THE RELATION BETWEEN COST AND UTILITY IN SOIL SURVEY (I–III)1

A series of five papers compares the cost-effectiveness of different procedures for soil survey at medium scale. The first three are presented here. The whole trial area of 120 km² in Berkshire, in south-central England, was mapped in soil series by free survey at 1:25 000 for publication at 1:63 360. Three contrasting sample areas of 1.26 km² were resurveyed to the same legend by free survey at 1:10 560, and by grid survey at a range of scales between 1:20 000 and 1:70 000, to both general purpose (soil series) and fifteen–twenty different single-property legends. The direct costs of producing each map were recorded. The study confirmed how much the free survey procedure depended on the external features of soil boundaries to locate them. The density of soil observations required to map soil series by free survey at the same map scale in different terrains was approximately proportional to the length of mapped boundary/km², or to the number of separately mapped soil occurrences/km². The density was least where the soil boundaries had the clearest external expression. Survey effort/km² increased in proportion to the density of observations but was also affected by local differences in the ease of cross-country access, or in the effort necessary (by spade or auger) to identify the soil at a point. For soil series grid surveys there are approximately linear relations between log(cost) and log(map scale) with gradients between 1.3 and 1.7. A map of soil series by grid survey is more expensive than a map of the same units, based upon the same density of observations by the same surveyor, by free survey. But a series map by grid survey by a scientific assistant is cheaper than a series map based on the same density of soil observations by free survey by a scientific officer (diplomate or graduate). The cost of an isoline map of a single soil property depends very much upon the cost of determining the property mapped, and to some extent upon the number of different isoline maps produced from a single set of samples or observations. Even at the unusually low costs of chemical analyses assumed here, an isoline map of one chemical property costs nearly twice as much as a series map by grid survey.     

The influence of organic nitrogen mineralization on the management of agricultural systems in the UK

Abstract. The understanding of nitrogen mineralization is central to providing good advice to ensure that nitrogen (N), from whatever source, is utilized by crops as efficiently as possible to minimize pollution. We have reviewed how mineralization is accounted for in current advice. It is clear that there is at least a qualitative understanding of the effects of soil and crop management on N mineralization and N supply, which has enabled the development of Codes of Good Agricultural Practice and fertilizer recommendations systems, based on sound scientific principles. However, to refine advice there is a need for a better quantitative understanding. Although soil organic matter (SOM) is a major source of N for crops, we are unable adequately to predict fertilizer requirement as affected by mineralization of SOM. Nitrogen returns from crop residues can vary considerably between fields; the provision of better field specific advice is restricted by our inability accurately to quantify this variability. The qualitative controls on the amount and timing of N release from ploughed grass are known, but better quantification of mineralization/immobilization over both the short- and long-term and better understanding of the relationship with sward age, inputs and management are essential. Much N can also be released from pasture and lost to the environment, especially where long-term leys have been grazed and there is a need to quantify the changing balance of mineralization and immobilization with the age of sward and N input. Whilst the overall principle of cultivation affecting mineralization is well known and appreciated, little is known about the mechanisms and quantification is only possible for a comparison of such extremes as ploughing and direct drilling.     

Soil aluminium availability in Andisols of southern Chile and its effect on forage production and animal metabolism

Soil acidification limits livestock production in many parts of the world. Two experiments were carried out to investigate the effect of aluminium (Al) on pasture yield and animal production. In experiment 1, the effect of raising soil pH (in water) from 5.1 (acid soil, A) to 5.6 (corrected soil, C) was tested on forage and animal production. In experiment 2, Friesian calves were individually fed either silage with or without the addition of 2000 mg kg^?1 of Al as aluminium sulphate. Al, P, Ca and Mg concentrations were measured in forage, and in animal blood and faeces. Live weight gain (LWG) was also measured. Soil acidification resulted in a 36% overall reduction in pasture yield in the A treatment (9.4 ± 0.31 and 14.7 ± 0.47 t ha^?1 year^?1 for the A and C treatments respectively) and in 15% reduction of the protein concentration in the herbage. No significant differences were found for the individual daily LWG (P > 0.05). Direct Al intake reduced animals daily LWG by 14% (P ≤ 0.05). The correction of soil acidification increased livestock production by 125% when stocking rate was strictly adjusted to grassland production.     

The influence of mountain pine beetle outbreaks and drought on severe wildfires in northwestern Colorado and southern Wyoming: A look at the past century

Outbreaks of bark beetles and drought both lead to concerns about increased fire risk, but the relative importance of these two factors is the subject of much debate. We examined how mountain pine beetle (MPB) outbreaks and drought have contributed to the fire regime of lodgepole pine forests in northwestern Colorado and adjacent areas of southern Wyoming over the past century. We used dendroecological methods to reconstruct the pre-fire history of MPB outbreaks in twenty lodgepole pine stands that had burned between 1939 and 2006 and in 20 nearby lodgepole pine stands that were otherwise similar but that had not burned. Our data represent c. 80% of all large fires that had occurred in lodgepole pine forests in this study area over the past century. We also compared Palmer Drought Severity Index (PDSI) and actual evapotranspiration (AET) values between fire years and non-fire years. Burned stands were no more likely to have been affected by outbreak prior to fires than were nearby unburned stands. However, PDSI and AET values were both lower during fire years than during non-fire years. This work indicates that climate has been more important than outbreaks to the fire regime of lodgepole pine forests in this region over the past century. Indeed, we found no detectable increase in the occurrence of high-severity fires following MPB outbreaks. Dry conditions, rather than changes in fuels associated with outbreaks, appear to be most limiting to the occurrence of severe fires in these forests.     

Modelling of rainfall interception loss in agroforestry systems

Two models of interception loss have been tested against new field data obtained in widely-spaced stands of Sitka spruce trees. The Gash model and a modified version of the Rutter model, have been used with data from an automatic weather station, to predict interception loss using parameters obtained from observations made in 1988 and 1989. The predictions for an eight-week period during 1987 were compared with measurements of interception loss. Good agreement between observed and predicted interception loss was obtained with both models over the whole period. The modified Rutter model gave better predictions than the Gash model for individual storm events and performed better at the wider spacings. The sensitivity of both models to the major characteristics of the tree stand structure in agroforestry systems was also investigated and it was shown that interception loss was most sensitive to boundary layer conductance and free throughfall coefficient.     

Calibration of Beta gauges for determining leaf water status

The recent development of beta gauges for the indirect determination of the water status of plants has had a widespread impact on plant ecological-physiological research. Calibration of these instruments has, however, been tedious and cumbersome, involving repeated simultaneous measurements of beta absorption and leaf water content. This procedure can be much simplified, as long as the beta absorption at a single known relative water content is measured, together with the turgid and dry weights of a sample of leaf discs.