Nutrient supply and water use

In fact, however, the opposite is true and water demand per unit of production decreases with yield.

What has Yara research revealed about the relation between nutrient supply, yield and water uptake?

The role of key nutrients

Potassium is essential for controlling stomata function. In case of deficiency, stomata don’t close appropriately and water is wasted.

Sufficient phosphorus availability supports early root and shoot development, contributing to early canopy closure and access to deep soil moisture.

Nitrogen is essential for chlorophyll and enzyme formation, both required to metabolize CO2 into biomass. Lack of nitrogen reduces photosynthesis, resulting in wasted water.

Nitrogen and water use

Under laboratory conditions, winter wheat was grown under different nutrient conditions in individual pots. Water consumption was measured daily and the resulting grain yield at harvest was weighted.

Grain yield increased with nitrogen supply. Water consumption also increased with nitrogen supply, but not to the same extent. As a result water demand per unit of grain decreases with increasing nitrogen supply. In other words, the better the nitrogen supply, the less water is required per kilogram of grain grown!

Conclusions

• Under rain-fed conditions, nitrogen supply needs to be tailored to available water so that optimum yield can be achieved. Targeted nitrogen supply with readily available nitrogen forms is key to convert available water into high yield.
• Balanced nutrition and timely sowing enable early canopy closure and thus reduce evaporation.
• Optimum nutrition creates the conditions for optimum water use, resulting in more crop per drop.

Nitrogen supply and transpiration

Reducing evaporation makes more water available for transpiration. Sufficient nitrogen availability ensures that the available water is converted into growth and yield.

How much water?

How much water is needed to grow a ton of grain? Findings from pot trials have been confirmed under real farming conditions. The relation between nitrogen supply and water use was evaluated in 200 field trials under rain fed conditions. All plots received the same amount of water, but different nitrogen supply. The corresponding response curves demonstrate that water demand decreases from 100 mm to 60 mm with increasing nitrogen supply up to the economic optimum.

• Under optimum nitrogen supply, producing 10 tons of grain requires 600 mm of water.
• Under nitrogen deficiency, producing 10 tons of grain requires 700 mm of water and more surface.