Providing evidence to improve practice

Action: Amend the soil using a mix of organic and inorganic amendments

Key messages

Biodiversity: Five controlled trials from China and India (four also randomized and replicated), and one study from Japan found higher microbial biomass and activity in soils with a mix of manure and inorganic fertilizers. Manure alone also increased microbial biomass. One trial found increased microbial diversity.

Erosion: One controlled, replicated trial from India found that mixed amendments were more effective at reducing the size of cracks in dry soil than inorganic fertilizers alone or no fertilizer.

SOC loss: Four controlled, randomized, replicated trials and one controlled trial from China and India found more organic carbon in soils with mixed fertilizers. Manure alone also increased organic carbon. One trial also found more carbon in soil amended with inorganic fertilizers and lime.

SOM loss: Two controlled, randomized, replicated trials from China and India found more nutrients in soils with manure and inorganic fertilizers. One controlled, randomized, replicated trial from China found inconsistent effects of using mixed manure and inorganic fertilizers.

Yield: Two controlled, randomized, replicated trials from China found increased maize Zea mays yield in soils with mixed manure and inorganic fertilizer amendments.

SOIL TYPES COVERED: clay, clay loam, sandy-loam, silt clay loam, silty-loam.


Supporting evidence from individual studies


A controlled, randomized, replicated experiment in 1990-1992 on silty-loam soil in India (Singh, 1995) found highest nitrogen levels in soil under fertilizer addition plus wheat residue(4.6-16.6 μg/g/month) followed by the fertilizer-only (4.2-14.3 μg/g/month) and wheat residue-only treatments (4-11.2 μg/g/month), compared to the untreated control (3.4-9.8 μg/g/month). The highest microbial biomass was 400 μg/g under fertilizer plus wheat residue (), compared to 254 μg/g in the control. There were four treatments replicated three times in 5 x 4.2 m plots: control, chemical fertilizer (NPK at 80/40/30 kg/ha), wheat residue (1 kg/m2), wheat residue plus fertilizer (at 50% fertilizer, 50% wheat residue). The crop sequence was a fallow-rice Oryza sativa-lentil Lens culinaris rotation. Wheat residue was lightly incorporated whereas fertilizer was applied to the soil surface. Soils were sampled at the end of the experiment to 10 cm depth.



A controlled, replicated experiment in 2000 on a non-chalky clay soil in Bhopal, India (Bandyopadhyay et al. 2003) found that application of farmyard manure plus inorganic fertilizers reduced the volume of cracks in a soybean Glycine max-linseed Linum usitatissimum rotation (63 m3 of cracks) compared to inorganic fertilizers alone (113 m3), or no fertilizers (161.8 m3). The crop was managed under conventional tillage or sub-soiling (deep tillage). Within each tillage treatment were plots of 8 x 5 m in which no fertilizer, inorganic fertilizer, or inorganic fertilizer plus farmyard manure was applied. There were three replicates per treatment. Crack length, depth and width, and the soil water content and density were measured.



A controlled, randomized, replicated experiment in 1990-2003 on sandy-loam in Fengqiu, China (Cai & Qin 2006) found that soil organic carbon increased by 12.2 Mg C/ha in the manure treatment, 7.8 Mg C/ha in the mixed, and 3.7 Mg C/ha in the nitrogen/phosphorus/potassium (NPK) treatments compared to the control, which lost 1.4 Mg C/ha. Wheat Triticum aestivum and maize Zea mays yields were 1.9% and 1.5% lower (respectively) in the mixed fertilizer treatment, and 23.7% and 18% lower  with manure-only than in the NPK treatment (5,261 and 7 808 kg/ha), in which yields were highest and most stable. A long-term wheat-maize rotation had the following treatments: inorganic fertilizer (NPK, NP, PK or NK), organic manure fertilizer, mixed nitrogen addition comprising half inorganic fertilizer and half compost (wheat straw, soybean Glycine max and cotton Gossypium herbaceum seed cake); and no fertilizer (control). Each treatment was replicated four times in 45.5 m2 plots.



