A simple algorithm for estimation of water requirement of shallow-rooted landscape cover crops independent of lysimeters. Case study: Frankenia

Document Type : Research Paper

Authors

1 PhD Candidate of Irrigation and Drainage, Department of Water Science and Engineering, Ferdowsi University of Mashhad (FUM), Iran

2 Department Water Engineering, College Agriculture, Ferdowsi University, Mashhad, Iran

3 Water Science and Engineering Department, Agriculture Faculty, Ferdowsi University of Mashhad, Iran

Abstract

Cover plants, among the most commonly used plants in the realm of green spaces, are typically characterized by shallow roots. In this research, a simple and flexible algorithm has been introduced for calculating the basal crop coefficient and evaporation coefficient of shallow-rooted plants without the use of (micro-) lysimeters. The presented algorithm requires measurements of moisture at three depths for short-term calculations and only surface layer moisture monitoring for long-term calculations. Using this algorithm, it is possible to calculate the potential evaporation and transpiration of the plant. Furthermore, the presented algorithm is independent of time steps. To evaluate this algorithm, nine experimental plots were utilized, including six Frankenia plots with full coverage and three bare soil plots during the peak water demand period. All experiments were conducted at the educational site of irrigation systems in the vicinity of the meteorological site of Ferdowsi University of Mashhad (FUM). For this purpose, the water content and irrigation of these plots was fulfilled (at most) every 48 hr. The results indicated that the presented algorithm has good capabilities for estimating the basal crop and evaporation coefficients. Additionally, the basal crop coefficient for Frankenia plant was found to be 1, and the evaporation coefficient was 0.58. Therefore, this method can be employed for estimating the water requirements of different plants without using (micro-) lysimeters.

Keywords

Main Subjects

A simple algorithm for estimation of water requirement of shallow-rooted landscape cover crops independent of lysimeters. Case study: Frankenia

EXTENDED ABSTRACT

 

Introduction

Water scarcity presents an acute global challenge, with significant impacts on countries in the arid zone, where urban green spaces offer essential benefits for air quality and recreation but also exacerbate water consumption demands. Precise quantification of urban green space water requirement is crucial for optimizing water management strategies. Conventional approaches for estimating evapotranspiration (ET) of cover crops frequently necessitate the use of costly and labor-intensive lysimeters. This study proposes a novel, readily applicable method for ET estimation, requiring solely soil moisture measurements at three distinct depths. This characteristic makes the presented approach particularly advantageous for researchers and urban green space managers.

Methods

The study was conducted at the Educational Site for Irrigation Systems at Ferdowsi University of Mashhad (FUM), Iran. Six experimental plots of 2 m x 2 m size were established and cultivated with Frankenia laevis, a shallow-rooted cover crop frequently employed in urban landscape design.  To obtain the transpiration component of evapotranspiration, three additional plots, prepared and maintained identically to the planted plots, served as plots for evaporation monitoring. This allowed for the differentiation between water loss solely due to evaporation from the soil surface and the combined effect of evaporation and crop transpiration in the planted plots.

Frankenia laevis seedlings were planted at a consistent density across all plots, and a precise irrigation delivered controlled water amounts based on calculated requirement. Soil moisture measurements, utilizing a FieldScout® TDR-350 device for accuracy and reliability, were taken at three depths (0-20 cm, 20-40 cm, and 40-60 cm) in each plot, capturing moisture dynamics within the root zone and deeper layers. Measurements were conducted at regular intervals throughout the growing season, and the meticulously collected data was analyzed using established equations and models to estimate evapotranspiration (ET), base crop coefficient (Kcb), and evaporation coefficient (Ke).

Results

The study observed consistent soil moisture levels near field capacity within the top 0-20 cm layer of the Frankenia laevis plots throughout the growing season, substantiating the efficacy of the implemented irrigation regime. These findings highlight the capacity of the method for accurate assessment of shallow-rooted crop water requirement.

At greater depths (20-40 cm and 40-60 cm), soil moisture exhibited initial fluctuations as the root system adapted. However, following a period of approximately 30 days, both layers exhibited a notable convergence towards a stable moisture level. This observed convergence aligns with the study's initial hypothesis, which suggested limited root activity beyond a depth of 20 cm. The observed stabilization of soil moisture in deeper layers simplifies long-term monitoring and provides further support for the suitability of the proposed approach for ET estimation in similar shallow-rooted plant systems.

Further analysis revealed a base crop coefficient (Kcb) for Frankenia laevis approaching 1.0. These results align with previous studies on comparable cover crops, further supporting the method's effectiveness in capturing plant-specific water utilization patterns. Moreover, the calculated evaporation coefficient (Ke) of 0.58 offers valuable insights into the relative contributions of soil evaporation and plant transpiration within the overall ET process.

Conclusion

This research effectively presents a straightforward and reliable method for estimating ET in shallow-rooted cover crops such as Frankenia laevis. Our method offers several key advantages, making it a valuable tool for researchers and urban green space managers. Unlike traditional approaches that rely on expensive and time-consuming lysimeters, our method utilizes readily available and affordable soil moisture measurements, significantly reducing the cost and complexity of water use monitoring. More clearly, the method focuses on measurements at three key depths, providing a comprehensive understanding of soil moisture dynamics while maintaining practicality and time efficiency.

This investigation, by presenting a reliable and cost-effective method for ET estimation in urban green spaces, holds the potential to significantly enhance water management practices within urban environments. Such improvements could contribute to the overall sustainability and environmental benefits associated with these crucial components of our urban landscapes.

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Iranian Journal of Soil and Water Research
Volume 55, Issue 5
August 2024
Pages 833-845

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