David Doll15 CommentsAugust 5, 2012Irrigation

Irrigating from Hull-split to Harvest

Irrigating during hull-split and prior to harvest can be tricky. Irrigating too much can increase diseases, the risk of shaker damage, and delay shaking. Too little can increase stick-tights, increase mites, and decrease kernel weights. During this time, consider maintaining the same frequency of irrigation, but making the adjustments in the duration of the irrigation sets. Reductions to irrigation (i.e. 50% at the onset of hullsplit) to apply a stress can be made by reducing the duration. Trees should be monitored by either a pressure chamber or observations (i.e. wilting) to identify stress levels. If the trees are over/under-stressed at the end of the cycle, adjust the duration. A basic strategy from hull-split through post harvest could be:  Hull split initiation, week 1: 50% reduction to reduce the incidence of hull rot and even up hull-split (-15 bars with the pressure chamber) Hull split, week 2: 30-50% reduction to reduce hull rot (-15 bars on the pressure chamber) Hull split, week 3: 0-30% reduction to reduce hull rot, based upon tree stress the past two weeks (2 bars more negative than baseline). A mild deficit at this point should cause minimal loss in kernel weights, but will save some water. It will not increase the process of hull-split – this is a physiological process. A severe deficit may impact kernel weights. Post Hull split, week 1: 100% ET – irrigation reductions at this time can decrease kernel weights until the final abscission layer between the peduncle and nut is formed (2 bars more negative than baseline). Post Hull Split, week 2: Depending upon timing of harvest – 100%ET if more than two weeks from harvest. Pre-Harvest week: 20%-50% reduction to help begin a slight dry down of the orchard. Harvest week: 30-50% ET – some water should be applied, but

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David Doll3 CommentsJanuary 5, 2012Irrigation

It’s Been Dry – Should I Irrigate? Part 2

I have had many inquiries about applying an irrigation since we have been lacking adequate (if any) rainfall. At this time of the year, with bloom 5-6 weeks away, the answer is “yes.” As bloom approaches, it is important to have adequate moisture within the soil to a depth of at least 30 inches to promote root growth during the first root flush. Research in peaches suggest that this first root flush occurs about two weeks prior to bloom. Irrigation sets should not last longer than 24 hours and should target around 0.5 – 0.75 acre inches of applied water. After the application, the water should have time to infiltrate the soil, about 3-4 days, before the next irrigation is applied. Following these practices will help reduce the saturated soil conditions that favor soilborne diseases such as Phytophthora. After each irrigation, check the depth of the added moisture. Once moisture reaches four to five feet, application of water can be discontinued. Rainfall will only help refill the soil profile. Keep in mind that at this point, we will need more than five inches of rain to refill the moisture in most soils without supplemental irrigations. If it rains within the next two weeks, irrigate before the rain event with another 0.5 to 0.75 inches. This will help increase the effectiveness of the rainfall. If there is no rain in the two weeks, plan for another irrigation. This may be a good time to apply a pre-emergent herbicide. An irrigation will “water in” the herbicide, but the effect will be limited to the wetting pattern of the irrigation system. Four weeks ago, the answer to this question was a “no.” Attempting a poor excuse for why I changed my mind — I thought we would have received some rain by now.

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David Doll0 commentsJanuary 5, 2012Irrigation

It’s Been Dry – Should I Irrigate? Part 2

I have had many inquiries about applying an irrigation since we have been lacking adequate (if any) rainfall. At this time of the year, with bloom 5-6 weeks away, the answer is “yes.” As bloom approaches, it is important to have adequate moisture within the soil to a depth of at least 30 inches to promote root growth during the first root flush. Research in peaches suggest that this first root flush occurs about two weeks prior to bloom. Irrigation sets should not last longer than 24 hours. After the application, the water should have time to infiltrate the soil, about 3-4 days, before the next irrigation is applied. Following these practices will help reduce the saturated soil conditions that favor soilborne diseases such as Phytophthora. After each irrigation, check the depth of the added moisture. Once moisture reaches four to five feet, application of water can be discontinued. Rainfall will only help refill the soil profile. Keep in mind that at this point, we will need more than five inches of rain to refill the moisture in most soils without supplemental irrigations. This may be a good time to apply a pre-emergent herbicide. An irrigation will “water in” the herbicide, but the effect will be limited to the wetting pattern of the irrigation system. Four weeks ago, the answer to this question was a “no.” Attempting a poor excuse for why I changed my mind — I thought we would have received some rain by now.

