Trial book mini - diverse rotations & early sowing strategies

Using diverse rotations and early sown crops in the Riverine Plains

Key messages from our 2022 & 2023 local demonstration trials

• Deep nitrogen analysis and farmer observations show that the use of a legume in a rotation provided more nitrogen (78 kg N/ha)  than a pure cereal history for the subsequent canola crop
• The application of nitrogen based on deep soil nitrogen testing, and the use of nitrogen budgeting by the farmer, resulted in more uniform nitrogen levels across the whole paddock and availability for crops
• Soil water measurements taken prior to sowing canola showed higher plant available water under wheat stubble compared to faba bean stubble, likely the result of greater ground cover provided by the wheat stubble over summer 
• Early sowing crops can provide opportunities for grazing and diversification of the farming system and can bring more crops into the ideal sowing window, reducing the risk of seasonal effects, such as frost.

We’ve recently wrapped up the Improved drought resilience through optimal management of soils and available water project, which looked at ways to improve management of natural capital through increased water use efficiency, soil organic carbon, and nitrogen utilisation, which are crucial to environmental and economic resilience during drought.

The project looked at three strategies which have been proven in small-scale NSW field trials to improve drought resilience, compared to conventional farming. These include:

1. Diverse legume rotations to increase soil organic carbon, carbon, nitrogen and soil water holding capacity
2. Early-sowing of slower-maturing crops to increase water holding capacity
3. Measuring residual nitrogen to prevent excess application, increasing profitability and decreasing runoff into waterways

As part of this project, Riverine Plains hosted local demonstration at Howlong and Mulwala during 2022 and 2023, so we're taking the opportunity to revisit some of the key takeaways from these trials.

Diverse rotations – Howlong NSW

A demonstration site at Howlong, NSW, consisted of a paddock half sown to faba beans and half sown to wheat in 2022. Extensive waterlogging reduced the yields of both the faba beans (0.98t/ha) and wheat (2.5t/ha) at the site in 2022. 

Canola was then sown across the whole paddock in mid-May 2023, with soil tests taken prior to sowing showing  the 2022 faba bean residue contributed 78 kg N/ha more nitrogen than the 2022 wheat residue. Based on soil tests and in-crop observations, the farmer then applied additional nitrogen and sulfur to meet crop needs and to balance differing nitrogen levels across the two halves of the paddock.  

Canola plant populations in 2023 were less than desirable due to a heavy stubble load and early wet conditions and the paddock yielded an average of 2.4 t/ha. 

Anecdotally, the farmer saved $95.70 /ha, due to a saving of 58 kg/ha in nitrogen application (based on urea at $700/t and application cost of $7.50/ha), which was a direct result of the inclusion of legumes in the previous paddock rotation.

Sulphur availability is often lower after wet, high yielding seasons and soil tests identified that an application of gypsum would also benefit the system by addressing the sodicity seen in elevated levels in the 10-20cm soil layer.

Soil moisture tests showed that the wheat residue stored 50 mm more plant available water (PAW) than the faba bean residue (Table 2), which was consistent with soil moisture tests taken previously. This is a likely result of the increased ground cover provided by the wheat stubble over the summer.

Early sowing of longer season varieties - Mulwala

Early sowing is a practice that introduces diversity into the system, with opportunities for grazing as well as harvesting for grain yield.

A site at Mulwala compared a flood irrigated paddock of Illabo wheat, sown in early April, with a dryland paddock 50 percent sown to Illabo wheat in early April and 50 percent sown to Scepter wheat in early May (the standard sowing window).  

A comparison of pre-sowing and post-harvest soil test nitrogen showed that the early sown crops used more nitrogen compared to the standard sown crop. This was attributed to the higher yield of the early sown Illabo, compared to the Scepter sown in the standard sowing window. Illabo is a long season wheat which likely produced more biomass over the course of the growing season than the mid-season sown Scepter, requiring more nutrition for growth. 

The comparison of dryland Illabo and dryland Scepter also showed that Illabo had a greater water use efficiency than Scepter, probably due to its higher yield (both crops were grown using the same available moisture), based on measures of plant available water taken after harvest. 

Both the irrigated and dryland early sown Illabo crops (8 t/ha and 7.6 t/ha respectively) showed a higher yield than the dryland standard-season sown Scepter (6.4 t/ha). This demonstrates the benefits of early sowing for improved crop yields, even when dual-purpose long season wheat crops aren’t grazed. 

These demonstration trials highlight key benefits of including early sown crops in a farming system. Additionally, longer season crops can also provide increased protection from erosion, as well as greater opportunities for microbial activity and the building of soil carbon because of the increased amount of time living roots are present in the soil. Starting the sowing program earlier also ensures more crops are sown at the optimal time, and avoids crops falling out of this window, which can make them more prone to seasonal risks at key growth stages, such as frost.

For more information about these demonstration trials, read the full article, published in Research for the Riverine Plains, 2024.  

Resources

This project included 12 demonstration trials across southern NSW, as well as case studies and videos – see our project page for more information.

Acknowledgements

This project is supported through funding from the Australian Government’s Future Drought Fund Drought Resilient Soils and Landscapes Grants Program and is co-funded by the Grains Research and Development Corporation.