Soil hydraulic properties determined by inverse modeling applied to crop water availability

• Grant number: 16/13318-7
• Support Opportunities: Regular Research Grants
• Start date: November 01, 2016
• End date: October 31, 2018
• Field of knowledge: Agronomical Sciences - Agronomy - Soil Science
• Principal Investigator: Quirijn de Jong van Lier
• Grantee: Quirijn de Jong van Lier
• Host Institution: Centro de Energia Nuclear na Agricultura (CENA). Universidade de São Paulo (USP). Piracicaba , SP, Brazil

Abstract

Crop water availability depends on dynamic processes in the soil, however, predictions of characteristic water contents like field capacity or permanent wilting point are usually based on a fixed pressure head value alone. The central hypothesis of this proposal is that crop water availability and the characterizing conditions depend on soil hydraulic properties, making an evaluation only by pressure head insufficient. On its turn, agricultural management affects the hydraulic properties, hence the evaluation of changes in crop water availability should include their determination. We propose to verify the changes in water availability limits in three soils with different management histories and, based on obtained values, make predictions of the available water fraction and how it is affected by soil management. Hydraulic properties will be determined by inverse modeling using data obtained by gamma ray attenuation in undisturbed samples under evaporation. Based on the obtained hydraulic properties, field capacity will be determined by a flux density criterion at the lower soil boundary. Critical and wilting point conditions will be estimated by a matric flux potential approach. Determined values for field capacity and critical and wilting point conditions will be evaluated by comparison to values obtained by the common practice using fixed pressure heads. Higher divergence is expected between both methods when comparing the effect of soil management. The set of information will allow to discuss the validity of the common method, suggest improvements for its interpretation and limitations to its use. (AU)