farmers