Furrow Irrigation Calculator

About the Furrow Irrigation Calculator

Furrow irrigation delivers water through small channels (furrows) between crop rows. Water advances along the furrow from the head to the tail, simultaneously infiltrating into the soil. The application depth at any point depends on how long water stands in contact with the soil — the opportunity time, which equals the difference between recession and advance times.

Efficient furrow irrigation requires balancing inflow rate, furrow length, and soil intake characteristics. Too high a flow causes tail-water runoff; too low a flow gives excessive deep percolation at the head end because water must stand there much longer.

This calculator estimates the average application depth from advance and recession times and the inflow rate, giving you a quick assessment of your furrow irrigation performance. Use it to review set times and inflow assumptions after an irrigation and see whether the furrow is applying about the depth you intended.

When This Page Helps

Furrow irrigation is the most common surface irrigation method but also one of the most variable in performance. This page gives you a quick check on whether the set is likely to be shallow, excessive at the head, or reasonably close to target.

How to Use the Inputs

1. Enter the average furrow inflow rate in GPM.
2. Enter the furrow length in feet.
3. Enter the furrow spacing in inches.
4. Enter the advance time (time for water to reach the furrow end) in minutes.
5. Enter the recession time (time after cutoff for water to recede) in minutes.
6. Review the estimated application depth and efficiency.

Example Calculation

Tips & Best Practices

• Shorten furrow length on steep slopes to reduce erosion.
• Surge flow (on/off cycling) improves advance uniformity.
• Use poly-pipe with punched holes for uniform inflow to each furrow.
• Cut off water when advance reaches 80–90% of furrow length.
• Collect tail-water in a ditch for reuse to boost efficiency.
• Measure advance and recession at several points for a uniformity assessment.

Furrow Irrigation Mechanics

Water enters the furrow at the upstream end and advances along the furrow driven by gravity and surface slope. As it moves, water infiltrates into the soil through the furrow perimeter. The head end sees the longest water contact time and receives the most water, while the tail end receives less.

Surge Flow Irrigation

Surge flow sends water down the furrow in pulses rather than continuously. The first pulse partially seals the soil surface, reducing intake rate on subsequent pulses. This speeds advance and improves uniformity between head and tail end.

Tail-Water Recovery

Collecting runoff at the tail end in a ditch or sump, then pumping it back to the head or to another field, recovers 10–20% of applied water. Tail-water recovery systems require a sump, pump, and return pipeline but pay for themselves quickly on larger fields.

Frequently Asked Questions

• What is advance time?

  Advance time is the duration for water to travel from the head of the furrow to the tail end. It depends on inflow rate, soil intake rate, furrow slope, and furrow length.

• What is recession time?

  Recession time is the period after water inflow is cut off until the water recedes from the soil surface. During recession, water continues to infiltrate into the soil.

• What flow rate should I use?

  The maximum non-erosive flow rate depends on soil type and slope: sandy loam on 0.5% slope may tolerate 20–30 GPM/furrow, while clay on 1% slope may only allow 8–15 GPM/furrow.

• How do I improve furrow irrigation efficiency?

  Level the field, use surge valves, optimize cutoff timing, shorten furrows on steep slopes, and collect and reuse tail-water runoff. Combining surge flow with tail-water recovery can improve furrow efficiency from 40–60% to 65–80%. Regular field evaluations measuring advance time and deep percolation help identify which improvements will have the greatest impact on your specific conditions.

• What is a typical furrow irrigation efficiency?

  Without improvements, furrow irrigation is 40–60% efficient. With surge flow and tail-water reuse, efficiency can reach 65–80%.

• Can I convert from furrow to drip?

  Yes. Many row-crop farmers are converting furrow to subsurface drip for significant water and labor savings. The capital cost is higher but efficiency jumps to 90–95%.