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David Doll2 CommentsDecember 18, 2011Irrigation

Its been dry, should I water?

Although we have received a bit of rain this past week, some inquiries about applying a winter irrigation have been made. There is concern that since the soil is dry from lack of rains, that the trees will be stressed, negatively affecting the fruit bud. Briefly, an irrigation in December to alleviate water stress in dormant trees is not needed in most cases. In order for water to move into the tree’s branches, it needs the “pull” created by the leaves (transpiration). Without leaves, the water may move into the roots, up a few inches into the wood through capillary action, but not into the branches and buds within the mid to upper canopy of the tree. The only exception may be in a situation of extreme drought, in which the trees have had considerable seasonal stress and complete defoliation. This occurs rarely in California. There are other reasons to apply a winter irrigation. These include refilling the soil profile to help with irrigations scheduling in the spring, and watering in an applied pre-emergent herbicide.

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David Doll1 CommentJune 15, 2010Irrigation

Irrigation Scheduling Part 3 – Taking in account irrigation efficiency

When water is applied to an orchard, loss of some amount of water should be expected. Growers must consider this loss of water when calculating the actual amount of water being applied. This amount will vary on the irrigation system used, soil and climatic conditions, and water management conditions. Water applied to a field can be lost by run-off, percolation below the root zone, sprinkler spray evaporation and off-target drift. Efforts to minimize these inefficiencies should be employed, and could include longer irrigation sets at lower rates, the construction of tailwater return systems, and/or sub-surface installed systems. Irrigation efficiency (Ea) is defined as the percentage of applied water that is held in the root zone. Mathematically, it would look as follows:Ea = water stored/water applied. Irrigation methods commonly used within the almond orchard include surface irrigation systems such as flood and furrow and pressurized systems that include sprinkler, drip, and micro-sprinkler. As we can see in table 1, irrigation efficiency differs with each system. With surface systems, fast movement of the water from the head end to the tail of the field end usually results in higher irrigation efficiency. Within pressurized systems, distribution depends on design parameters including spacing, nozzle type and size, riser height and operating presure.  Keep in mind that maintenance and filtration affect pressurized systems more than surface based systems. Pressurized systems, however, are usually more efficient due to the reduction of run-off and water loss through deep percolation. Table 1: Application efficiency typical of various irrigation systems. System Ea (%) Basin/Flood 65 – 80 Furrow 65 – 75 Solid Set Sprinkler 75-85 Microsprinkler 85-90 Drip 90-95 When calculation orchard water use, irrigation efficiency must be accounted or under-irrigation will occur. Below are some examples that show the different water application needs due to difference in irrigation efficiency. General

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David Doll1 CommentJune 8, 2010Irrigation

