Water balance monitoring tools
These monitoring tools have been developed to help farmers and advisers assess whether paddocks/farms are minimising water losses and thus reduce the risk of salinity. Note that there will be cases in the high rainfall zone where minimal leakage is neither possible, nor desirable for water quality reasons. The monitoring tools can be used in a 'stand-alone' way, or can be used as part of justifying and improving on-farm environmental performance using an Environmental Management System (EMS). They are suitable for winter-dominant rainfall environments in southern Australia.
The water monitoring tools have been developed on the basis rainfall and crop/pasture rotations records are collected. Farmers need to choose the nearest soil type in paddocks from a list provided. No other data recording is required, unless farmers choose to sample for more detailed information on soil texture or water holding ability.
There are three water monitoring tools to help farmers assess whether their farm is as environmentally acceptable as it could be – you can use some or all, and the most crucial tools are presented first.
Note that the terms leakage and perenniality are used regularly in this guide. Their definitions are below:
What is leakage?
Leakage is the water that is not used by the plant and/or stored in the soil. Leakage can occur either from below the root zone or as runoff to streams (either from the surface or shallow sub-surface soil.) Leakage from farming systems is often seen as a bad thing – especially when it carries salt or nutrients and results in poor water quality and/or salinity problems through rising water tables. If you are in a catchment which has developing salinity problems and/or known rising groundwater, you can assume that almost all leakage is bad for the environment. However, if you live in an environment where the rainfall is high (above 750 mm/year) and there is no known suspicion of developing salinity problems, then if the water leaking is clean, leakage is good for the environment. From a farm production point of view, minimising leakage is almost always a good thing – maximum use of rainfall is likely to result in better pasture, crop or animal production.
What is perenniality?
Perenniality is used to describe how much impact a plant type is likely to have on drying out the soil, and hence its ability to reduce leakage. Although many plants (eg phalaris, lucerne, trees, native grasses) are perennials (that is, they can live for a number of years), we know that not all perennials have the same ability to use rainfall and dry out the soil. Hence, a deep rooted perennial such as a tree has a much higher 'perenniality' rating than phalaris because it can dry the soil out to greater depth. Summer active perennials will have a higher perenniality rating than summer dormant varieties. The more green leaf area that plants have over summer, the more water they use. Therefore summer active perennials use more water (hence a higher perennialty rating) than summer dormant varieties. Similarly, deep-rooted plants will have a higher perenniality rating than shallow rooted plants because they take up more water and hence grow more. We have used available data and local knowledge of scientists to come up with perenniality ratings. As more research is done on the impact of different species on water use, the perenniality ratings can be modified and new species added.
Introducing the water monitoring tools
Three water monitoring tools have been developed. They are presented in order of their importance to help understand and monitor the impact of farming systems on the environment:
Perenniality of the farm
Perennial plants use water throughout the year but especially over the summer period, resulting in drier soils at the autumn break (the time when most leakage occurs). By determining the perenniality of your farm you can work towards a goal of how much perenniality you think you need for maximum environmental benefit. If you are in a salinity prone area this goal should be to have as much perenniality as practically possible (eg. in high rainfall areas over 40%). If you are not in a salinity prone area then a target perenniality may be less crucial for environmental purposes – however to maximise the use of precious resources (rainfall converted to pasture or crop production), then aiming for as much perenniality as possible is still the best strategy.
Frequency and amount of leakage below the root zone
Agriculture has unbalanced the plant water-use patterns of catchments. This has increased the salinity problem. It is important to try and design farming systems that stop these large occasional leaks, except in areas where there is known to be minimal risk of salinity developing. This tool helps you assess the leakage on your farm, with a view to reducing it (for production and/or environmental purposes) or at least understanding how much water you do not use from the rain that falls.
Water use efficiency of crops
Water use efficiency (WUE) is the amount of grain (or pasture/meat) produced per mm of effective growing season rainfall. High yielding crops/pastures use more water than low yielding crops/pastures. The more water used by the crop, the lower the risk of leakage from your farm. In addition the calculation of $/mm WUE allows you to assess how profitable a particular paddock was in terms of rainfall used. This figure, in combination with WUE, allows you to assess which paddocks were farmed both most profitably and in the most environmentally acceptable manner.
