Johannes Forkman

My position belongs to the Field Research Unit (SLU Fältforsk), which is a contact unit between SLU and external organizations. My office is at the Department of Crop Production Ecology. This gives me daily contact with researchers and graduate students at the department, but I also have a great deal of contact with researchers at other departments at SLU and with external organisations, for example the Swedish Board of Agriculture and the Swedish Rural Economy and Agricultural Societies. I give consultations, as long as the questions are about statistical methods for agricultural field experiments.

Many basic statistical methods, such as the analysis of variance, were originally developed for agricultural experiments. Although statistics for field experiments is a traditional area of statistics, new methods are developed constantly, and the subject is huge. It is part of my work to follow method development and to disseminate the new knowledge among researchers that carry out field experiments. I also conduct own research on statistics within this area.

I give the PhD course Statistics II: Analysis of Experiments using mixed-effects models. About once a year I give a short course in basic statistics, intended for people who work with agricultural field experiments.

Results from Swedish field experiments: crop variety evaluation trials, crop protection experiments, soil tillage experiments etc., are stored in a database. The Field Research Unit cooperates with Denmark and Norway concerning a common Scandinavian database: the Nordic Field Trial System (NFTS). This database provides statistical results. I am involved in the development of this database.

I am Director of Studies for Research Education at the Department of Crop Production Ecology and thus also Assistant Head of Department.

I have given the following courses:

• Statistics II: Experimental Design and ANOVA (4 hp) 2016-2022. PhD course. SLU.
• Grundläggande matematik och statistik för biologer (Basic mathematics and statistics for biologists), ST0059 (7,5 hp). 2018. Graduate level. SLU. I gave this course together with Linnéa Kjeldgård.
• Grundläggande statistik för biologer (Basic statistics for biologists), MS0052 (5 hp). 2016. Graduate level. SLU. I gave this course together with Prof. Dietrich von Rosen.
• Linear mixed models and experimental design (3 hp). 2014. PhD course. SLU.
• Statistical methods in agricultural field research (5 hp). 2011. PhD course. SLU.
• Experimental design (7,5 hp). 2010. Advanced level. Stockholm University.
• Experimentplanering (7,5 hp). 2010. Graduate level. Stockholms universitet.

I did my PhD on experimental design in non-linear regression and inference for the coefficient of variation. Nowadays, I do research on statistics for agricultural field experiments. I am especially interested in design and analysis of experiments, and linear mixed-effects models. As a consultant and supervisor, I am much involved in research on plant and soil science.

I studied statistics at Lund University and mathematics at Uppsala University. For twelve years I was employed as a statistician at the present Thermo Fisher Scientific in Uppsala. For shorter periods, I worked at Statisticon AB as consultant in statistics, and at Stockholm University as senior lecturer in statistics. I got my PhD in biometry with specialization in statistics/mathematical statistics at the Department of Energy and Technology, SLU. Since 2011, I am a senior lecturer in statistics, and since 2014, I am docent in biometry.

I have been the main supervisor for two PhD students in biometry, as well as assistant supervisor for three PhD students in crop science and one PhD student in biology.

