Papers by Johanna Wetterlind
Agronomy for Sustainable Development
Soil organic matter (SOM) is important in maintaining soil fertility and other ecosystem function... more Soil organic matter (SOM) is important in maintaining soil fertility and other ecosystem functions. Yet, land management in intensive agriculture has caused SOM level to decrease, with knock-on effects for soil fertility and quality. Therefore, land management options that ensure that SOM is not depleted and that soil functions are better sustained are of increasing interest. However, there is limited knowledge on how different land managements affect the composition of SOM and associated microbial functional profiles. Twelve long-term field experiments, covering a wide range of climatic zones and soil types, were selected in Sweden. They focused on the role of combining ley in crop rotations with the manure application (livestock farm), as opposed to the management without ley and receiving only inorganic fertilizer (arable farm). In ten out of the 12 study sites, livestock farm management tended to have higher proportions of aliphatic and double bonded C groups, as estimated by mi...
HAL (Le Centre pour la Communication Scientifique Directe), Jul 31, 2022
Remote Sensing
There is a need to update soil maps and monitor soil organic carbon (SOC) in the upper horizons o... more There is a need to update soil maps and monitor soil organic carbon (SOC) in the upper horizons or plough layer for enabling decision support and land management, while complying with several policies, especially those favoring soil carbon storage. This review paper is dedicated to the satellite-based spectral approaches for SOC assessment that have been achieved from several satellite sensors, study scales and geographical contexts in the past decade. Most approaches relying on pure spectral models have been carried out since 2019 and have dealt with temperate croplands in Europe, China and North America at the scale of small regions, of some hundreds of km2: dry combustion and wet oxidation were the analytical determination methods used for 50% and 35% of the satellite-derived SOC studies, for which measured topsoil SOC contents mainly referred to mineral soils, typically cambisols and luvisols and to a lesser extent, regosols, leptosols, stagnosols and chernozems, with annual cro...
Sensing Approaches for Precision Agriculture
International Fertiliser Society (IFS), Dec 1, 2015
Denna rapport bygger på resultat från projektet Transport pathways for pesticides to surface wate... more Denna rapport bygger på resultat från projektet Transport pathways for pesticides to surface water (SLFH1133108) vilket finansierades av Stiftelsen Lantbruksforskning. Målet med denna del av projektet var att ta fram detaljerade, digitala markkartor på textur (sand-och lerhalt) och mullhalt som skulle kunna användas för spatial modellering av läckage av olika typer av pesticider. Rapporten är på engelska med en svensk sammanfattning.
International Journal of Agricultural Sustainability, 2021
Rainfall variability is becoming more profound in East Africa. Smallholders relying on rainfed ag... more Rainfall variability is becoming more profound in East Africa. Smallholders relying on rainfed agriculture are particularly affected and need to adapt their farming systems accordingly. This study examined the measures small-scale farmers use to adapt to, or cope with rainfall variability and their rated perceived effectiveness. It also explored limitations to adoption of measures and sources of learning measures. Questionnairebased interviews were held with 80 smallholder farmers, both female and male, living in Kisumu and Trans Nzoia counties in Kenya who had regular or sporadic access to advisory services (denoted trained and non-trained farmers). Trained farmers used more adaptation measures, especially of the measures perceived to be more effective, than non-trained farmers. Female farmers felt more limited by lack of knowledge than male farmers, while money, land and labour limited the smallholder farmers equally. Few measures were used to overcome limitations, but several limitations were covered within the advisory package used for trained farmers, and therefore large differences were seen not only in numbers of measures used, but also in the choice of measures and perceived effectiveness of use. Thus advisory services and policy interventions can play important roles in future efforts to improve adoption of measures.
Precision Agriculture, 2021
Precision agriculture (PA) has a huge potential for growth in sub-Saharan Africa (SSA), but it fa... more Precision agriculture (PA) has a huge potential for growth in sub-Saharan Africa (SSA), but it faces a number of social-economic and technological challenges. This study sought to map existing PA research and application in SSA countries following the methodology for systematic mapping in environmental sciences. After screening for relevance, the initial about 7715 articles was reduced to 128. Results show that most of the studies were conducted in countries with socio-economic and technological advancement, mainly South Africa followed by Nigeria and Kenya. The studies were conducted at various scales ranging from field to country level with field scale studies being the most common. Most studies were conducted in relatively small farms typical of most farmlands in SSA. Studies done in relatively large farms are fewer, and such farms would likely belong to a few organisations and individuals with high economic capacity. Many of these studies have been conducted by researchers from ...
