Organic fertiliser sources for crop nutrition

WHY THIS PROJECT IS IMPORTANT 

The opportunity for the demonstration and validation of the value of biosolids and/or organic fertilisers (organic amendments) as a source of crop nutrition was raised as a priority area of interest at a Riverine Plains Research Advisory Committee and National Grower Network (NGN) meeting in northeast Victoria.

The development of this project coincided with an extreme rise in global fertiliser prices, prompting grain growers to consider pulses as a means of improving soil fertility, especially in the context of increasing soil nitrogen. However, it is often overlooked that nitrogen fixation provides most of the nitrogen demand of the grain legume crop (assuming adequate rhizobial function) at high yields, and a large part of this fixed nitrogen is exported in grain. This can affect the pulse crop’s potential to restore fertility and may not be enough to sustain higher-yielding wheat crops the following season.

In short: This project explores the role of organic fertilisers in crop nutrition, through the lens of rising fertiliser prices. Trials are assessing the impact of faba bean stubble and organic manures on wheat yield and soil fertility.

There are an abundance of organic amendment options in northeast Victoria, due to the proximity of feedlots and other intensive livestock operations. As such, there is local interest in using these by-products to supply nutrients for grain production systems and to improve soil conditions that may constrain yield (creating a circular economy).

Project focus

A replicated project trial site was established at Bundalong during 2022 to evaluate whether the benefits of nitrogen fixation by legume crops can be amplified with added organic amendments and if this can then buffer the farm business from high synthetic fertiliser inputs.

This project is specifically evaluating the value of faba bean stubble (from a crop grown in 2021 which yielded over 5t/ha), with and without organic manures, in restoring fertility and increasing yield in the following wheat crop.

The trial is using a local feedlot manure source, which is being evaluated at three different application rates (2.5, 5 and 10t/ha), for its effect on the following first wheat crop.

The project is also assessing the impact of two different application timings of nitrogen on the faba bean crop and in the subsequent wheat crop.

Measurements taken as part of the project include soil nutrient analysis, along with visual, dry matter, yield and quality assessments.

Project outcomes

Key points

• Early results of the trial show that application of manure at any level, with the addition of 75 kg N/ha were the only significant treatments that lead to a significant increase in yield from the control treatment.
• The quantity of manure added did not have an impact on yields.
• The reasons for results seen in the first season of the trial are unclear, however it is possible that soil background fertility was high, or that the wet season meant yield was not water-limited, and with good control of disease, the crop was essentially at yield potential. A further season of data is required to confirm the causes of these early results.

Method

Wheat trials were established in Bundalong, Victoria, in autumn 2022 on 7 t/ha (grain yield) faba bean stubble from 2021 crop. Trials were designed using a split-plot design with manure applied as shown in Table 1 to faba bean stubble as the main plot, and in-season nitrogen fertiliser in wheat as a sub-plot superimposed on manure.

Manure rates for treatments 3-8 were spread by hand in early April and then incorporated with an offset disc cultivator. Wheat was sown at the end of April and nutrient treatments 9-12 were applied shortly after. Soil samples were taken pre-sowing and again prior to GS30. In-season fertiliser applications (75kg N/ha) were applied after GS30, for the specified treatments. Fallow and green manure plots have been established in the 2022 faba bean paddock, ready for the 2023 trial. 

Table 1

Results

Early results of the trial show that application of manure at any level, with the addition of 75 kg/N per hectare were the only significant treatments that lead to a significant increase in yield from the control treatment (Figure 1). The quantity of manure added did not have an impact on yields.

Conclusion

At this stage, the reasons for results seen in the first season of the trial are unclear. However, possible causes could be that background fertility of the soil was high, or that the wet season did not create water limitation, and with good control of disease, the crop was essentially at yield potential. A further season of data is required to confirm the causes of these early results.

Acknowledgements

Thanks to the Inchbold family as co-collaborators on the project.
Authors: Dr Sara Hely, Riverine Plains; Ben Morris, FAR Australia.