Posts Tagged: ET
Zaccaria's International Team Showcase Irrigation Whiz During Foothill Field Day
With mounting pressure on growers to account for their precious water use, irrigation tools are...
New CIMIS weather station available in the Salinas Valley
The California Irrigation and Management Information System (CIMIS) operates and maintains more than 145 weather stations throughout California. The CIMIS program is funded by the California Department of Water Resources. Most stations are located on or near agricultural land, and provide measurements of reference evapotranspiration (ETo), which can be used to estimate how much water to apply to crops. Hourly, daily, and monthly averages of data are available through the CIMIS web site (http://www.cimis.water.ca.gov). The website includes an option to automatically email data from selected stations on a daily or weekly schedule. In addition to ET data, CIMIS stations record precipitation, relative humidity, air and soil temperature, solar radiation, wind speed, and dew point. Besides irrigation management, weather data can be used for plant disease forecasts, for calculating insect and crop degree-days, and for determining wind speeds during spray operations. Water management agencies use historical reference ET data to determine pumping demands, and to estimate future ground water supplies using mathematical computer simulation models.
The Central Coast region currently has 16 active CIMIS stations (Table 1). Stations are located in Monterey, San Benito, Santa Cruz, Santa Clara counties. The newest station is #252 (Figure 1), located near Soledad CA on the east side of the Salinas Valley. CIMIS is a cooperative program, requiring collaboration between a local entity to provide land, maintain the site, and provide periodic servicing of the station. In some cases, stations are owned by the CIMIS program, but in many situations the weather stations are purchased through grant funding obtained by a local agency. Funding for station 252 was from a proposition 84 grant administered by the Coastal Conservation and Research Inc. The installation of the station was a partnership among Monterey County Resource Conservation District, UC Cooperative Extension (Monterey County), Dole Food Company Inc., CIMIS, Monterey Bay National Marine Sanctuary, and the Central Coast Wetlands Group (CCWG). Because CIMIS stations need to be sited on well-watered grass to provide accurate estimates of reference ET, funds from this grant were also used to establish 2-acres of grass surrounding the weather station and to install an underground sprinkler system.
Table 1. CIMIS stations located in the Central Coast region.
Figure 1. CIMIS station 252 located near Camphora-Gloria Rd, Soledad CA.
Even if a ranch has a private weather station, CIMIS data can still be useful. Many private weather stations are not instrumented to monitor ET or are not sited on a well-watered reference crop. Frequently private weather stations are located near a building, parking lot, or tree that can confound micro-climatic measurements. Over time instrumentation on weather stations can malfunction and record inaccurate data. The CIMIS system uses both an automated and manual quality assurance program to flag data that appear inaccurate or outside the normal range. CIMIS staff also service and check that the instruments are working properly. Additionally, CIMIS data are archived so that historical data can be accessed by users. CIMIS weather station data also contributes to Spatial CIMIS, a hybrid ET product that uses weather station and satellite data to provide reference ET estimates at approximately a 1-mile resolution. Spatial CIMIS reference ET data are also available through the CIMIS website.
During the past decade, significant progress has been made in adding new CIMIS weather stations or revitalizing old stations with improved site maintenance on the Central Coast. In addition to the Soledad station, Station 209 was established in West Watsonville, Station 211 was installed in Gilroy, and Station 210 was located in the Carmel Valley. Permanent grass was planted at station 129 in Pajaro and also at station 214 in South Salinas. Although progress has been made to increase the number and accuracy of CIMIS stations, weather stations are still lacking in some important Central Coast growing regions. Closer to the coast, the Castroville (#19) and North Salinas (#116) Stations are no longer reporting reference ET because the sites do not have sufficient grass cover to accurate measure ET. Also, the Green Valley road station (#111), which represents a warmer zone of the Pajaro valley no longer reports reference ET data due to insufficient grass cover at the site.
Having reliable long-term weather data from the main growing regions on the Central Coast is becoming more important for our region. As water demands continue to increase on the Central Coast, the agriculture community is under increased pressure to demonstrate efficient irrigation practices. Online irrigation scheduling tools such as CropManage and the Satellite Irrigation Management Support (SIMS), use CIMIS data to help growers quickly determine crop water needs. These tools can also help growers justify water needs of their crops. To comply with the Sustainable Groundwater Management Act (SGMA), water management agencies will need accurate reference ET data for developing ground water extraction plans. My hope is that through partnerships among local and state agencies, private land owners, and grower groups, we can add new or revitalize existing CIMIS stations so that all growing regions on the Central Coast have accurate weather data.
