Improved drainage relationships for characterizing the agronomic and environmental performance of field crop production

Citation

Reynolds, W.D. 2019. Improved drainage relationships for characterizing the agronomic and environmental performance of field crop production. Geoderma xxx: xxx-xxx.

Plain language summary

The economic and environmental performance of agricultural crops depends heavily on effective water management in the crop root zone. For example, too much root zone water can “drown” crops and leach fertilizers into drainage tiles and streams, while too little water reduces crop yield and quality. This study developed improved mathematical relationships for characterizing soil water drainage rates and water contents, which are critical components of effective root zone water management. The study also showed how drainage relationships can be combined with crop production and environmental impact criteria to characterize the positive and negative impacts of irrigation strategies and application of inorganic soil amendments.

Abstract

Simple algebraic drainage equations produce useably accurate depth and time distributions for unsaturated soil water content and drainage flux, but they systematically underestimate matric head. The primary objective of this study was to improve the matric head estimate, and thereby increase the value of algebraic drainage equations in agri-environmental applications. A secondary objective was to illustrate how algebraic drainage equations can be used to inform and characterize the agronomic and environmental performance of field crop production.

A quasi-empirical correction factor was developed that reduced matric head error to an acceptable 0-22 % relative to numerical simulation results for weak, moderate and strong capillarity soils at profile depths of 0.3 m and 1.0 m, and for drainage from saturation times ranging from 0.01 to 30 days. Without correction, matric head error ranged from a barely acceptable maximum of 35-40 % in weak and moderate capillarity soils, to a clearly unacceptable maximum of 141 % in strong capillarity soil. The drainage equations, along with corrected matric head and target criteria from the literature, were used to illustrate how various silt loam addition rates impacted the agronomic and environmental functioning of an agricultural sand soil in terms of root zone drainage time, drainage flux, plant-available air and water, readily available water range, and potential for excess loss of water and nutrients through deep percolation and leaching.

Publication date

2019-02-20

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