Key Learnings from the IrrigationNZ Study Tour to Nebraska

I was part of a 24-person group who went to Nebraska at the start of September 2018.  The tour was organised by IrrigationNZ and was an amazing opportunity to go and see how another part of the world deals with the same issues that we have here.  Below is an overview of my key learnings from the tour.  

Governance of Water

The governance of water in Nebraska is complex. There is Federal legislation, such as the

Endangered Species Act, which the state has to abide by. Alongside this there are also Federal agencies, such as the Bureau of Reclamation that control most of the surface water through storage and diversion infrastructure. The state then sets its own laws around how it will manage its water.

In Nebraska the surface water is manged at state level by the Department of Natural Resources, but groundwater is managed by Natural Resource District’s (NRD) at a local level. For a number of surface water bodies, there are also interstate pacts that determine how much water must remain in the river to reach downstream states.

The NRD’s have a Board that is democratically elected, and are often dominated by rural people including farmers. Despite this, the farmer representatives have been proactive in driving practical change among their peers.  

The NRD system in Nebraska has been very successful in managing groundwater. All takes are controlled through a well permit system that allows for a given number of hectares to be irrigated per well.

Both of the NRD’s that we visited had invested heavily in science to help them better understand their resource. They also look for solutions as both a farm and catchment level, the latter including raising capital to build environmental infrastructure such as that required for augmentation projects.  

Conjunctive Management

‘Conjunctive management’ is a recent development in Nebraska that has largely come about through the management of ground and surface water takes in ‘conjunction’ to achieve interstate pacts. This has involved the NRD’s (the managers of the groundwater) working closely with irrigation districts and the Department of Natural Resources to ensure downstream flows are achieved.

This has included restriction of individual water takes (wells) – controlling any new ones, limiting the irrigated area from existing ones and in some cases placing a seasonal limit on usage. Alongside the implementation of environmental infrastructure such as Managed Aquifer Recharge and Stream Augmentation projects.

Managing Water Quality

Nitrates in groundwater are of significant concern in the heavily irrigated districts of central Nebraska. In some areas over 50% of the land is now under irrigated crop-farming. Historic poor nutrient management (type and timing) and poor irrigation practice resulted in nitrate concentrations being frequently observed over 30ppm – well over the US drinking water standard of 10ppm.

However, in recent years there has been a significant declining trend, with relatively few areas now exceeding 20ppm. This has largely been brought about by a non-regulatory approach.

State law requires the production of water quality and quantity management plans that identify the issues and then require the development of an implementation plan to address them. All the NRD’s have a rule framework, but most of the rules are currently focused on managing water takes and farming practice reporting. Incentives, knowledge and enabling peer to peer learning in combination with environmental infrastructure is currently seen as the way forward for water quality.

The widespread move from surface flood to centre pivot irrigation has been instrumental in reducing nitrate losses to groundwater. This has enabled soils to be irrigated on an ‘as and when’ basis to minimise nitrate leaching. There is now also a push towards the more widespread adoption of fertigation, as it allows ‘as and when’ nutrient applications – significantly reducing the risk of leaching from rainfall events.

Public perception

Despite the widespread use of intensive farming methods, and the water quality and quantity challenges facing Nebraska, the one issue currently not facing farmers at the state level is pressure from the anti-farming lobby or environmental groups.

Of the almost 2 million people living in Nebraska, the majority understand the role of crop farming and ranching in providing for their social-economic well-being. The Nebraskan economy is based on the irrigation of almost 4 million hectares of corn and soy beans and this is widely understood. 

The University of Nebraska research and extension service runs an outreach programme to attract the next generation to agriculture. This currently interacts with one in every three school age children in the state, providing an agriculture ‘101’ and highlighting the exciting career opportunities that exist within it.

Keri Johnston, Irricon

Natural Resources Engineer

It's starting to get dry...

