Irrigation Scheduling

Irrigation Scheduling

4 min read

In a perfect world there would be enough rainfall to supply agricultural crops with all the water they need in a growing season. This isn’t a perfect world though and farmers throughout the United States and around the world rely on irrigation systems to deliver water to crops. To meet the needs of growing populations they are working hard managing their operating systems to increase the efficiency of inputs, reduce waste, and maximize yields in a concerted effort to increase their net returns while conserving natural resources. Managing irrigation systems to foster efficiency and sustainability has become an important aspect of their businesses. Precision irrigation has become an invaluable tool in their arsenal, helping farmers to schedule and implement an irrigation strategy that encourages healthy root development, reduces nutrient, chemical, and water waste, while maximizing the utilization of water across every zone of every field.

Precision irrigation is changing how many farmers water their crops, turning irrigation into high tech systems. Efficient irrigation comes down to a key factor: applying only the amount of water plants needs, and ensuring they have it when they need it. Irrigation scheduling, in simple terms, is determining the “when” and “how much”.

The key factors in managing irrigation scheduling are:

  • Looking at how much water gets into the soil from rainfall
  • How much water the soil can hold overall, and
  • How much water the plant is using

Looking at these factors paints a picture explaining when and how much to water so crops don’t experience water stress and can efficiently utilize water available in the root zone.

Agriculture is changing, at what sometimes seems to be a rapid pace and more tools are becoming available for farmers to improve cropping systems management. A growing demand for increased food production, on less acreage and with fewer resources means the agricultural industry in general is constantly looking at ways to benefit production.

In irrigated cropland systems, irrigation scheduling and precision irrigation are becoming commonplace and provide many benefits:

  • Applying water to fields before plants experience water stress leads to yield maximization down the road
  • Efficiently scheduling irrigation so it’s only done when needed reduces water and labor costs
  • Fertilizer costs are reduced due to a minimization of runoff and leaching through to groundwater because water isn’t over applied and allowed to move out of the root zone
  • Water logging problems are minimized, helping to reduce soil salinity concerns in affected regions

Most importantly though, all of the benefits of precision irrigation are coming together to increase the net returns of farms.

When looking at irrigation scheduling for increased water use efficiency and plant growth, there are different approaches, varying in their methods and cost:

  • Checkbook method (Pro: easiest, Con: doesn't account for environmental factors)
  • Soil moisture sensors / probes (Pro: real-time data to make irrigation decisions, Con: some investment)
  • Modeling software (Pro: more complicated, Con: lots of data to consider)

The simplest route is to use basic calculators to roughly determine when to schedule irrigation. A common calculator used by farmers is the checkbook method1. This is a manual soil water balance accounting method taking into account available moisture levels and the amount of water a crop needs during each week of its life-cycle. The soil in the field is like a bank checking account; the checkbook method considers rain and irrigation as deposits to the account and crop water use as withdrawals from the soil water. Irrigation is scheduled to keep the checkbook balance in a range just below field holding capacity to prevent water stress, without over watering and causing leaching or runoff. It does not account for other environmental factors but simply uses mathematics to determine crop irrigation needs.

A slightly more technical method used for precision irrigation and scheduling involves using sensors to measure field conditions. They provide real-time readings of the amount of water available in the soil and the amount being lost to evapotranspiration through the plants.  Watching sensor measurements gives producers the ability to turn on water when plant and soil moisture levels drop below a certain threshold, and then shut it off when the desired level is obtained. Over application of water is significantly reduced reducing waste, input costs, and potential environmental impacts by only applying water when needed. Plant sensors take into account the water balance method; they measure water loss through evapotranspiration, showing crop use and then balance incoming and outgoing water levels to maintain adequate soil moisture for the plant. Soil moisture sensors assume that the soil moisture content largely determines the moisture status of the plant. If there is low soil moisture, the plant must work harder to take up that water, causing the plant stress. When soil moisture levels drop below a recommended threshold, irrigation is scheduled to prevent stress and yield reductions.

The most technologically advanced – and expensive – method of irrigation scheduling uses modeling software, and is a growing trend in cropping systems. Sophisticated tools combine soil and plant sensors, weather data, soil characteristics, historical trends, aerial and satellite imagery, and complicated computer algorithms to advise farmers when to water, and how much water volume to apply. Cloud computing brings the data directly to the farmer allowing access to it through a web or mobile platform. Farmers can control all aspects of their irrigation systems from turning pumps on and off, monitoring weather stations, viewing real time soil moisture levels from their smart phone or tablet allowing them to quickly assess irrigation needs and react accordingly.

