The Irrigation, Grazing Game

In this week’s H2Grow blog post we are pleased to introduce our first guest contributor - Nicole Mesman.

My name is Nicole Mesman and last year, since finishing my honours in soil science at Lincoln University, I have been working for Lindsay NZ to review the benefits that farmers are receiving from their Growsmart Precision VRI systems. My honours project looked at the effect of grazing and irrigation on soil porosity. While university projects are often published in journal articles I feel like research can sometimes take a long time to make its way to our farmers and end users, those who we are trying to help with this research in the first place. I am very happy that I am able to explain my findings to an audience that might be able to make use of this information.

I wanted to find out what, if any, effect irrigation was having on soil porosity and water holding capacity. From both my findings and the research of others I was able to suggest that a combination of irrigation and cattle grazing led to a decrease in soil macroporosity and those micropores holding water in the range readily available to plants. Also that there is an increase in very small micropores storing water that plants are unable to access.

Macropores are the largest pores, they don’t store water for the plant but provide aeration for the soil, space for root growth and allow water to infiltrate through them to the small micropores that the plant draws water from. Reduction in macropores can result in decreased root and plant growth and an increase in waterlogging and surface run-off as water is unable to infiltrate into the soil and instead pools and runs off the surface.

Macropores allow water to pass quickly through them and are occupied with air unless the soil is waterlogged. Micropores store water for plants to access, some micropores are so small that plants are unable to draw water out of them.

The result of a decrease in micropores is less water held between field capacity and refill point; readily available water for plants. In order to ensure plants have optimum water available to them irrigation volumes should be decreased but made more frequent to ensure neither overwatering or water stress is occurring. Once compaction of soil and decrease of microporosity has occurred it is easier for damage to continue. Soils take longer to dry out after irrigation and subsequent grazing events are more likely to damage the soil again.

When a soil becomes compacted under a combination of irrigation and grazing events the available water decreases as soil particles are compressed together. This means there is less water available to the plant and irrigation volumes should decrease while frequency increases to maintain water content.

If you think you may be seeing the negative effects of decreased macroporosity and microporosity on your property then there are steps you can take to avoid further damage:

• Soil moisture sensors that are calibrated for your soil type allow you to identify when your different soils require irrigating and mean that you can change your irrigation volumes according to your field capacity. Reduction in micropores may mean that soils retain a higher moisture content for longer and are more susceptible to further damage when grazed. Moisture sensors will also allow you to monitor areas that have been irrigated and determine when moisture content has decreased below field capacity and stock could be moved back to graze the area, avoiding further damage to soil structure. 
• Decreased macroporosity can be countered by leaving a paddock under pasture, allowing roots and organic matter additions to create structure while using variable rate technology to adapt your irrigation. Irrigation can be altered to avoid areas where decreased macroporosity has resulted in ponding, this can help the area dry out and encourage grass growth.

That’s all for now but please watch this space for my next post where I will tell you about the specifics of my trial, quantify the changes in macroporosity and microporosity that myself and others have measured, explain the role of these properties in soil quality and natural capital and how their importance in this system can be assessed.  

Blog post by Nicole Mesman - BSc (Hons) Soil Science

Tools For Growing Farm Profitability

Today I’m taking writer’s liberty and changing tack slightly. While we’ve been talking about variability and how to manage it and irrigation efficiency I’m going to share some insights from the knowledgeable Jim Wilson of Soil Essentials in the UK who is currently out in NZ sharing his almost 20 years of Precision Agriculture (PA) insights from the other side of the world with us.

This morning the Foundation for Arable Research held a field day at Craige Mackenzie’s place near Methven to talk about ‘Practical use of Precision Agriculture: A global perspective’. One of the main questions from farmers this morning was “where do I start with PA?”. While there are many different places that someone can start their PA journey depending on what they’re most interested in and where they see the most benefit the moral of the story today was to start where you’d see the most benefit or return from your investment. If the biggest expense to your business is fixed costs (eg labour, diesel etc for planting etc) then GPS and Autosteer is the likely starting point for you. If your biggest cost is your fertiliser bill then, grid sampling and variable rate fertiliser is likely the best starting point for you and if the cost of water and irrigation one of the biggest costs to your business, then EM Surveying and variable rate irrigation are likely your starting point. The key is to know your business and where your biggest & fastest gains can be made from utilising these PA techniques. Precision Ag at the end of the day is about fully utilising all of these tools and technologies to MAXIMISE ON FARM PROFITABILITY.

