Water Makes Grass Grow!

Jim Gerrish

6 years ago

That is a theme I frequently use in my grazing management presentations around the country. I often say I have learned more about grazing management by working the last dozen years in the extremes of irrigated and desert environments of Idaho than I did in 23 years of the high natural rainfall environment of Missouri.

We had a situation develop this summer on the pivots here at Circle Pi-Patterson that really brought the lesson home. The three pairs of pre- and post-grazing pasture pictures are from the same paddock, just at different distances from the pivot center.

To set the stage. We were having poor water flow on the upper pivot (150 acre) for some unidentified reason. Remember these are gravity flow water pressure, no pumping. Historically the lower pivot (300 acres) has run at about 80 psi & puts out tremendous amount of water. We shut the lower pivot valve to half-open. Water pressure should have been adequate. The output ‘looked’ good.

After a month of hot weather from mid-July to Mid-August, it was time to move the cattle onto the higher side of the lower pivot and I got a shock when we were grazing there. I had missed doing one of my biweekly pasture inventories and hadn’t been out to that part of the pasture for a month.

The pictures and graph tell the rest of the story.

This is between towers 7-8. Grass is green, lush & 18-20 inches tall. Cattle will be here for 24 hours at 75,000 lb stock density.

After grazing we have an acceptable 3-5″ residual.

This is between towers 9-10. Grass is only 6-7″ tall and dried out.

Post grazing residual is only about 2-3″. Very little green leaf left at all. This will be slow recovery.

Between towers 12-13 (2000 ft from the pivot center, pointed uphill, on thinner soil) the grass is about 6 inches.

Post-grazing residual is under 2″ & no green leaf at all. Remember, this is the same paddock with the same herd of cattle for the same length of time. All we are looking at is inadequate water flow as we get farther away from the pivot center.

Here is the water distribution measured on July 11-12. We put a rain gauge every 50-60 ft moving away from the pivot center. I love grazing my pivots, but worn nozzles & inadequate water flow leave us with horrible distribution pattern. The green line is our target application rate of 3/4″ of water every 3 days. Blue bars are the actual measurement & the red line is the linear regression trendline. The trendline pretty well perfectly predicts the photo series. Adequate water at towers 7-8, then a steady decline out to the end of the pivot.

Here is the punchline to the photo set. The graph below shows the water flow measured after we fixed the problem on the upper pivot and turned the water back to full-on for the lower pivot. Same lousy distribution pattern, but adequate water quantity all the way to the outer end.

Water grows grass.

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