Other than this slightly cooler snap we've had over the last couple of days you'd have to say spring is well and truly here! And with these nor-west winds (in Canterbury anyway) and warmer days things are starting to dry out and there's not much rain on the horizon. The seasonal weather outlook from NIWA suggests that we're in for a dryer than average season in most places (https://www.niwa.co.nz/climate/seasonal-climate-outlook/seasonal-climate-outlook-september-november-2018) and at this point I'd have to say they're about on the money. 

The joys of being a farmer or in the ag industry is that everything you do hinges on the weather, so we get really good (for the most-part) at managing timings and inputs and reading the signs to optimise what we do on farm. Now is no different. Whether you're an irrigated farmer or a dryland one now is the time to be installing your soil moisture probes if you haven't done so already so that you can accurately measure and manage your soil moisture and timings of related inputs on farm. 

Soil moisture probes allow you to know whats going on under your feet and make accurate and timely decisions to set yourself, your farm, your crops and your livestock up to perform to the best of their ability for the coming season. Soil moisture is one of the key drivers for plant growth so it's important that we know where we're currently sitting in terms of soil moisture levels so we can react to it accordingly. Decisions around fertiliser (and other input) timings, timing and amount of irrigation, stock carrying-capacity decisions etc can all be driven by more accurate information regarding soil moisture levels. 

If you want to find out more about some of the leading soil moisture probes in the NZ market have a look here: https://bit.ly/2OyeVj1 

And if you're wanting to get some installed for the coming season please pick up the phone and give the Agri Optics team a call now before you run out of time and you're left carrying a spade in the back of your ute or ruining the tip of your good pocket knife for the upcoming summer. 

All the best for an upcoming and prosperous season ahead! 

Cheers, 

Jemma

The Irrigation, Grazing Game - Digging Deeper

Following on from last week our guest contributor Nicole Mesman digs a little deeper into the findings from her research that looked at the effect of grazing and irrigation on soil porosity.

Soil natural capital and soil health may seem like unnecessary concepts, names that you already know the meaning of without having to learn them. However I will outline them briefly and how they relate to my findings so that you are, in turn, able to relate to them if you come across them in environmental plans, legislation or elsewhere in the future.

Soils are referred to as a stock of properties or natural capital which yield a flow of valuable ecosystem goods or services into the future. Both soil health/ quality and natural capital are similar in that they use soil indicators and parameters to determine the state or function of a soil system. However soil natural capital provides a more holistic analysis of the resource as it takes into account not only the state of the soil itself (through soil indicators) but also the effect of this state on the products and services that soils provide and the human needs that are catered for by soils.

In the soil natural capital framework macroporosity is identified as the key physical attribute. This is because macroporosity determines: water flow, solute transport and drainage through soil. As a result macroporosity influences ecosystem services such as flood mitigation and filtering of nutrients. Macroporosity and associated soil physical properties provide important services and it is important for land managers to be aware of the potential to change these properties and the ecosystem services they provide.

Research has been carried out to determine the effect of land use practices on other soil physical properties such as bulk density, aggregate stability, soil carbon and water holding capacity however macroporosity remains the main indicator of soil physical natural capital and health because of its sensitivity to intensification.

My research found that on average for the 0-30 cm increment macroporosity was significantly lower on the Dairy site (9 ± 1%) than both the Sheep farm (19 ± 1%) and the Control site (15 ± 1%). This suggests that intensification is having a significant effect on the Dairy site. Furthermore on the Dairy site the 0-10 cm and 10-20 cm depth increments both have values for macroporosity < 10%. Other researchers have proposed that macroporosity values of > 10% are needed to maintain pasture production near optimum.

Target ranges for macroporosity are given in Table 1 as part of the National Soil Quality Indicator Programme. Here, for soils under pasture, macroporosity values < 8% are considered low and could restrict pasture growth. Macroporosity for the 10-20 cm depth increment on the Dairy site was 7 ± 1%, a level where less than optimum production could be expected. Results from an AgResearch trial found similar values for and changes of macroporosity with stocking intensity.

