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Impacts of climate change on the potato (Solanum Tuberosum L.) productivity in Tasmania, Australia and Kenya

Borus, D 2017 , 'Impacts of climate change on the potato (Solanum Tuberosum L.) productivity in Tasmania, Australia and Kenya', PhD thesis, University of Tasmania.

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This study assessed the potential impact of climate change on potato production both in Australia (Tasmania) and Kenya. Potato is an important commodity in both regions but there is little information about how this crop will respond to projected changes in climate compared to other regions. Previous to this doctoral study, APSIM-potato had only been tested and calibrated with a small number of datasets from a long-term experiment conducted in Lincoln, New Zealand with ‘Russet Burbank’ and its application to productivity modelling required further parameterisation and evaluation. A first step in this study was therefore to parameterise and evaluate the Agricultural Production System sIMulator (APSIM-potato) model under both Tasmanian and Kenyan potato growing conditions. Throughout this thesis the word parameterisation refers to the process of determining a set of parameter values deemed suitable for model use in a specific study area, and evaluation as the process of assessing the level of precision and accuracy of a model in reproducing observed data using performance measures and statistical values.
Four on-farm monitoring plots located on different farms were established in North-West Tasmania within well–managed potato fields grown during the 2012/13 cropping season. ‘Russet Burbank’ cultivar was planted at two sites and ‘Moonlight’ at the other two sites. In Kenya, experiments were conducted at Kabete, Kiambu County during the short rains (SR2013) and in the long rains (LR2014). The design for the SR2013 experiment was a split-plot with two water levels (supplementary irrigation and rain-fed) as the main plot factor and three genotypes as the sub-plot factor, with four replications. A randomized complete block design was used in the LR2014 experiment, with three nitrogen levels (23, 63 and 104 kg N/ha, hereafter referred to as N23, N63 and N104 treatment levels) and four replicates. Measured soil, weather and crop datasets for ‘Russet Burbank’ and ‘Moonlight’ in Tasmania, and for ‘Unica’, CIP 300046.22 and ‘Shangi’ in Kenya were used to parameterise and evaluate the model.
In both Tasmania and Kenya, the model adequately captured the phenology and the partitioning of assimilates to the tuber state variable over time, with a good index of agreement using a Normalized Root Mean Squared Error (N-RMSE) and Modelling Efficiency (EF). In Tasmania, measured mean Tuber Dry Matter (TDM) was 17 t ha-1 for ‘Russet Burbank’ compared to a simulated value of 20 t ha-1. N-RMSE values between observed and simulated TDM ranged between 10 to 20%, with a mean of 16.3% for ‘Russet Burbank and 14.5% for ‘Moonlight’, and a mean EF of 1.0 for both cultivars. For ‘Moonlight’ the mean simulated TDM value was 16.0 t ha-1 compared to the measured value of 15.1 t ha-1. Similarly, prediction of phenology and tuber N-uptake was good: respectively a mean N-RMSE value of 25.7% and 20.9% for ‘Russet Burbank’, 24.2% and 32.7% for ‘Moonlight’. However, prediction of other parameters (leaf and stem dry biomass and LAI) were poor with N-RMSE values ranging from 27.6 to 40.8% for ‘Russet Burbank’, and 20.7 to 48.2% for ‘Moonlight’.
In Kenya, the model predicted TDM yield with good precision, providing a mean N-RMSE of 18.4% for SR2013 and 28.7% for LR2014, and a mean EF of 0.9 for both seasons. Similarly, prediction of phenology was good, the model providing a mean N-RMSE value of 20.8% and an EF value of 0.8 for both SR2013 and LR2014. In the SR2013 experiment, the measured TDM across the three cultivars under rain-fed conditions was 3.8 ±0.2 t ha-1 compared to simulated value of 4.4 t ha-1. With supplementary irrigation, the observed value was 6.2 ±0.2 t ha-1, close to the simulated value of 6.3 t ha-1. In the LR2014 experiment, when pooled across nitrogen levels, the model underestimated TDM, providing a mean simulated TDM at 6.6 t ha-1 against the measured value of 7.7 ±0.4 t ha-1. In contrast, the index of agreement between simulated and observed above ground biomass was generally low (a mean N-RMSE value of 37.2% in the LR2014 experiment and 47.5% in the SR2013 experiment, EF values ranging from -0.3 to 0.3 in the SR2013 and -0.5 to 0.4 for the long rains).
The simulation results provide a database for further testing of the model and this work provides future users with a foundation to further improve the model. While the model accurately predicts plant phenology and TDM, modification of other key crop specific parameters are still needed to improve its accuracy when simulating the development of other plant organs. Further refinement of the model will require collection of long-term field crop data.

Item Type: Thesis - PhD
Authors/Creators:Borus, D
Keywords: APSIM-potato, climate change, parameterisation, simulation, evaluation, tuber dry matter, climate scenario
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Copyright 2017 the Author

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