Submitted to: Agricultural and Forest Meteorology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 3/16/2014
Publication Date: 4/12/2014
Publication URL: http://handle.nal.usda.gov/10113/59631
Citation: Dathe, A., Fleisher, D.H., Timlin, D.J., Fisher, J.K., Reddy, V. 2014. Modeling potato root growth and water uptake under water stress conditions. Agricultural and Forest Meteorology. 194:37-49. Interpretive Summary: Potato is one of the major crops worldwide and the United States is one of the largest producers. The potato crop is sensitive to drought, starting at low levels of water stress. Plants take up water with their roots and it is important to know where in the soil profile these roots are situated and whether they can reach the soil water. It is difficult and tedious to investigate a root system in the field and that is why scientists use mathematical models to describe it. Nevertheless, a root model has to be compared to roots growing in the real-world. The root module in the potato model SPUDSIM was improved by implementing a diffusive root model. A diffusive root model describes densities of roots in a soil profile, and how these densities increase and move in the soil profile over time. Three parameters describe the direction of root growth, and their values were adjusted that the modeled root systems resembled the structure and function of a natural root profile. Experimental potato root data were available from an already published experiment, where potatoes had been grown under different irrigation levels and soil water content and water transpired by the plants had been measured. The improved root growth module implemented into SPUDSIM can guide in understanding interactions between spatial root distribution and efficient water uptake especially under drought conditions. Farmers who are irrigating their potato crops and plant breeders who breed drought resistant potato varieties will benefit from this knowledge.
Technical Abstract: Potato (Solanum tuberosum L.) growth and yield are sensitive to drought starting at mild stress levels. Accurate simulation of root growth is critical for estimating water and nutrient uptake dynamics of major crops and improving agricultural decision support tools for natural resource management. Not many data sets for potato roots are available in literature, because examination of root systems is a laborious task. In this work, we utilize experimental root data obtained from our soil-plant-atmospheric-research (SPAR) chambers to test the newly developed root growth module of the potato crop model SPUDSIM. Root growth of potato, water uptake by the roots, and above ground and tuber growth were simulated for six different irrigation treatments. A two dimensional diffusive root growth model was implemented. Parameters controlling the direction of root growth are the diffusion coefficients in x- and z- direction, and a convective term in z-direction (downwards). Carbon distribution between roots and shoot is simulated as a function of plant development stage, leaf growth and water status of the plant and soil. Water transport in the soil is estimated with the Richard’s equation and solute transport with the convection-diffusion equation. The improved SPUDSIM version was tested against observed root distribution in the soil profile at harvest, plant organ dry weights (DW) for leaves, stem, roots and tuber, and water uptake patterns observed with time-domain reflectometry (TDR) probes and transpiration measurements. The model was able to reproduce potato response to drought after the SPUDSIM variety coefficients were calibrated with the non-stressed treatment data and soil hydraulic properties and root diffusivity coefficients were calibrated towards the 25, 75 and 100% irrigation treatments. Agreement between simulated and observed plant organ DW was very good overall, though root DW were over predicted by the model for less water stressed plants. Patterns of root distribution in the soil profile were reproduced well by the model. Water contents per soil layer for different drought scenarios could be reproduced well, but the model estimated a higher water uptake from soil layers close to the surface than observed. With the root diffusivity coefficients kept constant for all irrigation treatments, differences in root growth patterns were solely caused by the position in the soil profile where carbon was assigned to and by the value of the convective term of the diffusion equation, both functions of water status of the soil, bulk density and root density.