• Forkman, J., Malik, W. A., Hadasch, S., Piepho, H. P. (2024). Testing components of two-way interaction in multi-environment trials. Communications in Statistics - Theory and Methods 53, 1716–1735.
• Piepho, H. P., Forkman, J., Malik, W. A. (2024). A REML method for the evidence‐splitting model in network meta‐analysis. Research Synthesis Methods 15, 198–212.
• Al-Sarraj, R., Forkman J. (2023). Notes on correctness of p-values when analyzing experiments using SAS and R. PLoS ONE 18: e0295066.
• Torppa, K. A., Forkman, J., Maaroufi, N. I., Taylor, A. R., Vahter, T., Vasar, M., Weih, M., Öpik, M., Viketoft, M. (2023). Soil compaction effects on arbuscular mycorrhizal symbiosis in wheat depend on host plant variety. Plant and Soil 493, 55–571.
• Micke, B., Adler, S., Forkman, J., Parsons, D. (2023). Production and nutrient composition of forage legume fractions produced by juicing and leaf stripping. Acta Agriculturae Scandinavica, Section B — Soil & Plant Science 73, 199-212.
• Selin, A. K., Lilliehöök, I., Forkman, J., Larsson, A., Pelander, L.,  Strage, E. M. (2023). Biological variation of biochemical urine and serum analytes in healthy dogs. Veterinary Clinical Pathology 52, 461-474.
• Rodrigues-Motta, M., Forkman J. (2022). Bayesian analysis of nonnegative data using dependency-extended two-part models. Journal of Agricultural, Biological and Environmental Statistics  27, 201-221.
• Bergqvist, S., Bergkvist, G., Forkman, J., Parsons, D., Nilsdotter-Linde, N. (2022). Crop rotation effect on red clover persistence in mixed grass-clover leys. In: L. Delaby et al. (Ed.), Grassland at the heart of circular and sustainable food systems. Proceedings of the 29th General Meeting of the
  European Grassland Federation.
• Buntaran, H., Forkman, J., Piepho, H. P. (2021). Projecting results of zoned multi-environment trials to new locations using environmental covariates with random coefficient models: accuracy and precision. Theoretical and Applied Genetics 134, 1513-1530.
• Strage, E. M., Ley, C. J., Forkman, J., Öhlund, M., Stadig, S., Bergh, A., Ley, C. (2021). Homeostasis model assessment, serum insulin and their relation to body fats in cats. BMC Veterinary Research 17:34.
• Buntaran, H., Piepho, H. P., Schmidt, P., Rydén, J., Halling, M., Forkman, J. (2020). Cross‐validation of stage‐wise mixed‐model analysis of Swedish variety trials with winter wheat and spring barley. Crop Science 60, 2221-2240.
• Forkman, J., Josse, J., Piepho, H. P. (2019). Hypothesis tests for principal component analysis when variables are standardized. Journal of Agricultural, Biological, and Environmental Statistics 24, 289-308.
• Malik W. A., Forkman J., Piepho, H. P. (2019). Testing multiplicative terms in AMMI and GGE models for multienvironment trials with replicates. Theoretical and Applied Genetics 132, 2087-2096.
• Al-Sarraj, R., von Brömssen, C., Forkman, J. (2019). Generalized prediction intervals for treatment effects in random-effects models. Biometrical Journal 61, 1242-1257.
• Buntaran, H., Piepho, H. P., Hagman J., Forkman, J. (2019). A cross-validation of statistical models for zoned-based prediction in cultivar testing. Crop Science 59, 1544-1553.
• Muoni, T., Mhlanga, B., Forkman, J., Sitali, M., Thierfelder, C. (2019). Tillage and crop rotations enhance populations of earthworms, termites, dung beetles and centipedes: evidence from a long-term trial in Zambia. Journal of Agricultural Science 157, 504-514.
• Mossadeghi-Björklund, M., Jarvis, N., Larsbo, M., Forkman, J., Keller, T. (2019). Effects of compaction on soil hydraulic properties, penetration resistance and water flow patterns at the soil profile scale. Soil Use and Management 35, 367-377.
  
