Effect of organic farming transition on crop productivity and soil biological health over a decade

Introduction

How quickly does a field recover its biological functions once chemical fertilisers and pesticides are withdrawn? Across Europe, organic land area doubled between 2010 and 2020, yet many growers still hesitate because the transition period often coincides with depressed yields [1] . Meta-analyses placed the organic yield penalty at roughly 20-25% for cereals [2] , though recent work reported smaller deficits once soils stabilised [3] . Soil biological health drives this stabilisation microbial communities break down residues, cycle nutrients, suppress pathogens, and build aggregates [4] . Under conventional management, repeated mineral nitrogen can depress microbial biomass while herbicides reduce root exudate diversity [5] . Russia holds about 10% of global arable land, much of it on fertile Chernozem, yet its certified organic area remains under 1% [7] . Despite growing domestic demand, controlled long-term trials on Russian Chernozem are scarce, and most published datasets span only three to five years [9,10] . This research tracked crop yield and three soil biological indicators microbial biomass carbon, dehydrogenase activity, and earthworm density across a full decade of organic and conventional management on Chernozem near Moscow.

Research area description

The trial occupied 4.8 ha at the Lomonosov Moscow State University experimental farm (55°42′N, 37°31′E, 178 m a.s.l.). Mean annual temperature was 5.8 °C; precipitation averaged 673 mm with 55-60% falling May-September. Soils were Haplic Chernozem with organic carbon 3.1%, clay 27.4%, and pH 6.7. The site had been under conventional cereal-pulse rotation for 18 years previously.

Material and methods

Material

Winter wheat (cv. Moskovskaya 56) and spring barley (cv. Zazersky 85) seeds came from the university's facility. Composted cattle manure (N 1.7%, P₂O₅ 0.9%, K₂O 1.3%) was sourced from the university dairy unit. Conventional inputs included ammonium nitrate, double superphosphate, potassium chloride, tribenuron-methyl and fenoxaprop-P-ethyl. Clover (Trifolium pratense cv. Taezhnik) served as the green-manure crop. All analytical reagents were from Sigma-Aldrich.

Methods

The experiment ran September 2012 to August 2022 in a randomised complete block design (four replications, plots 30 × 40 m). Both systems followed a four-course rotation: winter wheatspring barleyclover/fallowwinter wheat. The organic block received 15 t ha⁻¹ composted manure before wheat sowing; weeds were managed mechanically. The conventional block received N 120, P₂O₅ 60, K₂O 40 kg ha⁻¹ with one herbicide application per season. Grain yield was combine-harvested from the central 20 × 30 m, adjusted to 14% moisture. Microbial biomass carbon was measured by chloroform-fumigation extraction [12] . Dehydrogenase activity was assayed with TTC at 37 °C for 24 h [13] . Earthworm density was assessed by hand-sorting 0.25 m² monoliths each October [14] . Data were analysed by two-way ANOVA with Tukey's HSD (α = 0.05) in R v4.2.1.

Results

Table 1 Organic wheat yields climbed from 3.21 to 4.38 t ha⁻¹, shrinking the gap from 29.6% to 1.4% (Table 1). Barley followed similarly (28.5% to 3.7%). ANOVA confirmed a significant treatment × period interaction (p<0.001).

Comprehensive interpretation

Pearson correlation revealed a strong positive link between microbial biomass carbon and organic wheat yield (r = 0.94, p<0.001). The steepest biological gains appeared between years 3 and 7, coinciding with the fastest yield-gap closure.

Discussion

The yield trajectory mirrors long-running European trials such as the DOK experiment [15] , though convergence on Chernozem appears faster likely because it's high native organic carbon provides a larger microbial seed bank [10] . The initial 24-30% depression sits within the commonly cited range [2] . By the final period, organic wheat was statistically indistinguishable from conventional (p = 0.41), while barley held a non-significant 3.7% deficit. Earthworm density proved the most sensitive indicator. The 96.4 individuals m⁻² in year 10 ranks among the highest for Russian arable Chernozem, where conventional densities are typically 20-50 m⁻² [8] . Dehydrogenase tracked microbial biomass closely (r = 0.97), supporting its use as a low-cost monitoring proxy [13] .

Conclusion

A decade of comparison on Moscow-region Chernozem shows the organic yield penalty is not permanent. Wheat reached 98.6% of conventional levels by years 9-10, and barley 96.3%. This coincided with gains in microbial biomass carbon (+110.2%), dehydrogenase (+109.3%), and earthworm density (+239.4%). Policy measures extending support beyond the standard three-year conversion period would better match the biological timeline.

References

1. Lernoud J, Willer H. Current statistics on organic agriculture worldwide. In: Willer H, Lernoud J, editors. The world of organic agriculture: Statistics and emerging trends 2019. Frick: FiBL; Bonn: IFOAM-Organics International; 2019. p.35-74.
2. De Ponti T, Rijk B, Van Ittersum MK. The crop yield gap between organic and conventional agriculture. Agric Syst. 2012;108:1-9.
3. Seufert V, Ramankutty N, Foley JA. Comparing the yields of organic and conventional agriculture. Nature. 2012;485(7397):229-232.
4. Bender SF, Wagg C, Van der Heijden MGA. An underground revolution: Biodiversity and soil ecological engineering. Trends Ecol Evol. 2016;31(6):440-452.
5. Hartmann M, Frey B, Mayer J, Mäder P, Widmer F. Distinct soil microbial diversity under long-term organic and conventional farming. ISME J. 2015;9(5):1177-1194.
6. Pelosi C, Bertrand M, Capowiez Y, Boizard H, RogerEstrade J. Earthworm collection from agricultural fields. Eur J Soil Biol. 2009;45(2):176-183.
7. Khaliullin FA, Gorbunov AV. Organic agriculture in Russia: Current status and prospects. Russ Agric Sci. 2018;44(3):285-290.
8. Stolbovoi V, McCallum I. Land resources of Russia. Laxenburg: International Institute for Applied Systems Analysis (IIASA); Moscow: Russian Academy of Sciences; 2002.
9. Organic Monitor. The Russian organic market: Trends and outlook. Research report; 2020.
10. Mäder P, Fließbach A, Dubois D, Gunst L, Fried P, Niggli U. Soil fertility and biodiversity in organic farming. Science. 2002;296(5573):1694-1697.
11. Fließbach A, Oberholzer HR, Gunst L, Mäder P. Soil organic matter and biological soil quality indicators after 21 years of organic and conventional farming. Agric Ecosyst Environ. 2007;118(1-4):273-284.
12. Vance ED, Brookes PC, Jenkinson DS. An extraction method for measuring soil microbial biomass C. Soil Biol Biochem. 1987;19(6):703-707.
13. Casida LE Jr, Klein DA, Santoro T. Soil dehydrogenase activity. Soil Sci. 1964;98(6):371-376.
14. Edwards CA, Bohlen PJ. Biology and ecology of earthworms. 3rd ed. London: Chapman & Hall; 1996.
15. Pimentel D, Hepperly P, Hanson J, Douds D, Seidel R. Environmental, energetic, and economic comparisons of organic and conventional farming systems. Bioscience. 2005;55(7):573-582.
16. Gomiero T, Pimentel D, Paoletti MG. Environmental impact of different agricultural management practices. Crit Rev Plant Sci. 2011;30(1-2):95-124.