Category Archives: Irrigation

Mid-Season Peanut Irrigation

Here is an update from UGA Extension Irrigation Specialist Dr. Wesley Porter:

Our ample rainfall seemed to stop early later in May and into June. With the lack of rainfall we also had an excess of heat. Typically, peanuts do not require much water early in the season, but the lack of rainfall and extreme continual heat may have pushed some producers to turn their pivots on.  I would say this was a good decision and recommended practice. We had depleted much of our non-irrigated soil moisture due to the hot and dry period. 

As of June, we have began to pick up some rainfall from scattered mid-afternoon thunderstorms.  These rains are beneficial and very welcome. However, high intensity rainfall does not do a very good job of refilling your soil water profile. Do not bank fully on these high intensity events to fully provide the required water you need.

Based on the split planting of peanuts due to the warm early season weather we will be moving into one of two stages during July, either ramping up to peak water use and then dropping off, or just getting ready to move into peak water use.  The graphic below should give us an idea of where we will stand for the 4 weeks of July.  Keep track of rainfall, and supplement it with irrigation. On rainfall events from 0.25” to 1” it is good to assume a 90% efficiency, and on events over 1” it’s probably safest especially if it is a high intensity event to assume around a 75% efficiency.  Make sure not short yourself on soil moisture as this can be detrimental. Overwatering can hurt just as much as under-watering too.  Remember this requirement is IRRIGATION and RAINFALL!  Irrigation may not even be required in the first few weeks!

PeanutWeeklyWaterUse-W.Porter-2015

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Pre-Bloom Irrigation In Cotton

Cotton-Irrigation 007

We’ve had some rain the past few days and even some in the northwest part of the county that is usually dry. Today I was in the central part of the county and fields were still wet from rain yesterday. Although irrigation requirement is higher for blooming cotton than for pre-bloom cotton, stressing cotton during squaring has more negative effects than we realize. Cotton does not rebound if stressed from no irrigation through squaring. UGA Extension Cotton Agronomist Dr. Jared Whitaker conducted research on this using the UGA Checkbook Method where the pre-bloom irrigation was eliminated and they had no difference in non-irrigated cotton. The reason for this is that cotton grows vegetatively and reproductively at the same time. During its vegetative growth, cotton is setting nodes. If it is stressed during this time, less nodes are set. Below is a graph showing the research and UGA Checkbook Method.

ImpactofPre-BloomIrrigation-J.Whitaker-2012

UGACheckbookMethod

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Pecan Irrigation Schedule

The intense heat has arrived in South Georgia with high’s in the upper 90’s. This is also nut sizing period and water demand increases.  Below is information on irrigation from UGA Extension Horticulturalist Dr. Lenny Wells:

Through June, pecan trees benefit from irrigation but only need a fraction of the amount they require as the crop begins to develop. This demand will continue to increase through the nut sizing period and peaks during the kernel-filling process in August and September. As a result, the irrigation schedule for pecan production should reflect the tree’s demand throughout the growing season. Our recommended irrigation schedule for mature pecan trees (age at which an economically significant crop can be harvested—usually 8-10 yrs and beyond) is found below:

Pecan-Irrigation-Tables

Your maximum capacity to be applied in August and September is 3600-4000 gallons per acre per day within a 12 hour period. Percentages shown in the table above represent the percentage of this maximum capacity for each month. We are often asked, “Doesn’t a 60 year old orchard need more water than a 10 year old orchard?” The general answer is no. There is probably some wiggle room for certain situations, because many factors play into an orchard’s water demand – including the number of trees per acre, crop load, cultivar, nut size, hedging, etc. [For example, while an individual 10 year old tree’s water demand may not be as great as that for a 60 year old tree,  there are fewer trees per acre in an orchard full of 60 year old trees (if the orchard has been managed correctly), thus the water requirements per acre are about the same.] Hedging may change this somewhat and we are working to try and determine any differences in water demand for hedged vs. non-hedged trees under our conditions as this practice becomes more common in the Southeast.

For now, research has shown that the schedule above works for all bearing pecan trees grown under our conditions. In addition, it is a 38% reduction in the amount of irrigation water applied over the previously recommended schedule, with all the savings coming from April-July. Many are concerned that applying less water than we had applied previously in June and July would limit nut size. This is a very important question, because nut size rules the pecan market at this time. However, our work over a 3 year study – including 2 years with very dry weather during these two months – has shown no loss in nut size, yield, or quality for the above schedule compared to the old schedule. In fact, nut size was even a little larger for the reduced schedule. The requirement for June is a little more than 1,300 gal per acre per day. In July the requirement increases to 1600 gal per acre per day. While this represents less water, it is no small amount of water and is quite enough to size the nuts.

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Irrigating Young Pecan Trees

YoungPecans (3)

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

Corn-001

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

EstimatedWaterUseInCorn-Table-10

Water Holding Capacities of Coastal Plain Soils

WaterHoldingCapacities-Table-11

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.

Irrigation 015

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

SoybeansDry-Smith-Rye 005

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.

SoybeansDry-Matthews-PecanHarvest 001

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.

SoybeansDry-Matthews-PecanHarvest 003

 

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