Precision Agriculture, 2021
The article "Precision agriculture research in sub-Saharan Africa countries: a systematic map", w... more The article "Precision agriculture research in sub-Saharan Africa countries: a systematic map", written by "Justine M. Nyaga, Cecilia M. Onyango, Johanna Wetterlind, Mats Söderström" was originally published electronically on the publisher's internet portal on 15 Janu
Effective agricultural planning requires basic soil information. In recent decades near-infrared ... more Effective agricultural planning requires basic soil information. In recent decades near-infrared diffuse reflectance spectroscopy (NIRS) has been shown to be a viable alternative for rapidly analyzing soil properties. We studied 7171 samples of the soil Brazilian spectral library. The aim was to explore the possibility of enhancing the performance of NIRS data in predicting organic matter and clay content in this library by dividing it into smaller sub-libraries based on their vis-NIR spectra and to compare these results to two nonlinear calibration techniques (BT and SVM) applied to the whole library. The general predictive models for clay performed well (R 2 > 0.79), reflecting the influence of the direct spectral responses of this property in the NIRS range. Predictions of OM were reasonably good, especially with clustering, and in view of the very low variation in this parameter. Results showed that the division of the large library into smaller subsets based on the variation...
Agricultural Systems, 2020
Human beings are dependent on ecosystems and the services they provide. Some services are current... more Human beings are dependent on ecosystems and the services they provide. Some services are currently being overexploited, resulting in degradation and further pressure on already vulnerable people in e.g., sub-Saharan Africa. Long-term and stable delivery of ecosystem services (ES) is suggested to be enhanced by more diversified farming systems that e.g., mix crops with trees and livestock. Despite the amount of research on ES, few previous studies have identified and compared the roles of trees and livestock for ES considering farm priorities within smallholder systems. We studied the role of trees and livestock for ES provision as well as farm priorities for smallholders in Kenya. Twenty smallholder farms (0.2-0.8 ha) were studied for 1 year in a fully factorial design of high or low tree and livestock density systems. Data were collected on indicators for provisioning (crop, tree and livestock production), supporting/regulating (water infiltration, soil organic carbon and nutrients) and cultural (recreation and aesthetics) ESs. In addition, farm priorities were studied, considering nutrient management, on-and off-farm resources, food and consumption, and crop, tree and livestock species diversity. A mix of qualitative (e.g., semi-structured interviews, seasonal calendar) and quantitative (e.g., soil analyses, infiltration tests) methods were used to collect data. This study confirmed roles of trees and livestock for ES and farm priorities, although they in some cases appeared less important than family labour and farm size. Results showed that high tree density was related to higher workload, lower proportions of off-farm revenue as well as higher crop, fruit and tree diversity for the household. Tree or livestock density showed no clear relation to provisioning, supporting or regulating ES. However, cultural services were on average provided more by trees than livestock. Available family labour was positively related to both farm production (provisioning services) and crop, tree and livestock species diversity. The use of manure, compost and mineral fertilisers was overall low, and the application rate per unit area seemed higher on farms with less land which was reflected in higher soil P and Ca concentrations. The challenges of already small and reducing farm sizes need to be targeted seriously in research and development efforts. Also the issue of labour requirement and pathways for mechanization must be addressed to attract a new generation farmers to develop sustainable and profitable farm enterprises providing ES to the farm and the surrounding landscape.
Land, 2020
With growing global demand for food, unsustainable farming practices and large greenhouse gas emi... more With growing global demand for food, unsustainable farming practices and large greenhouse gas emissions, farming systems need to sequester more carbon than they emit, while also increasing productivity and food production. The Kenya Agricultural Carbon Project (KACP) recruited farmer groups committed to more Sustainable Agricultural Land Management (SALM) practices and provided these groups with initial advisory services on SALM, farm enterprise development and village savings and loan associations. Recommended SALM practices included agroforestry, cover crops, mulching, composting manure, terracing, reduced tillage and water harvesting. The effects of the KACP on the uptake of SALM practices, maize yield, perceived food self-sufficiency and savings during the initial four years were assessed comparing control and project farmers using interviews, field visits and measurements. Farmers participating in the KACP seemed to have increased uptake of most SALM practices and decreased the...