Tool A: Perenniality of farm
Goal: To have sufficient perenniality for benefits to both production and the environmental benefits.
Both this tool and the likelihood of leakage tool (Tool B) will give the best assessment of the risk of leakage and hence impact of your farming practices on salinity, water quality and making the best use of rainfall.
The perenniality tools are most suitable for dryland paddocks. The results for irrigated paddocks, even if they contain lucerne, are less clear because irrigation water is often applied well before the soil has a chance to dry out. Perenniality ratings for irrigated paddocks could be developed from soil water data collected by farmers but at present we do not have such. For the moment, let's assume that irrigated paddocks will result in at least as much leakage as under annual species.
Why is perenniality important?
Before European settlement, native perennials occurred over much of the Australian landscape and used almost all of the rainfall. This meant that there was little or no leakage below the root zone. With European settlement, most of the perennial natives were removed by grazing or cultivation and annuals established. This has changed the water balance so that leakage losses below the root zone are commonly 10-100 times greater than under natural systems. This is the major cause of the increasing salinity. Trees, native shrubs and native grasses used water throughout the year, but especially over the summer period, so that soils were very dry when the autumn rains came.
Maximising perenniality is especially crucial in salinity prone areas. If you are not in a high salinity prone area, then reducing leakage through increased perenniality is still important to make the best use of rainfall. To reduce leakage the key is to have the soil as dry as possible by the end of autumn. The soil 'bucket', in which winter rainfall can be stored before it "overflows", should be as large as possible, as leakage losses largely occur over winter and early spring in our winter dominant rainfall environment.
As soil drying really only occurs from mid-spring onwards over the summer and autumn, perennials must be used because annual plants do not use water over this period. Most pasture (both annuals and perennials) and crop species use similar amounts of water over the growing season, particularly from May-August for areas where rainfall is below 600 mm/year or until September or October where rainfall is higher and/or spring weather is cool. There are few options for increasing plant water use over the cooler winter-spring period. Maintaining sufficient green leaf from November through to March is the best way to increase plant water use, and to create the largest possible soil water storage 'bucket'. A 'perenniality factor' table has been developed (page 4) based on the size of the soil water storage 'bucket' created under different management situations.
A target of having 40% of your farm area growing perennial plants (eg. trees, lucerne) at any one time is something to work towards until you can analyse your own soil and rainfall data to determine your own farm-spe cific target. It is also useful to understand where your farm is in relation to catchment priorities (eg. is it in a high priority salinity area, are there major water quality problems in terms of nitrogen or phosphorus runoff?) Under most situations a dual production and environmental ideal goal is to have no or minimal leakage. To do this, use the leakage-monitoring tool B below. Look at the wettest years and assess how much water storage capacity you would need for no leakage to occur in those years. However, where average annual rainfall exceeds 750 mm/year it will not be possible to have no leakage.
Calculating the perenniality of your farm
Calculate the total area of the farm including individual paddocks, fenced-off remnants or established treed areas and reserves, and any other areas. If it is difficult to estimate the area of trees, try estimating the total treed area on the farm from an aerial photograph. Despite this seemingly relatively simple task, it can take quite a bit of time! Remember to include non-farmed areas such as the land around sheds.
Steps to calculate farm perenniality
- Step 1. Define the plant type in each paddock. Estimate the proportions (area) of the farm under each plant type listed in Table 1.
- Step 2. Add up the areas of each plant type
(eg. a 1000 ha farm might have 700 ha sown to a continuing crop or annual pasture phase, 100 ha sown as the first crop following lucerne, 50 ha of phalaris pasture, 100 ha of lucerne and 50 ha of trees/remnant vegetation).
- Step 3. Determine the perenniality rating of each plant type by referring to Table 1.
- Step 4. Calculate the perenniality of your farm by calculating the perenniality of each area of the farm sown to the different plant types, summing them and expressing the total as a percentage of the total farm area. You can use the proforma over the page to assist you.
e.g. [700 x 0 + 100 x 0.7 + 50 x 0.5 + 100 x 0.9 + 50 x 1] = 235 ha, which gives a perenniality of 235/1000 x 100 = 23.5%.