What Happens to Trees on a Hill?
Many orchards in California are planted on slopes, the most extreme examples are usually avocado orchards with some slopes exceeding 50%. They pose difficulties in harvesting because of the steepness, but also in their irrigation. These slopes can be north/south/east/west facing or all of the quadrants in the same orchard. The plantings can be of varying steepness and at different positions (toe, top, mid-slope). These positions affect solar radiation which is the main driver of evapotranspiration, but also wind interception. South and west facing slopes intercept the most sunlight, while north and east intercept the least. The top of the slope usually intercepts the most sunlight during the day and also the most wind. There can be 100% difference in the amount of ET depending on the position on the slope. That is, some trees require twice as much water as others because they are getting more energy that drives water loss.
When looking at an older avocado grove, the trees are usually larger at the bottom of the slope where there is the least wind and most irrigation water interception. This is where the soil is the deepest and has the greatest moisture reserve. The soils at the top of the slope are the shallowest and get the greatest amount of energy driving water loss. Trees on the north side are often tall from greater soil depth and moisture reserve and less ET demand. As the solar angle changes during the year (lower in the sky during the winter), the proportion of ET in these different positions changes.
Right. OK. We know this. The problem is that many smaller orchards are laid out so that there is one valve controlling the amount of water going to all the different positions. The trees at the bottom of the slopes get the same as those at the top. Those on the north side get the same as those on the south side. This basically sets up an orchard for stress. Stress that leads to disease and impacts on yields and ultimately the longevity of the orchard.
Add to this, irrigation performance varies with pressure and many orchards have very little pressure compensation. Often trees at the top of the slope have the lowest pressure and output. The distribution uniformity is often terrible. Not only are the normal problems of broken and clogged emitters an issue, but also pressure loss from elevation differences.
So where you plant on a hillside should be part of the irrigation design. In different positions on the hillside there are different water requirements and unless they are irrigated differently, there can be major differences in tree response. These different irrigation requirements should be incorporated into the irrigation design by creating as many different irrigation blocks as possible. A valve for the top of the slope, another for the north and south slopes, etc. These can be incorporated easily in the initial design and not so easily customized after the trees have been planted.
At some point, for optimum tree performance, tree health and water use efficiency, growers should recognize the need for irrigating to trees' needs according to slope position. Avocado growers have it harder than most growers.
Read more about an ET study done on a hill:
http://www.avocadosource.com/CAS_Yearbooks/CAS_86_2002/cas_2002_pg_099-104.pdf
hill trees
Fog Contributions to Avocado and Citrus Water Use - Adjusting Irrigation
Drought may not be the right time to be thinking about this, or maybe it is. It concerns managing water and any time a grower uses water more effectively the crop performs better. But fog can be a significant factor in water management.
As fog passes through a tree canopy, it is absorbed by leaves and coats them. Before the tree will transpire water, the water coating must first be evaporated before the tree loses internal water. This water use is not accounted for in a water budget schedule using evapotranspiration based inputs, such as from CIMIS. For deciduous trees, this is often not of concern, because in the winter they don't have leaves and therefore are not transpiring anyway. For evergreen subtropicals like citrus and avocado, this could be an important source of water.
In many situations in the Central Valley and along the coast there can be periods where fog can represent a significant proportion of the water requirement for an orchard. These periods would be for winter tule fog in the Valley and along the coast in the spring and early summer. A recent publication by Rick Snyder at UC Davis has just been released that shows how this fog water can be incorporated into an irrigation schedule. You can see it at the UC's California Institute for Water Resources website: http://anrcatalog.ucanr.edu/pdf/8532.pdf, http://ciwr.ucanr.edu/california_drought_expertise/droughttips/
fog
Capturing Rain
Capturing Precipitation - How much rainfall do I need to capture?
Managing precipitation to your advantage is really a three step process (Lal and Stewart, 2012).