Geoderma, 2021
The relative importance of various soil mineral constituents (e.g. clay-sized particles, aluminum... more The relative importance of various soil mineral constituents (e.g. clay-sized particles, aluminum-and ironbearing mineral reactive phases) in protecting soil organic carbon (SOC) from decomposition is not yet fully understood in arable soils formed from quaternary deposits in humid continental climates. In this study, we investigated the relationships between soil physico-chemical properties (i.e. contents of oxalate-extractable aluminum (Alox) and iron (Feox) and clay size particle < 2 µm), grain yield (as a proxy for carbon input) and total SOC as well as SOC in different soil fractions for samples taken from the topsoil of an arable field at Bjertorp in southwest Sweden. We found a positive correlation between Alox and total SOC content, where Alox explained ca. 48% of the spatial variation in SOC. We also found that ca. 80% of SOC was stored in silt-and claysized (SC) fractions, where Al-bearing reactive mineral phases (estimated by Alox) may be important for organicmineral associations and clay aggregation. Our results were supported by data collated from the literature for arable topsoil in similar climates, which also showed positive correlations between SOC and Alox contents (R 2 = 23.1-74.5%). Multiple linear regression showed that including spatially-variable crop yields as a proxy for carbon inputs improved the prediction of SOC variation across the Bjertorp field. Other unquantified soil properties such as exchangeable calcium may account for the remaining unexplained variation in topsoil SOC. We conclude that Al-bearing reactive mineral phases are more important than clay content and Fe-bearing reactive mineral phases for SOC stabilization in arable topsoil in humid continental climates.
Soil Use and Management, 2021
A systematic map is a summary of a research area based on systematic searches, screening and codi... more A systematic map is a summary of a research area based on systematic searches, screening and coding of scientific literature (James et al., 2016). It aims to give an overview of a subject area and identify trends, knowledge gaps and knowledge clusters in scientific reporting. In contrast to a systematic review, the aim is not to answer specific close-framed questions, but rather to describe the state of knowledge in the subject, in order to guide future research. Periodic reviewing of research areas can be a healthy exercise in order to discover trends in practices-good or bad-and guide future research, so that good trends can be continued, bad habits can be broken, and practice gaps can be filled. It also enables discussion on the implications of current practices for stakeholders such as policymakers and practitioners.
Sustainability, 2021
Opportunities exist for adoption of precision agriculture technologies in all parts of the world.... more Opportunities exist for adoption of precision agriculture technologies in all parts of the world. The form of precision agriculture may vary from region to region depending on technologies available, knowledge levels and mindsets. The current review examined research articles in the English language on precision agriculture practices for increased productivity among smallholder farmers in Sub-Saharan Africa. A total of 7715 articles were retrieved and after screening 128 were reviewed. The results indicate that a number of precision agriculture technologies have been tested under SSA conditions and show promising results. The most promising precision agriculture technologies identified were the use of soil and plant sensors for nutrient and water management, as well as use of satellite imagery, GIS and crop-soil simulation models for site-specific management. These technologies have been shown to be crucial in attainment of appropriate management strategies in terms of efficiency an...
Agroecology and Sustainable Food Systems, 2020
Farmers in Kisumu and Trans Nzoia counties, Kenya, were aware of more adaptation than coping meas... more Farmers in Kisumu and Trans Nzoia counties, Kenya, were aware of more adaptation than coping measures for dealing with rainfall variability both on and off-farm. Interviews with female and male farmer groups revealed that they all experienced challenges related to increasing rainfall variability whether or not they had regular access to advisory services. Men identified more measures than women and had better access to learning sources. Farmers in Kisumu were aware of more measures than those in Trans Nzoia but thought them less effective. Money, knowledge and labor were the most limiting factors preventing the uptake of adaptation measures.