An experiment in 2004 on light clay in Japan (Wada & Toyota, 2007) found that decomposition activity was higher under mixed amendment (18-49% of the control treatment activity) than under chemical amendment (1-37% of the control treatment activity). Decomposition activity under mixed amendment application recovered to control levels 2 (3 μg/g soil/h) and 10 weeks (0.9 μg/g soil/h) after disinfection (after metam sodium and chloropicrin application respectively), but under chemical amendment did not. Fungal contribution to decomposition recovered to control levels under mixed amendment application (1:1 with bacteria) compared with chemical amendment when disinfected with metam sodium. There were two 5 x 20 m treatments on soil which had previously grown melon Cucumis melo and cabbage Brassica oleracea: soil amended with chemical fertilizer, and amended with a mix of chemical and organic fertilizer (40 t/ha/y farmyard manure). Melon and cabbage had previously been grown. Soil samples were taken to 10 cm depth. Soils were disinfected with metam sodium or chloropicrin (to remove soil microorganisms) and incubated at 28˚C for 12 weeks.



A controlled, randomized, replicated experiment in 2001 on sandy loam in Ranchi, India (Hati et al. 2008) found that soil organic carbon decreased in all treatments over the cropping period. The decrease was less under NPK (nitrogen/phosphorus/potassium) plus manure (8.7%) and NPK plus lime (10.9%) compared to the nitrogen fertilizer treatment alone (28.3%). Soil organic carbon levels were much higher in NPK plus manure (7,167 kg/ha), NPK plus lime (6,633 kg/ha) and NPK-only (6,567 kg/ha) treatments compared to nitrogen fertilizer (4,800 kg/ha) and control (5,167 kg/ha) treatments. NPK with manure or lime improved soil structure, and nitrogen fertilizer worsened soil structure compared to the control. A long-term fertilizer experiment established in 1972 used an annual soybean Glycine max-wheat Triticum aestivum rotation. Six treatments were replicated four times on 10 x 10 m plots: control, nitrogen fertilizer, nitrogen and phosphorus, NPK, NPK plus manure and NPK plus lime. Soils were sampled in 2001 to 60 cm depth.



A controlled, randomized, replicated experiment between 1989 and 2007 on sandy-loam soil in Henan Province, China (Gong et al. 2009) found more bacteria and fungi in soil with mixed manure and inorganic fertilizer (5,626 and 21,000 CFU/g) and manure-only (6,725 and 24,000 CFU/g, respectively) treatments compared to the untreated control (2,238 and 7,000 CFU/g respectively). Soil organic carbon was also improved, with 7.2 and 9.4 g C/kg for mixed and manure-only treatments respectively, compared to 3.9 g C/kg in the control. The treatments used were: organic manure, half organic manure with mineral fertilizer, NPK, NP, PK and NK mineral fertilizers, and an unfertilized control treatment. The experiment was performed on wheat Triticum aestivum-maize Zea mays plots measuring 9.5 × 5 m, with four replicates of each treatment. Five soil samples were taken from each plot and mixed prior to analysis.



A randomized, replicated experiment from 1986 to 2007 on a sandy loam in China (Zhong et al. 2010) found higher organic carbon, nitrogen, phosphorus and potassium under manure (by 11.36, 1.25, 1.08 and 12.88 g/kg, respectively) and mixed applications (12.42, 1.36, 1.14 and 16.16 g/kg respectively), compared to the control. NPK (nitrogen/phosphorus/potassium) application alone increased carbon (by 11.3 g/kg) and nitrogen (by 1.3 g/kg) relative to the control. Microbial biomass was highest in the mixed and manure-only (265 and 252 nmol/g dry weight) applications, compared to nitrogen application (146 nmol/g dry weight) which had less than the control (198 nmol/g dry weight). Microbial diversity was highest under manure and mixed application (both with Shannon index ratings of 3.2) compared to the control (index of 2.8). Crop yield was highest under mixed (5,173 kg/ha) and manure-only (3,686 kg/ha) applications, followed by NPK alone (3,130 kg/ha). The experimental area was a maize Zea mays crop. Nine fertilizer treatments were replicated three times and included: control (no fertilizer), nitrogen fertilizer, phosphorus, potassium, nitrogen/phosphorus, nitrogen/potassium, nitrogen/phosphorus/potassium (NPK), organic manure (urea, calcium phosphate and composted pig manure) and manure plus NPK (mixed). Soils were sampled in each plot to 20 cm depth.



