DOI: 10.23637/rbk1-bknutrw-01
title: Dataset: Broadbalk Crop Nutrient Content, Wheat 1968-2017

description: From 1968 Broadbalk was divided into 10 sections. Wheat grain and straw from selected sections and plots were collected each year and analysed for macronutrient content: Nitrogen (N) each year, phosphorus (P), potassium (K), calcium (Ca), magnesium (Mg) and sodium (Na) all years except 1976-1985 and sulphur (S) from 1996. Data is presented as % nutrient in grain and straw and is the response to different fertiliser treatments and cropping. The sample preparation, digestion methods and analytical instruments changed with time, but results over time are generally comparable. 

Text updated February 2025.
description: **Sample preparation:** 
Crops are oven-dried to 80 degrees C. Grain samples are ground to &lt;0.5mm, originally with a TEMA DISC mill, and later in the 1990s with an Ultracentrifugal mill (Retsch). Straw samples are ground to &lt;1-mm using a Christy and Norris 8 inch Hammer Mill.

**Nitrogen (N)**
- 1968-1995: extraction by Kjeldahl digest, the digest analysed colorimetrically using a Technicon segmented flow analyser. If nitrate-N was expected to be high in the sample, the salicylic acid modification was used (Bremner, 1965).
- 1996 onwards: nitrogen content is determined by combustion analyser, based on the Dumas method. Originally a Heraeus Combustion analyser, currently a LECO combustion system is used.

**Phosphorus (P), Potassium (K), Calcium (Ca), Magnesium (Mg), Sodium (Na) and Sulphur (S)**
- 1968-late 1980s: dry ashing, as described by Piper (1942) was used to produce an acid extract. The extracts were analysed for P colorimetrically on a Technicon Auto Analyser, or later equivalents (Alpkem continuous flow system / Skalar SanPlus segmented flow system), using the modified Murphy & Riley (1962) molybdenum blue method developed from Fogg & Wilkinson (1958). K, Ca, Mg and Na were determined using atomic absorption methods. A Pye Unicam SP90 and later Perkin Elmer 372 atomic absorption spectrophotometer (AAS) was used to analyse Ca, Mg and Na; K was analysed by an EEL flame photometer until 1973, K was then analysed with Ca, Mg and Na by the AAS. S was not routinely measured until 1996.
- Late 1980s onwards: open tube nitric-perchloric digestion (Zarcinas, et al, 1987) has been used to produce an acid extract. P, K, Ca, Mg and Na have been determined by ICP-OES (Inductively coupled plasma optical emission Spectrometer) since 1982, and S since 1996. 

See <i>Additional Information</i> for references for analytical techniques. **For further information about comparison of methods, refer to the e-RA curators**.
description: - Broadbalk wheat grain and straw nutrient data, 1968-2017 - data file.
- Table of which years and which sections nutrient data is available for; includes cultivars, for grain - pdf.
- Table of which years and which sections nutrient data is available for; includes cultivars, for straw - pdf.
description: Blank (control) values: Data for sodium is presented after the analysis blanks (controls) have been subtracted from the raw data. Sodium blank values tend to be relatively large, and can be greater than the raw data. If subtracting the blank resulted in a negative value, this is shown as zero. **Thus the sodium data should be treated with some caution**. Blank (control) readings for the other nutrients are very small, relative to the treatment values, and have not been subtracted. 

Grain and straw samples were not taken from all Sections. Section 1 and the 1st wheat (Sections 2-5 and 7) were sampled every year, and some other sections in later years. Straw was not always available in the same years that grain was measured.
description: This dataset is derived from measurements made by the Analytical Chemistry Unit, Rothamsted Research, Harpenden. The Analytical Chemistry Unit follows the Joint Code of Practice (JCoPR) and participates in European Quality Assurance programmes. All performance is strictly monitored using certified external standards alongside in-house standard materials. Standards and check samples are monitored and recorded. When there were changes to analytical methods and equipment, results were carefully compared using standard samples, to ensure that results over time are as comparable as possible. For analytical techniques see the following references:

- Bremner, J. M. (1965). Total nitrogen. In Methods of Soil Analysis. Part 2 (Ed. C. A. Black), pp. 1149-1178. Madison. American Society of Agronomy.
- Fogg, D.N. and Wilkinson, N.T. (1958). The colorimetric determination of phosphorus. Analyst, London, 83:406-414.
- Murphy, J. and Riley, J.P. (1962) A Modified Single Solution Method for the Determination of Phosphate in Natural Waters. Analytica Chimica Acta, 27, 31-36. http://dx.doi.org/10.1016/S0003-2670(00)88444-5
- Piper, C.S. (1942) Soil and plant analysis. The University of Adelaide, Adelaide, Australia.
- Zarcinas, B.A., Cartwright, B., Spouncer, L.R., 1987. Nitric acid digestion and multi-element analysis of plant material by inductively coupled plasma spectrometry. Communications in Soil Science and Plant Analysis 18, 131-146. 
- Zhao, F., McGrath, S.P. and Crosland, A.R. (1994) Comparison of three wet digestion methods for the determination of plant sulphur by inductively coupled plasma atomic emission spectroscopy (ICP-AES). Communications in Soil Science and Plant Analysis 25, 407-418. https://doi.org/10.1080/00103629409369047