Know your Soil Better than your Bank Manager

A Practical Guide to Assessing your Soil Quality

The soil’s physical properties are vital to the ecological and economic sustainability of land. They control the movement of water and air through the soil, and the ease with which roots penetrate the soil. Damage to the soil can change these properties and reduce plant growth, regardless of nutrient status. Decline in soil physical properties takes considerable expense and many years to correct, and can increase the risk of soil erosion by water or wind.

The primary functions of the soil are to provide plants with air, water, nutrients and a rooting medium for growth and physical support (image sourced from the Landcare Research website) 

The Visual Soil Assessment (VSA) was developed by Landcare Research to give cropping and pastoral farmers a straight forward and time efficient checklist to use in the field to assess the state of their soil, primarily the physical soil quality.

The VSA can be found online here -> Visual Soil Assessment (VSA)

The VSA aims to help farmers identify changes occurring to soil physical properties so that they can assess the effect that these changes will have on their soil quality and the sustainability of their land management and long term profit.

Pictures in the VSA guide can be helpful when carrying out the assessment in the field (image sourced from: VSA Volume 1).

The assessment can be carried out quickly, reliably and cheaply with little equipment, training or technical skills. The scorecard below is to record those visual soil indicators used to assess soil quality. There is a similar scorecard for recording plant indicators. You are then able to compare the two sets of indicators to see if you have similar scores for both and if not why. For instance, is damage to soil quality not being seen in crops yet or are crops struggling to recover from previous soil damage?

VSA Scorecard (image sourced from: VSA Volume 1)

Below each indicator is a section in the online VSA booklet to refer to for assistance. Pictures are included so you can compare what you are viewing and refer to examples. You will need a spade, the score card, a surface to drop soil onto for a shatter test and a bin to contain soil. Each indicator is given a weighting and at the bottom of the scorecard you add the scores for the various indicators. Values falling within certain ranges are deemed “poor”, “moderate” and “good” quality. If your quality is poor or moderate it is suggested that you refer to Volume 2, also easily accessible from Landcare Research online. This volume contains tips on how to improve your soil quality or maintain it if it is already good.

Tips include:

• Cultivating at the correct moisture levels to avoid smearing of soil, formation of cultivation pans and reduced infiltration when the soils are too wet. 

  

  (image sourced from: VSA Volume 2)

• Use a sub-soiler to break cultivation pans and increase root growth
• Maintain soil organic matter levels to ensure porosity, drainage and root growth.

  

  (image sourced from: VSA Volume 2)

By utilising these resources, you will gain a better appreciation for the state of your soil and will be able to identify when changes are occurring and why. The VSA is a simple tool and when used regularly will help with building a picture of soil quality. There are a range of other resources that can continue from the VSA, further your knowledge of your soil and assist with management. SINDI, another resource for determining soil quality, will be discussed in a future blog post along with hands on ways to identify your soil type and S-Map, how its geomorphological (land formation) history can be used to assist your farming.

The blog post you have just read was written by Nicole Mesman - BSc (Hons) Soil Science.

Soil Moisture 101

Soils are made up of mineral matter, organic matter, water and air. The space between the soil particles are referred to as pores, air and water occupy these pores. Macro pores allow water to filter through the soil and then drain out the bottom. Micro pores store water that is available for plants to grow.

Soil texture is an important characteristic that influences water holding capacity, drainage characteristics and water infiltration rate. The finer the texture of the soil the greater volume of micro pores and therefore greater water holding capacity compared to coarser textured soils.

The total amount of water that a soil can store is referred to as the water holding capacity (WHC) of the soil. Coarse textured soils such as sandy and gravelly soils have a low WHC while silts and clays retain more water therefore have a higher WHC. WHC is usually expressed in miilimetres (similarly to rainfall) held per depth of soil e.g. Xmm/100mm.

Here are some common terms that you are likely to come across regularly on H2Grow and resources relating to soil moisture and irrigation scheduling:

Saturation – When all the macro and micro pores are full of water. If more water is added to a saturated soil it will either drain out the bottom, pond or run-off.

