Part of experiment rbk1

Broadbalk Earthworm measurements

Earthworm populations were assessed on Broadbalk in 1920-21, 1979, 2014 and 2015. Details are given below. The results are not directly comparable, as different methods were used for each assessment.

Feb 1920-Jan 1921 (Morris, 1922)

Morris recorded insect and other invertebrate fauna, including earthworms, on Broadbalk between February 1920 and January 1921. Samples were taken from two plots: FYM (Plot 2), receiving 35t/ha FYM annually since 1843 and the unfertilized plot (Plot 3) - no fertiliser or manure since 1843.

Samples were taken from the Western end of the plots, using a metal box 23x23cm with a total of five depths: 0-2.5cm, 2.5-7.6cm, 7.6-12.7cm, 12.7-17.8cm and 17.8-23cm. 23 samples were taken from each plot, approximately every 12 days, between Februrary 1920 and January 1921. Soil was not sampled on rainy days, due to the difficulty of examining wet soil. FYM was applied to Plot 2 and the Plots were ploughed on October 13th 1920. The plough depth was around 14-16cm, i.e. the fourth layer measured.

Earthworms were defined as belonging to the sub-order Terricolae in the order Oligochaeta, including Lumbricus sp.

Results:

Earthworms were recorded in all 12 months, and in all five depths (0-23cm)
Earthworms were most common in the second soil layer sampled (2.5-7.6cm deep)
Over twice as many earthworms were present in the plot given FYM since 1843 as in the plot never given fertiliser or manure
A total of 2.50 million earthworms/hectare (250/m2) were recorded in the FYM plot from 23 samples
A total of 1.13 million earthworms/hectare (113/m2) were recorded in the unfertilized plot from 23 samples
Earthworms were thought to occur at deeper depths than 23cm in both plots

September 1979 (Edwards & Lofty, 1982)

Edwards & Lofty measured earthworm numbers and total biomass in various Broadbalk plots growing continuous winter wheat, to investigate the effects of nitrogen (N) fertilizers. Earthworm populations were sampled in September 1979 by pouring dilute formalin on to 16 0.25 m ² quadrats and collecting the worms that were brought to the surface.

Results:

All species of earthworm were more numerous in plots treated with organic fertilizers
There was a strong positive correlation between the amounts of inorganic N fertilizer applied and populations of earthworms
Plots receiving both inorganic and organic N had the largest populations of earthworms

See September 1979 earthworm data (pdf) for summary of the Edwards & Lofty (1982) data from Broadbalk.

Spring 2014 (Sizmur et al, 2017)

Earthworm surveys were carried out on four parts of Broadbalk in spring 2014, receiving the following treatments each year:

NPK: 144kgN/ha plus PK since 1852. Straw removed (Plot 8, Section 1)

NPK+straw: 144kgN/ha plus PK since 1852. Since 1986 straw incorporated each year (Plot 8, Section 0)

FYM: 35t/ha FYM since 1885, plus fertilizer N since 1968 (96 kgN/ha 1968-2004, 144 kgN/ha since 2005). Straw removed (Plot 2.1, Section 1)

FYM+straw: 35t/ha FYM since 1885, plus fertilizer N since 1968 (96 kgN/ha 1968-2004, 144 kgN/ha since 2005). Since 1986 straw incorporated each year (Plot 2.1, Section 0)

A 1m x 14m area on the northern edge of each plot was used, divided into four equal sub-plots. Two earthworm surveys were carried out in each sub-plot, a total of 8 surveys per treatment.

Earthworm surveys were conducted by excavating a 20 x 20 x 20cm cube of soil, which was brought back to the laboratory and sorted to find and identify all the earthworms. Deep burrowing (anecic) earthworms were extracted by pouring a 5 L aqueous solution containing 6g/l of mustard flour (see Sizmur et al 2017 for full details).

Results:

Plots given FYM contained a significantly greater biomass and number of earthworms than the plots never given FYM
Total earthworm biomass was 109 g/m2 in plots given FYM, compared to 6 g/m2 in plots never given FYM
Total earthworm numbers were 400/m2 in plots given FYM, compared to 70/m2 in plots never given FYM
28 years of straw incorporation had no significant effect on the earthworm populations
There was no significant interaction between straw and FYM on earthworm abundance or biomass

Broadbalk total earthworm biomass and abundance, spring 2014 (Sizmur et al, 2017)

 

+/- standard errors of the mean, based on four replicate sub-plots and two surveys per sub-plot.

For further details of the different earthworm species recorded in the survey, see Spring 2014 biomass (pdf) and Spring 2014 abundance (pdf).

Earthworm biomass and abundance were also measured in spring 2014 on the long-term straw incorporation experiment at Rothamsted, which had four rates of cereal straw incorporated annually for 28 years. The highest rate of straw (20t/ha) resulted in significantly greater earthworm abundance and biomass. See Sizmur et al (2017) for more details.

Autumn 2015 (Stroud et al, 2016)

Stroud et al carried out midden counts on two Broadbalk plots in September 2015, to assess populations of anecic, deep burrowing Lumbricus terrestris earthworms. The plots received the following treatments each year:

NPK: 144kgN/ha plus PK since 1852. Straw removed (Plot 8, Section 1)

FYM+N: 35t/ha FYM since 1885, plus fertilizer N since 1968 (96 kgN/ha 1968-2004, 144 kgN/ha since 2005). Straw removed (Plot 2.1, Section 1)

Midden assays (5 m2 per plot) were carried out with 1 m2 mustard validation assays. 1.5l of mustard solution containing 20g mustard powder in water were poured within a 0.25 m2 square quadrat in a random location within the plot. Earthworms (L. terrestris) were collected for species analysis and then released. The results are not directly comparable with earlier assessments, as different methods were used.

Results:

The plot ammended with FYM + N contained 0.3 middens per m2
The plot ammended with NPK contained 0.13 middens per m2

Middens counts were also carried out on three other arable sites at Rothamsted and Woburn, with and without organic ammendments (straw, biosolids, and organic wastes). Organic matter applications enhanced L. terrestris populations, however these populations were very low, never exceeding 4.6 per m2. See Stroud et al (2016) for more details.

Key References