A controlled, randomized, replicated experiment in 1982-2005 on clay loams in China (Duan et al. 2011) found higher nitrogen levels under nitrogen, phosphorus and manure (141 and 90 kg N/ha, for rice Oryza sativa and wheat Triticum aestivum respectively) and nitrogen/phosphorus/potassium (NPK) and manure (140 and 89 kg N/ha), than nitrogen and manure (119 and 70 kg N/ha) or the control (58 and 41 kg N/ha) at Suining. Levels were similar between treatments at Wuchang (approximately 100 and 75 kg N/ha). Plant nitrogen uptake was 15.5 and 11.4% higher in rice and wheat under nitrogen and phosphorus plus manure, and 12.8 and 10% higher under NPK plus manure compared to nitrogen plus manure. Rice and wheat yields increased by 23-26% and 21-58% respectively under nitrogen and phosphorus plus manure, and NPK plus manure treatments, compared to nitrogen plus manure (8.4 and 9.1 t/ha/y overall for Suining and Wuchang respectively). Four treatments were applied to rice–wheat rotations at two sites in China: no fertilizer, nitrogen plus manure, nitrogen and phosphorus plus manure, and NPK plus manure. Each treatment was replicated four times in 4 x 3 m plots at each site. Soil samples were taken annually (20 cm depth).



A controlled, randomized, replicated experiment from 1988 to 2008 on sandy loam in northeast China (Lou et al. 2011) found more soil organic carbon under manure and manure plus nitrogen/phosphorus/potassium (NPK) fertilizer (18. 5 and 19 g C/kg respectively) compared to the control (11.8 g C/kg). Microbial biomass was higher in the manure (846 mg/kg) and manure plus NPK fertilizer treatments (885 mg/kg) than in the remaining treatments (496, 472 and 426 mg/kg for NPK, nitrogen-only and control treatments, respectively). Throughout the experiment celery cabbage Brassica rapa, frijole Phaseolus sp., radish Raphanus sativus, potato Solanum tuberosum, cucumber Cucumis sativus, onion Allium cepa, beet Beta vulgaris, tomato Solanum lycopersicum, mustard Brassica sp., and aubergine Solanum melongena were grown in rotation. Treatments included an unfertilized control, nitrogen fertilizer, NPK fertilizer, organic manure (horse compost) alone, and organic manure combined with NPK fertilizer. Plots were 1.5 m2 and replicated three times.



A controlled, randomized, replicated experiment in 2010 on clay loam in Kerala, India (Dinesh et al. 2012) found that soil organic carbon was higher under mixed amendments (16.3 g/kg) and organic amendments (17.4 g/kg) compared to chemical amendments (12 g/kg) or an untreated control (11 g/kg). Microbial biomass (indicated by carbon levels) was 28% and 52% higher under mixed and organic amendments respectively compared to chemical inputs. Ginger Zingiber officinale was grown in 3 × 1 × 0.15 m raised beds cleared of weeds. Treatments included organic amendments (farmyard manure, pressed neem Azadirachta indica waste, ash, vermicompost), chemical amendments (NPK – nitrogen/phosphorus/potassium at 75-50-50 kg/ha, urea, rock phosphate and potash), mixed (integrated) amendments (farmyard manure and NPK combined) and no fertilizer (control). There were five replicates. Four soil samples/bed were taken immediately after ginger harvest.



A controlled experiment from 1990 to 2010 on silt clay loam in Shaanxi, China (Yang et al. 2012) found highest organic carbon levels in cropped plots treated with nitrogen/phosphorus/potassium (NPK) and 20.6 t/ha manure treatment (13.88 g/kg). Levels were similar in the remaining treatments but higher than in the untreated control (by 34-45%). Microbial biomass was higher under mixed amendments (466 mg C/kg) compared to nitrogen/phosphorus (211 mg C/kg), NPK (247 mg C/kg) and the control (161 mg C/kg).  Three management treatments included land abandonment, bare fallow (both in 14 x 7 m plots) and a wheat Triticum aestivum-maize Zea mays system (14 x14 m plots). Within the wheat-maize system were fertilizer treatments: control (no addition), nitrogen only, nitrogen/potassium, phosphorus/potassium, nitrogen/phosphorus, NPK, NPK plus straw, NPK plus 13.7 t/ha manure, NPK plus 20.6 t/ha manure. All fertilizers were incorporated into the soil to 20 cm depth. Soils were sampled to 20 cm depth at the end of the experiment.


Referenced papers

Please cite as:

Key, G., Whitfield, M., Dicks, L.V., Sutherland, W.J. & Bardgett, R.D. (2017) Enhancing Soil Fertility. Pages 383-404 in: W.J. Sutherland, L.V. Dicks, N. Ockendon & R.K. Smith (eds) What Works in Conservation 2017. Open Book Publishers, Cambridge, UK.