Irrigation Scheduling Part 2 – Determining Water Holding Capacity

Last week we discussed how to calculate almond tree water usage by using evapo-transpiration data provided by CIMIS. Now that tree water use can be determined, we have to determine the amount of water that can be applied to the soil to maximize irrigation efficiency. It is important to understand a few terms when dealing and discussing soil water holding capacity.  Soil saturation is when all of the soil pores are filled with water – this occurs immediately after an irrigation and continues until gravity pulls the water through the pores of the soil (Figure 1). Once the soil has drained, usually 1-3 days after an irrigation/rain event, the soil is at field capacity. This water is held against gravity within small pores by the soil particles, and is the largest amount of water that the soil can hold between irrigations. In contrast, the permanent wilting point is when all the available water is gone. The amount of water between the field capacity and wilting point is termed allowable depletion – or the amount water available to the plant provided by irrigations. It is important to note that at field capacity not all of the pore space is filled with water (about 25% air space), and at permanent wilting point not all of the water is removed from the soil (it is stuck to the soil particles). Figure 1: Differing terms regarding water holding capacity of soils. Basically, when efficiently irrigating, water needs to be applied to refill the soil profile to field capacity but prevent the loss of water to deep percolation. The amount of water to refill the soil profile is related to the texture of the soil; coarser soils hold less water while fine, heavy soils hold more. This is due to the differing size of soil particles and pore space in

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David Doll1 CommentMay 31, 2010Irrigation

Irrigation Scheduling Part 1 – Calculating Orchard Water Use

Scheduling of irrigation must take into account the variables of weather, water availability, and plant stress. All of these variables change throughout the irrigation cycle, providing difficulty in determining irrigation timing and amounts of water applied. Today, lets start with a brief discussion on how to calculate irrigation needs based upon the weather. This weather driven demand for water by the almond tree is called evapotranspiration (ET). ET accounts for the loss of water through surface evaporation as well as the loss of water through the opening and closing of the stomates. We can calculate ET by knowing two things: the demand for water on a reference crop (ETo), and the crop coeficient (Kc) The Kc transforms the reference crop water use (ETo) into almond tree water use (ETc). The reference crop of use throughout California is grass pasture. Therefore, the multiplication of the reference crop water use and the almond crop coefficient will give us water use by an almond tree – or ETc = ETo x Kc. When we access CIMIS to view weather conditions and water use, the values are always presented for reference crop. Remember to transform these to represent almond water use. Since almonds change in canopy coverage throughout the year, the corresponding Kc will also change. Below is a list of crop coefficients as provided by the UN FAO* for almond orchards experiencing light to moderate winds with and without cover crops: Almond Orchard Kc by Month Dec/Jan Feb Mar Apr May June/July/Aug Sept Oct Nov With cover Crop 0.85 0.85 0.85 0.95 1.05 1.15 1.10 0.90 0.85 Without Cover Crop 0 0 0.50 0.70 0.85 0.90 0.80 0.75 0.65 Remember that these coefficients are based upon research and further research may refine the values listed above. There is currently ongoign research within California

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David Doll0 commentsMay 25, 2010Horticulture

April/May/June Almond Nut Development – Rationale for Proper Irrigation and Fertilization

The cool spring has brought up a few questions about almond development that I will do my best to answer today. Does the cool weather slow nut development? Yes, it does. By reducing the heating units, almond development is delayed. Similar to peaches, the cooler the weather, the longer it takes to complete the fruit sizing and kernel formation. This usually means that later season events will be delayed – such as hullsplit and harvest.   How can we determine if nut development is complete?  By pulling almonds off of tree and taking cross-sections, it is easy to observe the development of the embryo. As seen in figure 1, the embryo will grow from the tip and eventually fill the entire shell. Preceding embryo development is the endosperm and nucellus which makes up the “jelly” of the almond. The endosperm tends to be a bit more cloudier than the nucellus and proceeds embryo development. Once the embryo is completely developed (i.e. the kernel has filled the shell), weight accumulation will begin in the kernel  This generally tends to happen around early June and continue to hullsplit. Why is knowing when the completion of nut development important? Most of our UC recommended practices regarding irrigation and fertilization are based around nut development. If you are running short on water due to a curtailment, you might have heard that water can be cut back in Mid-June to help stretch your budget. This point in mid-June refers to when the embryo is completely developed and the dry weight accumulation is nearly done. Cutting water sooner than this will lead to reduction of crop weight, shrivels, and in some cases, nut abortion. In a cooler year, this point may be delayed – so if you are planning on deficit irrigating this summer, make sure your kernel development is complete.   This same principle is also the basis of most fertilizer timing recommendations. Fertilizer should

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