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!

Winter Grazing

It always amazes me how quickly time flies – as I write this, we are in June of 2018 already and winter is upon us.

With the onset of winter comes the slowing (or stopping) of pasture growth and the need to supplement feed with crops or imported supplements, so it is timely to discuss winter feed management and the environmental perils associated with feeding winter crops and supplements.

It’s a hard road finding the perfect paddock to plant your crops in, if the soil is too heavy the chances of pugging and the loss of soil and faecal matter is higher and if the soil is too light, the drainage is great but with more drainage comes higher nitrogen leaching, particularly in areas of high rainfall.  Planning ahead and selecting the right paddock or even the right areas within a paddock to grow crops can reduce the environmental risk.

 

There is a lot of information about good practice for feeding winter crops available, but as for any farming practice there is no one size fits all and it is a matter of taking those good practices that apply to your situation and putting them in place.  The key issues with the intensive grazing of stock over winter are the loss of soil and faecal matter through run off into water ways and the leaching of nitrogen into groundwater from intensive stocking. 

Any management practices that can be implemented to reduce run off into waterways are beneficial, this can help to reduce the soil/ sediment and faecal contamination of waterways.  These include grass strips or margins not planted in crops alongside waterways and planning the direction of cultivation so that it doesn’t lead to a flow path into a waterway carrying contamination with it.

   

Planning ahead and having a back up option such as taking the animals off the crop, allowing animals access to another paddock or grazing for only a few hours can make all the difference when the weather is too wet for intensive grazing.  Troughs and supplementary feed can be placed strategically so that pugging is minimised in these areas and so that if there is pugging it won’t run off into a waterway.

Some regional plans include rules with regards to the wintering of stock including requirements for intensively grazed stock and stock on winter crops to be excluded from waterbodies.   There may also be rules around standoff areas and feedpads to minimise the environmental impact of these.  In my view these rules constitute the absolute minimum with regards to the good management of stock in winter. 

For information on industry good practice, see the Beef and Lamb website, Deer Industry NZ or the DairyNZ website, in particular the following link provides some useful information which can be applied to beef cattle and deer also -
https://www.dairynz.co.nz/media/5786508/wintering-on-crops-in-the-south-island.pdf

Post grazing, following the crop with a whole-crop cereal silage crop, before putting the block back into winter crop, can greatly reduce the nitrogen in the soil and therefore, leaching. 

So, with winter already here it is not too late to do some research and plan how you will manage your winter grazing this year.

Lilian Sherman, Irricon Resource Solutions Limited (NI).

Phone: (021) 378 308

E-mail: lilian@irricon.co.nz
www.irricon.co.nz

Stock Exclusion - What's the go?

Out and about recently, Lilian Sherman, our North Island Rural Environmental Specialist, has heard a lot of discussion about the stock exclusion rules coming into play.  Unfortunately, a lot of what she has heard has had a serious dose of the ‘chinese whispers’ and the end result is that there are a lot of myths out there with regards to stock exclusion.  Below, Lilian dispels some of those myths and provides you with some confidence around the rules.

While there is no formal definition, stock exclusion generally means to exclude stock by some means from entering a waterbody.  In most cases, the stock exclusion definition does not include sheep or goats, as sheep and goats do not tend to linger in water!  In most cases the means of achieving stock exclusion is not specified, therefore the best method or technology for each situation can be used.  This may be a permanent fence, a hot wire, or as is currently being developed, virtual fencing.
Why is stock exclusion necessary? Stock entering waterways can cause significant damage by contributing nutrients (primarily nitrogen and phosphorus), sediment and faecal coliforms to our waterways. They do this though the direct deposition of dung and urine into rivers, treading damage and reduction in beneficial vegetation that results from grazing stream banks.

As part of the Clean Water package recently released by the Ministry for the Environment, there are proposed National Rules for Stock Exclusion.  Consultation on the proposed stock exclusion regulations and other aspects of the Clean Water package closed on 28 April 2017. This feedback is being considered and will inform the final decision on the National Rules.  The proposed stock exclusion rules are practical and there are different requirements for different classes of stock and for topography (plains, rolling and steep).  More details are available on the Ministry for the Environment Website (https://www.mfe.govt.nz/sites/default/files/media/Fresh%20water/next-steps-for-freshwater.pdf).

The proposed National Rules for Stock Exclusion recognise that for some landowners, there may be significant practical constraints that mean they are unable to meet the new requirements. In those cases, landowners can apply for permission to instead develop a stock exclusion plan with their regional council. The plan may include alternatives to fencing or mitigations to reduce the impact of stock access to waterways.  An example of this would be providing alternative areas of shade and reticulated stock drinking water, which may also provide other economic and animal health benefits.

It is important to note that the National Rules for Stock Exclusion will form the minimum requirements, and councils may choose to regulate over and above these in their regional plans.

There are some challenges excluding stock from waterways, including the effects of flooding, the proliferation of weeds and pests and access through vegetation to waterbodies.  These are valid issues and I have confidence that farmers will find practical solutions for these as the rules come into play.

In the meantime, if you are putting in new fence line or carrying out fencing maintenance, consider whether there is an opportunity to make a change to a fence line to exclude stock or make it easier to exclude stock in the future, but its also an important consideration for any development on farm such as irrigation (whether new or upgrading) and the location of waterways should be a key consideration in any design being undertaken. 

Keep an eye out for the final versions of the National Stock Exclusion Rules.

Lilian Sherman, Irricon Resource Solutions Limited.
Phone: (021) 378 308
E-mail: lilian@irricon.co.nz

Lilian is a Rural Environmental Specialist and Director at Irricon Resource Solutions, who works with farmers and horticulturists to prepare farm environment plans, resource consent applications and to assist with nutrient management and Overseer modelling. 

Lilian grew up on and lives on a sheep and beef farm, she has a practical knowledge of farming, including sheep, beef, deer, dairy, cropping and horticulture and combines her passion for farming with a wealth of nutrient management and environmental expertise in this role.

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