An Inverse Method to Estimate the Root Water Uptake Source-Sink Term in Soil Water Transport Equation under the Effect of Superabsorbent Polymer.

Renkuan Liao,Wenyong Wu,Peiling Yang,Shumei Ren,Ricardo Aroca

doi:10.1371/journal.pone.0159936

Abstract

The widespread use of superabsorbent polymers (SAPs) in arid regions improves the efficiency of local land and water use. However, SAPs’ repeated absorption and release of water has periodic and unstable effects on both soil’s physical and chemical properties and on the growth of plant roots, which complicates modeling of water movement in SAP-treated soils. In this paper, we proposea model of soil water movement for SAP-treated soils. The residence time of SAP in the soil and the duration of the experiment were considered as the same parameter t. This simplifies previously proposed models in which the residence time of SAP in the soil and the experiment’s duration were considered as two independent parameters. Numerical testing was carried out on the inverse method of estimating the source/sink term of root water uptake in the model of soil water movement under the effect of SAP. The test results show that time interval, hydraulic parameters, test error, and instrument precision had a significant influence on the stability of the inverse method, while time step, layering of soil, and boundary conditions had relatively smaller effects. A comprehensive analysis of the method’s stability, calculation, and accuracy suggests that the proposed inverse method applies if the following conditions are satisfied: the time interval is between 5 d and 17 d; the time step is between 1000 and 10000; the test error is ≥ 0.9; the instrument precision is ≤ 0.03; and the rate of soil surface evaporation is ≤ 0.6 mm/d.

Highlights

The study on law of soil water movement has great significance in understanding the process of material transport and energy transfer in Soil-Plant-Atmosphere Continuum (SPAC) system, and water uptake by crop roots is one of the most important processes in the transport and energy transfer of the soil in the farmland
We propose a soil water movement model based on the Richards equation, and we equate the time of water movement with the residence time of Superabsorbent polymers (SAPs), both designated as t, and takes into account root water uptake
The modeling method and numerical method proposed here provide a basis for constructing models of soil water movement under the effect of SAP that consider water uptake by plant roots

Summary

Introduction

The study on law of soil water movement has great significance in understanding the process of material transport and energy transfer in Soil-Plant-Atmosphere Continuum (SPAC) system, and water uptake by crop roots is one of the most important processes in the transport and energy transfer of the soil in the farmland. A method of obtaining a reliable “measurement” for root water uptake has been used widely in prior research on water and nutrient uptake by plant roots This method measures water uptake using inverse methods of estimating the water uptake source/sink term added to the Richards equation[8,9,10], which makes it possibility to study the relationship between soil moisture and crop water uptake. This method, proposed by Zuo Q, Shi JC et al[11,12], is based on two continuous soil moisture profiles to calculate the root water uptake rate, and has been successfully applied in research into water uptake by wheat’s roots.

Materials and Methods

Results

Findings

Discussion

Conclusions