Jim Wilson & Craige Mackenzie up the Mt Hutt skifield access road

 assessing the variability over the Canterbury Plains.

Another key theme that came from today was the use of yield mapping. While Jim said that adoption of yield mapping is still growing with his customers and in the UK in general, he emphasised that it was one of the most important layers of information on a cropping farm to help identify and quantify areas of yield variability and what that variability is. He said it was also a really important layer particularly for Scottish farmers (as you could imagine) they don’t like to spend money where it doesn't make them any. The yield maps enable them to identify areas of interest and manage them accordingly.

Jim Wilson talking at FAR’s field day on Precision Agriculture with soil variability

 and topography variability in the background.

Other PA techniques that are used widely in Jim’s area of the world are grid soil sampling and variable rate seeding. Grid soil sampling is where a soil core is taken in a uniform fashion across a paddock at either 4 samples per hectare for pH or 1 sample per hectare for phosphorus, potassisum  magnesium,  calcium & sulphur. This allows them to then variable rate apply fertiliser based on these soil test results.  Variable rate lime application based on pH test results is very common in the UK and has a significant return on investment, usually resulting in savings of lime of approximately 50%. Variable rate seeding on the other hand is where the seeding rate is varied according to soil type and the soil’s yield potential. Heavier soil typically gets a higher seed rate than lighter soil where less seeds are planted to allow less competition between the plants and optimally more seed fill per plant.

All of these techniques talked about today by Jim are by no means new to New Zealand’s precision ag scene, however some are done to varying degrees here.

So, what’s the take home messages from today?

1. Start your Precision Ag journey with what will give you the biggest financial change
2. Use your yield maps and turn them into something other than pretty wallpaper – talk to someone in the know on how they can be made useful J

Regular Farm Irrigation Assessments Pay-Off

The current soil moisture deficit conditions in many areas of New Zealand should prompt irrigators to assess the efficiency of their irrigation system and management practices. The information that this blog is beginning to build upon hopes to increase understanding and awareness of technologies so these improvements can be implemented.

What is yet to be defined is Irrigation System Efficiency, while you will find many variations in the wording of definitions in a nut-shell it is the ration of irrigation water available for plant growth to the total amount of irrigation water delivered to the farm. So 80% Irrigation System Efficiency means that 80% of the water delivered to the farm has been applied and stored in the crop root zone and therefore available for plant growth.

Recent roadside assessments of irrigation systems show there are some very simple irrigation management modifications that can be made with only the basic level of knowledge.

Irrigating the road = 0% irrigation efficiency as well as being a safety hazard. However much irrigation you put on the road it’s still not going to grow grass!

If your irrigator has an end gun control function then contact your irrigation dealer to find out how to program the end-gun to turn off at any point it is irrigating outside the boundary of the growing area. If your irrigator does not have an end-gun control function than you may consider a GPS End Gun Controller, for more info click here or contact your local Zimmatic Dealer.

Ensuring that the staff that are charged with managing your irrigation as well as those that occasionally help out are adequately trained is really important. If there is not the time or resources to carry out the training in-house there are courses run through IrrigationNZ and many online resources that are very helpful. Considering a guidance system for shifting K-line’s could resolve many issues and result in a significant increase in your irrigation efficiency.

Regular maintenance of your irrigation system can save wasted water as well as forgone growth from under-watering. As an example a blocked sprinkler near the end of a 500m centre-pivot could be causing ~5ha of your property to be under-watered. Many of these maintenance issues are easily identified provided staff are aware of what to look out for.

Limitations of irrigation infrastructure can be a constraint to improving your irrigation efficiency. As seen in the image above the irrigation water being applied within the ditch is not contributing to pasture growth, and is likely to cause wheel rutting and potentially a stuck pivot. Should your centre-pivot or linear-move irrigator run over non-productive areas, roads, tracks or water-ways then variable rate irrigation technology would allow you to avoid irrigating these areas. This not only will save you water and potentially energy costs but also prevent the other issues that arise.

Future blog posts will discuss variable rate irrigation technology in more detail and the many applications in addition to avoiding irrigating certain areas where the technology offers benefits.