Ahmadi, Seyed Hamid2; Sepaskhah, A R2; Andersen, Mathias Neumann5; Plauborg, Finn5; Jensen, Christian Richardt3; Hansen, Søren4
1 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University2 unknown3 2012 Institut for Jordbrug og Økologi, 2012 Afgrødevidenskab4 Institut for Plante- og Miljøvidenskab, Miljøkemi5 Department of Agroecology - Climate and Water, Department of Agroecology, Science and Technology, Aarhus University
Root length density (RLD) is a highly wanted parameter for use in crop growth modeling but difficult to measure under field conditions. Therefore, artificial neural networks (ANNs) were implemented to predict the RLD of field grown potatoes that were subject to three irrigation strategies and three soil textures with different soil water status and soil densities. The objectives of the study were to test whether soil textural information, soil water status, and soil density might be used by ANN to simulate RLD at harvest. In the study 63 data pairs were divided into data sets of training (80% of the data) and testing (20% of the data). A feed forward three-layer perceptron network and the sigmoid, hyperbolic tangent, and linear transfer functions were used for the ANN modeling. The RLDs (target variable) in different soil layers were predicted by nine ANNs representing combinations (models) of the eight input variables: soil layer intervals (D), percentages of sand (Sa), silt (Si), and clay (Cl), bulk density of soil layers (Bd), weighted soil moisture deficit during the irrigation strategies period (SMD), geometric mean particle size diameter (dg), and geometric standard deviation (σg). The results of the study showed that all the nine ANN models predicted the target RLD values satisfactorily with a correlation coefficient R2 > 0.98. The simplest and most complex ANN architectures were 3:2:1 and 5:5:1 consisting of D, SMD, dg, and D, Bd, SMD, σg, dg as the input variables, respectively. Low values of normalized root mean square error (NRMSE) (min = 0.101, max = 0.227) and mean absolute error (MAE) (min = 0.345 cm cm−3, max = 0.79 cm cm−3) proved the high capability of the ANN to predict RLD. The RLD prediction was more accurate in the top soil layers than in the deeper layers; this discrepancy could be possibly attributed to the non-homogenous root distribution in the three soil textures, soil pore structure, and nutrient availability. Results also implied that ANN is a strong modeling tool for simulating the RLD in small data sets. Conclusively, ANN is a powerful tool to predict RLD under a range of soil physical conditions with a high degree of accuracy and may be used in crop growth modeling.