Irrigation is a vital aspect of crop production for many farmers, without it their cropping systems would struggle to thrive and produce little harvestable commodities. It is though an expensive part of farming and producers are constantly looking for ways to reduce their inputs costs, increase the efficiency of their cropping systems, while maximizing yields and net returns. To better manage irrigation systems, many implement irrigation scheduling and precision irrigation to ensure water is applied when the plants need it most to reduce plant water stress and to reduce the problems that arise from overwatering. There are many options for irrigation scheduling ranging from simple calculators to intricate modeling software, providing farmers with choices to best fit their farming systems. Smart irrigation: yet another advance helping farmers to foster sustainable, efficient agriculture systems.

 

1 Irrigation scheduling checkbook method

3 Types of Soil Moisture Sensors - Which is Best For You?

3 Types of Soil Moisture Sensors - Which is Best For You?

5 min read

In this day and age, technology plays an integral role in many aspects of our lives. While it seems agriculture would be exempt from that — for it’s just putting seeds in the ground and growing plants — this is far from the case. Farming is not simple. As the population grows at an exponential rate it creates really dynamic problems in terms of feeding people. More people means more food needs to be produced. But more people also means more homes will be built and more water will be consumed, taking away valuable land and water resources needed for food production. In order to feed this growing population with fewer resources, the agricultural industry has to rely on technological improvements. Advancements such as genetic engineering, GPS technology, herbicide tolerance, aerial imagery, robots, soil sensors, and precision agriculture have turned farming into a sophisticated business.

Currently there are more than 55 million acres of cropland irrigated in the United States. Growers rely heavily on their irrigation systems to provide the right amount of water to their crops at the proper time. Drought stress on plants can easily and quickly reduce yields. Because of technology, soil moisture sensors can provide growers a detailed, comprehensive picture of their irrigation systems. Watching sensor readings allows them to turn on water when the moisture levels drop below a certain threshold, and then shut it off when field capacity is reached. In turn growers are only applying water when needed, reducing over application of water. This becomes both a financial and environmental win. They aren’t wasting water and money, nor are they leaching nutrients and chemical pesticides into groundwater. Using soil moisture sensors decreases input management costs while maximizing yields and profit.

There are three main types of soil moisture sensors, each differing in how they take field measurements and determine soil moisture levels. Each type has their own set of pros and cons, filling specific needs in the market.

 

 

Volumetric sensors

Volumetric soil moisture sensors directly measure the amount of water in the soil. This category has the most sensor types: neutron moisture probes, heat dissipation sensors, and the common, di-electric sensors. The di-electric sensors measure the di-electric constant of the soil, an electrical property dependent on soil moisture content, and can be purchased in 3 variations: Time Domain Refractometry (TDR) sensors, Time Domain Transmissiometry (TDT) sensors, and capacitance or Frequency Domain Refractometry (FDR) sensors.

 
Decagon ECH2O 5TM FDR Sensor

Decagon ECH2O 5TM FDR Sensor

 
GroPoint Pro TDT Sensor

GroPoint Pro TDT Sensor

 

Due to the technology used, volumetric sensors are the most expensive soil moisture sensors to purchase ($100+ per sensor, $400–1200 for an electronic reader). When installing them in fields they also require calibration to the individual soil type, making installation more cumbersome. On the flip side, they are incredibly accurate and provide instant data to growers. They are commonly used in research settings and in high-value crops where speed and accuracy justify the higher equipment cost.

Tensiometers

Soil particles hold water through either tension or adhesion. Tensiometers are soil moisture sensors that measure this tension between soil particles and water molecules. In order for plants to access this water they must overcome the tension to draw water molecules away from the soil particles and into their roots. The soil matric potential or soil moisture tension reading tells how hard the plant must work to extract water. A tensiometer is a vertical, water-filled tube with a porous tip that is inserted into the soil at recommended depths; the soil draws water out of the porous tip of the sealed tube, creating a vacuum. Drier soils create a stronger vacuum since water molecules are harder to pull off soil particles.

Overall, tensiometers are relatively simple and inexpensive equipment (sensors cost about $80–160 per unit1) to incorporate into your irrigation system; they are easy-to-use since the data collected is straightforward and doesn’t need to be interpreted. These sensors do however require higher maintenance throughout the growing season. The water in the sealed tubes needs to be refilled and cleaned, and they cannot stay in the field through the winter in colder climate zones. Tensiometers work best when installed in fields that maintain fairly adequate moisture content. They can only operate within certain levels of suction, rendering them useless in drier conditions.