• Hadasch, S., Forkman, J., Malik W. A., Piepho, H. P. (2018). Weighted Estimation of AMMI and GGE Models. Journal of Agricultural, Biological and Environmental Statistics 23, 255-275.
• Damesa, T. M., Möhring, J., Forkman, J., Piepho, H. P. (2018). Modeling Spatially Correlated and Heteroscedastic Errors in Ethiopian Maize Trials. Crop Science 58, 1575-1586.
• Malik, W. A., Hadasch, S., Forkman, J., Piepho, H. P. (2018). Non-parametric resampling methods for testing multiplicative terms in AMMI and GGE models for multi-environment trials. Crop Science 58, 752-761.
• Edelfeldt, S., Lundkvist A., Forkman J., Verwijst, T. (2018). Effects of cutting traits and competition on performance and size hierarchy development over two cutting cycles in willow. Biomass and Bioenergy 198, 66-73.
• Buntaran, H., Piepho, H. P., Hagman, J., Forkman J. (2018). Performance of empirical BLUE and empirical BLUP in Swedish crop variety trials. Biuletyn Oceny Odmian 35, 15-17.
• Forkman, J. (2017). Generalized confidence intervals for intra- and inter-subject coefficients of variation in linear mixed-effects models. International Journal of Biostatistics 13 (2).
• Hadasch, S., Forkman, J., Piepho H. P. (2017). Cross validation in AMMI and GGE models: A comparison of methods. Crop Science 57, 264-274.
• Jarvis N., Forkman, J., Koestel, J., Kätterer, T., Larsbo, M., Taylor, A. (2017). Long-term effects of grass-clover leys on the structure of a silt loam soil in a cold climat. Agriculture, Ecosystems and Environment 247, 319-328.
• Forkman, J. (2016). A comparison of super-valid restricted and row-column randomization. Journal of Agricultural, Biological, and Environmental Statistics 21, 242–260.
• Forkman, J. (2016). How many trials are needed in crop variety testing? Communications in Biometry and Crop Science 11, 164–180.
• Martinez, I., Chervet, A., Weisskopf, P., Stury, W. G., Etana A., Stettler, M., Forkman, J., Keller, T. (2016). Two decades of no-till in the Oberacker long-term field experiment: Part I. Crop yield, soil organic carbon and nutrient distribution in the soil profile. Soil and Tillage Research 163, 141–151.
• Edelfeldt, S., Lundkvist, A., Forkman, J., Verwijst T. (2016). Establishment and Early Growth of Willow at Different Levels of Weed Competition and Nitrogen Fertilization. Bioenergy Research 9, 763–772.
• Anbari, S., Lundkvist, A., Forkman, J., Verwijst, T. (2016). Population dynamics and nitrogen allocation of Sonchus arvensis L. in relation to initial root size. Acta Agriculturae Scandinavica B – Soil and Plant Science 66, 75–84.
• Anbari, S., Lundkvist, A., Forkman, J., Verwijst, T. (2016). Effects of root fragmentation on generative reproduction of Sonchus arvensis. Acta Agriculturae Scandinavica B – Soil and Plant Science 66, 391–398.
• Linse, L., Dahlin, S., Nadeau, E., Forkman, J., Öborn, I. (2015). Boron fertilisation of organically managed grass-clover swards on coarse-textured soils: Effects on botanical and element composition. Agricultural and Food Science 24, 261–272.
• Forkman, J., Piepho, H. P. (2015). Robustness of the simple parametric bootstrap method for the additive main effects and multiplicative interaction (AMMI) model. Biuletyn Oceny Odmian 34, 11–18.
• Forkman, J. (2015). A resampling test for principal component analysis of genotype-by-environment interaction. Acta et Commentationes Universitatis Tartuensis de Mathematica 19, 27–33.
• Liew, J., Forkman, J. (2015). A guide to generalized additive models in crop science using SAS and R. Communications in Biometry and Crop Science 10, 41–57.
• Edelfeldt, S., Lundkvist, A., Forkman, J., Verwijst, T. (2015). Effects of cutting length, orientation and planting depth on early willow shoot establishment. Bioenergy Research 8, 796–806.
• Forkman J., Piepho, H. P. (2014). Parametric bootstrap methods for testing multiplicative terms in GGE and AMMI models. Biometrics 70, 639–647.
