AquaCrop Flashcards
Explain the concept of crop water productivity and its relevance in the context of agricultural water management. [you can use formula 12 in your answers]
Water productivity = (biomass generated/yield)/ET
We want more crop per drop - do this with irrigation scheduling, optimal sowing time (make use of rainfall regime to limit irrigation requirement), reduce evaporation losses with mulching, drip irrigation, plastic lining (conserves moisture and prevent weeds)
Describe the main input variables considered in the AquaCrop conceptual framework. How do these input variables affect the estimation of crop water requirements and yield?
- Meteorological data (air temperature, reference evapotranspiration and rainfall)
- Soil texture data (sand, clay, loam, in %)
- Crop parameters - attached to growing season (sowing and harvesting dates);
> initial, final and rate of change in % Canopy Cover;
> initial, final and rate of deepening in root depth;
> biomass water productivity
> harvest index - Field management: management conditions, degree of mulching, weed management
- Irrigation management: Net Irrigation Requirement, user defined schedule, generated schedule
- Affect the estimation of crop water requirements:
> T influences ETo and phenology (so the different life stages)
> Precipitation will also influence ETo, which is the main factor we will be looking at here
> ETo, reference evapotranspiration → ETc. The part that evaporates is non-consumptive, the other part (transpiration) goes to water productivity -> can be translated into yield
> Soil parameters affect how water is retained in the soil (see above for comparison of sand and silt)
> Irrigation inputs will affect yield:
» Full irrigation - full yield vs deficit irrigation
Discuss the importance of accurate meteorological data in AquaCrop modelling. Describe the types of meteorological data required and their influence on the accuracy of simulation results.
- ETo (mm/d), Tmax (C), Tmin (C) and precipitation (mm) data
-It is vital to have accurate ETo and P data as they are two major fluxes in the soil water balance that govern the amount of irrigation required. If the ETo and P data are inaccurate and are under or overestimate they may produce results that in real life cause deep percolation losses with over irrigating or water stress from under-irrigating. - The minimum and maximum temperatures govern the average temperature calculated in the Aquacrop software, which is compared to the base temperature set on the software. If the average temperature is below the base temperature, crop development does not progress. Therefore, if inaccurate data is used the development of the crop will be modelled poorly.
Provide an overview of different stress factors and their effects on crop growth stages and water management strategies.
- Soil water stress
> Soil water stress inhibits seed germination, stunts growth and affects the development of the canopy cover (reduced leaf expansion), the expansion of the root zone, results in stomata closure and a reduction of crop transpiration rate, and alters the Harvest Index.
> When the depletion rate in the root zone exceeds the RAW, water stress begins to occur as the root zone depletion is high enough to limit evapotranspiration
> Strategy: use drip irrigation to ensure adequate water supply at critical growth stages, use sensors to assess soil moisture content, use irrigation scheduling - Air Temperature Stress
> Inhibits germination, affects crop transpiration and pollination
> Colder temperatures lead to stomata closure which reduced crop transpiration and extreme cold or high temperatures
> Strategy: shading techniques, mulching, protective structures - Soil Fertility Stress
> Canopy development and biomass production affected by soil fertility stress
> Adequate water availability supports nutrient uptake and transport within the plant
> Strategy: conduct soil testing to identify nutrient deficiencies, apply appropriate fertilisers, use drip irrigation to apply fertilisers directly to root zone - Soil Salinity Stress
> Affects the biomass production, reduces water uptake
> Strategy: apply leaching requirement, use irrigation water with low salts
Explain the purpose and importance of AquaCrop in irrigated agricultural water management. How does Aquacrop contribute to optimising crop water management and productivity?
-Estimating Crop Water Requirements: AquaCrop helps in estimating the water requirements of different crops at various growth stages. It considers factors such as crop type, climate, soil characteristics, and management practices to calculate the crop’s water needs accurately. This information is crucial for determining irrigation scheduling and optimizing water allocation in irrigated agriculture.
- Assessing Crop Response to Water Stress: AquaCrop simulates the response of crops to varying levels of water availability. It can model the effects of both water deficit and water excess on crop growth and yield. This feature allows farmers and water managers to understand the crop’s tolerance to water stress and make informed decisions regarding irrigation strategies.
- Optimizing Irrigation Practices: By simulating the water dynamics within the root zone, AquaCrop helps optimize irrigation practices. It provides insights into the timing, duration, and amount of water required to meet the crop’s needs effectively. This enables farmers to schedule irrigation events based on the crop’s growth stage, soil moisture levels, and climate conditions, reducing water wastage and improving irrigation efficiency.