Field Capacity – Macro pores are full of air, micro pores are full of water. Silt and clay soils generally reach field capacity after 2-3 days of drainage from saturation, sandy and gravelly soils much faster. Field capacity may also be referred to as full point.

Stress Point – At this point the plant has to work to harvest the water from the soil, therefore plant growth is slowed and yield potential is reduced. The plant will survive beyond this point but will become increasingly stressed. Stress point is related to crop type, rooting depth and soil type. Stress point may also be referred to as trigger point or refill point.

Wilting Point – At this point although there is still water held in the soil the plant is not able to access it as it is held to tightly (hydroscopic water). The plant will therefore permanently wilt and die. Wilting point may also be referred to as permanent wilting point.

Water Holding Capacity (WHC) – Is a measure of the water that is extractable by plants. This can be calculated by taking the difference between the soil water at field capacity and at permanent wilting point. Water holding capacity may also be referred to as total available water or available water.

Readily Available Water (RAW) – Is a measure of the amount of water in the soil that supports optimum plant growth. This can be calculated by taking the difference between field capacity and stress point. As a general rule of thumb half of the WHC is readily available to the plant, therefore RAW = 0.5 x WHC.

Soil Infiltration Rate – Is the speed at which applied water can enter the soil. It is described as the millimetres depth of water infiltrated per hour (mm/hr).

Figure 1 below may help to illustrate the difference between saturation, field capacity and wilting point.

Figure 1

While this theory is all very useful, nothing beats seeing like in the real world. So I’d encourage you the next time you’re doing a paddock walk to take a spade with you and locate what appears to be the driest and the wettest spots in a paddock. Dig a hole in these two spots and compare the soil type/texture, the depth of topsoil, depth of the roots and other obvious visual differences. You will see posts over the next month that explain how to carry out a visual soil assessment and then how to apply this in your irrigation scheduling.

Posted by Sarah Elliot from Lindsay NZ

Is Your Irrigator in Top Nick?

The spring weather has brought more rain to many parts of New Zealand compared to previous seasons which has meant many irrigators have barely got off the starting blocks. This extended downtime is a perfect opportunity to give your irrigator a bit of TLC which will help ensure it is running at full capacity when the heat comes on.

Many simple checks and servicing like lubricating joints, replacing oil in gearboxes and looking for signs of fatigue can often be carried out by farm staff. However, should you be unsure or think that you might have detected an issue don’t hesitate to contact your irrigation dealer.

Grafton Irrigation (Zimmatic dealer based in South Canterbury) have put together a handy checklist to guide you through the checks and maintenance that will help prevent mid-season issues. The checklist covers your intake, pump shed and mainline, and pivot, hard hose, soft hose, K-line and G-set (solid set) type irrigation systems. Print yourself a copy using the link below.

Pre-Season and Maintenance Check Sheets - By Grafton Irrigation

This post has been written by Sarah Elliot - thanks to Grafton Irrigation for your input!

Am I a Responsible Irrigator?

The current Government's focus on water as the way to double New Zealand's farm exports by 2025 is reflected in the increasing accessibility of irrigation to farms around the country. Although a resource consent may state a Farmers right to use this water to irrigate and an irrigation dealership would be more than obliging to install the hardware - this ability to irrigate comes with responsibility.

To achieve a high level of irrigation performance requires a well-designed, well managed and well maintained irrigation system.

Choosing an Accredited Irrigation Dealer will ensure that your irrigation system is well-designed and meets the Irrigation Design Code of Practice and Standards. To view the list of currently accredited companies, click here.

Once the system is up and running ensuring it is well managed and maintained is up the those that own and operate it. The following questions should be considered by all those who irrigate.

1. Does my irrigation system apply what I tell it to in a uniform manner?

Poor distribution uniformity and low irrigation efficiency costs money. An irrigation evaluation is a way to assess the efficiency and distribution uniformity of your irrigation system to ensure it is performing as expected.

An irrigation evaluation will help identify causes of any poor performance and (sometimes with the assistance of a qualified professional) show how these can be resolved. Increasing irrigation effectiveness and efficiency will allow you to grow more for less.