ü Step 1 - maximize preciptitation captured in the soil
ü Step 2 - minimize the evaporation of the stored soil moisture
ü Step 3 - maximize plant water use efficiency
The first step of the process is often thought of as “effective rain”. Effective rainfall refers to the percentage of rainfall which becomes available to plants and crops. It considers “losses” due to runoff, evaporation and deep percolation (Klein, 2011). In the past we might have considered deep percolation as a loss. We now know that percolation “losses” may be a vital resource in sustaining our groundwater basins. As we move into the fall of 2015, we have the opportunity to plan for effective rainfall by managing the orchard floor for maximum capture of precipitation. This will help provide stored soil moisture for plant growth as well as deep percolation of water to groundwater
The following figure illustrates some of the important points about effective rainfall and reminds us of what we can do to maximize capture of precipitation (1). We want to maximize 2 (infiltration during a rain event), 3 (surface capture), 6 (infiltration from surface capture), 7 (percolation to ground water), and 8 (rootzone storage for use by the crop). We want to minimize 4 (runoff) and 5 (evaporation).
When rain water ((1) falls on the soil surface, some of it infiltrates into the soil (2), some stagnates on the surface (3), while some flows over the surface as runoff (4). When the rainfall stops, some of the water stagnating on the surface (3) evaporates to the atmosphere (5), while the rest slowly infiltrates into the soil (6). From all the water that infiltrates into the soil ((2) and (6)), some percolates below the rootzone (7), while the rest remains stored in the rootzone (8). From FAO Irrigation Water Management 1985 http://www.fao.org/docrep/r4082e/r4082e05.htm#4.1.4 effective rainfall
Larry Stein from Texas A&M wrote a very good basic explanation “So What Constitutes an Effective Rain Event ?” (Stein, 2011) We can use his approach to look at managing precipitation in the Central Coast. Understanding these concepts can help you manage precipitation in your operation.
For example, the majority of olive roots are in the top 18 inches of soil. So how much rainfall do we need to capture to refill the rootzone of an olive grove in Paso Robles? We need to know:
ü The amount and intensity of rainfall
ü The infiltration rate of the soil (how fast the soil takes in water). Sandy soils take water in more quickly.
ü How much water the soil will hold in the rootzone of the grove
Average rainfall for Paso Robles in January is about 2.75 inches. Table 1 shows that olives on a sandy loam soil might be able to infiltrate 1 to 1.5 inches per hour. If all that rain comes in one storm then as much as 1.25 inches may either run off (4) or pond (3) in the low spots until it can infiltrate.
Average rainfall in Paso Robles in January would be adequate to refill the rootzone of olives (8) on a sandy loam soil, IF all of the rainfall infiltrates (2), and none is lost to evaporation (5) or runoff (4).
Table 1. General soil water storage and depletion characteristics for three different soil types (Klein, 2011)
|
Soil Texture |
||
|
Sands |
Loams |
Clays |
Water infiltration rate (inches / hour) |
2.0 – 6.0 |
0.6 – 2.0 |
0.2 – 0.6 |
Available water (inches / foot) |
1.0 – 1.5 |
1.5 – 2.5 |
2.5 – 4.0 |
Days to depletion when ET – 0.2 inches / day |
5 – 7.5 |
7.5 – 12.5 |
12.5 – 20.0 |
Amount of water to wet to 18 inches in a dry soil (inches) |
1.5 |
2.25 – 3.0 |
3.75 |
Cover crops help keep the soil surface from crusting as well as protecting the soil surface from erosion. Their roots provide channels for water to infiltrate into the soil. Remember that cover crops may also be using water stored in the rootzone (8). When facing drought conditions, it may be advantageous to manage with low residue cover crops to reduce the amount of water extracted from the rootzone. Here's a link to a video on low residue cover crops and their impact on runoff from work by UC Cooperative Extension Advisors in Monterey County https://www.youtube.com/watch?v=k0oVVJ_BA7s
Klein, L. 2011. So What Constitutes an Effective Rain Event? http://aggie-horticulture.tamu.edu/earthkind/drought/drought-management-for-commercial-horticulture/so-what-constitutes-an-effective-rain-event/ .
Lal. R.and, B.A. Stewart. 2012. Soil Water and Agronomic Productivity
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rain