A Preliminary Review of the Influence of Soil Organic Matter on the Mineral Content of Food Plants.

By John Reeves

 

There is now very extensive research indicating the adverse effects on human health of low levels of minerals in food. The decline of minerals in British food has been monitored by M.A.F.F. since 1940. A review from this data has recently been carried out and published (1).

In vegetables only phosphorus has risen since 1940.  Six other important elements have fallen, with copper falling as much as 76%. Similarly in fruit, phosphorus is 2% up and the others are down, with iron down 24%.

Declines have also been recorded in milk, meat and cheese.

At Eastleigh, over the past 14 years, we have carried out extensive research into increased plant mineral content in the presence of the symbiotic Mycorrhizal-forming fungi.  This group of beneficial root fungi occur naturally in association with 80% of land plants. Mycorrhiza is reduced or eliminated by soil disturbance and destroyed by chemical fertilizer. (2)

In two of our trials we investigated the mineral content effects of chemical fertilizer or Organic Matter.  In the Organic Matter part of these trials we found considerable variation. See Below.

 

Mineral Score.

In order to achieve a simple comparison of plant minerals, each mineral was averaged for all samples, then the appropriate mineral in each sample was taken as a percentage of the average. Finally the percentage for each mineral in a sample was averaged to give a mineral score. Before considering the Eastleigh data, what do other reports tell us?

One of the first to add science to organic farming was E.B.Balfour in her book "The Living Soil". One set of data in this book compares the minerals in crops from 3 differently managed farms.

1. Mixed organic farming.

2. Stockless organic farming.

3. Mixed farming using some chemical fertilizer.

Aggregating 10 minerals in a variety of crops the mineral scores are:-

1. Mixed organic - 103

2.  Stockless organic - 102

3. Mixed, using some chemical fertilizer - 94.

 

 

F.F publication "Inorganic Pollution and Agriculture"  1977 (3). Here there is extensive analysis of soil and plants, before and after the application of sewage sludge. There is also data on the effects on plant minerals when two levels of town compost (solid waste and sewage sludge) are used. The mineral scores are as follows:-

 

 

Dwarf Beans

Lettuce

Potato

Spinach

Control

70

187

28

137

Single Compost

77

148

33

154

Triple Compost

80

126

34

197

 

High mineral scores in spinach grown in compost are largely due to high zinc levels.

In further trials 4 minerals were measured in 4 vegetables, before and after the use of town compost or pig slurry. Here the minerals are shown as a percentage of the untreated control.

 

 

Control

Town Compost

Pig Slurry

Copper

100%

110%

87%

Nickel

100%

45%

39%

Lead

100%

111%

103%

Zinc

100%

53%

64%

 

Two reports from the U.S.A. indicate higher levels of minerals in organic produce than in those conventionally grown. (4) & (5). Trials carried out by Eastleigh Research. TRIAL 1.

Carrots grown in Eastleigh soil. Neutral to high pH

Control.                                               87

+ mushroom compost                    86

A farm near Ashburton, Devon. Neutral pH

Control                                                70

+ Organic matter                                   101

TRIAL 2.

Carrots. In soil neutral to high pH

Control                                                107

+ O.M. 20 tonnes/ha mushroom compost    80

+ O.M. 40 tonnes/ha mushroom compost    109

In soil neutral to acid

Control                                                107

+ O.M. 20 tonnes/ha mushroom compost    150

+ O.M. 40 tonnes/ha mushroom compost    160

This variation also occurs in a pasture trial.

Permanent pasture on limestone               108

After application of dairy herd slurry          97

A pasture established for 12 years, managed organically after conventional arable.

Control                                                107

After dairy slurry as above                      127

The different response to organic matter on different soil pH raises the question "why"?

The next trial was conducted on Eastleigh soil alone with neutral to high pH. In this trial broad beans.and carrots were grown with and without Mycorrhiza and with 3 or 4 levels of mushroom compost.

 

From the new trial:

 

Broad Beans

Onions

Control

70

92

+ 10 tonnes/ha mushroom compost

76

99

+ 20 tonnes/ha mushroom compost

87

105

+ 30 tonnes/ha mushroom compost

98

114

+ introduced Mycorrhiza

103

132

+ Mycorrhiza + 10 tonnes Compost

112

141

+ Mycorrhiza + 20 tonnes Compost

129

149

+ Mycorrhiza + 30 tonnes Compost

144

196

+ Mycorrhiza + 40 tonnes Compost

167

218

 

 

From a previous trial:

 

Broad Beans

Onions

Control

98

84

+ fertilizer Phosphorus

75

75

+ introduced Mycorrhiza

130

107

 

These progressive increases in the mineral content of broad beans and onions seem to provide the possibility of carrying on for ever. There are, however, some unpublished data which indicate that in excess, organic matter can have the opposite effect.

 

Trials with wheat in the Eastleigh soil.

Continuous wheat.

The inverted turf used in this trial came from an adjoining field, uncultivated and unfertilized for many years, and would have had native Mycorrhiza adapted to local conditions.

Spelt wheat in cultivated soil         114

Spelt wheat on inverted turf           123

Year 2 No cultivation or fertilizer     123

Year 5 No cultivation or fertilizer     128.

 

Organic Matter and wheat

About 30 tonnes/ha compost was incorporated into the soil before the introduction of Mycorrhiza.

 

 

Bearded wheat

Spelt wheat

Year 1

No Organic Matter

+ Organic Matter

 

112

125

 

98

120

Year 2

No Organic Matter

+ Organic Matter

 

107

122

 

 

108

145

 

From a field near Exeter, where a soil sterilizer had been regularly used, the two previous crops of kale and peas had been unsatisfactory. Before the wheat crop, dairy herd slurry was cultivated into the soil. No sterilizer- was used. The mineral score for the wheat was 113.

Considerable additional trials are required to confirm the above patterns of mineral uptake.

 

 

REFERENCES.

(1) Thomas, D M.Sc., D.I.C. Mineral Depletion in Food Over the Period 1940-1991. The Nutrition Practitioner. Vol.3. July 2001 .pp2?-29.

(2) Reeves J.  Influence of Agriculture on Mineral Nutrition and Health. Eastleigh Research. Greenfield Close. Joys Green. Lydbrook. Glos.GL17 9QU.

(3) Inorganic Pollution and Agriculture. Ministry of Agriculture, Fisheries and Food. Reference Book 326. From H.M.Stationery Office

(4) Firman E. Bear. Variation in Mineral Content in Vegetables. Proceedings of the Soil Science of America. 1998 November.

(5) Smith B.L. Comparison of Element Levels in Organic and Commercial Foods. Trace Elements in Man and Animals. Eds: Meissner, MD & Mills, CF. T.E.M.A. Conference 1993.