DIVERSE Project Field Experiment Dataset

Description

A field plot experiment was located on the University of Reading farm at Sonning in Berkshire, UK (51°28'21"N -0°54'13"E) and was established in August 2018. Plots were 2 x 11m in size, arranged in a randomised complete block design with 4 blocks/replicates. Each summer, after the harvest of a cereal crop, cover crops were planted and then mowed in the autumn using a lawn mower and either incorporated into the soil of the same plot (Mulch), or removed from the plot (Remove) and added to a plot where cover crops were not grown (Add). Cover crop residues were incorporated by ploughing prior to planting the next autumn sown cereal crop. The cereal rotation was Winter Wheat (2017/18); Winter Barley (2018/19); Winter Oats (2019/20); and Winter Wheat (2020/21). The cover crop treatments were control (no cover crops), buckwheat (Fagopyrum esculentum; variety Hajnalka), berseem clover (Trifolium alexandrinum; variety TIM), oil radish (Raphanus raphanistrum; variety Barracuda), sunflower (Helianthus annuus; variety M6103), and a 4-species mixture of these four. Nitrogen fertiliser was applied at a rate equivalent to 75% of the AHDB RB209 recommended rate for the crop. All other fertiliser and crop protection was applied in line with standard farm practice. Timeline: Cover crops drilled on 14th August 2018 Cover crops terminated on 10th October 2018 Barley drilled on 23rd October 2018 Barley harvested on 12th and 15th July 2019 Cover crops drilled on 12th August 2019 Cover crops terminated on 21st October 2019 Oats drilled on 29th October 2019 Oats harvested on 24th August 2020 Cover crops drilled on 1st September 2020 Cover crops terminated on 2nd November 2020 Wheat drilled on 6th November 2020 Wheat harvested on 13th August 2021 Soil samples were taken as a composite sample of three gauge auger cores per plot to a depth of 0-20 cm each summer after cereal crop harvest and before cover crop planting. Soil samples were sieved moist to 4 mm and analysed for soil moisture and available nitrate and ammonium. The remainder of the soil was air dried and sieved to 2 mm and analysed for organic matter, soil pH, Olsen P, and EDTA extractable Cu, Fe, K, Mg, Mn, Na, Ni, S, and Zn. Dry soil was ball milled to a fine powder and analysed for total C and N. Samples (air dried and 2 mm sieved) taken in 2018 only were analysed for soil texture and total (reverse aqua regia digestable) Ca, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, and Zn. Grain yield was measured using a plot combine and expressed after moisture correction in dry kg per Ha. Grain was milled and analysed for total N, C, Ca, Cu, Fe, K, Mg, Mn, Mo, Na, Mi, P, S, and Zn. The statistical design of the experiment allows analysis using the following nested ANOVA model: Cover/Treatment/Mixture/Species. Cover has two levels (Yes and No). Treatment has four levels (Mulch, Add, Remove, and Control). Mixture has two levels (Yes and No), and Species has six levels (Control, Buck, Sun, Clover, Radish, and Mix).

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The total (reverse aqua regia digestible) concentration of Ca, Cu, Fe, K, Mg, Mn, Na, Ni, P, S, and Zn in soils was determined by ICP-OES (Inductively Coupled Plasma Optical Emission Spectrometry) analysis of 0.5 g digested in reverse aqua regia (9 ml of nitric acid and 3 ml of hydrochloric acid) using a MARS 6 microwave digestion system. Soil texture was determined using laser granulometry (Malvern Mastersizer 3000). Representative subsamples were dispersed using a dispersing agent (3.3% sodium hexametaphosphate +0.7% sodium carbonate). Disaggregation of the sample was achieved using a rubber pestle for up to 1 min before analysis. Data was reported as the median particle size, Dx (50), and the 10 and 90 percentile (Dx (10) and Dx(90) particle sizes all reported in µm. %sand, % silt, and %clay were quantified using the texture class intervals of the Soil Survey of England and Wales. Because the particle size distribution obtained by laser-diffraction methods differ from those achieved using the classical sieve pipette method, we used the equations reported by Yang et al. (2015) to ‘correct’ our particle size distribution data from a volume % basis to a mass % basis. Yang, X., Zhang, Q., Li, X., Jia, X., Wei, X., & Shao, M. (2015). Determination of soil texture by laser diffraction method. Soil Science Society of America Journal, 79(6), 1556–1566. https://doi.org/10.2136/sssaj2015.04.0164 Total C and N of soils and grain samples was determined by dry combustion using a Thermo Scientific Flash 2000 Organic Elemental Analyser. 10 mg (soil) or 5 mg (grain) subsamples were weighed into tin capsules and analysed. Each sample was analysed in duplicate. Soil pH was determined using a using a pH electrode (3310, Jenway) in a soil-water suspension after shaking with water for 15 min at a 1:10 w/v ratio. EDTA extractable elements were quantified by extracting 2.5 g of soil with 25 ml of 0.05M EDTA (Ethylenediaminetetraacetic acid) at 20 °C for one hour, centrifuging, filtering and analysing Cu, Fe, K, Mg, Mn, Na, Ni, S, and Zn in the extract using ICP-OES. Soil moisture and Organic matter were determined based on mass loss by heating to 105 °C or ignition at 500 °C, respectively. Olsen P was measured by shaking 5 g of air dried soil with 100 ml of a pH 8.5 sodium hydrogen carbonate at 20 °C for 30 minutes before filtration and analysis colourimetrically on a Skalar San + + continuous flow analyser. Available nitrate and ammonium (NO3− and NH4+) was extracted by shaking the equivalent of 40 g of dry soil for 30 min in 200 ml 1 M KCl. Extracts were filtered and analysed colourimetrically on a Skalar San + + continuous flow analyser. The concentration of Ca, Cu, Fe, K, Mg, Mn, Mo, Na, Mi, P, S, and Zn in grain samples was determined by ICP-OES analysis of 0.5 g samples digested in slightly diluted nitric acid (2 ml of ultra-pure water and 8 ml of nitric acid) using a MARS 6 microwave digestion system.

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