Table 1: Plant types and perenniality ratings for calculation of % perenniality of the farm
|Plant type||Perenniality rating|
|Average annual crops or pastures||0|
|Crops or annual pastures with very high levels of dry matter production||0.1|
|Trees (either planted or remnants)||1|
|Lucerne-based pasture (at least 5 plants/m2 or 10% lucerne)||0.9|
|Perennial grass pasture, eg phalaris (at least 5 plants/m2 or 10% perennial)A||0.5|
|Native grass pastureA||0.5|
|First crop following lucerne pasture||0.7|
|Second crop following lucerne pasture||0.5|
|Third crop following lucerne pasture||0.2|
|Fourth and subsequent crops following lucerne||0|
|Irrigated pastures||Assume 0|
A Note that not all perennial grasses are likely to have the same perenniality ratings – summer active grasses will have a higher rating than winter active ones. As more research information becomes available we should be able to modify the perenniality ratings for species like fescue, cocksfoot, wallaby grass, red grass etc.
Tool A: Pro forma sheet for calculating the perenniality of your farm
|Column A||Column B||Column C||Column D|
|Hectares (from calculation of farm areas)||% area (Column A/total farm area) x 100||Perennial Rating (from Table 1)||% Perenniality (Column B x Column C)|
|Native perennial grass pasture||0.5|
|Other perennial grass pasture||0.5|
|Total area of the farm|
Tool B: frequency of leakage
The leakage tool is designed to give you an idea of whether/how much your farming systems leak the figures are indicative only, as would be expected for no additional data collection apart from rainfall and plant type.
Introduction to leakage
Natural woodlands and grasslands that were cleared for cropping and annual pastures once had very little leakage of rainfall from below the root zone. Trees, native shrubs and grasses used water throughout the year but especially over summer. As a result, soils were very dry by the time of the autumn break. Agriculture has markedly changed the balance and water losses have now increased 10 to 100 times.
Leakage losses mostly occur over the wet winter period in southern Australia (commonly June-August for cropping areas, June-October for most high rainfall catchments or areas, which have cool spring conditions); however leakage does not occur in all years. It is the large but occasional losses (eg. 40 mm leakage may occur in a 450 mm rainfall environment only 5 times in 20 years) that are mainly responsible for the increasing salinity problem. Therefore it is important to try and design farming systems that limit these large occasional losses.
Deep-rooted perennial species (particularly lucerne and trees) have the most potential to control most losses of water to below the root zone. Both soil type and the plant type affect the likelihood of leakage loss. For example, sandy soils often have high infiltration rates as well as low soil water holding capacities and are at greater risk of leakage losses. Growing deep-rooted perennials on these soils is of highest priority.
Before you start, find out whether you are in a salinity prone region
Prior to assessing the frequency of leakage, you should find out whether you are in a salinity prone area. Start with either contacting your local Department agency (Victoria -Department of Primary Industries or Sustainability and Environment in Victoria; NSW - NSW Agriculture or Department of Infrastructure, Planning and Natural Resources) or local Catchment Management Authority. Most areas have prioritised salinity management zones. However if you are not in one of these designated areas it does not mean that a salinity threat does not exist. Until otherwise informed reliably, your starting point should be that future salinity might be a problem. In some catchments, the 'high priority' salinity management zones have been decided upon on the basis of where it is currently worst, rather than where it has the potential to cause most damage to assets in the future. Areas without a threat of salinity tend to be in above 800 mm/year rainfall areas, but this is not always the case.
