Lecture 1 - Water Footprinting, Agricultural Sustainability and Drought Tolerance

Lecture 1 Notes: Agriculture and Sustainability

Introduction

  • The lecture focuses on how plants respond to their environment, particularly water availability.
  • Lecture 2 will delve deeper into plant responses to water in the soil.
  • Practical activities are scheduled for Wednesdays at 3 PM or Thursdays at 4 PM, starting next week.
  • This week only lecture material will be covered.
  • The practical involves planning and planting an experiment with microbial inoculants, growing plants, harvesting, and statistical analysis.
  • A virtual farm management exercise will also be conducted.

Assessment

  • 50% of the module assessment is a practical report, completed in groups of six or seven.
  • Collaboration is encouraged during the experiment, but the final report must be individual work.
  • Use of artificial intelligence is prohibited for the report.
  • The report is due in April.
  • The module also includes a two-part exam, each part lasting about an hour, with a choice of questions.

Agriculture in the News

  • Agriculture is a critical and dynamic sector, frequently featured in the news.
  • Examples include farmers protesting inheritance tax, herbicide-resistant weeds, fertilizer safety concerns, and climate change impacts on coffee production.
  • Farmers' decisions are primarily driven by economic sustainability.

News Examples

  • Farmers protesting government policy on inheritance tax, citing unfairness and compromised profitability.
  • Discovery of a herbicide-resistant weed, raising biosecurity concerns.
  • Concerns over the safety of ammonium nitrate fertilizer, reminiscent of the Beirut explosion.
  • A coffee picker in Kenya concerned about the industry's viability due to climate change, earning about one coffee cup's worth of money daily.

Global Perspective

  • The module takes a global perspective, drawing examples from around the world.
  • By 2050, Africa's population is projected to reach 2 billion, necessitating sustainable agricultural development.

Agriculture's Environmental Footprint

  • Agriculture accounts for approximately 70% of global water withdrawals.
  • In the USA, agriculture contributes about 10% of greenhouse gas emissions.
  • Globally, agriculture, including land use change, accounts for about 25% of greenhouse gas emissions.

Measuring Sustainability

  • The lecture introduces ways to measure agricultural sustainability, focusing on the water footprint.
  • The lecture will consider how to increase crop yields under water limitation.
  • Rain-fed agriculture accounts for 80% of global crops and 60% of the world's food.
  • Irrigated agriculture accounts for 20% of croplands and 40% of the world's food.

Historical Context

  • Historically, agriculture relied on animal and human labor, with limited chemical inputs.
  • Modern agriculture relies on mechanization, chemical fertilizers, plant breeding, and pesticides.

Sustainability Definitions

  • Sustainability involves environmental health, economic profitability, and social equity.

Rothamsted Experiment

  • The Rothamsted experiment, running since the 1840s, demonstrates the impact of fertilizers on crop yields.
  • Adding fertilizer, organic or synthetic, boosts yield.
  • Historical yield data helps assess the sustainability of agricultural systems.

Resource Use Efficiency

  • Resource use efficiency is a key indicator of sustainability.
  • Resource use efficiency is represented by the slope of the yield versus resource line.
  • Applied resource use efficiency is crop yield divided by resource applied.
  • Intrinsic resource use efficiency is crop yield divided by resource uptake.

Peak Water

  • The concept of peak water is analogous to peak oil, considering water as a non-renewable resource.
  • Peak nonrenewable water occurs when groundwater abstraction exceeds recharge.
  • Peak renewable water refers to river systems where water is over-extracted for irrigation upstream.
  • Peak ecological water is when environmental damage costs exceed the value of human water use.

North China Plain

  • The North China Plain faces declining water tables due to double cropping and irrigation.
  • Water table height declines by 0.5 to 3 meters annually.

Key Takeaways

  • Agriculture has sustained the human population but at an environmental cost.
  • Crops are increasingly dependent on fertilizers, irrigation, and pesticides.
  • Resource use efficiency is a key metric for assessing agricultural sustainability.

