PAANZ Workshops - Technology to Reduce N Leaching

If you are a farmer or involved in the primary sector and wanting to further understand the issues around N leaching and the potential solutions available to better manage nutrients on farms then the "Technology to Reduce N Leaching" workshop may be of interest to you.

These workshops are being run by Precision Agriculture Association NZ in the North Island on the following dates:

1st September - Palmerston North
2nd September - Hastings 

For more information visit precisionagriculture.org.nz

Downfalls of a Long Irrigator

Up until the early 2000’s when dairy conversions were a plenty, the centre pivot irrigators that were being installed seemed to be getting longer and longer. It seemed that the longer the pivot you could put on, the cheaper the per ha cost of the system became. However, several studies more recently carried out have brought to light the negative effects and inefficiencies of some poorly designed long pivot irrigators.

A standard pivot in the USA is a quarter mile long (approx. 400m) which enables it to irrigate a half mile by half mile section, the development of centre pivot technology has primarily been based on these standard specifications. Akin to the common Kiwi approach of creating innovative solutions to suit our farming conditions Kiwi’s went about lengthening these standard pivot designs. It didn’t take long though for farmers and irrigation installers to realise that there was a major trade-off between system length and the instantaneous application rate of water going on out towards the end of the irrigator. The problem being that the further out you get the faster the machine is travelling, therefore the higher the instantaneous application rate needs to be. This introduces major issues including crop and soil damage and surface ponding. With surface ponding comes runoff, bypass flow and leaching – all things that should be avoided!

Alarm bells should start ringing when you start talking about pivots longer than 660m. Now, a pivot longer than 660m isn’t necessarily bad, but you need to consider the design carefully to ensure that you are irrigating within tolerances of the soil and farming system. The Irrigation New Zealand Design Code Of Practice has some great information about what soil features should be considered during the design process.

In a nutshell, when looking at the length of an irrigator, you need to consider:

1. Soil type
2. The infiltration rate of that soil
3. And the maximum instantaneous application rate of the pivot

The latter should not exceed the infiltration rate of the soil as otherwise the negative outcomes previously mentioned are likely to occur. There are also other properties such as the water holding capacity and the effective crop root depth that should be factored into the design to ensure that you are getting enough water to the plant, but not over-watering and causing problems.

The other issue is engineering. A longer, higher discharge rate machine must have bigger pipes which means more weight and stress on motors and gearboxes (and soil). And also all the water has to be pressurised to meet the requirements of only a little of the water right at the end of the machine - which is not energy efficient. A short machine can cover the extra capital cost per hectare very quickly by reducing operating costs, obviously each situation is different, but it may be worth getting your irrigation dealer to help you do some figures.

If you do happen to have a very long pivot, you may be experiencing some of the problems mentioned inherent with the design. If you are seeing some of these issues, there are a few steps you can take to help improve the performance of your system.

1. Increase the wetted footprint of your sprinklers, effectively lowering the instantaneous application rate over any particular point. You can do this by alternately attaching sprinkler drops to the forward and rear truss rods, changing the sprinkler heads on your machine to sprinklers with a larger throw, or putting tees in and increasing the number of sprinklers while still slinging them over truss rods. This will only go so far towards solving the problem but it may help.
2. Using Variable Rate Irrigation could help depending on the variation in your soils and your topography. By knowing more about the physical constraints beneath your irrigator, you can then use Precision VRI to better manage to those constraints. Agri Optics can help with their EM Mapping and Data Management services.
3. And the most expensive capital-wise, but potentially the most effective and highest potential for reducing operating costs is to decrease the length of your pivot. This may mean reconfiguring pivots on your farm to still irrigate the greatest area. There is a significant capital cost, but if you do the numbers as some research studies have shown, it could well be worth it to increase your irrigation efficiency.

The one thing in common with all of these approaches is that you need to know the characteristics of your soils (including the variability in soils) and then design your system to work within the constraints.

But there is no substitute for a well-designed system. For well-designed irrigation solutions or to discuss how you could improve the efficiency of your centre pivot contact your local Zimmatic dealer.

We hope you find the information in this post useful. The information was supplied by Stu Bradbury who has many years of experience creating irrigation solutions from the ground up so to speak. The ideas began to spark while spinning spanners and installing irrigators in the early 2000's. He has gained a wealth of knowledge through numerous research studies and much trial and error over the years. Stu's current role is VRI Solutions Advisor for Lindsay NZ.

Stu Bradbury working on a Precision VRI system on a centre pivot

Event Reminder: B+LNZ South Canterbury Farming for Profit Technology Expo - August 11th

Farmers in Canterbury and North Otago don't forget to head along to the Phar Lap Raceway in Timaru tomorrow for the B+LNZ South Canterbury Farming for Profit Technology Expo.

There is a great line up of presentations including a number relating to precision agriculture and efficient irrigation. And if you would like to meet some of the connections and contributors to the H2Grow blog in person than be sure to grab a front row seat in the following presentations:

4pm - Variable rate irrigation and the latest irrigation technology from Lindsay, manufacturers of Zimmatic, Growsmart and FieldNET irrigation solutions.