- Evaluating Water Productivity: AquaCrop assesses crop water productivity, which is the amount of yield produced per unit of water consumed. It allows comparisons between different irrigation strategies, crop varieties, or management practices to identify the most water-efficient approaches. This information helps in making informed decisions to maximize crop productivity while minimizing water use, contributing to sustainable water management in agriculture.
- Supporting Decision-Making: AquaCrop provides a user-friendly interface and can be used as a decision-support tool. Farmers, water managers, and policymakers can utilize the model’s outputs to evaluate the impact of different scenarios, such as changes in irrigation techniques, crop rotations, or climate conditions. This aids in formulating effective water management strategies and policies at various scales, from individual farms to regional planning.
Explain how thresholds in the water balance contribute to simulating water stress and crop development. Provide a schematic diagram to support your explanations.
- Thresholds of stress indicators are used to give a stress coefficient value, Ks, based on the quantified stress indicator. For example, for water stress, if minimum and maximum thresholds are set for depletion rate (fraction of the TAW depleted), the parameter that governs stress coefficients for soil water, the stress coefficient can be calculated. The diagram below explains this:
- FIGURE
- In the diagram, above the upper threshold, the stress is non existent while maximum stress is experienced at the lower threshold
- When the Ks value falls below the threshold, the potential energy of the soil water drops and therefore it becomes more difficult to extract water from the soil as it is strongly bound by capillary and absorptive forces. This hinders the crop development as the lack of water reduces plant growth, thus decreasing the crop yield
Discuss the steps involved in using AquaCrop for irrigation scheduling. Explain how the model assists in determining the optimal timing and amount of irrigation water. Highlight the advantages of using AquaCrop in water-limited environments. Provide an overview of the main applications of AquaCrop in irrigated agricultural systems. Discuss how the model can be used to generate irrigation schedules, mitigate the effects of water scarcity on crop production and improve water productivity.
- Irrigation scheduling refers to the process of determining when and how much water should be applied to crops through irrigation to meet their water requirements effectively. It involves managing the timing, duration, and amount of irrigation water to optimize crop growth and productivity while minimizing water waste. The goal of irrigation scheduling is to maintain the soil moisture at an optimal level for crop growth throughout the growing season. This ensures that plants receive an adequate water supply when needed, preventing water stress or waterlogging, which can negatively impact crop development and yield.
- Irrigation scheduling takes into account soil characteristics (storage potential, drainage, ..), crop water requirement, climate conditions.
- E.g. Aquacrop can show you, based on your preset allowable depletion percentage, which kind of irrigation brings forth which result in terms of water productivity, biomass and yield. …
- Use trial and error to see which allowed deficit gives highest yield under given climatic conditions (including droughts) or can input irrigation schedules to see which is best
Discuss the concept of deficit irrigation and its potential benefits and challenges in agricultural systems. How can AquaCrop assist in optimising deficit irrigation strategies for different crops and water-limited environments? Provide examples of how AquaCrop can help establish the appropriate deficit irrigation levels and schedules to maximise water use efficiency and minimise yield loss.
- Deficit irrigation: spatially and/or temporally deficit.
> Partial root zone drying: half the root system is irrigated, remaining half is exposed to drying soil
> Regulated deficit: define which stages are fit for deficit, effective way to solve water shortage - Benefits: maximises the productivity of water (reduces loss through evaporation), can still have high yield but uses less resources, especially important for drought conditions or when competing for water resource, will need to do more with climate change concerns, reduces risk of fungal concerns (less humid around crop), reduces nutrient loss through leaching = improved ground water quality
- Challenges: have to decide which kind of deficit is best, provide deficit for whole season or just at certain times, need to ensure soil doesn’t get too saline, need accurate soil water content monitoring, not good in soils where water not well retained
How can AquaCrop be used to evaluate and improve crop water productivity?
- Can use trial and error to find the MAD which allows for maximum water productivity for the respective soil
- It can generate irrigation schedules for you, use trial and error to see which full irrigation has max water productivity or which deficit irrigation schedule has max yield for x amount of water that is available
- See below for more info
Discuss farm practices to enhance crop water productivity.
Improving yield with same water use:
- Deficit irrigation - if applied during critical crop growth stages results in good yield and high WP
- Minimise transpiration: use mulch, irrigate at night
- Optimization of irrigation system: check for leaks, good maintenance etc
- Increase soil fertility increases yield
- Some crops benefit from seed priming - soak seeds in water for specific period, surface dry and then sow
