In 2017 a startling study from Germany reported around 80 percent decline of total flying insect biomass from protected nature reserves in just 27 years (1989–2014) [1
]. The authors attributed the plausible cause of this major and hitherto unrecognized loss of insects to “agricultural intensification
” in surrounding areas. They noted few similar studies citing just one previous report from Rothamsted Insect Survey (RIS) that plotted a decline over a 30 year period (1973–2002) in one of four UK sites [2
]. This UK report noted rapid agricultural intensification from the 1950s and suspected that three stable sites—having much lower biomass and this mainly of insect pest species—had already collapsed before monitoring commenced in the 1970s. This situation is characteristic of a broader and critical extinction issue [3
]. Authors of a global review (Rockström et al. 2009) [5
] identified both “rate of biodiversity loss
” and synthetic fertilizer overuse as the most severe and pressing of global problems, more so than climate change, solutions for which they suggest as an immediate 25% reduction in N fertilizers and: “Agricultural systems that better mimic natural processes (e.g., complex agro-ecosystems)
”. A good measure of proper ecological functioning of such systems is past and current status of soil fauna, in particular earthworms (Oligochaeta: Megadrilacea)—the subjects of this report—that both monitor and mediate natural soil processes.
While comprehensive summaries of earthworm ecology, their role in humic SOM (soil organic matter) formation, and absolute population values are available following Darwin (1881) [6
], comparative information is quite limited such that a recent meta-analysis of soil biodiversity under organic farming [9
] entirely excluded earthworms “due to small sample sizes (n < 5)
The present article is a quantitative re-analysis of the scant historical data on earthworm biomass from long-term studies in an attempt to derive similar starting references as in the two insect biomass reports. However, earthworm survey results often differ considerably depending upon soil, season, or sampling method, thus relative or relational findings are required. In lieu of consistent historical records, comparative sites that have not undergone extreme agricultural intensification are sought to provide de facto
control metrics. Irregular earthworm surveys have been conducted at Sir John Lawes’ Rothamsted Research Station, the earliest established and longest-running Long-Term Experiment (LTE) facility to test agronomic effects of agricultural chemicals, with various levels of controls, during its 175 year operation since 1843. Reports of soil faunal surveys at Rothamsted conducted between 1921 and 2014 are available [10
]. Another set of earthworm data [15
] of intensified versus organic soil management is from Lady Eve Balfour’s Haughley Experiment that ran for more than forty years from 1939 to 1984 [18
]. Other comparable earthworm data are from the Swiss FiBL DOK agronomic field trials that have been operational for almost forty years, since 1978, on land that, as for parts of the other two sites, was originally pasture grassland [20
The a priori assumption in the current study is that the non-intensified plots or sections of these facilities would support an earthworm fauna not dissimilar in composition and scale to those present before agrichemical intensification. The chemical fields or plots typically represent contemporary management regimes but, prior to this, Rothamsted estate and Haughley farm have heritage from Roman times (about two millennia ago) or subsequent Anglo-Saxon settlement (about 1500 years ago), respectively. To forestall the obvious argument that Rothamsted plots with zero fertilizer application are a better control check, it is certain that no current nor historical farmer would consider such an unproductive operation. However, when available, nil fertilizer data are included for the sake of thoroughness.
Rothamsted’s Broadbalk arable, Barnfield roots and Park Grass pasture experiments—begun in 1843 (or 1839?), 1843 and 1856, respectively—are the world’s oldest operational ecological experiments; before this Broadbalk is thought to have been in arable cropping since at least 1623 and Park Grass similarly under pasture for many centuries [22
]. Regarding statistical reliability of long-term studies, it is unrealistic and impossible to wholly replicate such unique sites as chemical Rothamsted or organic Haughley without great commitment in time and investment in funds, nevertheless their insightful findings provide most useful scientific indicators [23
Whilst giving no account of Haughley’s resident populations, estimated numbers of earthworms in the soils of the Rothamsted Experimental Station were quoted by Balfour (1948: 203) [25
] as roughly 8.6, 2.8 and 0.5 million worms per acre in grassland, manured arable and unmanured land, and she also noted that both earthworms and fungi appear particularly sensitive to sulphate of ammonia fertilizer. Her information was seemingly based upon studies by earlier workers: Morris (1922: 303) [10
] gave Rothamsted’s Broadbalk earthworm counts of about one million in manured arable plots and 0.46 million per acre in nil “control
” plots (equivalent to 250 m–2
and 113 m–2
or a decline of about –55%). More in-depth surveys for Barnfield recorded starker loss of invertebrates and for earthworms alone declines up to –100% (Morris 1927: Table 1; Figures 1 and 3) [11
]. These data are summarized in Table 1
Thus, 80 years since introduction of the world’s first synthetic fertilizer at Rothamsted, deleterious soil effects were so severe that remedial reversions to traditional management methods (e.g., liming or marling and crop-ley or fallow rotations) were required [12
The present analysis reasonably compares such historical surveys to most recent studies from the same and from similar agronomic sites and concludes that, as with the insects, the earthworms too remain in jeopardy.
For flying insects, recent Rothamsted RIS data [2
] as quoted by the German study [1
] are normalized (untransformed) for better comparison with these latest German findings, and the historical soil invertebrate surveys at Rothamsted [10
] are re-evaluated.
