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Introduction to salinity - workshop manual for participants

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This workshop was developed as part of the GRDC/NDSP funded "A Million Hectares for the Future" project with support and input from key staff from the Department of Agriculture, Western Australia (DAWA). Thanks also to the farmers who participated in the pilot workshops, who provided valuable feedback on structure and content. The Chief Executive Officer of the Department of Agriculture and the State of Western Australia accepts no liability whatsoever in negligence or otherwise arising out of the use or release of this information or any part thereof.

This publication may be reproduced in whole or in part provided that acknowledgment to the Department of Agriculture is included, citing full publication details (series information, author, title, year). These participant notes cover all the topics discussed and general expenses presented within the workshop, with space to add your own comments. These notes are a record of your discussions and any conclusions that emerge from this workshop.

14:20 Assess the salinity risk to your farmland - Cost of doing nothing 14:45 Preliminary assessment of the main potential management options for your. Surface water management - Is it for me?, Lucerne - Is it for me?, Perennial grasses - Is it for me?, Grazing saline soils - Is it for me.

I NTRODUCTION

Understanding the need to develop transition strategies Assessing the risk of salinization for farms Awareness of some options to manage risks.

U NDERSTANDING THE CAUSE OF SALINITY

The difference between the soil moisture behind perennials compared to annual species is the size of the buffer. High leaf area index (LAI) throughout the year - this is essentially the size of the pump that drives the extraction of water from the soil profile by the roots. It is understood that replanting up to 80% of the landscape to trees is not a current option for profitable agriculture.

Without high quality plantation options available for most of the wheat belt, it is unrealistic to replant large areas (60-80%) of farms to woody perennial vegetation. Profitable options are needed that mimic some functions of the previous remaining vegetation so that agriculture can continue on most of the land. The leakage level is indicated as high, medium or low, based on the total mm of leakage and the permeability of the soil.

The total mm of runoff coming from different parts of the agricultural system is based on soil types and crop rotations (calculated by AgET). It is important that the length of the sowing phase after three years of alfalfa is modified to suit the period of the seasons and specific soil types rather than being harvested for a fixed period. This is thought to result from clearing over a longer time (often the best soils that were cleared first) and additional water received as runoff from other parts of the catchment.

Slope interruption - Water is often forced to the surface by a reduction in the slope of the water table or by a narrowing of the water table (decreased thickness or permeability of the aquifer).

Table 1. Leakage Calculator output
Table 1. Leakage Calculator output

R ECOGNISING SALINITY

Local flow systems are more visible in the higher relief, more compartmentalized western catchment. Significant elevation difference along a confined or semi-confined aquifer increases the groundwater pressure head of the lower portions of the aquifer. In artesian systems, the pressure head in the downgradient portion of the aquifer is above the.

The groundwater level becomes sufficiently low, which enables evaporation of the capillary edges and the salt concentration in the surface, as is the case in most valleys. The rate of capillary rise and the height of the capillary edges depend on the soil type. Capillary rise can occur in fine-textured (heavy) soils when the water table is within 2 m of the surface (eg clay may have a 2 m capillary fringe).

The use of alfalfa and woody perennials in agricultural systems is considered very beneficial as they use almost all of the annual rainfall. These maps show areas where salinity has reduced plant cover in the low-lying areas and valleys. They are not 100 percent accurate, but are better than 90 percent in the wheat belt.

The lower series (0-0.5 m above stream path) will be most vulnerable to a shallow water table, followed by the rest of the series (Overhead 19). For example, in some parts of the river basin, the groundwater may be fresh and therefore not a major threat. In many of the relatively stable parts of the wheat belt, groundwater may never get close enough to the surface for salinity to be reflected.

These maps are also useful in determining the overall shape of the landscape and showing where watershed divides occur (especially in non-renovated landscapes where slope changes are difficult to determine by eye). From the assessment of the East Mortlock catchment, salinity patterns indicate that geological structures (eg faults, quartz veins) control much of the groundwater flow and salinity development. Examples of such areas include stretches of the Mortlock East River, particularly on the western flank of the catchment around the Dowerin-Meckering Road and south of the Great Eastern Freeway between Meckering and Cunderdin.

Look on the right side of the home page for the box labeled "Publication Series" and click directly on "Farmnotes". A summary of the Farmnote in question will appear, and you need to click on the title for the full document (it is best to print the PDF format).

Figure 1. Example of local groundwater trends.
Figure 1. Example of local groundwater trends.

P RE - FIELD ACTIVITY

F IELD TRIP

T HE EFFECT OF SALINITY ON FARM PRODUCTION AND PROFITABILITY

Waterlogging saturates the pores in the soil that are normally filled with gas, making them oxygen-deficient. If salt accumulates to a significant extent in the shoots, plant growth and survival are affected. The two pots on the left are water tolerant, while the two pots on the right are freely drained.

The combined effect of salinity and flooding has a much harder effect on plant growth than salinity alone. Do nothing (living with salinization) and continue farming with the current system and accept that in the future a percentage of the land will be lost to salinization. The risk associated with this depends on what part of the farm is likely to be affected or lost.

However, if you have large areas of valley floors that are likely to pass salt before the new equilibrium is reached, then the cost to your farm will be greater. Soil that is saline will often be some of the most productive on the farm. There will be a lag period in seeing results even if switching to 100% perennials, as there is already an excess of water in the groundwater system.

Recent modeling work is showing that areas with wide valley floors (primarily in ancient drainage areas) will receive the greatest response. buying time) from recharge management on the valley floors themselves. Do nothing - Cost of lost productive land and land value Restraint - Costs of switching to a new profitable system, reducing loss of productive land, land value, feel good etc. Water tables are salty and rising, leading to the salinity zones shown in the scenario above.

The spreadsheet is based on "Broad Flat Valley Floors", where planting 40 to 50% of the area at risk of salinization into perennials can extend the time to salinity development by 40 years (buy 40 years ). The spreadsheet allows you to change the farm area, the future salinity, the current profit of non-saline soil and how profitable the new management options are compared to the current management of the farm. When management options endangering 40% of the area in perennials, the same final salinity is reached, but instead of being reached in the year 2075, it takes 40 years longer (final salinity is reached in 2115).

A SSESS THE SALINITY RISK FOR YOUR FARMLAND

P RELIMINARY APPRAISAL OF MAJOR POTENTIAL MANAGEMENT OPTIONS FOR YOUR BUSINESS

For the future farm, perennials replaced annual pasture on the less productive areas and cattle replaced sheep. STEP was first used to look at the 10-year cumulative profit of the current farm for different combinations of stock numbers, sheep price and flock structure as shown. The only combination that shows a positive cumulative profit for the current system is the egg flock with a high stocking rate and high sheep sale price.

Only the future scenario with a low stocking rate and low cattle price ($600) was slightly less profitable than the best scenario for the current farm. Since the economic viability of the future farm looked promising, the next step was to assess the economic viability of the transition to the future system. For each transition strategy, lambs were sold each year and cattle were gradually introduced into the system.

This process took place faster with the shorter four-year transition than with the longer 10-year transition. The chart shows that at a low cattle price of $600, a longer transition period of 10 years looks more financially sustainable than a shorter transition. If you are interested in using STEP to assess the economic consequences of changing your farm, then the STEP workshops are for you.

The first workshop is an introduction where you will gain an understanding of how the STEP tool can be used to assess the economic potential of any proposed change to an agricultural system.

Figure

Table 1. Leakage Calculator output
Figure 1. Example of local groundwater trends.
Figure 2. Example of valley hazard map

References

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