|Luuk Fleskens, Coen Ritsema, Zhanguo Bai, Violette Geissen, Jorge Mendes de Jesus, Vera da Silva, Aleid Teeuwen, Xiaomei Yang
|Fleskens, L et al. (2020) Tested and validated final version of SQAPP. iSQAPER Project Deliverable 4.2, 143 pp
SQAPP was designed with the idea that it should provide the user with the opportunity to access fragmented data on soil quality and soil threats in an easy-to-use way. Moreover, the user should not only receive indicator values, but be guided in interpreting these values by providing more contextual information: is a certain indicator value high or low in a given context? Such contextual information is provided through analysing indicators within combinations of climate zones and soil types, and by distinguishing between arable land and grazing land. Finally, the user should receive, based on an assessment of the most critical issues, management recommendations on how soil quality can be improved and soil threats be overcome.
A second consideration in designing SQAPP was the idea to use soil quality and soil threat indicators for which spatial data exist. This way, it is possible to provide the user with data for any indicator for which data exist for a given location, in combination with the comparative contextual information. The comparative aspect of the soil indicator data is then realized by calculating cumulative probability density functions for each pedo-climatic zone. All indicator values are given as ‘best guestimate’ for the location. The user can proceed with generating management recommendations based on these standard values, or replace some or all indicator values with own data to get more accurate recommendations. This design helps to make the SQAPP directly helpful by visualizing available soil information in a systematic and easy-to-access way.
Thirdly, the SQAPP recommends agricultural management practices to improve soil quality and/or mitigate soil threats based on an integrated assessment of the aspects most urgently needing attention. This integrated way of considering soil quality indicators is new in comparison to existing soil apps and indicator systems. This integration avoids consideration of poor single indicator scores in isolation, which could have trade-offs with other soil quality indicators that are also suboptimal.
Fourthly, although the iSQAPER project focuses on Europe and China, it quickly became clear that the amount of work required to develop SQAPP would be more appropriately justified by building an app with global coverage. This inclination to go global was reinforced by some hurdles experienced along the way to harmonise European and Chinese data (see below). As a consequence, the app was designed with global functionality in mind. The overall procedure to develop SQAPP is given in Figure 12.
These steps include:
- Selecting soil quality indicators; based on the review of soil quality indicators in »Soil quality - a critical review, a selection of the most commonly used was made. For these indicators, we examined availability in terms of global datasets. All relevant indicators for which maps existed were retained as input data layers. Similarly, maps of soil threats were reviewed. Here, available global datasets were used; in Europe some further soil threats were included based on soil threat maps with European coverage.
- Defining pedo-climatic zones; as one of the principles underpinning SQAPP is a relative assessment of soil indicators, appropriate zones with similar conditions need to be defined. Within iSQAPER pedo-climatic zones were developed for both Europe and China (»Pedo-climatic zones of Europe and »Pedo-climatic zones of China). As the basic climate zones distinguished in these classifications were not comparable and because there were some conversion issues to reclassify Chinese soil types to WRB (World Reference Base) soil types, the resulting pedo-climatic zones in Europe and China were not directly comparable, and moreover, did not cover other areas of the world. This became an issue for calculating relative soil indicator scores at global level. To resolve this issue, a new pedo-climatic zonation was produced for the purpose of calculating consistent data layers for the app.
»Defining pedo-climatic zones
- Ranging soil quality indicators; once indicators are selected and pedo-climatic zones are defined, it is possible to calculate cumulative probability density functions for each indicator in each pedo-climatic zone. These cumulative probability density functions become the basis for the relative assessment of soil quality. Moreover, within each pedo-climatic zone, attention also needs to be paid to the land use/cover, as land use is known to greatly influence the indicator scores of several soil indicators. To account for this issue, separate calculations are made for the minimum and maximum scores of each indicator in each pedo-climatic zone, specific for arable and grazing land respectively.
»Ranging soil quality indicators
- Scoring indicators; the relative scores of soil property values are considered based on their position on the cumulative probability density curves. That means (considering whether indicators are of the ‘more is better’ or ‘more is worse’ type), that the bottom 33% of the frequency distribution are considered as low, and the top 33% as high, with medium the outcome for intermediate values. For soil threats, absolute, expert-based values were considered based on the work conducted in »Calculating the soil quality index in SQAPP.
»Scoring soil quality indicators
- Assessing indicators; this step concerns the calculation of the potential for soil improvement (percent score) across all soil property indicators, and the calculation of the average soil threat level (on a bar slider between low and high). All poor performing soil property indicators and soil threats are considered as urgent aspects to be addressed.
- Recommended practices; the final step in the SQAPP is to recommend agricultural management practices based on the overall soil quality score and most urgent soil quality aspects to be addressed. Underlying the recommendations is the development of a large matrix table of the agricultural management practices and a) applicability factors – defining where each of the AMPs is applicable; and b) effectiveness – where the impact on soil property and soil threat indicators of each AMP are scored. The 10 AMPs reaching the highest overall score for the combination of soil properties and soil threats to be addressed in a given location are presented to the app user.
Practical considerations: The pilot app was developed for mobile phones/notepads operating under either Apple iOS or Android. These two platforms together cover >97% of smartphones. For geolocation, Bing maps was used as Google products are banned from use in China.