Table 1 – target values for macroporosity for pasture, cropping & horticulture and forestry

I did not find any changes in water holding capacity within the plant available range with increasing land use intensification. This result in itself was interesting as it shows that intensifying land use practices did not have a measureable impact on the readily available water (RAW, that available to plants) of the soil. In comparison other studies have found that there is a significant decrease in RAW with irrigation and increased compaction.

Finally my study did find that there was an increase in small micropores holding water at suctions too great for the plant to overcome. These findings all highlight the importance of on farm soil testing to determine the RAW of the specific soil textures and under different land uses to increase management efficiency.

Bulk density values were found to be significantly higher on the Dairy site (1.40 ± 0.02 g cm^-3) than both the Sheep farm (1.26 gcm-3± 0.02) and the Control site (1.31 ± 0.02 g cm^-3), indicating increased compaction on the DF in agreement with macroporosity values. Bulk density is not as sensitive an indicator of compaction as macroporosity and this can be seen by the large target range 0.7–1.4 gcm^-3 that has been identified for Pallic soils (Table 2). Therefore it is not recommended as an indicator for determining the effect of land use intensification on soils.

Table 2 – target ranges for bulk density are large indicating that this is not as sensitive an indicator as macroporosity for determining the effect of land use intensification on soils.

Landcare Research has developed a tool which can be used by everyone to determine the quality of their soil based on a number of indicators.

sindi.landcareresearch.co.nz

The tool allows you to measure your soil against current understanding of optimal values for: Macroporosity, bulk density, Total N, Total C, Mineraliseable N, pH and Olsen P

It will tell you about the effect each indicator has on soil quality alongside some general management practices that can be used to improve your soil.

In addition to thinking about the effect of these indicators on your soil quality I encourage you to take a step back and also think about the long term effect of the state of these indicators/ properties on your farm’s functions and the importance of each of these functions to your profitability. 

Thanks to Nicole Mesman (BSc (Hons) Soil Science) for the content of this post!

The Irrigation, Grazing Game

In this week’s blog we welcome guest contributor - Nicole Mesman. Nicole achieved honours in soil science through Lincoln University. Her honours project looked at the effect of grazing and irrigation on soil porosity, here she shares what was discovered through this project.

While university projects are often published in journal articles I feel 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.  

Post by Lindsay NZ, informative content created by Nicole Mesman - BSc (Hons) Soil Science

Rain gauges – why they're a powerful tool for your operation

Do you know how much rain has fallen on your farm?  Or on your block of land down the road?  Do you sometimes forget to tip out the rain gauge?  Accurate rainfall figures for farm records are becoming more and more important in this age of transparency.  Knowing how much rain fell on any given day on your own farm or on a particular crop will give you the ability to make more accurate decisions.  Telemetered rain gauges save you the hassle of manually reading the rain gauge and provide up to date data straight to your phone or computer. 

Rain gauges can be installed along with your soil moisture probe and positioned under the irrigator or installed in a dryland area.  Positioning the rain gauge under the irrigator enables you to monitor exactly what application depth the irrigator is applying.  Application depths can change as a result of adding extra irrigators to the system, blocked or broken nozzles and changes to system pressures to name a few.  Excessive application depths are expected to account for on average 10% of water losses on an average irrigation system, that’s wasted power, water and most importantly money.  Not applying enough water may result in yield losses and shallow rooted plants.    

A telemetered rain gauge installed under the irrigator will also enable you to see the application rate applied.  If it is above the rates described for your situation in the table below you may be wasting water.  

Agri Optics can add a rain gauge to your soil moisture system to help your decision making.  Ring us today to talk about the options for your farm. 

Agri Optics office: (03) 302 9227

Cindy Lowe 021 796 834 or cindy@agrioptics.co.nz

Email: info@agrioptics.co.nz