|STEPS TO CALCULATE FREQUENCY OF LEAKAGE|
|1||Record paddock name on Tool B proforma (next page).|
|2||Define plant type in the paddock using the categories in Table 2 for dryland paddocks (choose either the North-East, North-Central or Glenelg Hopkins options).|
|3||Define dominant soil type in the paddock on which the plant is grown (use Table 2). Note that the combination of slope and soil type is crucial to determining how much water runs off and how much is leakage below the root zone. We will refine these tools to include slope considerations in the near future. This will allow you to partition water loss between runoff and water loss below the root zone.|
|4||Look up the estimated plant available water capacity of the soil for your plant/soil combination from Table 2 for dryland paddocks.|
|5||Calculate winter rainfall from records. Use May-August rainfall except in years where September and/or October rainfall exceeds 60mm; in this case use May-September or May-October rainfall.|
|6||Assume plant water use of any species (crop, pasture or lucerne) from May-August is 120 mm or if May-September rainfall has been used, assume plant water use to be 180 mm (240 mm if May-October rainfall has been used).|
|7||Calculate estimated leakage from the sum of May-August rainfall (or May-September or October where September or October rainfall exceeds 60 mm/month) minus plant water use minus soil water holding capacity. A positive value is the estimated mm of leakage; zero or negative values indicate no leakage is likely.|
|8||Repeat for other paddocks of interest on the farm. (It is highly unlikely that leakage ever occurs under trees or lucerne, so to test for likelihood of leakage in a particular year calculate it initially for annual crops or pastures).|
|9||Calculate the megalitres of water leaving the farm as leakage. (Lets say that 20 mm leakage occurred from a 100 ha paddock in a particular year. 1 mm leakage from a hectare of land = 10,000 litres or 0.01 megalitres. So 20 mm leakage from 100 ha of land on the farm is 0.01 x 20 x 100 = 20 megalitres water lost in that year.|
|10||Use long-term rainfall records to see how often leakage is likely to occur under annual species in particular paddocks. Check whether the winter rainfall value exceeds a 'threshold' for predicted leakage. The threshold value is the sum of plant water use plus soil water holding capacity for your particular soil and vegetation type. If the May-August (or May-September, May-October) rainfall exceeds this threshold value, then leakage is likely to occur.|
|11||Determine long-term leakage losses from your farm by recording for particular years the paddocks in which leakage occurred. This information will provide a useful basis on which to discuss relative losses of water (and thus salinity risk) in your area, and to compare irrigation and dryland water losses. In future, when there are discussions about the relative contributions of irrigation and dryland farming to salinity, these figures can be used to show the likely degree of leakiness of particular farming systems.|
The maximum amount of 'soil water storage' occurs immediately prior to the autumn break when soils are at their driest. Note that it is the combination of plant type (the depths to which their roots are likely to dry soils to) and the soil type which determines the amount of water that the soil can store before drainage occurs.
Table 2: Estimated amount of water (mm) which the soil could store (called plant available water capacity) before leakage would occur (can choose Riverina, North east Victoria or South west Victoria options or just choose the best soil description for your area) for dryland paddocks.
|Plant type||Assumed Plant Available Water Capacity of the soil (mm)|
|Plant available water capacity:||Very High||High||Medium||Low|
|Description||Deep well structured, heavy textured soils||Good cropping/grazing soils||Shallow soils||Soils with major limitationsA|
|Riverina NSW||Well structured heavy soils||Red cropping soils||Duplex soils - poor drainage (inc. podzolics)||Soils with major limitationsA (inc. sands)|
|North east Victoria||Most good river flats including silty soils||Very heavy floodplains (eg grey, yellow clays), sandy river flatsB , break of slope river terrace soils, red and yellow||Red and yellow duplex soils||Saline areas, sodic soils, shallow granite soils, stony hill country|
|South west Victoria Glenelg Hopkins, Corangamite||Older basalt plains soils||Deep sands and Merino Tablelands||Steep hills, Dundas Tablelands, stony rises, Buckshot soils,||Saline areas, acid sulphate soils, sodic soils|
|Annual speciesc (crop or pasture) following an annual||140||100||80||60|
|1st crop following lucerne||240||175||140||105|
|2nd crop following lucerne||200||150||120||90|
|3rd crop following lucerne||160||125||100||75|
|4th and subsequent crops||140||100||80||60|
A Major limitations could be strongly sodic soils, saline soils acidity to depth, major and waterlogging problems and poorly structured soils.
B The reason for lower water holding capacity of heavy floodplains than most river flats is that heavy clays can have less favourable environment for roots to live. Clay soils can also hold water very tightly compared with sandier soils.
