Manuscript Outline

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1. Introduction

Plant Available Water (PAW) is a crucial concept in irrigation management, as it determines the amount of water that plants can access from the soil. However, the upper limits of PAW are not well-defined, and previous studies have reported discrepancies in estimates. This manuscript aims to assess the upper limits of PAW under different climatic conditions and evaluate its implications for irrigation recommendations, crop yield, and nitrate leaching.

Defining Plant Available Water

PAW is the amount of water that plants can extract from the soil, and it is influenced by various factors, including soil type, texture, and structure. The upper limit of PAW is the maximum amount of water that plants can access from the soil, and it is a critical parameter in irrigation management. However, conventional definitions of PAW have limitations, as they do not account for the complex interactions between soil, plants, and climate.

Previous Studies and Knowledge Gap

Previous studies have reported discrepancies in upper limit estimates of PAW, with some studies suggesting that the upper limit is as low as 0.1 cm/d, while others suggest that it is as high as 0.5 cm/d (de Jong van Lier, 2017; Logsdon, 2019). These discrepancies highlight the need for a more comprehensive understanding of PAW and its upper limits. Furthermore, previous studies have not assessed the impact of climate change on PAW estimates, which is a critical knowledge gap in the field.

Study Objectives

The primary objectives of this study are to:

  1. Assess the upper limits of PAW under different climatic conditions.
  2. Evaluate the implications of PAW estimates on irrigation recommendations, crop yield, and nitrate leaching.
  3. Investigate the influence of climate change on PAW estimates.

2. Materials and Methods

2.1. Study Site and Experiment Description

The study was conducted at a research site in a temperate region with a Mediterranean climate. The site was characterized by a sandy loam soil with a moderate water-holding capacity.

2.2. SWAP-WOFOST Model Parameterization

The Soil-Water-Atmosphere-Plant (SWAP) model was used to simulate soil water dynamics, and the WOFOST model was used to simulate crop growth and yield. The models were parameterized using field measurements of soil water content, temperature, and crop growth.

2.3. Climate Change Scenarios

Climate change scenarios were derived from the Coupled Model Intercomparison Project Phase 6 (CMIP6) projections. The scenarios included a moderate warming scenario (2°C) and a high warming scenario (4°C).

2.4. Analysis of Root Water Uptake, Yield, Irrigation Recommendations, and Nitrate Leaching

Metrics used to assess discrepancies across PAW estimates included:

  1. Root water uptake (RWU)
  2. Crop yield
  3. Irrigation recommendations
  4. Nitrate leaching

3. Results

3.1. SWAP Calibration Results

The SWAP model was calibrated using field measurements of soil water content at different soil depths. The results showed that the model was able to simulate soil water dynamics accurately (Fig 1).

3.2. Discrepancies in RWU, Yield, Irrigation Recommendation, and Nitrate Leaching

The results showed that discrepancies in PAW estimates led to significant differences in RWU, yield, irrigation recommendations, and nitrate leaching (Table 3).

3.3. Influence of Climate Scenarios on PAW Estimates

The results showed that climate change scenarios had a significant impact on PAW estimates, with the high warming scenario leading to higher PAW estimates than the moderate warming scenario (Fig 3).

4. Discussion

The results of this study highlight the importance of assessing the upper limits of PAW under different climatic conditions. The study shows that discrepancies in PAW estimates can lead to significant differences in RWU, yield, irrigation recommendations, and nitrate leaching. The results also suggest that climate change scenarios have a significant impact on PAW estimates.

Driving Factors for Discrepancies

The driving factors for discrepancies in PAW estimates include:

  1. Climate impact: Climate change scenarios have a significant impact on PAW estimates.
  2. Influence of theoretical thresholds/definitions: Conventional definitions of PAW have limitations, and previous studies have reported discrepancies in upper limit estimates.
  3. Comparison with previous studies: Previous studies have reported discrepancies in upper limit estimates, highlighting the need for a more comprehensive understanding of PAW.

Implications for Irrigation Management

The results of this study have significant implications for irrigation management. The study shows that dynamic, site-specific upper limit estimates are necessary to ensure optimal irrigation management. The study also highlights the need for more research on the impact of climate change on PAW estimates.

5. Conclusion

In conclusion, this study assessed the upper limits of PAW under different climatic conditions and evaluated its implications for irrigation recommendations, crop yield, and nitrate leaching. The results showed that discrepancies in PAW estimates can lead to significant differences in RWU, yield, irrigation recommendations, and nitrate leaching. The study also highlighted the importance of assessing the impact of climate change on PAW estimates. The results of this study have significant implications for irrigation management and highlight the need for more research on the impact of climate change on PAW estimates.

Frequently Asked Questions

Q: What is Plant Available Water (PAW)?

A: Plant Available Water (PAW) is the amount of water that plants can extract from the soil. It is influenced by various factors, including soil type, texture, and structure.

Q: Why is it important to assess the upper limits of PAW?

A: Assessing the upper limits of PAW is crucial for irrigation management, as it determines the amount of water that plants can access from the soil. Discrepancies in PAW estimates can lead to significant differences in root water uptake, crop yield, irrigation recommendations, and nitrate leaching.

Q: What are the conventional definitions of PAW?

A: Conventional definitions of PAW have limitations, as they do not account for the complex interactions between soil, plants, and climate. Previous studies have reported discrepancies in upper limit estimates, highlighting the need for a more comprehensive understanding of PAW.

Q: What are the climate change scenarios used in this study?

A: The climate change scenarios used in this study were derived from the Coupled Model Intercomparison Project Phase 6 (CMIP6) projections. The scenarios included a moderate warming scenario (2°C) and a high warming scenario (4°C).

Q: How did the study assess the impact of climate change on PAW estimates?

A: The study used the SWAP-WOFOST model to simulate soil water dynamics and crop growth under different climate change scenarios. The results showed that climate change scenarios had a significant impact on PAW estimates, with the high warming scenario leading to higher PAW estimates than the moderate warming scenario.

Q: What are the implications of this study for irrigation management?

A: The results of this study have significant implications for irrigation management. The study shows that dynamic, site-specific upper limit estimates are necessary to ensure optimal irrigation management. The study also highlights the need for more research on the impact of climate change on PAW estimates.

Q: What are the limitations of this study?

A: The limitations of this study include:

  1. The study was conducted in a temperate region with a Mediterranean climate, and the results may not be applicable to other regions.
  2. The study used a simplified climate change scenario, and the results may not reflect the complexity of real-world climate change.
  3. The study did not account for other factors that may influence PAW estimates, such as soil salinity and nutrient availability.

Q: What are the future research directions?

A: Future research directions include:

  1. Conducting studies in different regions and climates to assess the applicability of the results.
  2. Using more complex climate change scenarios to reflect the complexity of real-world climate change.
  3. Accounting for other factors that may influence PAW estimates, such as soil salinity and nutrient availability.

Q: What are the practical applications of this study?

A: The practical applications of this study include:

  1. Developing dynamic, site-specific upper limit estimates for irrigation management.
  2. Improving crop yield and water use efficiency through optimal irrigation management.
  3. Reducing nitrate leaching and environmental pollution through optimal irrigation management.

Q: What are the policy implications of this study?

A: The policy implications of this study include:

  1. Developing policies and guidelines for irrigation management that take into account the impact of climate change on PAW estimates.
  2. Providing support and resources for farmers and irrigation managers to adopt optimal irrigation management practices.
  3. Encouraging research and development of new technologies and practices that can improve crop yield and water use efficiency.