Regional trends in Scottish advisory soil acidity and phosphorus results: significance of management history, land use and soil attributes

Abstract

Four geographically distinct regions of Scotland are used to describe temporal and spatial trends in soil phosphorus (P) using ca. 180 000 routine advisory samples which included information on previous and next crop. Regional differences in Modified Morgan's extractable P concentrations exist primarily in response to differences in land use and particularly the greater role of livestock in the west compared to arable cropping in the east. No obvious or consistent temporal trend in extractable P was apparent, but a very wide range of soil properties and extractable P concentrations was evident. The current (since 2010) target soil P status is moderate (M) for cereal-based arable rotations and the upper half of moderate (M+) for rotations with potatoes, and more than half the samples fell into this range (with 40% MÀ). Some ca. 30% of samples fell below this, while 14% had high or very high P status, most noticeably where the previous crop was either potatoes, vegetables or berries. Half (ca. 13 000) of the samples with a low soil P status also had a below optimum pH. An apparent contradiction between the regularly reported long-term declines in agricultural P surplus not being matched by a drop in extractable soil P status is discussed. This 'lag effect' means many Scottish agricultural soils have the capability to buffer change in extractable soil P. We make the first attempt to link advisory P data with information from the National Soil Database of Scotland and explore the value of introducing 'soil type' into the P fertilizer recommendation system.

Changes in the carbon concentrations and other soil properties of some Scottish agricultural soils: Evidence from a resampling campaign

“…By 1980, the pH more closely reflected the optimum target value of 6.2 for arable land and 6.0 for grassland. This provides the background and legacy of soil fertility against which current fertilizer recommendations continue to be developed (Crooks, Sinclair, Edwards, & Coull, ; Edwards et al., ) where a greater balance between inputs and outputs resulting in improved nutrient use efficiency has resulted in a decline in extractable soil P. Over this same time period, no significant change in loss on ignition was detected (Table and Figure ).…”

“…By 1980, the pH more closely reflected the optimum target value of 6.2 for arable land and 6.0 for grassland. This provides the background and legacy of soil fertility against which current fertilizer recommendations continue to be developed (Crooks, Sinclair, Edwards, & Coull, 2019;Edwards et al, 2016) where a greater balance between inputs and outputs resulting in improved nutrient use efficiency has resulted in a decline in extractable soil P. Over this same time period, no significant change in loss on ignition was detected (Table 1 and Figure 1). In 2017, 37 sites (Figure 2) were located when we were confident that we could identify the position of the original plots within a field from the hard copy paper records, descriptions of key landscape and farmscape features and successfully pair these with the original sample.…”

Soil health – What should the doctor order?

“…However, there is no universal method of measurement for pH. In England and Wales, pH is normally measured in a suspension of soil and water (Defra, ), whereas in Scotland a suspension of soil and 0.01 m CaCl 2 is used, and to compare results with values obtained in water 0.6 are added to the value obtained in CaCl 2 (Edwards et al ., ).…”

“…The principle of soil analysis linked to soil management practices is illustrated by the methodology used for managing soil P. This can be considered in terms of three steps: (i) measurement of the available P in soil, (ii) interpretation of the results of this measurement in terms of the sufficiency of P availability in soil for the crop(s) to be grown, (iii) estimation of a recommended application of P as inorganic or organic fertiliser (Jordan‐Meille et al ., ). Once again there is no universal method of measurement: in England, Wales and Northern Ireland the Olsen P method is used (Johnston et al ., ), whereas in Scotland the Modified Morgans method is used (Edwards et al ., ), largely because of differences in the levels of calcium ions in the soils that were derived from basic or acidic rocks. There is an even greater diversity in methods used across continental Europe (Jordan‐Meille et al ., ) prompting these authors to conclude that ‘…the chemical methods in common use and their utilization in global P fertilizer strategies have a poor theoretical background and are lacking any scientific rationale’.…”

The relationship between water‐soluble P and modified Morgan P: results based on data and chemical modelling.

“…For example, in 1953 the Irish soil testing service was testing 100 000 samples per year (Gallagher et al ., ), and changes in soil extractable P have been summarized from more than 5 million samples from the Netherlands (Reijneveld et al ., ). Likewise, the Scottish Agricultural College which has used the modified Morgan (MMP) method for advisory work since 1993 has an extensive database averaging about 9000 samples per year (Edwards et al ., ). In North America, the MMP method is also routinely used (Magdoff et al ., ).…”