Water Footprint

  • Each individual has a water footprint determined by consumption of agricultural goods.
  • Water footprint is related to national gross domestic product and individual choices.
  • Plant-based diets generally have a lower water footprint.
  • The water footprint of crops depends on location and crop management.

Mince Pie Example

  • The water footprint of a mince pie includes all the water transpired by plants to produce the ingredients.
  • Water footprint >> water content.

Components of Water Footprint

  • Green water footprint: water from rainfall stored in the soil, which is transpired in the plant (H_2O).
  • Blue water footprint: surface or groundwater used for irrigation, which is transpired in the plant (H_2O).
  • Gray water footprint: freshwater needed to assimilate pollutants from agricultural systems.

UK Water Footprint

  • The UK water footprint is about 4,500 liters per day, mostly from agricultural goods.
  • The UK relies on imports for many crops, exporting its water footprint to drier regions.

Crop Water Footprints

  • UK-produced wheat has about half the global average water footprint due to humidity.
  • Consumption patterns in the UK affect water stress in other countries.
  • Imports from Brazil, Ghana, and the European Union contribute significantly to the UK's water footprint.

Spanish Tomatoes Case Study

  • Spanish tomatoes account for a significant portion of the UK's tomato water footprint.
  • Tomatoes are grown in polytunnels to reduce evaporative demand.
  • One tomato requires about 50 liters of water on average.

Reducing Water Footprint

  • Grafted plants and different rootstocks can substantially vary water requirements.
  • Deploying specific rootstocks could save enough water for domestic supply for a hundred thousand people.
  • Small tweaks to agricultural systems can make resources more widely available.

Conclusion

  • Agriculture is the dominant contributor to water footprint.
  • Crop genotype and management determine the water footprint during production.
  • Global trade in virtual water means individual consumption patterns have distant impacts.

Rain-fed Agriculture

  • Maximize our water use to enhance our yields or alternatively increase our water limited yields
  • Rain-fed agriculture depends on maximizing water use to enhance yields.
  • Increase our water limited yields.
  • Crop yield can be broken down into water use, water use efficiency, and harvest index.
  • Stomatal conductance is the tendency for water to move from inside the leaf to outside the leaf regulated by stomatal pores on the underside of the leaf. If we select these varieties here, we should get more yield, but there's a caveat in a water limited environment.
  • Characterize the stress environment that the plant is actually growing in.
  • Saving water during pre-grain filling can improve yields.
  • Smaller diameter xylan vessels. So in in high yielding environments, they yield the same as the as the check variety that hasn't been hasn't had been bred for these small xylan vessels, but in drier environments, they produce about 10% more yield and there's a range of traits that we could look at to either save water, escape drought, or indeed spend more water to try and boost our crop yields in water limited environments.
  • Traits for improved drought tolerance include stomatal regulation, rapid development, and deep root systems.

Seed Producers

  • Seed producers offer varieties with traits like advanced tomato control (greater transpiration efficiency), better stay green (longer photosynthesis), and aggressive silking (drought escape).

Genetic Modification

  • Genetic modification can enhance drought tolerance by restricting water use during early growth stages.
  • Restriction of water use during the early life cycle of the crop so that it's got more water available at the time that it's actually reproducing. So you can see it's got lower leaf area at this critical silking or flowering stage and what that allows it to do is prioritize the use of water for growing the ears of of the grain.

Passura Identity

  • Plant breeders can target traits like improved root growth, reduced xylem vessel diameter, and stomatal sensitivity to improve drought tolerance.

Lecture Summary

  • Agricultural sustainability can be evaluated using different perspectives and metrics.
  • Crop production is a water-demanding activity with local ecosystem impacts.
  • Crop yields can be enhanced by spending or saving water.

Key Terms

  • Definitions of key terms are provided in the glossary.