Category Archives: Irrigation

Irrigating Young Pecan Trees

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We were having a conversation recently about irrigation on young pecan trees and what those requirements were. UGA Extension Pecan Horticulturalist Dr. Lenny Wells has information from research on young pecan tree irrigation below:

“Young pecan trees require two key ingredients for establishment…

  1. Water
  2. Elimination of weed competition.

There is no published data on required irrigation amounts for young pecan trees that I have been able to find. So, we began a study in 2014 to determine this for trees grown under Southeastern U.S. conditions. Looking at trees in the year of planting (1st year trees), we used microsprinklers that supplied either 6.7 gallons per hour (gph) or 14.3 gallons per hour (gph) and compared these with non-irrigated trees. Trees were irrigated 3 times per week (M,W, F) at 4 hours per application. Preliminary results show that young pecan trees respond to more water than expected. Trees receiving 80 gallons per week had significantly more growth than non-irrigated trees. But, trees receiving 172 gallons per week had even more growth than those receiving 80 gallons per week.

YoungTreeIrrigation-L.Wells2015

Many people try to water young trees by hauling water to them once a week. While this is better than nothing, and will keep the tree alive, the trees require more water for the best results on most soils in our area. While 80 gallons per week improved growth over non-irrigated trees, it appears that young pecan trees require as much as 172 gallons per week for optimal growth on a loamy sand soil. Heavier clay soils may not require quite this much, while deep sandy soils may require even a little more.”

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Corn Needs Water

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Our earliest corn is progressing through the V9-V11 growth stage. This is planted in what is usually our driest part of the county, so we must be on top of irrigation. With no rain in more than 10 days, keeping up with irrigation is critical, especially for corn around V6 growth stage where yield potential is being determined. Many growers may be using moisture monitors or other technology to determine when and how much to irrigate.  If you do not use one of these methods, consider using the checkbook method for scheduling their irrigation events. Terrell County Agent Nick McGhee has put together tables from the “checkbook method” from the 2015 UGA Corn Production Guide:

Corn Water Use At Various Growth Stages

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Water Holding Capacities of Coastal Plain Soils

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Checkbook Method Example

This example shows how to use the two tables above and the “checkbook method” to determine when and how much to irrigate.

Step 1. The soil type of the corn field is a Tifton soil series. In Table 11, look at the average available water holding capacity in in/ft increments. Assuming a rooting depth of 24 inches (2 ft), the total available water is 2.2 inches (2 ft x 1.1 in/ft)

Step 2. The corn crop is 65 days old. From Table 10, the daily water use is about .31 inches/day

Step 3. Determine the irrigation by setting a lower limit of available water due to soil tension. For this example use 50% of allowable soil water depletion. In other words, only half of the water in the root zone will be allowed to be depleted. Therefore, 1.1 inches of water will be needed to replace the soil water that was either used or lost.

Step 4. Determine the amount of irrigation to apply by dividing the amount replaced by an irrigation efficiency. Assuming 75% as the irrigation efficiency, the amount of irrigation to required is 1.1/.75 = 1.47 or 1.5 inches.

Step 5. Determine the frequency of irrigation by dividing the amount of water replaced by water use per day. An example of frequency of water (either rainfall or irrigation) need: 1.1 in /.31 in per day = 3.5 days.

Step 6. Therefore, it is necessary to apply 1.5 inches of water every 3.5 days to maintain 50% available water for 65 day old corn.

We are also seeing some nitrogen burn and herbicide drift causing these spots on the leaves. Below is drift from herbicide and is common in all corn fields, but nothing to worry about.

Corn-Herbicide 007

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Chemical & Fertilization Injection Into Pivot Irrigation Systems

During times where we need high inputs on irrigated land but field conditions are not suitable for ground equipment, you may work with putting chemicals and fertilizer through the pivot. Below is information from UGA Extension Irrigation Specialist Dr. Wes Porter on using pivot irrigation systems and an example of calculating rates:

Due to excessive rainfall during the growing season and in some cases excessive plant growth and height, it becomes difficult and sometimes impossible to enter a field to apply the proper chemicals and/or fertilizers.  In this case the addition of an injection pump for chemigation and fertigation can be very advantageous.  A center pivot can typically walk around the field when the moisture level is much higher than can a ground based sprayer.  Thus, one main advantage is the ability to apply nutrients at critical periods of crop demand.

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One of the most daunting tasks in using a center pivot for chemigation or fertigation is calculating the injection rate of the fertilizer or chemical.  Fertigation of Row Crops Using Overhead Irrigation has information about specifics on fertigation of row-crops.