 
Irrometer SR Tensiometer

Irrometer SR Tensiometer

 

Solid state sensors

The most inexpensive option for measuring soil moisture content is solid state sensors which cost about $35–60 per sensor unit1. Common types of solid state soil moisture sensors are gypsum blocks and granular matrix sensors. They work by using two electrodes to measure the electrical resistance in the soil. More water in the soil will reduce electrical resistance because the electrical current can pass through the water easier; less water will increase the resistance. After the electrical resistance is measured the water tension is calculated to determine the plant available soil moisture. In gypsum blocks the electrodes are embedded in a porous block of gypsum that has to maintain contact with soil. Granular matrix sensors have a granular matrix inside a metal case. The electrical sensors are embedded in the granular matrix above a gypsum wafer.

Irrometer's Watermark Solid State Soil Moisture Sensor

Irrometer's Watermark Solid State Soil Moisture Sensor

Solid state sensors are the least expensive option for soil moisture sensors and do not require calibration for soil texture. However, they do need to be installed correctly and replaced periodically as the gypsum dissipates. They are much slower to measure field conditions, and are slightly less accurate in very sandy soils due to the larger soil particles. The biggest drawback to solid state sensors is that they do not work accurately in high salinity soils as readings are skewed by the elevated salt content. Because of their drawbacks, they do not work well in extremely arid conditions, or crops that are highly sensitive to water stress.

 

 

Increasing populations continue to put a strain on the agriculture industry. As communities continue to grow, more food needs to be produced on less acreage and with less water available for crop production. In order to meet these demands, it’s become necessary to incorporate technological advances in farming. Irrigation is no exception. In the last decade, monitoring the soil moisture content of fields using remote sensors has become a critical management tool for many producers. It helps to irrigate exactly when fields need water, limits nutrients runoff from over-saturation, and reduces input costs through precision techniques. Soil moisture sensors vary in the technology used to measure soil moisture, as well as their advantages and cost.

Methods to Monitor Soil Moisture

Trellis Partners with UGA for Water Conservation Project

TRELLIS COMPLETES WATER CONSERVATION PROJECT

Easy-to-use soil moisture monitoring system helped growers in southern counties

Using Trellis' soil moisture sensors helps farmers maximize plant growth. Above is shown one of the farms participating in the water conservation project.

Using Trellis' soil moisture sensors helps farmers maximize plant growth. Above is shown one of the farms participating in the water conservation project.

Together with the UGA Extension Office, the metro Atlanta-based AgTech company Trellis completed a 2017 water conservation project with local cotton growers from eleven counties across southwest and southeast Georgia. Trellis supplied and installed three wireless soil moisture stations (66 total) and a cellular base on each of the selected farms (22 total) to help growers make better irrigation decisions during the growing season.

The goal of the project was for growers in Georgia to conserve water while still irrigating efficiently and affordably: Existing soil moisture systems cost thousands of dollars, but Trellis’ cost-effective product made this project possible. The initiative also introduced many growers to soil moisture sensors, a tool many had never used before, and improved the experience for those who had.

“I’ve been working with soil moisture probes for 15 years and Trellis’ are the first ones that I trust,” said Evan Mobley, a grower from Burke County.

Before the sensors were installed, Trellis helped train county agents on the system and how to interpret the soil moisture and temperature data collected by the sensors.

“Since installation, Trellis has configured their dashboard to provide secure access to informative views of the soil moisture data to all the project agents and farmers,” said Calvin Perry, superintendent of UGA’s Stripling Irrigation Research Park in Camilla, GA, and one of the managers of the project. “Trellis has proven to be a solid, responsive, and reliable vendor for providing soil moisture sensing hardware and data visualization dashboard," Perry said.

Last month, Trellis removed the wireless sensor stations and cellular base stations in preparation for harvest, but already growers have seen positive effects as a result of Trellis’ easy-to-use soil moisture monitoring system. “When I’m out of town, I trust what these sensors say,” Mobley said. “I love them - they work great. I know exactly what’s going on & am able to understand it.” 

 

Trellis, Inc. is an AgTech company founded in 2015 and currently operating out of the hardware startup incubator Prototype Prime in Peachtree Corners, GA. Trellis helps growers and consultants save on irrigation costs and improve crop yields with its easy-to-use and cost effective (10x less expensive than comparable products) soil moisture monitoring system.

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