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Module 01 >

Monitoring Soils

Module 02 >

Interpreting Soil Results

Module 03 >

Soil Fertility and Nutrient Management

Module 04 >

Common Soil Constraints

Module 05 >

Soil Carbon Capture

Module 06 >

Digital Agriculture for Soils

Module 07 >

Using Biologicals to Build Soil Organic Matter and Resilient Soils

Module 08 >

Managing Irrigated Soils in the Riverina Region of NSW

08

Managing Irrigated Soils in the Riverina Region of NSW

Module 01 >

Monitoring Soils

Module 02 >

Interpreting Soil Results

Module 03 >

Soil Fertility and Nutrient Management

Module 04 >

Common Soil Constraints

Module 05 >

Soil Carbon Capture

Module 06 >

Digital Agriculture for Soils

Module 07 >

Using Biologicals to Build Soil Organic Matter and Resilient Soils

Module 08 >

Managing Irrigated Soils in the Riverina Region of NSW

Section 8A

Managing Irrigated Soils in the Riverina

The Riverina region is known for its fertile soil and abundant water supply, making it a prime agricultural area for the production of high value crops. Here the soil types are highly variable due to the action of ancient streams upon the remnants of mountainous or hilly landscape. Most have been formed over thousands of years from alluvial deposits from flowing rivers, specifically the action of the Lachlan, Murrumbidgee, and Murray rivers and aeolian or wind deposits west of the Great Dividing Range.

The main soil type in the Riverina region is red-brown earth, referred to as kandosol or chromosol soils. Other soil types vary from grey, brown, to red clays which are often saline. These soils are known as sodosols and often have sands and gravels embedded in clays. This diverse soil composition historically supports a variety of natural vegetation, from river red gums along river channels to saltbush on the plains. Currently these soils support considerable acreage of high value irrigated broadacre and pasture crops for production of prime Australian broadacre and horticultural crops as well as livestock.

Figure 1. Distribution of soil classes in the Riverina.
Source: eSPADE

Section 8B

Soil types underlying irrigated cropping in Riverina

The region consists of several gently sloping alluvial fans and floodplains. These fans merge to form a single low-gradient fan between the Loddon and Lachlan Rivers. Soils along current and ancient riverbeds are frequently sandy, but towards the outer perimeter of the floodplains, soils are more saline and classified as heavy grey and brown clays. Fertile alluvial sediments are deeper and older in the western half of the Murray-Darling basin whereas soil and water salinity tend to increase traveling downstream on the Murrumbidgee.    

In the southeastern Riverina where irrigated cropping is performed, chromosol soils overlay the granite hills and kandosols lie over deposits of parna (wind-blown clay) across the southern slopes. Fertile vertosols are found in floodplains where alluvium is mixed with parna deposits. Rudosols with poor structure are found in very sandy deposits along riverbeds.

Remember

Chromosol, kandosol, vertosol, and rudosol soils are the four major soil types found in the Riverina.

Figure 2. Profiles of four major soil types found in the Riverina.
Source: Link: The Australian Soil Classification.

Section 8C

Soil-water relations in irrigated soils

Soil properties, including physical, chemical, and biological characteristics play a crucial role in water absorption, movement, and retention in the soil.

Physical properties

The physical structure of the soil, including its texture and porosity, directly influences its ability to absorb and retain water. For instance, sandy soils with larger particles have larger pores and drain quickly, while heavy clay soils with smaller particles have smaller pores and retain water longer.

Figure 3 Soil-Water relationships
Source: University of Minnesota Extension

Biological properties

The soil hosts a complex web of fauna and microbes involved in many biological processes, which can affect its physical and chemical properties. The composition of soil flora and fauna changes depending on soil water availability.

In summary, the interplay of these properties determines the soil’s capacity to sustain productivity in a cropping system, impacting its water holding capacity while maintaining environmental quality. It’s important to note that these properties are also influenced by land use and management.

Did you know?

The amount of water extracted by a plant depends on the soil’s physical and chemical properties, and on plant’s root depth, root density and plant’s water demand based on plant growth tage. The plant available water in each soil type varies depending on the crop type. Soil type also impacts a soil’s water holding capacity.
Figure 4. Soils water holding capacity
Source: Dalgliesh & Foale (1998)

Section 8D

Irrigation systems in the Riverina

The diverse and productive agricultural sector in the Riverina is supported by various irrigation systems. Some common irrigation systems are frequently used in the Riverina region and are compared below in terms of water use efficiency, application uniformity, and suitability for different soils and crops.

Surface irrigation

This traditional method involves flooding the field with water. It’s simple and inexpensive but has a lower water use efficiency of about 30-40%.

 

Furrow irrigation

In this method, water is delivered in furrows or ditches made between crop rows. It’s more efficient than flooding, with water use efficiency ranging between 55-70%.

 

Drip irrigation

Also known as trickle irrigation, this system delivers water directly to the root zone of plants through a network of tubes, pipes, and emitters. It’s highly efficient, with water use efficiency reaching up to 95%. Drip irrigation is becoming increasingly popular in the Riverina region.