• Forkman J. (2013). The use of a reference variety for comparisons in incomplete series of crop variety trials. Journal of Applied Statistics 40, 2681–2698.
• Edelfeldt;S. Verwijst, T., Lundkvist, A., Forkman J. (2013). Effects of mechanical planting on establishment and early growth of willow. Biomass and Bioenergy 55, 234–242.
• Liew, J., Andersson, L., Boström, U., Forkman, J., Hakman, I., Magnuski, E. (2013). Regeneration capacity from buds on roots and rhizomes in five herbaceous perennials as affected by time of fragmentation. Plant Ecology 214, 1199–1209.
• Forkman, J., Piepho, H.-P. (2013). Performance of empirical BLUP and Bayesian prediction in small randomized complete block experiments. Journal of Agricultural Science 151, 381-395.
• Andersson, L., Boström, U., Forkman J., Hakman, I., Liew, J., Magnuski, E. (2013). Sprouting capacity from intact root systems of Cirsium arvense and Sonchus arvensis decrease in autumn. Weed Research 53, 183–191.
• Berisso, F. E., Schjønning, P., Keller, T., Lamande, M., Simojoki, A., Iversen, B. V., Alakukku, L., Forkman, J. (2013) Gas transport and subsoil pore characteristics: Anisotropy and long-term effects of compaction. Geoderma 195, 184–191.
• Boström, U., Andersson, L., Forkman, J., Hakman I., Liew, J., Magnuski, E. (2013). Seasonal variation in sprouting capacity from intact rhizome systems of three perennial weeds. Weed research 53, 387–398.
• Etana, A., Larsbo, M., Keller T., Arvidsson, J., Schjønning, P., Forkman J., Jarvis, N. (2013). Persistent subsoil compaction and its effects on preferential flow patterns in a loamy till soil. Geoderma 192, 430–436.
• Forkman, J., Amiri, S., von Rosen, D. (2012). Effect of region on the uncertainty in crop variety trial programs with a reduced number of trials. Euphytica 186, 489–500.
• Berisso, F. E., Schjønning, P., Keller, T., Lamandé, M., Etana, A., de Jonge, L. W., Iversen, B. V, Arvidsson, J., Forkman, J. (2012). Persistent effects of subsoil compaction on pore size distribution and gas transport in a loamy soil. Soil & Tillage Research 122, 42–51.
• Verwijst, T., Lundkvist, A., Edelfeldt, S., Forkman, J., Nordh, N.-E. (2012). Effects of clone and cutting traits on shoot emergence and early growth of willow. Biomass and Bioenergy 37, 257–264.
• Liew J., Andersson L, Boström U., Forkman J, Hakman I & Magnuski E (2012). Influence of temperature and photoperiod on sprouting capacity of Cirsium arvense and Sonchus arvensis root buds. Weed Research 52, 449–457.
• Forkman, J. (2011). Linear mixed models for series of variety trials. Biuletyn Oceny Odmian (Cultivar Testing Bulletin) 33, 63–72.
• Eckersten, H., Kornher, A., Bergkvist, G., Forkman, J., Sondhoj E., Torsell, B. and Nyman P. (2010). Crop yield trends in relation to temperature indices and a growth model. Climate Research 42, 119-131.
• Frankow-Lindberg, B. E., Halling, M., Höglind, M. and Forkman J. (2009). Yield and stability of yield of single- and multi-clover grass-clover swards in two contrasting temperate environments. Grass and Forage Science 64, 236-245.
• Riesinger, P., Eckersten, H., Torssell, B. and Forkman, J. (2009) Radiation use efficiency in leys: influences of growth period and clover proportion. Acta Agriculturae Scandinavica, Section B - Plant Soil Science 59, 465-474.
• Forkman, J. (2009). Estimator and tests for common coefficients of variation in normal distributions. Communications in Statistics – Theory and Methods 38, 233-251.
• Forkman, J. (2008). A method for designing nonlinear univariate calibration. Technometrics 50, 479-486.
• Forkman J., Verrill S. (2008). The distribution of McKay’s approximation for the coefficient of variation. Statistics & Probability Letters 78:10-14.
• Salmerón-Miranda F., Båth  B., Eckersten H., Forkman J. and Wivstad M. (2007). Aboveground nitrogen in relation to estimated total plant uptake in maize and bean. Nutrient cycling in agroecosystems 79:125-139.

Field Research Unit (SLU Fältforsk)

Department of Crop Production Ecology, SLU

Centre for Statistics at SLU (statistics@slu)