Steps for calculating fertilizer injection rate:

  1. Determine the irrigated area (acres)
  2. Determine the required application rate of product (in gallons per acre)
  3. Determine the amount required
  4. Determine the injection rate

For a practical example:

Let’s assume that you want to apply 30 lbs N/ac of UAN-32 through a 1,500 ft long center pivot at a rate of 0.3 inches in 12 hours (one complete circle).

  1. Irrigated area = = 3.14 * 1,5002= 7,065,000 ft2
    1. Divide ft2 by 43,560 to get acres = 7,065,000 ÷ 43,560 = 162.2 acres
  2. Determine application rate: = 30 lbs N/ac ÷ 3.5 lb N/gal = 8.6 gal/ac
  3. Determine required amount:  = 8.6 gal/ac * 162.2 acres = 1390.3 gallons
  4. Injection Rate:  = 1390.3 gal ÷ 12 h = 115.9 gal/h

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Soybeans Drying Down

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Here is a picture of early planted soybeans last Monday. Leaves are turning yellow and brown and falling off. The beans in the pods are at full maturity. Below is a photo of the same field taken yesterday.

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Seminole Ag Agent Rome Ethredge posted about irrigation termination on Seminole Crop E-News saying, You are generally safe to terminate irrigation if you have good soil moisture when the seeds fill the pods and the pods start to change to the yellow color in the top 4 nodes of the plant. Mississippi State also has a good blog post concerning Soybean Irrigation Termination that goes into growth stage specifics.

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Cotton – When To Cut Off Irrigation?

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Some spots in the county got 5 inches of rain last night after getting a few inches over Labor Day weekend. We got at least an inch in town last night. Once we make it to 7th week of bloom and beyond, we follow with an inch of irrigation per week. Since cotton is already set and its been hot and dry, we are having to continue irrigation. But when do we cut it off? It’s still a difficult decision to make – based on environmental conditions, how many bolls open, and how many bolls are mature. Below is information from 2014 UGA Cotton Production Guide from Extension Agronomist Dr. Guy Collins:

“It is generally recommended that irrigation be discontinued when a noticeable number of bolls have opened, especially when the majority of harvestable bolls are located on lower plant nodes. However, if the majority of the targeted harvestable bolls remain immature when just a few lower bolls begin to open, irrigation may still be needed for a short time.

Irrigation termination is a difficult decision. A final watering is often made when the crop begins to open. Commonly, no additional irrigation is applied once the time the crop is 10 percent open to minimize problems with boll rot, hard lock, and light spot. Common sense factors include prevailing weather patterns and predictions, available soil moisture, and time of year.”

2014 Georgia Cotton Production Guide

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Ultra-Late Soybeans Need Water

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Here is a field of ultra-late soybeans planted after corn. They need to be planted as soon as they can right after corn is Ultra-LateSoybeans 003harvested, by the first week of August. These were drilled at 7.5 inch no-till drill at a high seeding rate. UGA Extension Soybean Agronomist Dr. Jared Whitaker says we need to shoot for a seeding rate of at least 175,000 seed / acre. Dr. Whitaker recommends using either a hula-hoop or a yard stick to lay out over the rows to count a 5 x 5 area for stand counts. We did a stand count this morning which showed about 180,000 plants per acre (below).

Ultra-LateSoybeans 007With the ultra-late system, one issue is having pods produced on lower nodes and located too low to be harvested. Irrigation and addition nitrogen help increase the height of soybean crop and potentially help increase the height of pods produced on the bottom of the plant. In any case, irrigation is a must with ultra-late soybeans. Colquitt County Ag Agent Jeremy Kichler shared this soybean irrigation chart which shoots for 45 to 50 bushel yields:

 

SoybeanIrrigation

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August: Critical Month For Pecans

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Here is some information from UGA Extension Pecan Specialist Dr. Lenny Wells:

Some early pecan varieties have reached shell hardening and others are still approaching. This means that the water use requirements of pecan are nearing peak demand and will remain so through kernel filling. Growers should have irrigation systems running at full capacity at least by next week for most mid-season varieties like Stuart, Desirable, Schley, etc.  This means 3600-4000 gallons per acre per day. Solid-set sprinkler irrigated orchards should be applying 1.5″-2″ per acre week, depending on soil type (the sandier the soil, the more water). Ideally, systems should be designed to meet these water requirements within 12 hours.

Peanuts-Pecans 011Its amazing how much water a pecan tree with a heavy crop load can use at this time. The heavier the crop, the more water required. Sure, you can still make some nuts and have a decent harvest with less water but this will maximize percent kernel, which is required for good pecan prices. If the trees don’t have a crop, you won’t have to water this much because it is the kernel-filling process that creates the enormous demand for water. Adequate irrigation at this time will also relieve undue stress on the trees, which helps them to  to return a better crop the following year.