 

Centre pivot irrigation

This system consists of sprinklers mounted on wheeled towers that rotate around a pivot. While not as efficient as drip irrigation, centre pivot systems can cover large areas and are easier to manage.

Figure 5. Matching irrigation systems to various soil types in the Riverina
Source: NSW DPI

In terms of application uniformity, the goal of irrigation system designers and operators should be to maximise irrigation uniformity within practical and economic constraints. Drip and centre pivot irrigation systems generally provide better application uniformity compared to surface and furrow irrigation. As for suitability for different soils and crops, it’s important to note that different soils have different abilities to retain water or allow drainage. For example, sandy soils need a more frequent watering rate with smaller amounts than clay soil. The type of crop also plays a role in determining the most suitable irrigation system. For instance, crops that are sensitive to waterlogging might not do well with surface or furrow irrigation but may thrive under drip or centre pivot irrigation.
 
In conclusion, the choice of irrigation system in the Riverina region depends on a variety of factors including the type of crop, soil characteristics, water availability, and economic considerations. Before designing an irrigation system, it’s important to  conduct a thorough analysis of these factors.

Figure 6 (snippet). Matching irrigation systems to soil type in the Riverina Plains South-East Australia
Source: NSW DPI

Section 8E

Challenges in Managing Irrigated Soils in the Riverina

Managing irrigated soils in the Riverina region presents several challenges.

Variability of soil types

The diverse range of soil types, from heavy clays to sandy loams in the Riverina can create challenges associated with irrigation, particularly with heavy soils that have low infiltration rates. For instance, many growers who have installed centre pivots on very heavy Riverina soils (transitional red-brown earths and non-self-mulching clays) experience serious infiltration and tracking problems.

Sodic soils

Sodic soils, which have a high exchangeable sodium percentage, can also pose challenges for irrigation in the Riverina in terms of rising salinity.

How to address the issues with irrigated sodic soils?

Water management
Managing surface water flows and minimising potential for localised ponding can help reduce the impacts of sodic soils.

Soil amendments
Applying soil amendments like gypsum, organic matter, or polyacrylamides can modify the Exchangeable Sodium Percentage (ESP) or directly influence aggregate stability. Gypsum is particularly effective as it provides calcium, which can replace sodium on the clay particles, improving soil structure.

Increase organic matter
Increasing the organic matter content of the soil can improve its structure and water-holding capacity.

Deep ripping
Deep ripping in conjunction with slotting or trenching with added gypsum can help break up compacted layers and improve water infiltration.

Avoid disturbance
Avoiding disturbance of already productive sodic soils can prevent exacerbating sodicity issues.

Destocking
Destocking paddocks when the soil is wet can prevent damage to surface soil structure and increase surface sealing caused by livestock.

Design and operational issues
The design and operation of irrigation systems can also present challenges. For example, an overhead irrigation system’s maximum water delivery rate is effectively set and is only able to irrigate adequately a specific area. A common reason for growers complaining about their irrigation system performance is that they have overcommitted or attempted to irrigate too large an area.

Diseases
Moist or damp soil conditions can favour the development of soil-borne diseases such as Pythium, and Phytophthora spp.

Remember

These challenges highlight the need for careful planning, design, and management when implementing irrigation systems in the Riverina region. A combination of strategies often generates the best outcome.

How do irrigation practices significantly influence soil salinity, sodicity, acidity, and nutrient availability in soil?

Soil salinity

Irrigation can lead to salinity issues, particularly when the water table rises due to increased rates of leakage and groundwater recharge. This brings salts into the plant root zone, affecting plant growth and soil structure.
Using saline water for irrigation adds salt to the soil and necessitates more water to leach the salts past the root zone.

Soil sodicity

Irrigating with water high in sodium can lead to sodicity problems, where sodium ions displace calcium and magnesium, affecting soil structure. High volumes of fertilisers and lack of adequate drainage can exacerbate sodicity issues.

Soil acidity

The use of acidifying fertilisers and the removal of alkalinity through crop harvesting or leaching can lead to soil acidification. The quality of irrigation water, especially if it contains certain ions, can influence the pH of the soil.

Nutrient availability

Efficient irrigation practices can reduce nutrient leaching, potentially leading to a re-examination of nitrogen budgets and recommendations for crops. Practices like cover cropping and non-tillage can improve soil organic carbon and nutrient availability.

Section 8F

Best management practices for irrigated soils in Riverina

The best management practices for irrigated soils in the Riverina region involve a combination of efficient irrigation systems, comprehensive management plans, adoption of drought resilient practices, regular soil health monitoring, and strong knowledge-sharing networks.

Efficient irrigation systems
Centre pivot irrigation system offers precise control of irrigation application and has a low labour requirement. Centre pivot is capable of providing high returns per megalitre (ML) of water applied, particularly with winter cropping in the Riverina. However, these high returns are only possible if associated agronomy and water management practices are of a high standard.

Land and water management plans
These are the cornerstone of environmental initiatives in the irrigation areas of the Riverina. Each plan is an integrated natural resource management strategy prepared by landholders and local communities with technical and financial assistance in partnership with the NSW and Federal governments.