C Rooting depths under annual species generally assumed to be about 1 m depth, unless other information is available. For example a good cropping soil at Burrumbuttock NSW had a measured Plant Available Water Content (PAWC) of 115 mm under triticale – due to this crop being able to extract water to 130 cm depth. Thus, there will be cases where the PAWC figures can be increased from those in the table. The table is a guide only where no better information exists.
Tool B: Pro forma for calculating frequency of leakage on dryland paddocks
|Column A||Column B||Column C||Column D||Column E||Column F|
|Paddock Name||Plant type (Table 1)||Dominant soil type (Table 2)||Plant available water capacity (mm) (Table 2 according to paddock soil and plant type)||Year of interest||Calculate rainfall available for leakage (Step 7) (winter rainfall minus plant water use over winter)||Estimated leakage (mm) (Column E minus Column C)|
|e.g. Hill||Crop||Red cropping||100||1995||e.g. 244-120 = 124||124 – 100 = 24|
Tool C: Water use efficiency of crops
Water use efficiency (WUE) is the amount of grain or livestock production produced per mm of effective growing season rainfall. High yielding crops use more water than low yielding crops where dry matter production is correspondingly higher. In some cases, high yields can occur with relatively lower dry matter production (high harvest index); thus WUE is a not necessarily always a good indicator of the water-using ability of crops. The more water used by the crop, the lower the risk of leakage from your farm; WUE figures themselves are not a good indicator for amount of likely leakage which is why we think tools B and A are most important.
(Proforma sheets for this tool are following $WUE instructions).
Goal: To achieve at least 80% maximum water use efficiency for all crops grown on the farm, and preferably 100%.
Steps to calculate WUE of crops
Step 1. Calculate grain yields for each paddock (t grain/ha)
(as an example, let's assume 3.2 t/ha for wheat and 1.6 t/ha for canola).
Step 2. Calculate growing season rainfall as the sum of April-October rainfall figures plus one third of January-March rainfall (mm) to determine growing season rainfall. The 1/3 of January-March figure is used to account for extra soil moisture stored in the profile at sowing time.
Some farmers use the software program Pycal to estimate the amount of stored soil water, in which case the January-March figures for rainfall are not needed. For the example, let's say 267 mm fell in April-October plus 76 mm in January-March. Therefore growing season rainfall is calculated as 267+ 25 mm = 292 mm.
Step 3. For each crop type, select the evaporation loss from Table 3 (eg. 110 mm for both wheat and canola).
Step 4. Calculate water use efficiency (WUE) [kg grain/ha/(mm growing season rainfall minus evaporation)] using Tool C proforma on page 11.
(In our example wheat WUE = 3,200/(292-110)=17.6; canola WUE 1,600/(292-110) = 8.8)
Step 5. Calculate your WUE as a percentage of the potential WUE (see Table 4) for each paddock by dividing your calculated WUE by the potential values listed in Table 4 and expressing them as a percentage (wheat 17.6/20 x 100 =88% of potential WUE; canola 8.8/10 x 100 = 88%).
Step 6. Rate water use efficiency figures as excellent (95% of potential or greater), good (8095%), marginal (60-80%) or poor (<60%).
Step 7. Compare your maximum and minimum figures for % potential WUE both within and between crop types and think about the reasons for the differences (eg. differences in weed burdens, soil fertility, diseases, sowing times, etc?) for future planning/action. If your figures are generally marginal to poor, discuss figures with others to see whether the poor figures are district wide (and therefore due to seasonal conditions, such as a particularly wet year). Alternatively your rating could be associated with some aspects of your farm management, which could be improved, and analysing the best and worst % potential WUE figures for your paddocks may help indicate how you could improve yields.
Step 8. Consider how you might improve poor % potential WUE values in particular paddocks – seek advice if you wish to discuss this issue further.
Table 3: Assumed evaporation during the growing season
|Crop type||Evaporation (mm)|
Table 4: Potential water use efficiency values for crop types
|Crop type||Potential WUE (kg grain/mm/ha)|
Calculating $ /mm WUE for crops
Calculation of $/mm WUE allows you to assess how profitable a particular paddock was in terms of rainfall used. This figure, in combination with WUE, allows you to assess which paddocks were both more profitable and more environmentally acceptable.
