How is crop water requirement calculated?

Crop water requirement = ET₀ × Kc, where ET₀ is the reference evapotranspiration (mm/day) for your climate and Kc is the FAO-56 crop coefficient. The result is the daily water depth the crop needs. Multiply by field area (in m²) to get total litres (1 mm over 1 m² = 1 litre).

What is ET₀ in irrigation?

ET₀ (reference evapotranspiration) is the amount of water evaporated from a standardised short grass surface under your local climate conditions, expressed in mm/day. It accounts for temperature, humidity, wind, and solar radiation. Arid regions typically see 7–9 mm/day while temperate climates see 2–4 mm/day.

What is a crop coefficient (Kc)?

The crop coefficient (Kc) adjusts ET₀ for the specific crop type and growth stage. Values come from FAO Irrigation and Drainage Paper 56. Grass has Kc ≈1.0, maize mid-season Kc ≈1.2, and tomatoes mid-season Kc ≈1.15.

Why does applied water exceed needed water?

No irrigation system is 100% efficient. Drip irrigation loses ≈8% to dripper variation and soil wetting losses. Sprinklers lose ≈20% to wind drift and evaporation. Surface flooding loses 40% or more to runoff and deep percolation. The calculator automatically inflates the applied volume to account for these losses.

How do I calculate irrigation run time?

Run time (hours) = Total volume to apply (litres) ÷ System flow rate (litres/hour). Enter your pump or system flow rate in the calculator and it computes the run time automatically.

灌溉计算器

计算每日作物需水量、总施水量和灌溉系统运行时间。基于FAO-56标准。

IrrigationCalculator.climateEt0

IrrigationCalculator.climateZone

IrrigationCalculator.crop

IrrigationCalculator.fieldArea

≈ 10,000 m²

IrrigationCalculator.measureOnMap

IrrigationCalculator.irrigationSystem

IrrigationCalculator.systemType

IrrigationCalculator.flowRate

L/hr

结果

IrrigationCalculator.waterNeeded

4.5 mm/day

ET₀ 4.5 × Kc 1

IrrigationCalculator.waterNeeded

crop demand

45,000 L

IrrigationCalculator.waterToApply

at 92% efficiency

48,913 L

IrrigationCalculator.runTime

97.8 h

IrrigationCalculator.flowRate

500 L/hr

92% system efficiency — 8% lost to evaporation & runoff

灌溉需求如何计算

行业标准FAO Penman-Monteith方法(FAO-56)分两步计算作物需水量:

每日需求(毫米/天) = ET₀ × Kc

总体积(升) = 每日需求 × 面积(平方米)

ET₀是您气候的参考蒸散(良好灌溉的草坪使用的水量)。Kc是为您的特定植物调整的作物系数。一平方米一毫米的水深精确等于一升。

灌溉系统效率

System	Efficiency	Main losses
滴灌/微灌	90–95%	滴头变化、土壤润湿
中心枢纽喷灌	82–88%	风漂、蒸发
悬式喷灌	75–85%	风漂、截流
地面/洪水灌溉	55–65%	地表径流、深层入渗

灌溉规划用例

每日日程安排

计算每天运行滴灌或喷灌系统多久,以满足作物需求而不过度或不足灌溉。

水预算

估计农场或地产的总季节性用水量。将日体积乘以生长季节长度,规划水库或井的容量。

系统设计

通过将总日体积除以可用运行时数来调整泵容量,以获得每小时升数的最小流量。

比较系统

看看从洪水灌溉转换到滴灌如何将用水量减少30–40%,相应降低泵能耗和用水成本。

常见问题

作物灌溉水需求如何计算?

作物灌溉水需求 = ET₀ × Kc。ET₀是您气候的参考蒸散(毫米/天),Kc是FAO-56作物系数。将结果乘以田地面积(平方米)以获得每日升数(1毫米 × 1平方米 = 1升)。

灌溉中的ET₀是什么?

ET₀是当地气候条件下参考草坪的蒸散速率。它考虑温度、湿度、风速和太阳辐射。干旱气候为7–9毫米/天;温带气候为2–4毫米/天。

什么是作物系数(Kc)?

Kc针对特定作物和生长阶段调整ET₀,来自FAO灌溉纸56。草≈1.0,玉米盛期≈1.2,番茄≈1.15。使用您的种子供应商的农学指南以获得最准确的值。

为什么应用的水超过所需的水?

系统效率低意味着水因蒸发、风漂、地表径流或深层入渗而在到达根系之前损失。滴灌的效率约为90%;地表灌溉通常为60%。计算器自动增加应用体积以补偿。

我如何计算灌溉运行时间?

运行时间(小时) = 总应用体积(升) ÷ 流量(升/小时)。输入您的泵或系统流量,计算器自动执行。对于以1,000升/小时流动且需要5,000升的系统,运行时间= 5小时。

用GPS测量田地面积

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