Drought resilient practices
A drought resilience plan implementis practices to improve landscape-level drought resilience including enhanced farm dams, native shelterbelts, and stock management areas. The Riverina Drought Resilient Soils and Landscapes project aims to support producers in adopting drought resilient practices and enhance their landscape and soil monitoring capabilities.

Soil health monitoring
Establishing a long-term soil health monitoring site and undertaking regular in-field observations to monitor change. This is particularly important in irrigated soils given that pests and soil health can be clearly impacted by available water.

The following agronomic practices can support the health and productivity of irrigated soils:

Tillage
The type and extent of tillage can significantly affect soil quality and productivity. However, practices like ploughing, tilling, and cultivating can decrease the amount of organic matter in the soil. Therefore, reduced tillage is often recommended to enhance soil fertility, structure, and water-holding capacity.

Stubble retention
Stubble retention helps maintain or increase soil organic matter. It also provides a protective layer on the soil surface, reducing erosion and moisture loss. Over time, as the stubble decomposes, it contributes to the organic matter content of the soil, improving soil structure and nutrient availability.

Crop rotation
Crop rotation involves growing different types of crops in the same area in sequential seasons. It helps break pest and disease cycles, improve soil structure and fertility by diversifying the range of plant roots, and enhance the efficiency of water use.

Cover crops
Cover crops are typically grown not for harvest but to protect and enrich the soil. They help enhance soil fertility, structure, and water-holding capacity. Cover crops can also suppress weeds, manage soil erosion, and promote biodiversity.

Did you know?

Agronomic practices such as tillage, stubble retention, crop rotation and cover crops are all excellent methods to support productivity of irrigated soils.

How do agronomic practices promote nutrient availability?

These practices promote nutrient availability, reduce erosion, and sequester carbon, contributing to healthier and more productive soils. However, the efficacy of these practices can depend on various factors, including the specific characteristics of the soil and the local climate. Therefore, it’s important to tailor soil management practices to the specific conditions of each field.

Here are some of the current and emerging trends in irrigated soil management in the Riverina:

Climate adaptation
The Riverina region is an irrigated arid region with low rainfall and high evaporation. A future climate is likely to be warmer and possibly drier. Therefore, farmers need to adapt their practices to these changing conditions.
 
Efficient use of nitrogen fertiliser
Seasonal conditions can cause poor nitrogen fertiliser uptake in Riverina irrigated crops. Innovative methods like mid-row banding of high rates of nitrogen every second row are being explored to maintain a concentrated zone of ammonium nitrogen a distance from the plant row.
 
Precision agriculture and AI
Emerging technologies like artificial intelligence (AI) are being used to make “intelligent” decisions based on the most accurate predictions we’ve ever had access to. This includes creating optimal irrigation scheduling and distribution.
 
Innovative technologies irrigation
These include smart irrigation controllers, soil moisture sensors, and micro-irrigation systems. These technologies aim to increase water-use efficiency, reduce water consumption, and minimise environmental impacts caused by irrigation.

Remember

The effectiveness of new technologies can depend on various factors, including the specific characteristics of the soil and the local climate. Therefore, it’s important to tailor soil management

Section 8G

Environmental considerations in managing irrigated soils in the Riverina

Environmental considerations for irrigated soils in the Riverina region are crucial due to the region’s unique characteristics and challenges. Some key considerations are demonstrated in this section.

Soil conservation
Australia is home to soils that are prone to erosion and usually have low levels of nutrients and organic matter. Effective soil management is needed to prevent erosion and maintain nutrient levels. Soil conservation practices such as cover cropping, crop rotation, and reduced tillage can help maintain soil health, prevent erosion, and reduce runoff.
 
Efficient use of fertilisers
Overuse of fertilisers can lead to nutrient runoff into water bodies, causing water pollution. Efficient use of nitrogen fertiliser in Riverina irrigated cropping could help minimise these risks. For example, placing fertiliser into a concentrated mid-row band at sowing can offer a low-risk alternative for meeting crop nitrogen requirements while minimising water pollution.
 
Efficient water use
Proper water management is crucial to prevent waterlogging and runoff. This includes using modern irrigation systems and practices to minimise water losses.
 
Protecting local biodiversity
Over 25% of the biodiversity on our planet is associated with the soil rhizosphere. Therefore, maintaining healthy soils is crucial for supporting biodiversity. This can be achieved through practices such as creating native shelterbelts, managing stock areas, and implementing practices to improve landscape-level drought resilience.
 
Climate adaptation strategies
The Riverina region is an irrigated arid region with low rainfall and high evaporation. The future climate is likely to be warmer and possibly drier, which could impact soil health and productivity. Implementing strategies to adapt to a changing climate, such as changing crop varieties or adjusting planting dates, can help manage the risks associated with climate change.

Carbon sequestration
Improved soil management is required to meet the demands of the growing Australian agricultural industry while capturing carbon and meeting emission reduction targets.

Remember

Farmers in the Riverina region need to consider these environmental factors when managing their irrigated soils. They should also stay informed about the latest research and developments in soil and water management and adapt their practices to the specific conditions of each field.

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