4:30pm - The benefits of EM surveying and precision agriculture products and services offered by Agri Optics NZ.

For full details of the agenda click here.

... and I will give you a heads up that H2Grow will be kicking off an exciting competition from 1pm tomorrow. Entries can be made at the Technology Expo and online, so head along tomorrow or watch this space for more details!!

From your friendly H2Grow Team

Reduce the Cost of Nutrient Loss with Precision Ag (Part 3)

In the last two blogs we looked at how Precision Ag can help with managing the nutrient and moisture levels in the soil profile. This blog looks at how an EM survey can assist in relation to the physical characteristics of the land for your farm environment plan.

As an EM survey is conducted, the readings are logged by 2 cm horizontally accurate RTK GPS. This allows us to not only build a great picture of your soil profile but also the surface of the area surveyed as well. This in its own right can be a very powerful tool for overall land management and also the farm environment plan. As the flow of water can cause the movement of soil and nutrients.

With this layer of data we can make 3D contour or water flow maps. So you can see where water will move in a rain or irrigation event and where potential areas of soil/nutrient issues may occur, so buffer zones may be necessary to mitigate this potential problem.

 

Picture 1: 3D elevation map showing the potential water flow across the area.

Our software platform, VA Gateway, can model the flow of water and we make an animated model of how the surface water will react over time. On the first image (picture 2) below you can see the surface water after a rain event then moving down the images how the water moves from the higher area and ponds in others. This sort of information is of great use to the client for highlighting potential issue zones.

Picture 2: Simulator showing the water flow after a large rain event.

Picture 3: The water is flowing from the higher areas.

Picture 4: The water is ponding in the low lying areas.

With variable rate irrigation application maps on ‘hilly’ land we can combine the EM and slope maps, to take into consideration the severity of slope over the EM. That is to say it may be a soil type that requires a higher water rate but when you take into consideration the degree of slope, then higher application rates would be moving down the slope as well infiltrating the soil profile, so therefore a lower application rate is needed on the steeper sloped areas to reduce the chance of runoff. By managing the potential flow of water across your property you are also managing the movement of soil and nutrients.

 

Picture 5: At the top left the EM zone map, on the bottom left the slope map. On the right the two maps have been combined to form an application map using both characteristics.

In Picture 5, on the right side is the application map where is red low EM, green Medium EM and blue high EM - the matt colours indicate low slope, the bright colours higher slope.

So with the use of Precision Ag you can gather very comprehensive maps showing the levels variability in nutrient levels, in soil characteristics and in topography for your property. By measuring these variables you can then monitor them and manage them, which are prime requisites for your farm environment plan.

Chris Smith

Agri Optics NZ Ltd

Reduce the Cost of Nutrient Loss with Precision Ag (Part 2 of 3)

In the last blog post we looked at nutrients and how Precision Ag can help with your Farm Environment Plans (FEP). This blog post looks at how an EM survey can help with identifying your soil types for your Farm Environment Plan.

An EM survey illustrates the relative variability in soil characteristics including soil texture that can be potentially related to water holding properties within that soil profile, this can help you manage water application through the use of variable rate irrigation technology. When combined with the use of soil moisture probes you have the data and technology you need to be able to retain nutrients within the soil profile itself. 

EM surveys can be ground-truthed to find the correlation between the EM value and water holding capacity (WHC).  From that you can create a WHC map and site-specifically place moisture probes to monitor the soil moisture levels within each identified zone.

Ground-truthing sites are identified within each zone (shown on the left). The graph illustrates the correlation between the EM values and WHC in the top 55cm of the soil profile for this paddock.

In the image above we can see the correlation between EM value and WHC at this site has an R2 of 0.97 (R2 quantifies goodness of fit. It is a fraction between 0.0 and 1.0, higher values indicate that the model fits the data better). We can then use the equation in VA Gateway, one of the PA software platforms supported by Agri Optics, to create a water holding capacity (WHC) map out of the EM values map.

The EM map converted into a Water Holding Capacity map

This water holding capacity map can then be used in conjunction with soil moisture probes and VRI to maintain the moisture levels between field capacity and critical moisture. This not only reduces any potential yield loss from moisture stress but it also ensures that you aren't saturating the soil profile, and therefore avoid leaching nutrients out of the root zone.

It’s all about balancing crop requirements, real-time moisture levels, rainfall (when it comes!) and application rates with irrigation return times as precisely as possible to keep everything at an optimum level.

An AquaCheck soil moisture probe graph showing soil moisture levels and how they are affected my irrigation or rain events on this soil profile.

As can be seen above by keeping the moisture between upper and lower readily available water levels you ensure yield isn’t compromised and eliminate leaching. The rooting depth used for the probe profile can be tailored to the crops specific needs on the moisture monitoring website.

Next time we will discuss how the EM maps and topography data can help you with your FEP.

Chris Smith

Agri Optics NZ Ltd