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Smart Irrigation Month Tips

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Stripling Irrigation Research Park has the Smart Irrigation Month campaign to send out tips to our clientele throughout the month of July. Here are 2014’s tips:

Tip #1 – The average life of a sprinkler head / nozzle is about 7 to 10 years. Check your center pivot application uniformity by having a “catch can” test performed, fix leaks, and replace worn nozzles. Nelson (www.nelsonirrigation.com) and Senninger (www.senninger.com) make several types and models of sprinklers.

Georgia Soil & Water Conservation Commission (gaswcc.georgia.gov), USDA-NRCS, or your local UGA Extension Service office can provide assistance.

Here’s a link to a UGA extension publication on uniformity: http://extension.uga.edu/publications/detail.cfm?number=C911

Tip #2 – UGA’s Calvin Perry (Stripling Park) and Wes Porter (Extension Irrigation Specialist) have put together a Center Pivot Spring Check List. It includes items to get your irrigation system in top shape. Many of the things covered can be applied to your system year-round.

Tip #3 – A quick way to increase the efficiency of an ag irrigation system is to repair all leaks on the center pivot or other type system as soon as you notice them. Buried pipes seldom leak. However, above ground pipes frequently have worn gaskets and considerable amounts of water (up to 30%) can be lost before it gets to the actual discharge point (sprinkler). Replace leaking gaskets, boots, etc. and plug any holes in the pipes.

Tip #4 – Variable Rate Irrigation (VRI) is a tool of precision agriculture that optimizes irrigation water application. UGA and SIRP have been at the forefront of development and adoption of this important technology. Research shows that implementing a VRI system can result in water savings averaging 15% vs. conventional water application.

For more info, go to http://striplingpark.org/agricultural-water-conservation/ and scroll down to Variable Rate Irrigation.

Fullscreen capture 8132014 55025 PMTip #5 – To practice smart irrigation, consider using soil moisture sensors to help you decide when to trigger irrigation on your crop/field. There are a number of commercially available sensor systems, such as AquaSpy, AquaCheck, Decagon, John Deere, Irrometer, Sentek, etc.

Over the last years, University of Georgia researchers, led by George Vellidis, have been developing their own affordable system – the UGA Smart Sensor Array – consisting of Watermark soil moisture sensors, temperature sensors, wireless mesh radio transmitter, and base station with cell modem. A web portal provides secure access to the soil moisture data.

For more info, go to http://vellidis.org/research-projects/smart-irrigation/uga-smart-sensor-array/.

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August Peanut Water Requirements

EddieRedding-Cotton-Peanuts 007Since July 25th, the Georgia Weather Station shows no rainfall measured in Dixie, GA. Our 6 month average rain is not bad, but recent dry weather is causing more issues with crops. We have been needing rain for a few weeks now and soil is really dry. UGA Extension Agronomist Dr. Scott Tubbs says whether peanuts were planted in April or June, weather conditions are dry for a critical reproductive development time. Peanuts are setting blooms and filling pods with too less moisture. The majority of the harvestable peanut pods initiate from around 35-40 days after planting through around 90-95 days after planting.

UGA Extension Scientist Dr. Gary Hawkins has this to say about water requirements for August:

The first week of August (if the peanuts were planted by May 1), is the peak of the water use curve, requiring about 2.1 inches per week.  The good news is that we’re about to move past the peak water use period and start requiring less water.  If your peanuts were delayed by 2-4 weeks they will move into the highest water used period soon.  Please see the figure below for the ranges of peanuts planted from late April (yellow) and peanuts planted in middle May (blue).  Hopefully we’ll begin to pick up some more rainfall to help with these water requirements.

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Peanut Water Requirements

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The high amount of rainfall during our peanut planting window caused growers not to get their peanuts planted until mid-to-late May. We now face a higher water use period falling in time with less rain period. We have be getting scattered showers in the afternoons, but not enough to provide the water we need. To make sure the crop has enough water UGA Extension Scientist, Dr. Gary Hawkins, has the chart below representing water use throughout the growing season.  This indicates what peanuts need at different maturities and can also be used as a guide to how much water is needed.

We need to also be aware that soil type has an impact on the amount of water available to the crop.  For sandy soils, a high intensity rain will likely infiltrate and may provide needed water, however, in heavier soil, the same intensity rainfall will potentially have high losses due to runoff because it will not be able to absorb the water as well as the sandy soil. On the other hand the heavier soils have a higher water holding capacity and will retain moisture for longer than sandy soils.

PeanutWaterUse-Dr.Hawkins

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