An initial evaluation (often referred to as a Bucket Test) is simple enough to carry out yourself, there are several good guides freely available to walk you through this process. For more information check out ->
- IrrigationNZ
- Irrig8lite
- DairyNZ

If you are not in favour of the DIY option then consider contacting an Accredited Evaluator, this would also be recommended if your own test identifies potential issues that warrant further investigation.

The Hydro Services Team carrying out an Irrigation System Evaluation

2. Am I applying the right amount of water to optimise growth and avoid drainage or leaching? 

Measuring and monitoring your soil moisture is the best way to manage your irrigation efficiently.  If you don’t know what your soil moisture content is then how do you know how much you need to apply? Without this information, you risk either under-irrigating which can affect plant growth or over-irrigating which can also be detrimental to plant growth and the environment. Both these scenarios impact profitability.

There are a number of options when it comes to measuring soil moisture, choosing the best option for your farm and then ensuring it is giving you accurate information however cannot be covered in one paragraph. There are many posts already on H2Grow that discuss this topic, use the “WHAT ARE YOU INTERESTED IN” menu to navigate to these, or subscribe so that you do not miss out on these in the future.

3. Is my irrigation system working as it should, and will it continue to do so in the long run?

Irrigation system checks and maintenance should be undertaken during the off-season and at scheduled times over the irrigation season (the more hours your irrigator runs for the more regularly these checks should be carried out).  Recommended irrigation system maintenance will be covered in more detail in the next H2Grow blog post, this will include a checklist that you can download and print off to help you with this task.

Keep an eye out for the next post or subscribe to ensure that you don't miss it!

Legumes + Efficient Water Use = Great Results at Omarama Station

Omarama Station recently played host to the "Legumes in the High Country" field day, organised by Lincoln University and Beef + Lamb NZ. There was a good turnout of farmers and industry professionals to the farm owned and run by Richard and Annabelle Subtil, 2015 winners of the South Island Farmer of the Year competition. The focus for the day was the use of legume species in the high country environment with a short session on the use of irrigation and soil moisture monitoring in the arid environment that is the Mackenzie Country.

Omarama Station (Courtesty of Richard Subtil)

Omarama Station covers 12,000ha with a mixture of dryland high country and irrigated flats. The property has had significant development work undertaken and a number of centre pivot irrigators installed that irrigate 560ha. A large water storage pond has been constructed to supply water to the irrigation system.

Dr MS Srinivasan from NIWA gave the first presentation for the day at the site of the lysimeter that has recently been installed on the station. The lysimeter is the first in the Waitaki catchment and aims to build knowledge around drainage and soil water under the developing soils at Omarama Station. The site contains three catchment sleeves one of which has soil moisture sensors installed. Any drainage water from the site is measured which gives an indication of the soil moisture status and how drainage from the soil profile is taking place.

From a soil moisture point of view the lysimeter is important as the soils at Omarama Station have exceptionally variable fertility, structure and water holding capacity. Irrigation is not new to the area however the shift from border-dyke irrigation to more efficient spray irrigation has seen a massive change in the water use efficiency on extensive properties such as Omarama Station. Soil development under irrigation is an interesting concept and soils mapped on Omarama Station have shown to have varying levels of water holding capacity based on how long they have been irrigated for in the past. Investigation has shown that the depth of soil and the water holding capacity has improved under 30 years of irrigation. 

Irrigation at Omarama Station (Courtesy of Richard Subtil)

Agri Optics has installed three sub-surface AquaCheck probes that will complement the work being undertaken at the lysimeter site. This information will flow into the decision making process that is used around timing and quantity of irrigation water applied by the team at Omarama Station. 

Derrick Moot spoke on how selection of species was important to maximising water use efficiency in moisture deficient environments such as the Mackenzie Basin. As we know lucerne is a great fit into dryland high country systems. It has the ability to maximise the water use efficiency and has a high water to dry matter conversion ratio (kg DM/mm/ha). The selection of species going forward and the development of novel species all points towards maximising the efficiency of water use in dry high country areas.

Write up by Nick Evans