Sensors, 2016
Four proximal soil sensors were tested at four smallholder farms in Embu County, Kenya: a portabl... more Four proximal soil sensors were tested at four smallholder farms in Embu County, Kenya: a portable X-ray fluorescence sensor (PXRF), a mobile phone application for soil color determination by photography, a dual-depth electromagnetic induction (EMI) sensor, and a LED-based soil optical reflectance sensor. Measurements were made at 32-43 locations at each site. Topsoil samples were analyzed for plant-available nutrients (N, P, K, Mg, Ca, S, B, Mn, Zn, Cu, and Fe), pH, total nitrogen (TN) and total carbon (TC), soil texture, cation exchange capacity (CEC), and exchangeable aluminum (Al). Multivariate prediction models of each of the lab-analyzed soil properties were parameterized for 576 sensor-variable combinations. Prediction models for K, N, Ca and S, B, Zn, Mn, Fe, TC, Al, and CEC met the setup criteria for functional, robust, and accurate models. The PXRF sensor was the sensor most often included in successful models. We concluded that the combination of a PXRF and a portable soil reflectance sensor is a promising combination of handheld soil sensors for the development of in situ soil assessments as a field-based alternative or complement to laboratory measurements.
First Conference on Proximal Sensing Supporting Precision Agriculture, 2015
Remote and proximal sensors allow for the collection of data at a high resolution and to low cost... more Remote and proximal sensors allow for the collection of data at a high resolution and to low costs, but for the approach to be cost-effective the number of calibration samples needs to be kept low. On the other hand, too few calibration samples can lead to unstable calibration models. In a small study on three adjacent fields (55 ha) at a farm in southwest Sweden, in-situ vis-NIR spectroscopy was used to increase the number of calibration samples used in a multiple adaptive regression spline (MARS) model for mapping clay and sand content. The present study did not find support for an improvement of MARS models when the number of calibration samples was increased from 20 to 100 by vis-NIR predictions of the 80 extra samples. This was probably because the 20 soil samples carried enough information to calibrate the exhaustive predictor data to sand and clay and all the extra samples did was only introduced noise. There were some indications of more stable models when the number of reference samples was reduced to 10 or when the best single predictor was excluded. In this study the number of calibration samples seemed to be less critical than their accuracy.
Soil and Tillage Research, 2016
Abstract Near infrared (NIR) spectroscopy was used to predict the soil organic carbon (SOC) conte... more Abstract Near infrared (NIR) spectroscopy was used to predict the soil organic carbon (SOC) contents at local scale in eleven target sites. For that, eight spectral libraries of different sizes (ranging from 3482 to 36 samples) were used to construct national, provincial and local scale models. Inaccurate predictions were obtained except when the largest national library was used to construct the model. We also obtained SOC predictions once the models were adapted to target sites characteristics. For the models’ adaptation, we used a two-step approach consisting on spiking (as first step) and extra-weighting (as second step). The effect of spiking was small in larger-sized models and high in smaller-sized models, whereas the effect of extra-weighting was small in smaller-sized models and large in larger-sized models. The very high accuracy obtained after models’ adaptation (R2 > 0.95; RPIQ > 5.48), regardless of the size of the spectral library, suggests that large spectral libraries are not needed for local scale SOC assessment. These results have important implications regarding the way that NIR spectroscopy can result highly effective for land management and how users can focus and organize the analytical efforts.
Advances in Agronomy, 2015
ABSTRACT The soil science community is facing a growing demand of regional, continental, and worl... more ABSTRACT The soil science community is facing a growing demand of regional, continental, and worldwide databases in order to monitor the status of the soil. However, the availability of such data is very scarce. Cost-effective tools to measure soil properties for large areas (e.g., Europe) are required. Soil spectroscopy has shown to be a fast, cost-effective, environmental-friendly, nondestructive, reproducible, and repeatable analytical technique. The main aim of this paper is to describe the state of the art of soil spectroscopy as well as its potential to facilitating soil monitoring. The factors constraining the application of soil spectroscopy as an alternative to traditional laboratory analyses, together with the limits of the technique, are addressed. The paper also highlights that the widespread use of spectroscopy to monitor the status of the soil should be encouraged by (1) the creation of a standard for the collection of laboratory soil spectra, to promote the sharing of spectral libraries, and (2) the scanning of existing soil archives, reducing the need for costly sampling campaigns. Finally, routine soil analysis using soil spectroscopy would be beneficial for the end users by a reduction in analytical costs, and an increased comparability of results between laboratories. This ambitious project will materialize only through (1) the establishment of local and regional partnerships among existent institutions able to generate the necessary technical competence, and (2) the support of international organizations. The Food and Agriculture Organization (FAO) of United Nations and the Joint Research Centre of the European Commission are well placed to promote the use of laboratory and field spectrometers for monitoring the state of soils.
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Papers by Johanna Wetterlind