Earthworm data from field surveys by various authors are re-analyzed as comparative data for intensified (i.e., synthetic agrichemical) versus non-intensified (i.e., organic) farm soils. Rothamsted surveys are of Broadbalk, Park Grass and Barnfield long-term trial sites [10
] (Figure 1
, Figure 2
and Figure 3
From 1939, Haughley farm in Suffolk, UK was divided into three (with approval of Rothamsted researchers) comprising self-contained Organic, Mixed and Stockless non-organic sections [16
] as shown in Figure 4
The Swiss FiBL-DOK trial [for bio-dynamic (D), organic (O) and conventional (K from German: “konventionell
”)] has several treatment combinations but, for comparison to these other two LTE sites, only survey data from their Organic, Mixed and Conventional wheat crops [20
] are considered.
As tropical organic reports are particularly scarce, a recent Philippines eco-taxonomic earthworm study on organic paddy rice and broad-acre sugarcane is included [17
] for comparison.
The premise for survey review is that, firstly, the organically fertilized plots best preserve the soil situation more typical of the prevailing management before agricultural intensification and thus represent the probable starting condition of earthworm (and other invertebrate) populations from earlier times. Therefore, the continuous organically fertilized Broadbalk or Barnfield arable and Park Grass pasture sites that are thought to have been so for prior centuries at Rothamsted, as with the 1000 year-old “Saxon” permanent pastures at Haughley, best represent the antecedent state prior to cultivation and/or synthetic fertilization. Secondly, any crop, soil, plant or soil biota changes are reasonably assumed to be due to the cumulative agronomic management effects. Thirdly, any geological, seasonal or sampling variables are nullified by simultaneity and sympatric proximity using the same method of earthworm extraction per site and per author.
Whereas most other reports give misconstrued values as open-ended percentage increases from the lowest biodiversity figure, the present study—possibly uniquely—measures relative changes from assumed optimal starting points giving statistical changes (declines ranging from 0–100%) rather than as percentage differences. The formula used is:
Percentage change (%) = ((y2 − y1)/y1) × 100
where y1 is original and y2 is final value.
Throughout, FYM is Farm-Yard-Manure (or coarse compost), N-P-K are chemical fertilizers, and SOM (Soil Organic Matter) is humus that, from a van Bemmelen factor, is ~58% carbon (SOC).
“We must turn all our resources to repairing the natural world” (Dr Bill Mollison, 1928–2016).
Critical biotic declines are linked to widespread intensive agrichemical practices that use simplistic chemical synthetics in non-laboratory settings as a replacement for natural processes. As stated in the laws of thermodynamics, it takes energy to maintain any system in a complex, ordered and sustainable state, and proportionately it takes twice the effort to double a vital resource (e.g., 50 to 100 is +100%) than to halve it (e.g., 100 to 50 is −50%). Rothamsted’s long-term trials clearly demonstrate that supply of organic FYM fertilizer (SOM) is most crucial to preservation of earthworms that otherwise decline by −50–100%, and that differing levels of synthetic fertilizers provide little, if any, overall benefit. Higher abundance and biodiversity appear attainable only when organic husbandry is fully implemented. Cases using mixed (i.e., combination of organic and chemical) compromises were demonstrated at Rothamsted’s Broadbalk or Barnfield, as at Haughley and in the Swiss DOK trials, to be just as deleterious as agrichemicals alone. Although this was less conclusively shown at Rothamsted, neither were fully non-chemical, organic methods meaningfully applied nor sought to be tested there.
Thus is it concluded that cascading soil fauna depletion occurs when woodland is cleared for pasture, when pasture is cultivated for crops, when synthetic fertilizers replaced organics, especially after WW1, and when excessive toxic and systemic biocides are introduced, especially after WW2, followed by the onslaught of alien/invasive species and diseases. Continued catastrophic trajectory for earthworms—the builders of fertile topsoils and humic SOM, upon which most life on Earth ultimately depends—seems as serious as for insects and most other organisms. Demonstrated solutions to restore biotic abundance and curtail loss of biodiversity are to readopt or to re-invest in more natural farming by recycling organic fertilizers and avoiding both waste and chemical poisons. Concomitant with a shift by farmers and consumers, governments may need to reallocate funding from agri-chemistry that continues to seek stop-gap solutions to problems often caused by chemical toxins themselves, and to raise support for practical, applied agro-ecology and sustainable Permaculture for efficient and flexible natural designs. It is timely to restore earthworms in order to rebuild topsoil humus thus allowing organic transition farming to rapidly reach its full capacity and to finally go “Beyond Organic
The findings of this report support the conclusions that excess N in agriculture leads to soil acidification, accelerates soil-organic-matter turnover and alters and/or disrupts soil faunal and microfloral communities [99
]. This has resulted in declines in over half of UK wildlife species in recent decades with one in ten now heading towards extinction with the key drivers being “intensive agricultural practices and climate change
]. On a positive note, an incontrovertible loss of regional plant biodiversity due to atmospheric and soil nitrogen pollution reversed in just 20 years after synthetic fertilizer application ceased on some Rothamsted plots [101
]. Although as yet unobserved in a wider landscape, such restoration, if pertaining to animals too, indicates a viable solution to earthworm depletions and, from this, a possible reversal in the insect and other species declines too.
Further monitoring with survey standardization is required on well-managed organic farms that likely retain heritage soil faunas, as well as in reservoir refuges which may yet support healthy earthworm populations for re-colonization and species recruitment into the intensified non-organic/agrichemical neighbours. Currently only limited information is available such that Global Biodiversity Information Facility search (www.gbif.org/search?q=earthworms%20organic
, December 2017) yields one report, underscoring a deficit in knowledge of basic agroecosystem functioning and soil ecology. Our biospheric focus needs to shift from flying organisms to the vital underground web-of-life keeping our soils, and us, alive.