Goal: To maximise $/mm WUE and understand differences between paddocks. Note, due to large annual variations in crop price, it is sensible only to make relative comparisons between paddocks for each season.
Steps to calculate $/ mm WUE for crops
Step 1. Calculate gross margin/ha. Gross margins are calculated by multiplying together the yield and gross price and subtracting the enterprise (or variable costs) costs. Variable costs do not include fixed costs of production.
(In this example we will use an average gross margin of $334/ha for wheat and $329/ha for canola).
Step 2. Calculate effective growing season rainfall as per steps 2 and 3 of the water use efficiency calculations, that is (April-October)+ 1/3 (Jan-March) – Evaporation (Table 3).
(For this example we will use an effective growing season rainfall figure of 232 mm).
Step 3. Divide gross margin per ha by growing season rainfall.
(334/232 = $1.44/mm for wheat and 329/232 = $1.42/mm for canola).
Step 4. Compare $ /mm WUE figures of various paddocks and analyse why some paddocks might have been both more profitable and used more water than others.
Tool C: Pro forma sheet for calculating water use efficiency of crops (WUE)
|Column A||Column B||Column C||Column D||Column E||Column F|
|Paddock name||Crop type||Yield (t/ha) (from paddock records)||April-Oct Rain +1/3 Jan-March (mm) (from rainfall records)||Assumed Evaporat'n (mm) (Table 3)||Actual WUE (kg grain /mm/ha) [Column A x 1000 / (Column B – Column C)]||Potential WUE (Table 4)||% of Potential (Column D / Column E) x 100|
|e.g. Hill||Wheat||3.2||292||110||3.2 x 1000/(29 2-110) = 17.6||20||(17.6/20) x 100 = 88%|
Tool C: Pro forma for calculating $/mm WUE
|Column A||Column B||Column C||Column D|
|Paddock name||Gross margin/ ha ($/ha)||April-Oct Rain +1/3 Jan-March (mm) (from rainfall records)||Assumed Evaporation (mm) (Table 3)||$ WUE ($/mm/ha) [Column A /(Column B – Column C)]||Comments|
|e.g. Hill||203||292||110||203 / (232-110) = 1.66|
Note: Prograze and Prograze Update manuals and information for pastures and grazing are supplied as part of workshops coordinated Meat and Livestock Australia (MLA). Search MLA's EDGEnetwork for contact details and workshop information.
Breaches of the Water Act
Breaches of the Water Act may occur if appropriate approval has not been sought from the local Water Authority when soil sampling, installing piezometers or neutron probe access tubes. In general, if any soil sample, piezometer, soil moisture tube, is greater than 3 metres deep, or if it intercepts the groundwater, it may have to be registered with the relevant water authority. Individual water authorities could have different approaches to registration. Breaches of the Water Act are an offence that involves a financial penalty.
Registration requires a series of steps that generally involve:
- contacting the local water authority and applying for installation licence
- this licence will require maps of locations, depth, purpose and information regarding near by infrastructure. A dial before you dig, that locates underground infrastructure, power etc may also be required. If the person has never registered a bore, or a hole in the ground so to speak, then it is strongly advised they contact the water authority to determine the steps involved.
- the cost to register - roughly $400 for first hole and an additional $50 for second etc, but this may vary with the water authority.
The registration process exists for several reasons. For example:
- in an attempt to prevent pollution by aquifer leakage, this is why soil sampling is included in the registration process if groundwater is intercepted.
- to provide an identification number and location of groundwater bores, and generate funds to run the groundwater data bases.
- to ensure no illegal groundwater extraction.
The registration process also means that only a registered driller can install the holes or collect the soil samples. If you unsure of the groundwater depth in your region, then using a registered driller removes any risk.
There are generally no exceptions to the rule, however there are variations in how water authorities govern the Act, so contact with water authorities is essential. Also, as a low cost risk management strategy, it is recommended to contact the Dial Before You Dig website or hotline (phone 1100) and ascertain the location of any infrastructure (power, telecommunications, gas etc.).