Reference table of average daily water demand for various crops

2025-09-26

Important Note: The data in the table below represents averages under standard meteorological conditions (moderate temperature, humidity, and sunlight). In practical applications, adjustments should be made based on actual local weather conditions. For high temperatures, dryness, or windy weather, an increase of 20% to 50% should be considered, whereas for low temperatures, humidity, or calm winds, a corresponding decrease should be made.

Crop Category	Crop Name	Growth stage	Daily water demand range (mm/day)	Total water requirement during the entire growth period (m³/mu)	Critical water demand period
Food crops	paddy	Entire growth period	4.0 - 8.0+ (Paddy field evaporation)	300 - 500	Tillering stage, booting and flowering stage
	wheat	Overwintering period	0.5 - 2.0
		Jointing - Anthesis	4.0 - 7.0	250 - 400	The jointing stage, the heading and flowering stage
	corn	Seedling stage	1.5 - 3.0
		Anthesis - Filling	5.0 - 8.0	200 - 350	"Flowering and Fruiting Period" to "Filling Period"
Cash crops	Cotton	Seedling bud stage	2.0 - 4.0	300 - 500	Flowering and Boll Development Period
		Bloom - Podding	5.0 - 8.0
	Beans	Bloom - Pod filling	4.5 - 7.5	250 - 400	Flowering period, pod formation and grain filling stage
Vegetable crops	Leafy vegetables (lettuce, spinach)	Whole growth period	3.0 - 6.0	200 - 300	Rapid growth stage
	Fruit vegetables (tomato, cucumber)	Seedling stage	2.0 - 3.0	300 - 450	From flowering and fruit setting stage to peak fruiting stage
		Bearing stage	5.0 - 8.0+
	Root vegetables (carrots, potatoes)	Root/ stem expansion stage	4.5 - 7.0	250 - 400	Root and tuber expansion period
Fruit trees	citrus fruits	Spring and summer shoot growth stage	3.0 - 6.0	400 - 700	Spring shoot emergence period, fruit expansion period
	Apples	New shoot growth / Fruit expansion	3.5 - 6.5	350 - 600	New shoot rapid growth period, fruit expansion period
	Grapes	Bloom - Fruit expansion	4.0 - 7.0	400 - 650	Bud emergence period, flowering period, fruit expansion period

1.Determine the total dynamic head (H_total)

The total elevation that the pump needs to overcome, including vertical height and pipe friction resistance.

How to calculate:

Vertical head (HVertical): The vertical height difference from the water level of the source (the height of the water surface when pumping) to the highest point of the outlet. This value must be measured in practice.

Friction Head (H_fiction): The pressure loss caused by friction when water flows through pipes, elbows, and valves. This value depends on factors such as pipe length, diameter, material type (e.g., PVC, PE), flow rate, and the number of fittings. It can typically be estimated as 10% -20% of the vertical head or calculated precisely using hydraulic calculation tables/software.

Total dynamic head H_total = H_vertical + H_friction Example: The vertical head measured is 50 meters, the pipeline is long and complex, and the friction head is estimated to be 10 meters.

H_total = 50 m + 10 m = 60 m

The second stage: system calculation and selection (matching core components)

2.Calculate the required pump flow rate (Q_pump)

Core formula: Q_pump (m³/h) = Q_day (m³/day) ÷ [daily average peak sunshine hours (T, unit: hours) × irrigation efficiency (η)]

Parameter analysis：

-Daily peak sunshine hours (T): A standardized reference value, not the duration of sunshine. It can be understood as "effective power generation hours", usually 4-6 hours. You can check the specific value in your location through NASA database or weather software.

-Irrigation efficiency (η): must be considered! Different irrigation methods result in huge differences in water loss. This is an efficiency coefficient less than 1.

-Flood irrigation: η ≈ 0.5

-Furrow irrigation: η ≈ 0.6-0.7-

-Sprinkler irrigation: η ≈ 0.7-0.8-

-Drip irrigation (highly recommended): η ≈ 0.85-0.95-

This formula means that the pump needs to draw out the water required for a full day (and consider losses) within T hours.

Example:

Take T=5 hours and use drip irrigation η=0.9.

Q_pump = 180 m³/ day ÷ (5 h/ day × 0.9) = 40 m³/h

Conclusion: You need to choose a pump with a flow rate of no less than 40 m³/h at a lift of 60 meters.